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SANDRA MORELLI

COLLABORATORE DI RICERCA
Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica

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Pubblicazioni

2013 - Combined observations of a Bora event in the Adriatic Sea by means of ETA model and SAR data [Abstract in Rivista]
M., Adamo; G., De Carolis; Morelli, Sandra; F., Rana
abstract

The Bora is a cold, strong, low level wind which blows from the northeast along the Adriatic coast (Ivančan-Picek and Tutiš, 1996, Lazić and Tošić, 1998, Morelli and Berni, 2002). Bora wind is known to have multiple surface wind jets linked to the orography of the Dinaric Alps and alters significantly the sea status (Cesini et al, 2004). A recent version of the Eta model (Mesinger et al, 2012), which is a three-dimensional, primitive equation, grid-point model, was used to represent the low level wind field corresponding to the Bora event occurred at the beginning of February 2012. Numerical simulations, initialized by ECMWF data, were performed with different horizontal resolutions (approximately 20 km and 4 km) and domain extent. The numerical simulations describe the atmospheric conditions of the period and reveal the spatial structure of the wind, in good agreement with the understanding as well as the observational knowledge of the bora. In addition, the wind speed and direction was estimated on the ASAR images. Wind directions were obtained by exploiting a novel technique based on the use of 2D continuous wavelets (Zecchetto and De Biasio, 2001, 2008). Then, the retrieved wind directions were used to estimate the wind speed from the ASAR NRCS by inverting the semi-empirical backscatter model CMOD-5 (Hersbach, 2005). The ASAR observed morphology, wake patterns and, where present, dual-jet structure of the Bora wind were analysed for 2 and 5 February at the two different Eta resolution scales. Results of the comparisons between Eta prediction and ASAR data will be shown. Cesini D., Morelli S., Parmiggiani F.: Analysis of an intense bora event in the Adriatic area, Natural Hazards and Earth System Sciences, 4, 323-337, 2004. Hersbach H.: CMOD-5. An improved geophysical model function for ERS C-band scatterometry, ECMWF Technical Memorandum 395, Reading, England, pp. 1-50, 2003. Ivančan-Picek, B., Tutiš, V.: A case study of a severe Adriatic bora on 28 December 1992, Tellus, 48A, 357-367,1996. Lazić, L., Tošić, I.: A real data simulation of the Adriatic bora and the impact of mountain height on bora trajectories, Meteorol. Atmos. Phys., 66, 143-155, 1998. Mesinger F., Chou S.C., Gomes J.L., Jovic D., Bastos P., Bustamante J.F., Lazic L., Lyra A.A., Morelli S., Ristic I., Veljovic K.: An upgraded version of the Eta model, Meteorol Atmos Phys, 116, 63–79, 2012, DOI 10.1007/s00703-012-0182-z. Morelli, S., Berni, N.: On a bora event simulated by the Eta model, Meteorol. Atmos. Phys., 000, 1-12, 2002.

2013 - Quantitative analysis of Bora event in the Adriatic Sea by means of SAR-based techniques and the ETA model [Relazione in Atti di Convegno]
M., Adamo; G., De Carolis; Morelli, Sandra; G., Pasquariello; F. M., Rana
abstract

Bora is a north-eastern wind which blows in the Adriatic sea and is characterized by multiple surface wind jets linked to the orography of the Dinaric Alps ([1], [2], [3]). It is a cold, intense, low level wind which is known to strongly modify the sea surface status ([4]). As the Bora usually causes detectable wind-derived features in SAR imagery, well-suited image processing algorithms have been implemented in order to extract wind direction directly from SAR images. In particular, SAR sea surface wind directions have been obtained by exploiting both the Local Gradient (LG) method ([5]) and the relatively novel technique based on the use of 2D continuous wavelet transform (CWT2) ([6], [7], [8]) on ENVISAT C-band ASAR data. The exceptional Bora events of the beginning of February 2012 over the Gulf of Trieste have been studied by means of two Wide Swath (WS) mode ASAR images, acquired on the 2nd and 5th of February and available from ESA archive. The retrieved wind directions extracted by the above mentioned methods have been used to estimate the wind speeds with a classical inversion procedure applied to the forward semi-empirical backscatter model CMOD-5 ([9]). Indeed, CMOD-5 improves performances of the previous CMOD-4 for high wind conditions, as those expected during Bora events. Moreover, a recent version of the atmospheric ETA model ([10]), which is a three-dimensional, primitive equation, grid-point model, has been also adopted to estimate the low level wind fields corresponding to the Bora events under investigation.

2013 - Wind over Terra Nova Bay (Antarctica) during a polynya event: Eta model simulations and satellite microwave observations [Articolo su rivista]
Morelli, Sandra; F., Parmiggiani
abstract

A study of Terra Nova Bay (TNB) winter polynya, based on the combined use of satellite observations and limited area model simulations, is presented. First, data from passive microwave observations are used to investigate the polynya area daily variability. Second, Eta model is run to simulate the low level wind over a defined TNB polynya, located in according to the satellite images, during the period 15 – 17 September 2003. A preliminary set up of initial and boundary conditions is used. Eta model is initialized with European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, with National Centers for Environmental Prediction (NCEP) of the U.S. National Weather Service data and with information from satellite images providing a realistic extension of the polynya under study. Eta model simulates a katabatic wind system which develops qualitatively in agreement with the polynya extent, as shown from satellite images during the same period. The results demonstrate the strong effect of the polynya when included in the initialization of model integrations: the low level wind is intensified by the presence of the warm area corresponding to polynya, it is spatially variable and significantly different from one simulated along the coast of the Nansen Ice Sheet. The results of numerical simulations with different surface temperature in the polynya area are shown as well, thus an assessment of the range of variability of the wind intensity in relation to polynya surface temperature is provided.

2012 - An upgraded version of the Eta Model applied to Antarctic case studies [Abstract in Rivista]
Morelli, Sandra
abstract

Upgrades have been implemented over a number of years in an open source version of the Eta Model, posted at its CPTEC web site (http://etamodel.cptec.inpe.br/). They were summarized in Mesinger et al. (2011) and examined in detail in Mesinger et al.( 2012). In short: within dynamics, two major upgrades are the introduction of "sloping steps" and the use of the piecewise-linear vertical advection of dynamic variables. Several refinements on the calculation of exchange coefficients, conservation in the vertical diffusion, and diagnostic calculation of 10-m winds have been made. Vapor and hydrometeor loading in the hydrostatic equation were included. Within physics, efforts in refining the two Eta convection schemes received most attention. This recent version of the Eta Model has been applied to polynya events, accompanied by katabatic wind, at Terra Nova Bay (TNB), Antarctica. The TNB polynya is an area of coupling between the components of the sea ice-ocean-atmosphere system. Locally enhanced surface exchange processes are considered to have important consequences for the atmosphere (Morelli, 2011) and ocean processes, as well as for ice formation and the associated brine release. Adjustments of the Eta pre-processor have been made to allow for the distinctive polar conditions and for the use of ECMWF data as initial and boundary conditions. It is also being developed a thermodynamic model of sea ice interaction for a more realistic treatment of the sea ice-atmosphere. The numerical simulations have a horizontal resolution of about 8 Km. The results will be compared with observational data at the surface, with soundings and satellite images. The observations, used for the comparison, are available by Antarctic Meteorological Research Center, Space Science and Engineering Center, University of Wisconsin-Madison and the Programma Nazionale di Ricerche in Antartide (P.N.R.A.), Osservatorio Meteo-Climatologico.F Mesinger, Chou S C, Gomes J, Jovic D, Lazic L, Lyra A, Bustamante J, Bastos P, Morelli S, Ristic I (2011) An upgraded Version of the Eta Model. Geophysical Research Abstracts Vol. 13, EGU2011-3753-1.F Mesinger, Chou S C, Gomes J, Jovic D, Lazic L, Lyra A, Bustamante J, Bastos P, Morelli S, Ristic I (2012) An upgraded Version of the Eta Model.. Accepted for publication in Meteorol. Atmos Phys.S Morelli (2011) A modeling study of an Antarctica polynya event Meteorol Atmos Phys, 114:67-81 DOI 10.1007/s00703-011-0157-5

2012 - An upgraded version of the Eta model [Articolo su rivista]
F., Mesinger; S. C., Chou; J. L., Gomes; D., Jovic; P., Bastos; J. F., Bustamante; L., Lazar; A. A., Lyra; Morelli, Sandra; I., Ristic; K., Veljovic
abstract

Upgrades implemented over a number of years in an open source version of the Eta Model, posted at the CPTEC web site http://etamodel.cptec.inpe.br/, are summarized and examples of benefits are shown. The version originates from the NCEP's Workstation Eta code posted on the NCEP web site http://www.emc.ncep.noaa.gov/mmb/wrkstn_eta, which differs from the NCEP's latest operational Eta by having the WRF-NMM nonhydrostatic option included. Most of the upgrades made resulted from attention paid to less than satisfactory performance noted in several Eta results, and identification of the reasons for the problem. Others came from simple expectation that including a feature that is physically justified but is missing in the code should help. The most notable of the upgrades are the introduction of the so-called sloping steps, or discretized shaved cells topography; piecewise-linear finite-volume vertical advection of dynamic variables; vapor and hydrometeor loading in the hydrostatic equation, and changes aimed at refining the convection schemes available in the Eta. Several other modifications have to do with the calculation of exchange coefficients, conservation in the vertical diffusion, and diagnostic calculation of 10-m winds. Several examples showing improved performance resulting from the dynamics changes are given. One includes a case of unrealistically low temperatures in several mountain basins generated by a centered vertical advection difference scheme's unphysical advection from below ground, removed by its replacement with a finite-volume scheme. Another is that of increased katabatic winds in the Terra Nova Bay Antarctica region. Successful forecast of the severe downslope zonda winds case in the lee of the highest peaks of the Andes is also shown, and some of the recent successful verification results of the use of the upgraded model are pointed out. The code is used at numerous places, and along with setup information it is available for outside users at the CPTEC Eta web site given above.

2012 - ETA Model Simulations and AMSR Images to Study an Event of Polynya at Terra Nova Bay, Antarctica [Capitolo/Saggio]
Morelli, Sandra; F., Parmiggiani
abstract

In the Terra Nova Bay (TNB) region, the near-surface winds are persistently strong (in particular during the winter season) and blow offshore with a high degree of directional constancy. This region is also known as a preferential zone of coastal polynyas. Polynyas are recurring areas of open waters/thin ice surrounded by an ice covered sea. Coastal polynyas form along ice bound coasts; they are believed to be due to strong and persistent offshore winds and/or ocean currents which drive the sea ice away. As the ice is removed from the region of origin, open water is exposed, refrozen and the new ice is pushed away, so that coastal polynyas provide a source of new ice production. The horizontal surface temperature differences among the land ice, water and sea ice are strong, because the open water is close to the freezing point (-1.8 °C for typical salt water). The energy exchange between the ocean and the atmosphere in the Antarctic marginal sea ice zone is influenced by the extent of sea-ice cover. While the sea ice acts as insulation, a direct contact is established in areas with open water and intense energy exchanges occur, due to the large difference of temperature between the water and the air above it. This implies that the polynyas are areas where the ocean exchanges energy with the atmosphere and as a result they have an effect on the polar meteorology/climate. In Antarctica, the atmospheric numerical models which provide good results at the mid latitude, are put to the test, because the observations are scarce, the initial and boundary conditions are sometimes inadequate, complex terrain, sea ice and polynyas are present. Here, the numerical simulation of a real event of coastal polynya at TNB is shown, using a recent version of the Eta Model. The horizontal resolution is approximately 20 km and 50 level are considered in the vertical up to 25 hPa. Initial and boundary conditions are obtained from ECMWF analyses. The event, occurred from 12 to 18 July 2006, was selected by the analysis of the sequence of daily AMSR- derived Sea-Ice Concentration (SIC) maps. The computation of the sea ice free area provided information on the temporal development of the polynya which reached its maximum extent of about 4000 km2 on 16 July. Therefore, a realistic polynya size was included in the initial conditions for the simulation of the period 15 – 17 July. The Eta Model reproduces very well the evolution of upper and mid-level conditions in agreement with AVHRR observations. Also, the evolution of the simulated 10m wind is strictly correlated to the observed extent of the polynya. In order to isolate the effect of the presence of the open water area on the structure of the atmospheric boundary layer and on the atmospheric circulation, a further simulation was performed without the presence of the polynya, i.e. with its extent covered with sea ice. The numerical simulations show that the polynya acts to increase the speed of the air above it and strong heat fluxes warm the air. As a result, the polynya modifies the atmosphere over a long distance from its location and till to a height of several hundred meters.

2012 - Osservazioni SAR durante l'evento eccezionale di Bora di inizio Febbraio 2012 [Relazione in Atti di Convegno]
M., Adamo; G., De Carolis; C., Fragiacomo; Morelli, Sandra; F., Parmiggiani; M., Bastianini
abstract

Abstract The exceptional Bora event of the beginning of February 2012 over the Gulf of Trieste was studied by means of Envisat/ASAR images and by numerical 72-h simulations carried out with the atmospheric Eta model. Quantitative information on the surface wind field were extracted from ASAR images with an inversion procedure which makes use of the semi-empiric CMOD5 model which links the ‘normalized radar backscatter cross section’ (NRCS) to the 10 m wind vector. Wind data, extracted from ASAR images by CMOD5 model, are then compared with those measured by the meteo station of ISMAR-CNR of Trieste and with the results provided only by the numerical simulations of the Eta model. Riassunto L’evento eccezionale di Bora di inizio Febbraio 2012 sul Golfo di Trieste è stato studiato con l’impiego di immagini Envisat/ASAR e mediante simulazioni numeriche di 72 ore effettuate con il modello atmosferico Eta. Le informazioni quantitative sul campo di vento superficiale sono state estratte dalle immagini ASAR con un procedimento di inversione che utilizza il modello semi-empirico CMOD5 che lega la sezione d’urto normalizzata (NRCS) misurata al vettore velocità del vento a 10 m. I dati di vento, estratti mediante il modello CMOD5 dalle immagini ASAR, sono poi confrontati con quelli registrati dalla stazione meteo dell’ISMAR-CNR, UOS di Trieste, e con i risultati prodotti solo dalle simulazioni del modello Eta.

2011 - A modeling study of an Antarctica polynya event. [Articolo su rivista]
Morelli, Sandra
abstract

An event of polynya at Terra Nova Bay (TNB),occurring from 15 July to 17 July 2006, is simulated by arecent version of the mesoscale Eta model. Simulationresults and observational data describe the surface conditionsduring the period. The spatial and temporal structureof the atmospheric boundary layer in response to the warmarea of the polynya is also investigated. Numerical experimentsshow that the latter influences significantly the windintensity, the temperature and the specific humidity of theair over Terra Nova Bay. The significant heating of the lowatmosphere results in a three-dimensional anomaly in thebaric field, which extends far in the Ross Sea, embedded inthe complex pressure field obtained by the Eta model alsowithout taking into account the polynya. A turbulentkinetic energy plume, indicating turbulent mixing, and anincreased vertical diffusion of horizontal momentum arealso simulated over the polynya. The downward flux ofhigh momentum air and the modified pressure gradientforce change the wind speed at low level over TNB.

2011 - An upgraded Version of the Eta Model [Abstract in Rivista]
F., Mesinger; S., Chan Chou; J., Gomes; D., Jovic; L., Lazic; A., Lyra; J., Bustamante; P., Bastos; Morelli, Sandra; I., Ristic
abstract

Upgrades implemented over a number of years in an open source version of the Eta Model, posted at its CPTECweb site (http://etamodel.cptec.inpe.br/) are summarized and examples of benefits are shown. The versionoriginates from the NCEP’s so-called Workstation Eta that used to be maintained at NCEP, and posted on itsweb site, which differs from the NCEP latest operational Eta by having the WRF-NMM nonhydrostatic optionincluded. Most of the upgrades made resulted from attention paid to less than satisfactory performance noted inone or another aspect of various Eta operational results, and identification of the reasons for the problem. Otherscame from simple expectation that including a feature that is physically justified but is missing in the code shouldhelp.Within dynamics, a major upgrade is that of the introduction of "sloping steps", or of a discretized versionof the shaved cells of Adcroft et al. (1997). This addresses the problem of the insufficient strength of downslopewinds in two real data cases, and the Gallus and Klemp simulation of the flow in the lee of the "Witch of Agnesi"topography. Use of the piecewise-linear vertical advection of dynamic variables is another dynamics change.This makes the code approximately finite-volume, given that flux-type schemes are then used for all dynamicsvariables, and that sides of the cell volumes are very nearly equal due to the use of the eta coordinate. Severalrefinements having to do with the calculation of exchange coefficients, conservation in the vertical diffusion,and diagnostic calculation of 10-m winds have been made. Vapor and hydrometeor loading in the hydrostaticequation was included. Within physics, efforts in refining the two Eta convection schemes received most attention.The upgrades address the model’s well established problem of underdoing the heavy rain thresholds when theBetts-Miller-Janjic convection scheme is used. Momentum fluxes were added to the Kain-Fritsch convectionscheme. The molecular sublayer treatment was refined by making the molecular sublayer depth dependent on theroughness Reynolds number, following a suggestion of Brutsaert (1982).Examples showing improved performance resulting from the dynamics changes include a case of the impossiblycold temperatures in several mountain basins generated by a centered vertical advection finite differencescheme’s unphysical vertical advection from below ground, removed by its replacement with a finite-volumescheme; and of increased katabatic winds in the Terra Nova Bay Antarctica region. Successful hindcasts of thesevere downslope zonda winds in the lee of the highest peaks of the Andes are also shown. Finally, results of recenttests of the value added by the upgraded Eta in RCM ensemble experiments achieved over its driver ECMWF32-day global ensemble members (Veljovic et al. 2010) are recalled.

2011 - Modeled surface heat fluxes over Terra Nova Bay polynya [Abstract in Rivista]
Morelli, Sandra
abstract

Polynyas play an important role in the meteorology and oceanography of the polar regions and in the oceangeneral circulation.A winter event of Terra Nova Bay polynya, is studied by a recent version of the atmospheric, mesoscale Etamodel. Currently, the Eta model distinguishes open water grid points and thick sea ice grid points by a maskwhich is established as initial condition and remains fixed in the simulations. In the days of the event the mostof the model integration domain is under polar night condition and, in particular, the Sun is below the horizon atTNB. Thus, available AVHRR image does not contain the visible channels but only the thermal ones. In channel4 (11.5 m), AVHRR imagery show the area of TNB with a well developed warm area, corresponding to thepolynya as revealed by AMSR-derived SIC maps, surrounded by much colder pack ice. Brightness temperature,hailing from the satellite observations, decreases as one moves away from the coast towards the Ross Sea. Amulti-regions polynya was introduced in the model using different skin temperatures in order to take some accountof the variation of temperature with the distance from the coast. The polynya is therefore depicted as consisting ofa warm inner region, and two zones gradually colder. The surface heat fluxes, calculated over the polynya, and theimpact of polynya on the air above it will be presented.

2011 - Surface-Atmosphere Interactions during a Polynya Event at Terra Nova Bay (Antarctica). [Relazione in Atti di Convegno]
Morelli, Sandra; F., Parmiggiani
abstract

Numerical three-dimensional weather simulations, satellite imagery and automatic weather station (AWS) data are used to study a real event of coastal polynya at Terra Nova Bay (TNB), Antarctica. The event, detected with satellite images, occurred in the period 12–17 July 2006. The atmospheric simulations are performed by the limited area Eta Model. Passive microwave satellite images, which are not affected by cloud cover, are used to evaluate the daily polynya size, while thermal infrared satellite images are only used to follow cloud dynamics. The synoptic and sub-synoptic fields are very well represented by the model results when they are compared with AVHRR imagery. Comparisons between simulated data and wind measurements by Manuela AWS are presented as well. The results are considered satisfactory. Simulation results show the striking relationship of surface winds and temperatures with the development of the polynya as inferred by satellite images

2010 - Meteorological impact of realistic Terra Nova Bay polynyas [Abstract in Rivista]
Morelli, Sandra
abstract

The energy exchange between the ocean and the atmosphere in the Antarctic marginal sea ice zone is influenced by the extent of sea-ice cover. In areas of open water, a direct contact is established and intense energy exchanges occur, due to the large difference of temperature between the water and the air above it. This implies that the polynyas are areas where the ocean exchanges energy with the atmosphere and as a result they have an effect on the polar meteorology/climate. The work presented here concerns real polynya events in the region of Terra Nova Bay (TNB), Antarctica, where a recurring coastal polynya occurs nearby the Italian Antarctic Base. The aim is the study of the impact of polynyas on the atmosphere by three-dimensional numerical simulations. The ETA model (Mesinger et al., 2006) is used and ECMWF and NCEP data provided the initial and boundary conditions. The model had already been successfully used in the Antarctic area (Casini and Morelli, 2007) A polynya of realistic size (as observed by satellite image) was included in the initial conditions for the simulations and a study of the air circulation during the events is found in Morelli et al. (2007), Morelli and Casini (2008), Morelli et al. (2009). The Eta Model reproduced the evolution of upper and mod-level conditions in good agreement with AVHRR observations (Morelli, 2008, Morelli and Parmiggiani, 2009). Also, the simulated 10 m wind was well correlated with the observed extension of the polynya.In order to isolate the effect of the presence of the open water area on the structure of the atmospheric boundary layer and on the atmospheric circulation, further simulations were performed without the presence of the polynya, i.e. with its extent covered with sea ice. The numerical simulations show that the polynyas act to increase the speed of the air above them and generate strong heat fluxes that warm the air. The effects are found over and downwind the sea ice free area.Results from the Eta Model runs show that a polynya modifies the atmosphere up to a height of several hundred meters and over a long distance from its location. A structure, as a thermal cyclone, develops over the eastern side of the polynyas. This structure is embedded in the pressure field simulated also without taking into account the polynya.

2009 - Atmospheric response to a realistic coastal polynya in Terra Nova Bay (Antarctica) simulated by ETA model [Abstract in Rivista]
Morelli, Sandra; G., Casini; F., Parmiggiani
abstract

Coastal polynyas are areas of open water (and/or very thin ice) which form adjacent to coasts or blocking feature in polar regions during the wintertime, when the sea water is expected to be ice covered. They are thought to be maintained by strong offshore winds blowing over these area and/or by ocean currents. Sea ice is removed as it forms and drifted offshore. In polynya areas a direct contact is established between the relatively warm sea water and the cold, dry atmosphere. As a consequence, the physical characteristics of the atmospheric boundary layer change. The work presented here concerns a real polynya event in the region of Terra Nova Bay (TNB), Antarctica, where a recurring coastal polynya occurs nearby the Italian Antarctic Base. The aim is the study of atmospheric response to the presence of a open water area of realistic size by three-dimensional numerical simulations. Atmospheric numerical modelling is a fundamental tool for the study of air - polynya interactions in the remote polar regions, where observational data are difficult. The numerical model used for the simulations is a recent version of ETA model (Mesinger et al., 2006), with the addition of a piecewise linear advection for the wind field. ECMWF and NCEP data provided the initial and boundary conditions. A previous version of the model had already been successfully used in the Antarctic area (De Carolis et al, 2006, Casini and Morelli, 2007). As a first step to analyze the polynya event, numerical simulation was performed for the period from 12 to 17 July 2006 in order to study the development of the katabatic wind (Morelli and Casini, 2008; Morelli, 2008). Daily satellite images, concerning the period, display that a sea ice free area formed on 15 and 16 July, reaching its maximum extension of about 4000 km2 on 16 July (Morelli et al.,2007). In order to gain insight on the atmospheric response to open water area within a sea ice field, ETA model runs were carried out from 15 to 17 July 2006 both with and without the polynya (as derived by satellite image) included in the initial conditions. Results from these experiments will be presented. Simulations were performed with 50 layers in the vertical from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0,125x0,125 transformed degrees (about 20kmx20km). Numerical simulations show that the polynya had significant effects on temperature, specific humidity, vertical velocity and horizontal wind speed throughout the boundary layer. The effects are found over and downwind the sea ice free area. The presence of polynya produced significant thermal modifications in atmosphere. Turbulent kinetic energy also responded to its presence and the low level wind speed changed over the open water area. References: Casini, G., Morelli, S. (2007) ‘Katabatic wind and Terra Nova Bay polynya: a study using two different versions of ETA model’, Geophysical Research Abstract, vol. 9, 02656.De Carolis G., Morelli, S., Parmiggiani, F., and Casini G. (2006) ‘Terra Nova Bay polynya: a study by satellite microwave observations and Eta model simulations’,Geophysical Research Abstract, vol. 8, 08433Mesinger F., Jovic D., Sin Chan Chou, Gomes J.L., Bustamante J.F. (2006) ‘Wind forecast around the andes using the sloping discretization of the Eta coordinate’, Proceedings of 8 ICSHMO, Foz do Iguacu, Brazil, 24-28 April 2006, INPE.Morelli S., Casini G., Parmiggiani F. (2007) ‘Wintertime katabatic event and polynya at Terra Nova Bay: a study by ETA simulations and AMSR-E images’, Extended Abstract of 2nd Antarctic Meteorological Observation, Modeling and Forecasting (AMOMF) Workshop, June 2007.Morelli S., Casini G. (2008) ‘Antarctic katabatic winds and their interaction with a coastal polynya in Terra Nova Bay, studied by ETA model simulations and satellite images’, Geophysical Research Abstract, vol. 10.Morelli S. (2008) ‘ETA Mode

2009 - Low level wind and coastal Terra Nova Bay polynya:A study by Eta model simulations. [Relazione in Atti di Convegno]
Morelli, Sandra; G., Casini
abstract

The study focuses on a real event of katabatic wind and polynya at Terra Nova Bay (TNB). The katabatic winds and the impact of an open polynya on their intensity are simulated by a numerical atmospheric model. The event was selected as satellite images of September 2003 displaying a fluctuating TNB polynya, in particular on 16 September, the area of open water was of about 3100 km2. Simulations of the meteorological conditions of 15-16-17 September were carried on with the limited area Eta model, which is a three-dimensional, primitive equation, grid-point model. It is one of the mesoscale numerical weather prediction models operational at the National Centers for Environmental Prediction of the U.S. National Weather Service. The Eta model is coupled with a land surface model derived from the Oregon State University model and it is able to perform hydrostatic and non-hydrostatic runs. Further, terrain following or quasi-horizontal coordinates can be selected. Eta has been used for applications at mid-latitudes and, in an older version, for the study of Antarctic summer conditions. Eta runs were performed, both including the sea ice cover in the TNB area and a polynya of realistic extension, as shown from the satellite images in order to get an insight into the sensitivity of the katabatic wind to the presence of a polynya of realistic extension. The results show the strong effect of the polynya, included in the initialization of model simulations: the low level katabatic wind is intensified from the presence of the sea ice free area.The simulations were carried on using terrain following coordinates with 45 layers from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0.05×0.05 transformed degrees (about 8 Km × 8 Km as approximate distance between two mass points on the semi-staggered Arakawa E grid). ECMWF and NCEP data provided initial and boundary conditions.Numerical simulations and results are presented and discussed.

2008 - Antarctic katabatic winds and their interaction with a coastal polynya in Terra Nova Bay, studied by Eta Model simulations and satellite images [Abstract in Rivista]
Morelli, Sandra; G., Casini
abstract

Coastal polynyas are areas of partially or totally ice free water which form in coastal regions during the wintertime in spite of the low air temperatures. Coastal polynyas are often referred to as ‘latent heat polynyas’ .They are thought to be opened and maintained by strong offshore winds blowing over the area, and by the curvature of the coastline. Sea ice is removed by the wind and new ice is constantly formed and exported (Smith et al, 1990) with a consequent release of latent heat . Atmospheric numerical modelling and satellite observations are fundamental tools for the analysis of winter polynya events occurring over remote and often data sparse polar regions.This study concerns the region of Terra Nova Bay (TNB) in Antarctica, where a recurring coastal polynya occurs offshore the Italian Antarctic Base ‘Mario Zucchelli Station’ (MZS). The aim is the study of a real event of TNB polynya and the two way interaction between strong katabatic winds, blowing from the coast, and development of the polynya. The atmospheric circulation of the area is studied by simulations performed with ETA model in its last version (Mesinger et al., 2006), also with a piecewise linear advection for the wind field. A previous version of the model was yet successfully used for simulations in the Antarctic area (De Carolis et al, 2006, Casini e Morelli, 2007). Satellite images from AMSR-E (Morelli et al, 2007) and AVHRR and observational data integrate the analysis. The presented case study is a polynya event happened during the period 12-17 July 2006. AMSR-E images displayed the presence of a sea ice free area, that reached an extension of 4000 km2 on 16 July 2006. 72 hours simulations were carried on in order to study the atmospheric circulation of the period over a large area; ECMWF analyses provided the initial and boundary conditions. Furthermore, ETA simulations, nested in the previous domain, were performed with a finer resolution. To gain some insight on atmospheric response to open water within a sea ice field, simulations were carried on both with and without a prescribed open polynya (derived by AMSR-E images) forced in the initial conditions . Simulations were performed with 50 layers in the vertical from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0,125x0,125 transformed degrees (about 15kmx15km) for the coarser grid, and 0,05x0,05 transformed degrees for the finer grid (about 8kmx8km), respectively. Numerical simulations show that cyclonic structures were moving over the Ross Sea, and that the polynya development, displayed by satellite images, was related to the katabatic wind field blowing from the Reeves glacier. ETA simulations performed with an realistic open water region in the initial conditions show a strengthening of the surface wind field over the ice free area.

2007 - Comparison of MODIS and ETA profiles of atmospheric parameters in coastal zones with radiosonde data [Articolo su rivista]
M., Adamo; G., DE CAROLIS; Morelli, Sandra
abstract

The quality of atmospheric profiles gathered by the spaceborne Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the Terra platform and those predicted by the ETA atmospheric circulation model are assessed against corresponding radiosonde (RS) measurements. The analysis is carried out on a statistical basis taking as reference the radiosoundings collected at two coastal stations, namely Ajaccio (France) and Pratica di Mare (Italy), during the spring 2000. The examined days were characterized by smooth and slow variations of the atmospheric conditions so that a temporal lag up to about three hours between RS and MODIS profiles could be considered for comparison purposes. Both ETA predictions and MODIS retrievals compare well with RS data and their relative agreement is good. Although, as expected, the profiles of the analyzed quantities, namely temperature and moisture for both MODIS and ETA outputs and horizontal wind components predicted by ETA model, could not follow the largest fluctuations measured by RS, their averages are reproduced with a satisfactory degree of reliability. These results encourage the perspective to exploit remote measurements from the MODIS sensor of atmospheric temperature and water vapour as input to operative circulation models, such as ETA, for reliable forecasts and detailed monitoring on global scale of the atmospheric structure and dynamics.

2007 - Katabatic wind and Terra Nova Bay polynya: a study using two different versions of the Eta model [Abstract in Rivista]
G., Casini; Morelli, Sandra
abstract

Eta model is an international model, used for research or development in a lot of countries. Moreover, it is one of the mesoscale numerical weather prediction model operational at National Center for Environmental Prediction (NCEP) and at Center for Weather Prediction and Climate Studies (CPTEC).In the late nineties came out a problem about strong downslope winds, that tend to be underestimated in Eta model simulations; in recent publications of Mesinger and Jovic [1], and Mesinger, Jovic et al. [2] is suggested that the problem could be due to step-mountain eta discretization, and is proposed a simple scheme to address it (eta ‘sloping steps’). An updated version of Eta model that contains in particular this modification (available at CPTEC web site www.cptec.inpe.br/etaweb) was used in this work. Strong interactions take place between katabatic winds and coastal polynyas, like Terra Nova Bay (TNB) polynya [3]. Because of the almost impossible access to TNB in winter, model simulations are an important tool for the study of polynya’s events, besides the Eta model has been used with good results for studying Antarctic conditions [4]. This study is focused on a TNB polynya case happened in period September 15-16-17/2003; the presence of coastal polynya of about 3100 Km2 in that days over TNB is displayed in ASAR satellite images [3]. 72-h simulations of the meteorological conditions in that period were carried on with Eta model in old (NCEP) and new (CPTEC) version, both coupled with a land surface model derived from the Oregon State University (OSU). The simulations were performed with 50 layers from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0.05x0.05 transformed degrees (about 8Kmx8Km).Using the NCEP and CPTEC versions of the Eta model, descriptions of the event, in particular the representation of the katabatic wind, are presented and discussed.

2006 - Comparison of Modis and Eta profiles of atmospheric parameters in coastal zones with radiosonde data. [Abstract in Rivista]
M., Adamo; G., De Carolis; Morelli, Sandra
abstract

The quality of atmospheric profiles gathered by the spaceborne Moderate Resolution Imaging Spectroradiometer (Modis) sensor onboard the Terra platform and predicted by the Eta atmospheric circulation model are assessed against corresponding radiosonde (RS) measurements. The quality analysis is carried out on a statistical basis taking as reference the radiosoundings collected at two coastal stations, namely Ajaccio (France) and Pratica di Mare (Italy), during the spring 2000. Both Eta predictions and Modis retrievals compare well with RS data and their relative agreement is good. Although, as expected, the profiles of the analyzed quantities, namely temperature and moisture for both Modis and Eta outputs and horizontal wind components predicted by Eta model, could not follow the largest fluctuations measured by RS, their averages are reproduced with a satisfactory degree of reliability. These results encourage the perspective to exploit remote measurements from space of atmospheric parameters as input to operative circulation models, such as Eta, for reliable forecasts and detailed monitoring on global scale of the atmospheric structure and dynamics.

2006 - Monitoring atmospheric gravity waves by means of SAR, MODIS imagery and high resolution ETA atmospheric model: a case study [Relazione in Atti di Convegno]
Adamo, M; G., DE CAROLIS; Morelli, Sandra; Parmiggiani, F.
abstract

A study aimed at retrieving sea surface wind fields of semi-enclosed basins from combined use of SAR imageryand a high resolution mesoscale numerical atmospheric model, is presented. Two consecutive ERS-2 SAR framesand a set of NOAA/AVHRR and MODIS images acquired over the North Tyrrhenian Sea on March 30, 2000were used for the analysis. SAR wind speeds and directions at 10 m above the sea surface were retrieved using thesemi-empirical backscatter model CMOD4. Surface wind vectors predicted by the meteorological ETA modelwere exploited as guess input to SAR wind inversion procedure. ETA is a three-dimensional, primitive equation,grid-point model currently operational at the National Centers for Environmental Prediction of the U.S.National Weather Service. The model was adapted to run with a resolution up to about 4.0 Km. It was foundthat the inversion methodology was not able to resolve wind speed modulations due to the action of anatmospheric gravity wave, called “lee wave”, which occurred in the analyzed area. A simple atmospheric wavepropagation model was thus used to account for the SAR observed surface wind speed modulation. Synergy withETA model outputs was further exploited in simulations where atmospheric parameters up-wind the atmosphericwave were provided as input to the lee wave propagation model.

2006 - Synergic use of SAR imagery and high resolution atmospheric model to estimate marine wind fields : an application in presence of an atmospheric gravity wave episode. [Articolo su rivista]
M., Adamo; G., DE CAROLIS; Morelli, Sandra; F., Parmiggiani
abstract

A study aimed at retrieving sea surface wind fields of semi-enclosed basins from combined use of SAR imagery and a high resolution mesoscale numerical atmospheric model, is presented. Two consecutive ERS-2 SAR frames and a set of NOAA/AVHRR and MODIS images acquired over the North Tyrrhenian Sea on March 30, 2000 were used for the analysis. SAR wind speeds and directions at 10 m above the sea surface were retrieved using the semi-empirical backscatter models CMOD4 and CMOD-IFREMER. Surface wind vectors predicted by the meteorological ETA model were exploited as guess input to SAR wind inversion procedure. ETA is a three-dimensional, primitive equation, grid-point model currently operational at the National Centers for Environmental Prediction of the U.S. National Weather Service. The model was adapted to run with a resolution up to about 4.0 Km. It was found that the inversion methodology was not able to resolve wind speed modulations due to the action of an atmospheric gravity wave, called “lee wave”, which occurred in the analyzed area. A simple atmospheric wave propagation model was thus used to account for the SAR observed surface wind speed modulation. Synergy with ETA model outputs was further exploited in simulations where atmospheric parameters up-wind the atmospheric wave were provided as input to the lee wave propagation model.

2006 - Terra Nova Bay polynya: a study by satellite microwave observations and Eta Model simulations [Abstract in Rivista]
G., De Carolis; Morelli, Sandra; F., Parmiggiani; G., Casini
abstract

Antarctic coastal polynyas have been the subject of great scientific interest in the last two decades. Being regions of intense heat loss from the ocean to the atmosphere, polynyas can behave as “ice factories'” contributing a significant fraction of total annual sea ice production and, thus, to the climate of the Antarctic continent. This study focuses on Terra Nova Bay (TNB) polynya as it is one of the most important of the whole Antarctic continent, and also because the Italian Antarctic Base “Mario Zucchelli Station” is located in that area. Being the access to TNB polynya almost impossible in winter; remote sensing and model simulations remain the only available tools to study winter polynya phenomena. Because of the very frequent cloud cover of polar regions in winter, optical and thermal sensors are practically useless and profitable observations are reduced to active (SAR) and passive microwave sensors. Two major microwave sensors have become available in recent years to the scientific community: 1. the Advanced Synthetic Aperture Radar (ASAR) on Envisat satellite; and 2. the passive microwave radiometer AMSR-E (Advanced Microwave Scanning Radiometer for EOS) on Aqua satellite. From the ESA archive of ASAR scenes of winter 2003 over TNB, the image of Sept.16, which displays an open polynya of about 3100 Km2, and the image of Sept.25, with the polynya completely shut down, were selected. For the period 10-30 September 2003, daily images of the AMSR-E radiometer, covering the whole Ross Sea, were acquired and analyzed [1]. Wind data were retrieved from the Antarctic Automatic Weather Stations Project of the University of Wisconsin (uwamrc.ssec.wisc.edu).Simulations of the meteorological conditions of Sept. 15-16-17 were carried on with the limited area model Eta, which is a three-dimensional, primitive equation, grid-point model. It is one of the mesoscale numerical weather prediction models currently operational at the National Centers for Environmental Prediction of the U.S. National Weather Service. The Eta model is coupled with a land surface model derived from the Oregon State University model and it is able to perform hydrostatic and non-hydrostatic runs. Eta has been used for applications at mid-latitudes [2] and, in an older version, for the study of Antarctic summer conditions [3].Eta runs were performed, both including the sea ice cover in the Ross Sea area, as retrieved from the ECMWF at a spatial resolution of 0.36° and a polynya of realistic extension, as shown from the satellite images.The simulations were carried on with 50 layers from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0.05×0.05 transformed degrees (about 8 Km × 8 Km as approximate distance between two mass points on the semi-staggered Arakawa E grid).Results of this combined analysis of the physical properties of TNB polynya are presented and discussed.

2005 - A study of " Prestige" oil spill by the combined use of ENVISAT/ASAR, quikSCAT scatterometer and limited area model simulations [Abstract in Rivista]
M., Adamo; G., De Carolis; Morelli, Sandra; F., Parmiggiani
abstract

The "Prestige" tanker wreck of November 2002 was a major disaster affecting the environment of north-western coasts of Spain (Galicia). The consequences of "Prestige" accident have been studied by several research groups in the last two years. Hereafter we present a study of "Prestige" oil spill by means of a combined use of remote sensing tools and limited-area model simulations.Two Envisat/ASAR Wide Swath (WS) images over the area of the disaster, Nov. 17 and Dec. 3, were retrieved from ESA archive. ASAR WS processing consists of 2 main steps: 1. Ingestion and geo-location, performed by means of the commercial software package TeraScan (www.seaspace.com); and 2. Speckle filtering and segmentation, performed according to the algorithms described in [1] and [2].A major question in oil spill detection with SAR images is the discrimination between "real" oil slicks and "lookalikes". To operate this distinction we adopted an approach, based on local meteo-marine condition analysis, which implies:1. Wind and wave information retrieval from SAR image itself, performed according to the methods described in [3] and [4];2. QuikSCAT scatterometer wind data from the 2 daily passes of the satellite, as obtained from PODAAC/JPL;3. Simulations by means of the limited-area meteorological model Eta [5], a three-dimensional, primitive equation, grid-point model currently operational at the National Center for Environmental Prediction of the U.S. National Weather Service.We shall present and discuss the results of the analysis outlined above.[1] A. Baraldi and F. Parmiggiani, "A refined Gamma MAP SAR speckle filter with improved geometrical adaptivity", IEEE Trans. Geosci. Remote Sensing, vol. 33, No. 5, (1995), 1245-1257.[2] A. Baraldi, P. Blonda, F. Parmiggiani and G. Satalino, "Contextual clustering for image segmeation", Optical Engineering, vol. 39 (2000), no. 4, pp. 1-17[3] P. Wadhams, F. Parmiggiani and G. De Carolis, "The use of SAR to measure ocean wave dispersion by frazil-pancake ice fields", J. Phys. Oceanography, Vol. 32 (2002), no. 6, 1721-1746.[4] Giacomo De Carolis, Flavio Parmiggiani and Elena Arabini, "Observations of wind and ocean wave fields using ERS Synthetic Aperture Radar imagery", Int. J. Remote Sensing, Vol. 25, No. 7-8 (2004) 1283 - 1290.[5] D. Cesini, S. Morelli, F. Parmiggiani, "Analysis of an intense bora event in the Adriatic area", Natural Hazards and Earth System Sciences, (2004) vol. 4, Issue 2: 323 - 337.

2004 - An experiment of comparison of SAR wind analysis with Eta Model output in the North Thyrrenhian Sea [Abstract in Rivista]
D., Cesini; G., De Carolis; Morelli, Sandra; F., Parmiggiani
abstract

An experiment of comparison between SAR wind analysis and Eta model output for the North Thyrrenhian Sea is presented. Two consecutive SAR frames, covering large part of the North Thyrrenhian Sea, from ERS2 pass of March 30, 2000, were acquired from ESA. The empirical backscatter model CMOD4 was used to obtain wind stress while wind direction could be resolved without ambiguity either from PODAAC/JPL archive of QuikSCAT satellite data or from ECMWF. In situ reference data were supplied by the open sea ODAS Italia1 buoy located at 43.8N, 9.1E. The meteorological Eta model is used to study the features in the area. Eta is a three dimensional, primitive equation, grid point model which is operational at the National Centers for Environmental Prediction of the U.S. National Weather Service. The SAR wind analysis was applied to a region north of Corsica and to a region between Corsica and the continent which is in the shadow of the wind coming from NW. We will show how the Eta model outputs perfectly match the SAR analysis in the same regions. To complete the study, we also applied the SAR wave analysis to the two regions cited above.

2004 - Analysis of an intense bora event in the Adriatic area [Articolo su rivista]
D., Cesini; Morelli, Sandra; F., Parmiggiani
abstract

Numerical simulations of a bora event, recently occurred in the Adriatic area, are presented. Two reference runs at different horizontal resolution (about 20 km and 8 km) describe the case. Initial conditions for the atmospheric model integration are obtained from ECMWF analyses. Satellite data are used for comparisons. A further run at horizontal resolution of 8 km, using initial satellite sea surface temperatures, is per-formed to evaluate their impact on the low level wind over the Adriatic Sea. All the simulations are carried out with 50 layers in the vertical. Numerous aspects of the simulations are found to be in agreement with the understanding as well as the observational knowledge of bora distinctive characteristics. Satellite data and model results indicate that a more realistic simulation of the bora wind over the sea is achieved using the model with 8 km horizontal resolution and that the low level wind in this case is sensitive, though weakly, to the difference between the used sea surface temperature fields. Simulation results also show that both wind intensity and the area around wind peaks tend to increase when relatively higher sea surface temperatures are used.

2004 - Intercomparison of two models, ETA and RAMS, with TRACT field campaign data [Articolo su rivista]
S., TRINI CASTELLI; Morelli, Sandra; D., Anfossi; J., Carvalho; S., ZAULI SAJANI
abstract

In this work a model intercomparison between RAMS and ETA models is carried out, with the aim of evaluating the quality and accuracy of these mesoscale models in reproducing the time evolution of the meteorology in real complex terrain. This is of great importance not only for meteorological forecast but also for air quality assessment. Numerical simulations are performed to reproduce the mean variables' fields and to compare them with measurements collected during the field campaign TRACT. The domain covers the Rhine valley and surrounding mountainous region and we consider a time period of two days. Results from simulations are compared to observations relative to ground stations and radiosoundings. A qualitative analysis is joined to a quantitative estimation of some reference statistical indexes. Both RAMS and ETA models performances are satisfactory when compared to the measured data and also their relative agreement is good. The mean variable fields are reproduced with a satisfactory degree of reliability, even if the simulated profiles are not able to describe the largest fluctuations of the variables. At the surface stations, the best agreement between predictions and observations is obtained for the wind velocity, while the quality of the results is lower for temperature and humidity.

2004 - Synergic use of Sar Imagery and High- Resolution Atmospheric Model to Estimate Wind Vector over the Mediterranean Sea [Relazione in Atti di Convegno]
Adamo, M.; G., DE CAROLIS; Morelli, Sandra; F., Parmiggiani
abstract

An experiment whose aim is the retrieval of surface wind fields from SAR imagery coupled to a high resolution mesoscale numerical atmospheric model in semi-enclosed sea basin, is presented. A sea region belonging to North-Western Mediterranean Sea, which spans in W-E direction from Corsica (8.8 E) to Italian coast (10.5 E) and in N-S direction from Lygurian Sea (44.0 N) to North Tyrrhenian Sea (42.2 N), was selected as test area. Two consecutive ERS-2 SAR frames from the pass of March 30, 2000, along with a set of NOAA/AVHRR and MODIS images acquired on the same day were used for the analysis. SAR wind speeds and directions at 10 m above the sea surface were retrieved from predictions of the semi-empirical backscatter models CMOD4 and CMOD-IFREMER, which describe the dependency of the normalized radar cross section (NRCS) on wind vector and ERS-2 SAR image geometry. Surface wind vectors predicted by the meteorological ETA model were exploited as guess input to SAR wind inversion procedure to describe atmospheric conditions in the area, according a Bayesian approach recently proposed in literature. ETA is a three-dimensional, primitive equation, grid-point operational model running at the National Centers for Environmental Prediction of the U.S. National Weather Service. The model was adapted to run on selected regions of the Mediterranean basin with a nested very high, up to about 4.0 Km, resolution. The latter feature makes ETA model particularly suitble for its use in combination with SAR images. Besides, to simulate and predict several specific atmospheric weather phenomena, ETA outputs also include the vertical distributions of physical parameters such as air pressure, temperature, moisture up to about 25 Km. Apart some discrepancies in sparse and small areas, an overall agreement between SAR inversion results and ETA predictions was found. More importantly, it was found that the inversion methodology was not able to resolve wind speed modulations due to the manifestation of an atmospheric gravity wave, which occurred in the analyzed area as a result of the terrain disturbance to the air flow imposed by the peninsula located North of Corsica. Temporal evolution of the wave propagation phenomenon was allowed by inspection of NOAA/AVHRR and MODIS images through the detection of a cloud band associated to the atmospheric wave. A wave propagation model describing waves in the atmosphere owing to the disturbing action on the primary air flux by terrain features was thus used to account for the observed surface wind speed modulation on SAR image. Synergy with ETA model outputs was further exploited as atmospheric parameters up-wind the atmospheric wave were considered as input to the wave propagation model.

2003 - Analysis of an intense bora event in the Adriatic area. [Abstract in Rivista]
D., Cesini; Morelli, Sandra; F., Parmiggiani
abstract

Bora is a cold, strong, low level wind which blows mainly from NE along the Adriatic coast. However, bora-like winds occur in other regions i.e. Antarctic slope winds, Boulder windstorms. Cold air, forced through channels between higher terrain and accelerated by katabatic effects, can reach downslope very high speed, with strong spatial gradient and temporal variations. This wind affects coastal area and alters significantly the Adriatic sea status. Nowadays is still difficult to predict accurately its intensity, longevity and internal structure, which are related to mesoscale features as well as to local effects. Moreover, high resolution is needed. The meteorological Eta model is used to study the features of an intense real bora event recently occurred in the Adriatic area. Eta is a three-dimensional, primitive equation, hydrostatic, grid-point model. It is operational at the National Center for Environmental Prediction of the U.S. National Weather Service. ECMWF data are used to initialize model integration. Both single run and one-way nested run are performed. Model output is compared to ECMWF data, to composite sea surface temperature (SST) maps of northern Adriatic and to scatterometric measurements from QuikSCAT satellite. The daily SST maps are obtained by processing AVHRR data and by composing maps of 8-10 satellite passes in the day, in order to reduce cloud cover which affects their quality. QuikSCAT Level3 wind data are obtained from the PODAAC/JPL web site at the spatial resolution of 0.25 degrees, two times a day, in the morning (ascending) and in the afternoon (descending) satellite pass.

2003 - On a bora event simulated by the Eta Model [Articolo su rivista]
Morelli, Sandra; N., Berni
abstract

This study presents a numerical simulation of the bora wind as it occurs in form of a severe wind blowing down coastal mountains and over the Adriatic Sea. A typical cyclonic bora event, occurring during the period January 3-6, 1995, is simulated using a nested limited area model. An integration, with horizontal resolution of about 14 km and a nested one, with higher resolution, about 5.5 km, are presented. The 1997 version of the Eta Model is used for both the lower resolution and the higher resolution runs. Numerous details of the simulation are found to be in good agreement with the understanding as well as the observational knowledge of the bora, thus supporting confidence in the realism of the results. In particular, features of the simulated flow are seen strongly indicative of some basic characteristics of the hydraulic model of the phenomenon, such as the mountain wave breaking and the upstream flow acceleration. Moreover, the increase in horizontal resolution, in combination with an improvement of the coastal SST information, led to a still improved realism of the low-level wind representation over the Adriatic Sea.

2002 - A case study of severe windstorm in the Adriatic region [Abstract in Rivista]
Morelli, Sandra; M. S., Tesini
abstract

Downslope windstorm ( bora wind ) are observed, mostly during the winter season, in the adriatic area. Bora, a cold dry northeasterly wind, influences a region, which extends from Trieste ( Italy) southward for nearly 500km. It shows an alongshore variability in speed, mainly affected by the orography of the mountain chain along the eastern adriatic coast. The rapresentation of this characteristic needs high horizontal resolution for the previsional model; moreover, the strong wind speed changes the sea status, so that the marine forecasting can not leave out this space and time varying atmospheric forcing field. A three dimensional, hydrostatic meteorological model ( Eta model ) is used to investigate a bora episode, occurred on 3-6 January 1995. This work provides a description of the meteorological conditions able to develop the event and an analysis of the interaction between the flow and Dinaric Alps. The simulation results highline the presence of mountain wave breking over the lee slope and the propagation of the wind over the Adriatic Sea.

2000 - Modelling study of Mesoscale Cyclogenesis over Ross Sea,Antarctica,on February 18,1988 [Articolo su rivista]
M., Stortini; Morelli, Sandra; S., Marchesi
abstract

This paper examines the development of a summer event of mesoscale cyclogenesis off the coast of Victoria Land in the presence of katabatic winds, by means of numerical simulations. These refer to the period from 00 UTC 17 February to 00 UTC 19 February 1988 and were performed using the hydrostatic ETA (1993 version) limited area model with resolution 55 km x 55 km x 17 levels. The ETA model reproduces katabatic winds from Terra Nova Bay and a trough on the southwestern Ross Sea. A cyclonic vortex is simulated in the trough, even though it is weaker than the one present in the analyses initialized by the European Center for Medium Range Weather Forecast (Reading, UK). Idealized simulations with varied surface conditions were also performed. In particular, an ice-covered ocean acts to weaken the atmospheric phenomena, while a no-mountain simulation emphasizes the influence of the orography and the cold winds from the coast of Victoria Land on the mesocyclonic activity.

2000 - Simulation of a katabatic wind event at Terra Nova Bay [Relazione in Atti di Convegno]
Morelli, Sandra; Stortini, M.
abstract

In the framework of the Italian Antarctic Programme, a numerical simulation of a katabatic event near Terra Nova Bay on 5-6 February 1995 is performed. The three-dimensional Hydrostatic mesoscale Eta model is used. The aim is to investigate the coupling between wind, radiation balance and turbulent fluxes at the surface. The analysis is carried out by means of time series of boundary layer parameters averaged over a selected area. In this case study the absolute magnitudes of the turbulent fluxes of sensible and latent heat are comparable and the latent heat flux seems to be an important component of the surface energy balance.

1999 - ETA and RAMS numerical mesoscale simulations at high resolution in complex terrain [Abstract in Rivista]
D., Anfossi; J., Carvalho; Morelli, Sandra; S., Trini Castelli; S., Zauli Sajani
abstract

An intercomparison between numerical simulations obtained by ETA model and RAMS model during a period of about 48 hours is presented. A nesting procedure was performed, so that the highest horizontal resolution is about 4 km. The domain covers the Rhine Valley and surroundings and the time window is from 00 UTC September 16, to 00 UTC September 18. During this period, the TRACT Field Measurement Campaign was performed, so that further comparisons between simulations and observations are presented, using statistical indices such as root-mean-square error and fractional bias.

1999 - Impact of modified resolutions on the numerical simulations of Vaison-La-Romaine flash-flood [Articolo su rivista]
S., Marchesi; Morelli, Sandra; M., Stortini
abstract

The Vaison-la-Romaine flash-flood occurred on September 22nd 1992 is an example of intense precipitation events characterising the fall season in the Mediterranean area. Numerical simulations of the Vaison-la-Romaine case have been carried out using the 1993 version of the Eta Model, which is a grid point model, based on the primitive equations in hydrostatic approximation. The series of numerical simulations was done combining different horizontal (40 and 20 km) and vertical (16 and 38 levels) resolutions, in order to point out their impact on the representation of precipitation field in respect to the observations available from MAP Data Center.

1999 - Simulation of Antarctic Surface Wind Using the Eta Model [Abstract in Rivista]
S., Marchesi; Morelli, Sandra; Stortini, Michele
abstract

In recent years numerical studies of Antarctic atmosphere have been performed using three-dimensional (3-D) mesoscale models. Katabatic winds and low surface temperatures are perhaps the most remarkable features of the Antarctic climate: the the annual mean wind speed reachs 19 m/s along the Adelie Coast (East Antarctica). A simulation using the limited area model ETA, with a horizontal grid resolution of 40 km and 38 levels in vertical, nested within the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses is shown. The simulation of the period from 00 UTC January 16 to 00 UTC January 19 1994 captures many synoptic features seen in ECMWF analyses. Realistic confluence zones over the continent are evident in the wind at the lowest levels and, as expected , the wind speeds are high along the steep escarpment. Comparisons between simulated wind and AWS data at Adelie Land and Dome C will be presented.

1999 - The Vaison-La-Romaine Intense Precipitation Event: Mesoscale Simulations [Abstract in Rivista]
S., Marchesi; Morelli, Sandra; Stortini, Michele
abstract

Some intense precipitation events are currently object of intensive study by means of numerical simulations in the framework of MAP (Mesoscale Alpine Program) Project. Among the others, the so called Vaison case, which occurred on September 22nd, 1992 has been selected for this work and the associated meteorological situation has been simulated using the Eta model. The flash flood associated with the intense precipitation resulted in serious damages, so that the correct meteorological forecast turns out to be of fundamental importance in order to try to reduce the dramatic impact of such episodes. This case seems to be a prototype intense rainfall event for the fall season in the Alpine Region. Nevertheless, several different numerical models are giving only partially successful representation of the episode, both in terms of the correct location and amplitude of the observed rainfall and of the actual chronology of the precipitation. The presence of a large amount of rain of convective origin due to the combination of several mesoscale convective systems in advance of a cold front crossing the French region during September 22nd seems to be one of the crucial aspects related to this failure. In this work, the results of Eta model simulations are presented, with a particular reference to the influence of initial conditions on the location of precipitation nuclei and to the simulated temperature and humidity fields with respect to the available observations and the ECMWF analysis.

1998 - Numerical Mesoscale Analysis of selected MAP intense precipitation episodes [Articolo su rivista]
S., Marchesi; Morelli, Sandra; M., Stortini
abstract

In the framework of the International MAP Project, several intense precipitation events were selected and are currently object of intensive study in the pre-campaign phase of the project, in order to verify the capability of the atmospheric numerical models to reproduce the pattern of precipitation field and the main features of the atmospheric flow and to analyze in details the meteorological situations leading to such events. In this respect, two of the selected MAP episodes were simulated using a mesoscale version of the Eta Model which is run operationally in various national and regional Meteorological Services.

1998 - Numerical mesoscale simulations of the atmospheric flow over Antarctica [Relazione in Atti di Convegno]
M., Stortini; Morelli, Sandra; S., Marchesi; S., Davolio
abstract

The atmospheric circulation over Antarctica during January 1994 is simulated using a limited area model, Eta model (version 1993, 55km horizontal resolution, 17 levels). The simulations are performed with initialized analyses from European Centre for Medium Range Weather Forecasts (ECMWF) as initial and boundary conditions. The results are in good agreement with the analyses even if the mesoscale features on the high Plateau are poorly represented. The model deficiency over the Plateau is emphasised in the medium-range simulation. Additional comparisons of model results and AWS observations will be presented.

1998 - Numerical simulations of intense precipitation events using the Eta model. [Abstract in Rivista]
S., Marchesi; Morelli, Sandra; Stortini, Michele
abstract

In the framework of the international MAP project (Mesoscale Alpine Program) some events of intense precipitation were selectec and were object of intensive study, also using numerical models, in order to understand in details the features of the related atmospheric flow. Therefore, simulations of some of these episodes using a mesoscale operational model were performed and the results shown, with particular attention to the quantitative precipitation prediction. The used model is the Eta model, version 1993, and comparisons with ECMWF data and with observations were also shown.

1997 - Effect of the elimination of the sea surface fluxes on Piedmont flood [Articolo su rivista]
S., Marchesi; Morelli, Sandra; M., Stortini
abstract

In the framework of the Internationa MAP Project, a series of simulations using the Eta Model relative to the intense precipitation event was performed in order to point out the influence of the sea on this episode. On the whole, the results suggest that the sea surface fluxes affect the convective precipitation on the local scale, while the large scale component of the precipitation is almost unaffected.

1997 - Influence of the Mediterranean Sea over intense precipitation events [Relazione in Atti di Convegno]
S., Marchesi; Morelli, Sandra; M., Stortini
abstract

The Mediterranean basin and, in particular the Alpine region, was affected by some intense precipitation events during recent years. The complex orography surrounding the region and the presence of a relatively warm sea like the Mediterranean make this region very difficult to study from the point of view of the features of the atmospheric flow. Some of these events were selected inside an International Project called MAP (Mesoscale Alpine Program) and are object of intensive study in order to go into the knowledge of aspects which are not fully understood or not adequately represented in the atmospheric models. A series of simulations of one of these events events was analyzed in order to point out the main forcing which played an important role in the spatial and temporal determination of the episode and in the intensity of precipitation.

1996 - A first approach on the use of eta model in the antarctic region [Relazione in Atti di Convegno]
Stortini, Michele; Morelli, Sandra; S., Marchesi
abstract

Some preprocessing and postprocessing characteristics of the Eta model are shown. The preprocessing routines (version 1989) seem to be inadequate if the model runs in polar regions and thus the horizontal interpolation procedure must be checked very carefully in these cases. New preprocessing routines have been developed and an application of a new horizontal interpolation is shown. New postprocessing routines, based on an operational version of the Eta model, are also implemented.

1996 - Analysis of pyrheliometric measurements at Modena (Italy) from 1990 to 1991 [Articolo su rivista]
Morelli, Sandra; M., Stortini
abstract

During the last few years continuous measurements of direct solar irradiance have been taken in Modena (37 m. a.s.l.) using pyrheliometers with three filters (quartz filters, OG51, RG61). The apparent atmospheric transmission calculated using the so-called rationing technique can be utilised as a useful parameter to monitor the atmosphere. Preliminary results suggest that the atmospheric transmission seems be able to highlight meteorological events such as the transport of dust.

1996 - Confronto tra previsioni di modelli numerici operazionali: caso dell'alluvione in Piemonte 4-6 Novembre 1994 [Articolo su rivista]
S., Marchesi; Morelli, Sandra; Stortini, Michele
abstract

La previsione fornita da due diversi modelli numerici (il modello Eta versione 1993 ed il modello tedesco del Deutscher Wetterdienst) viene confrontata per la situazione che ha portato alla disastrosa alluvione in Piemonte del novembre 1994, sia dal punto di vista degli usuali campi meteorologici che dei campi di precipitazione accumulata in periodi di 12 ore. Per questi ultimi sono riportati anche confronti con dati osservativi. Questo studio preliminare mostra come il modello Eta riproduca in modo complessivamente buono le caratteristiche salienti del flusso atmosferico, così come la struttura e l'evoluzione del campo di precipitazione.

1996 - Intense precipitation as simulated by a limited area model [Articolo su rivista]
S., Marchesi; Morelli, Sandra; Stortini, Michele
abstract

Event of intense precipitations which occurred over southern France and northern Italy from 4 to 6 November 1994 has been studied by means of an atmospheric Limited Area Model (LAM). The aim of this work is to analyse the behaviour of the model in order to evaluate its performance. The model used is called Eta model (1993 version) originally developed through joint effort between Belgrade University and NMC (National Meteorological Center), Washington, USA. Eta model belongs to the class of LAM and it is currently operational at NMC. Initial and boundary conditions are obtained from ECMWF (European Center for Medium-range Weather Forecasting), Reading, UK, while orographic values are obtained from US Navy dataset. Eta model gives total precipitation cumulated over a specified time interval, as well as common meteorological fields. Both usual synoptic fields and cumulated precipitations over 24 hours and comparisons with observational data for Piedmont are shown for the above 3 day period.

1996 - Some relevant aspects of the atmospheric flow in the period 3-6 November 1994 [Articolo su rivista]
S., Marchesi; Morelli, Sandra; Stortini, Michele
abstract

The event of intense precipitation causing flood and heavy damages over Piedmont in November 1994 has been simulated by means of the hydrostatic limited area model, the Eta model version 1993, at an horizontal resolution of about 25 km and 17 levels in the vertical.We analyse total and convective precipitation fields cumulated over a 6 hour period obtained from the Eta model, in order to select some areas and time intervals, in which the convective component of precipitation is prevailing. We analyse the behaviour of the convective adjustament process by comparing vertical cross sections and profiles obtained from Eta model against those obtained from ECMWF initialised analysis.

1994 - L'uso di un modello ad area limitata (UB/NMC) nella simulazione della ciclogenesi alpina: risultati preliminari [Articolo su rivista]
S., Marchesi; Morelli, Sandra; R., Purini
abstract

Viene utilizzato un modello ad area limitata (UB/NMC) per simulare lo sviluppo di un ciclone, considerato di moderata intensità, sul Mediterraneo occidentale nel marzo 1982.La risoluzione del modello è di 0.5° di latitudine e di longitudine e la rappresentazione orografica è di tipo "silhouette". Al fine della "validazione" del modello sono state effettuate prove in assenza di montagne e con modifiche delle altezze "silhouette", che hanno mostrato come il modello riproduca l'importante ruolo dell'orografia nell'innesco della ciclogenesi alpina. Montagne molto "smussate" non riescono a riprodurre le caratteristiche essenziali del fenomeno, mentre montagne molto più pronunciate rispetto ai profili reali le modificano in modo sensibile, causando un anticipo temporale ed uno spostamento verso nord dello sviluppo, ciò in accordo con precedenti risultati.

1994 - Statistics of some Synthetic Parameters of Vertical Profiles of Pressure and Temperature obtained by One Year of ECMWF’s Analysis over Europe [Articolo su rivista]
Boccolari, Mauro; Morelli, Sandra; Santangelo, Renato
abstract

In this paper monthly distributions of synthetic parameters of vertical profiles of temperture and pressure over Europe are shown. the data have been obtained by fits of one-year data analysis of the ECMWF model. In particular, distributions of lapse rates, distribution of heights of the layers and distributions of temperature and dry-air pressure of the lower level are reported. Within the precision of the input data and by disregarding the boundary layer, a finer subdivision of layered troposphere and lower stratosphere has been obtained.

1992 - Direct and total irradiance: measurement, calculation and comparison with Lowtran 6 and Lowtran 7 predictions [Articolo su rivista]
Morelli, Sandra; Stortini, Michele
abstract

The Lowtran code is used to determine solar transmission, direct solar irradiance and total radiance. In this paper results of comparisons between Lowtran 6 and Lowtran 7, the second including multiple scattering, are presented. These simulations are also compared with measurements of global irradiance carried out with a radiometer UV, in the range (295 divided-by 385) nm.

1992 - Distribuzione dei giorni continuativi di nebbia e delle annesse piccole precipitazioni a Modena [Relazione in Atti di Convegno]
Frontero, Paolo; Lombroso, Luca; Morelli, Sandra; Santangelo, Renato
abstract

Vengono studiate le serie storiche di osservazioni sulla nebbia a Modena, risalenti fino al 1892.Come schema interpretativo delle distribuzioni statistiche è stato adottato quello già considerato a riguardo delle precipitazioni idriche (Morelli e Santangelo, 1989).Nel caso della nebbia si suppone che essa sia conseguenza principale dei fenomeni di blocco. L'anno verrà suddiviso in periodi di 28 giorni per un totale di 13 periodi in un anno. I dati relativi a periodi omologhi in anni diversi sono stati accumulati nell'ipotesi di ciclostazionarietà e di evoluzione stagionale lenta. Precisamente verranno presentate le distribuzioni delle catene dei giorni consecutivi contrassegnati da presenza di nebbia e iniziate nel periodo considerato. La catena di giorni di nebbia viene interrotta per cause dinamiche che a fini statistici vengono considerate come casuali. A fini di agrometeorologia verranno anche riportate le concomitanti osservazioni di precipitazione idrica da nebbia (precipitazione < = 0.4 mm in 24 ore).Per meglio interpretare il fenomeno nebbioso verranno anche considerate le concomitanti distribuzioni di pressione.

1991 - Confined Diffusion [Articolo su rivista]
Morelli, Sandra; R., Santangelo; S., Vincenzi
abstract

An equation for the unidimensional confined diffusion is proposed. The equation coincides with the well-known homogeneous equation except the presence of a source term. This term which has the form of a dipole distribution is located on a moving front which sharply separates two distinct regions. In the first region (from the boundary up to the front) the confined solution coincides with a suitable solution of the homogeneous equation; in the second region (besides the front) it vanishes. The source term, moreover, switches off the diffusing flux at the front. The sharp confinement allows to relax the original boundary conditions of the homogeneous equation. Precisely, to the function depending on the time at the boundary, another arbitrary function depending on the space at the initial time is added. This new function (provided not vanishing) allows to obtain in general an acceptable evolution of the front and does not prevent the validity of the conservation law: flux at the boundary is equal to the time variation of the diffusing quantity contained between the boundary and the front. By a suitable choice of this new function, so that it results to be connected to the other boundary condition (that depending on time) it is possible to arrive at an evolution of the front such as: lÖ{4Kt}\lambda \sqrt {4Kt} , where λ,K, corresponding, respectively, to a dimensionless parameter and diffusivity, depend on the medium. Under such simplifying assumption, it is possible to obtain an analytical expression for the confined solution. This solution, evaluated in a point of the space, arrives asymptotically at the same value reached by the solution of the homogeneous equation.

1991 - Continuità della temperatura e delle concentrazioni [Relazione in Atti di Convegno]
V., Dallari; Morelli, Sandra; Santangelo, Renato; S., Vincenzi
abstract

Si propone di introdurre un principio di continuità della temperatura e della concentrazione nei mezzi materiali. Gli attuali modelli di tipo conduttivo (eventualmente anche in forma turbolenta) o di tipo diffusivo vengono spesso considerati in esempi nei quali si ipotizza un improvviso salto di temperatura o un improvviso rilascio di sostanza in un certo punto. Nel caso unidimensionale è noto che questi esempi, sono esattamente risolubili in termini analitici. Tuttavia, all'istante e nel punto in cui avviene il salto brusco, i modelli danno luogo a flussi infiniti e velocità infinite. Tale situazione non appare molto accettabile da un punto di vista fisico.

1991 - Strutture dell'Osservatorio Geofisico di Modena a supporto di campagne di misura sul clima mediterraneo [Relazione in Atti di Convegno]
Boccolari, Mauro; Frontero, Paolo; Lombroso, Luca; Morelli, Sandra; Pugnaghi, Sergio; Santangelo, Renato
abstract

L'Osservatorio Geofisico vanta una secolare tradizione nella raccolta di dati meteorologici, la serie storica delle osservazioni inizia infatti nel 1827. Già da alcuni anni la maggior parte dei dati è stata trasferita su supporto magnetico direttamente utilizzabile da calcolatore ed è continuamente aggiornata.

1991 - Un metodo per la determinazione automatica della quota in un qualsiasi punto del territorio italiano [Articolo su rivista]
Boccolari, Mauro; Morelli, Sandra; Santangelo, Renato
abstract

In alcune applicazioni scientifiche è richiesta la conoscenza della quota in punti generici di un vasto territorio. In questa nota viene descritta una nuova metodologia per la stima automatica della altezza, utilizzante come banca dati la cartografia digitalizzata 1:500000 dell'Istituto Geografico Militare. Tali carte digitalizzate hanno il vantaggio di ricoprire l'intero territorio italiano, anche se esse sono un insieme di dati di altimetria spazialmente meno denso di campioni già utilizzati in altri lavori.

1990 - Analisi di sondaggi meteorologici e dati di previsione di modelli a circolazione generale [Relazione in Atti di Convegno]
Morelli, Sandra
abstract

Sono presentati i primi risultati di un confronto tra temperature previste a 24 ore dal Centro Europeo per la Previsione del Tempo a Medio Termine di Reading e dati TEMP per stazioni della pianura padana. I dati di previsione numerica disponibili nei nodi di una griglia di circa 300 km di lato sono stati interpolati mediante trasformate di Fourier a due dimensioni. La tecnica permette di stimare il valore della previsione in un qualunque punto. Il lavoro è preliminare ad un modello di previsione combinato deterministico-statistico.

1989 - Il banco dati meteorologico ed i modelli di previsione statistica dell'Osservatorio Geofisico di Modena [Articolo su rivista]
Morelli, Sandra
abstract

L'importanza della raccolta di osservazioni meteorologiche dell'Osservatorio Geofisico dell'Università di Modena e Reggio Emilia, oltre che dalla sua estensione, è data dal fatto che per buona parte esse possono essere considerate omogenee o riconducibili all'omogeneità. Sono state analizzate le serie storiche (circa 130 anni) di temperatura giornaliera minima media e massima e quella di precipitazione e sono stati messi a punto modelli statistici. Nella pubblicazione sono descritti tali modelli statistici. Le temperature sono rappresentate tramite la somma di un segnale deterministico ed un segnale stocastico, quest'ultimo analizzato nell'ambito dei processi AR-MA. Per le precipitazioni si è adottato un modello ad urna.

1989 - Statistical forecasting of daily precipitations [Articolo su rivista]
Morelli, Sandra; Santangelo, Renato
abstract

From the time series of daily precipitation observed in Modena (Italy) since 1830, a model for the daily statistical forecasting has been built. The main tool of the model is an urn which contains balls labelled by «wet» and «dry». The daily extraction from the urn determines whether, on that day, there will be a precipitation,i.e. if that day will be «wet» or «dry». If the day is dry, the content of the urn is changed by adding other balls some labelled by dry and some other labelled by wet. The numbers of added balls depend on the day of the year (seasonal dependence). If the day is wet, the urn is reset to an initial condition, which depends on the day of the year (seasonal dependence). Moreover, if the day was wet, the likely quantity of precipitation is deduced from a gamma distribution with parameters which are seasonally dependent. All the seasonally dependent parameters in the statistical processes previously discussed can be expressed by Fourier expansions, having one year as fundamental period. The observed distributions are adequately fitted by expansions which do not exceed the second harmonic. Although the model has been tuned on the observations in Modena, it can presumably be extended to the entire region having same climate,i.e. the Po Plain. È presentato un modello per la previsione statistica giornaliera di precipitazione, messo a punto mediante la serie temporale delle osservazioni giornaliere a Modena (Italia) che inizia dal 1830. Si tratta di un modello ad «urna» la quale contiene palline etichettate «pioggia» e «secco». L'estrazione giornaliera dall'urna determina se in quel giorno ci sarà precipitazione, ossia se il giorno è di pioggia» o «secco». Se il giorno è secco, il contenuto dell'urna è variato con l'aggiunta di altre palline etichettate da «secco» e «pioggia». Il numero di palline aggiunte dipende dal giorno dell'anno (dipendenza stagionale). Se il giorno è piovoso, il contenuto dell'urna è riportato ad una condizione iniziale, che dipende dal giorno dell'anno (dipendenza stagionale). Inoltre, nel caso di giorno piovoso, la quantità di pioggia è dedotta da una distribuzione gamma con parametri dipendenti dal tempo. Tutti i parametri con dipendenza stagionale del precedente processo statistico sono stati espressi mediante uno sviluppo in serie di Fourier, avente un periodo fondamentale di un anno. Le distribuzioni osservate sono adeguatamente rappresentate da sviluppi in serie che non superano la seconda armonica. Questo metodo di previsione statistica giornaliera può essere facilmente combinato con metodi di previsione giornaliera dinamica, poiché le previsioni (sia statistica che dinamica) sono effettuate ogni giorno. Sebbene il modello sia stato messo a punto mediante le osservazioni di precipitazione a Modena, presumibilmente esso può essere esteso all'intera regione climaticamente omogenea, ossia la Pianura Padana. Из временной последовательности суточных выпадений осадков, зарегистрированных в Модене (Италия) с

1988 - Modelli statistici di serie storiche. [Relazione in Atti di Convegno]
Morelli, Sandra
abstract

Sono discussi i modelli statistici messi a punto fino alla data del Convegno messi a punto esaminando le serie storiche di temperatura e precipitazione osservate a Modena.

1988 - Particular exact solutions for a small area [Abstract in Rivista]
Santangelo, Renato; Morelli, Sandra
abstract

Particular exact solutions of the hydrodynamic equations for a small sea are presented. They have been obtained under the following assumptions: sea on Earth's tangent plane; constant density; viscous-like stress tensor made up by an isotropic part and two other parts only horizontally isotropic; traceless and dissipative viscous-like stress tensor. In the search of particular exact solutions a supplementary hypothesis has been assumed: the advective part results from the gradient of suitable potentials (kinetic energy and rotational potential). Since the exact solution is considered as an initial solution in a perturbation approximation, the small Coriolis force has been neglected. For a small rectangular sea as the Adriatic sea, the solutions satisfy the conditions on the fixed boundaries (bottom and coastlines of the sea) with a very good approximation. The conditions at the free surface will be also discussed.

1987 - Particular analytical solutions of the hydrodinamic equations [Articolo su rivista]
Morelli, Sandra; Pugnaghi, Sergio; Santangelo, Renato
abstract

Some particular solutions of the hydrodynamic equations are presented. In the solutions the velocity is a complex exponential on space variables, i.e. it is a real exponential multiplied by sine and cosine functions. The amplitude of the exponential is a time dependent complex vector. These particular solutions have been obtained using the approximation of a constant density fluid lying in the Earth’s tangent plane. The equations in eulerian approach contain the advective part which is balanced by two pressure terms. The first term corresponds to the kinetic energy, the second term to a rotational energy. The existence of this last energy implies rather strict conditions on the possible solutions. The exponential solutions are obtained neatly under the assumption of a vanishing Coriolis force. However the solutions obtained under this approximation may still be a good initial solution of the hydrodynamic equations for a sea like the Adriatic. The friction has been represented by a symmetric tensor with vanishing trace and constant coefficients, which operates linearly on the components of the velocity. The tensor is not assumed to be necessarily isotropic in the vertical direction.

1987 - Soluzioni particolari per fluidi anisotropi in verticale. [Abstract in Rivista]
Morelli, Sandra; Santangelo, Renato
abstract

Viene introdotto nelle equazioni della idrodinamica un tensore degli sforzi modificato avente una traccia uguale a -3p. Trascurando la forza di Coriolis sono state ottenute alcune soluzioni particolari aventi un andamento esponenziale in dipendenza della quota. E’ ipotizzabile utilizzare tali soluzioni particolari nella descrizione dello strato superficiale dell’atmosfera.

1985 - Hydric precipitation as joint statistical process: dry or wet day and amount of water [Articolo su rivista]
Morelli, Sandra; R., Santangelo
abstract

The long time series of daily hydric precipitations in Modena, Italy, allows homogeneity tests which do not involve the assumption of particular models. The tests show that the number of dry days which have just preceded any wet day and the amount of precipitated water are independent. This result, which is likely to be valid for the Po Valley, implies that the hydric precipitation considered as a joint process can be factorized into two independent processes. The first concerns the probability that the particular day considered is dry or wet; the second concerns the probability of a certain amount of precipitated water in that wet day. The probabilities of each process have been often studied in the literature, whereas studies on the joint process are absent. È stata analizzata la lunga serie temporale di precipitazioni idriche registrata dal 1830 a Modena, Italia, al fine di verificare se la quantità di acqua precipitata ed il numero di giorni secchi precedenti il giorno piovoso possano considerarsi variabili statistiche indipendenti. Le variabili sono risultate indipendenti. Ciò permette di semplificare il processo considerato bivariato, scomponendolo nel prodotto di due processi indipendenti. Il primo relativo alla probabilità che un certo giorno sia secco o piovoso ed il secondo relativo alla probabilità di una certa quantità di acqua precipitata in quel giorno piovoso. L'indipendenza consente di utilizzare i risultati di studi precedenti nei quali sono stati analizzati soltanto i dati sulle quantità di precipitazione oppure i dati sui numeri di giorni secchi consecutivi. Проводится анализ длинной временной последовательности выпадения осадков в Модене (Италия), который не включает никаких предположений конкретных моделей. Проведенный анализ показывает, что число сухих дней, которым предшествовал влажный день, и количество выпавших осадков можно рассматривать как независимые статистические переменные. Этот результат, по-видимому, справедлив для всей долины По. Полученный результат предполагает, что рассматриваемое выпадение осадков, как объединенный процесс, может быть факторизован в виде двух независимых продессов. Первый множитель описывает вероятность того, что рассматриваемый конкретный день является сухим или влажным; второй множитель описывает вероятность выпадения определенного количества осадков в этот влажный день. Вероятность каждого процесса довольно часто рассматривалась в литературе, однако исследования объединенного процесса отсутсвуют.

1984 - Statistical model for daily precipitation [Relazione in Atti di Convegno]
Morelli, Sandra; Santangelo, Renato
abstract

Daily records of precipitation measured in Modena (Po Plain in Italy) since March 1830, were analyzed in the framework of a stochastic bivariate model. The following stochastic variables were chosen: q, equivalent height of water precipitated during the wet day; d, number of dry days which precede the wet day. The two variables appear reasonably independent so that, in a wet day, the overall probability that the next wet day is labelled by q and d is given by the product of two independent probabilities. The probability that the next wet day occurs after d+1 days follows a Polya distribution. This distribution has two parameters which show a seasonal dependence. The probability distribution of the equivalent height of precipitated water, q follows a gamma distribution. This distribution has also two parameters which show a seasonal dependence.

1984 - Struttura statistica delle precipitazioni [Abstract in Rivista]
Morelli, Sandra; Santangelo, Renato
abstract

Sono stati analizzati dati di precipitazioni idriche, registrati giornalmente dall'Osservatorio Geofisico fin dal 1830. Una serie temporale così lunga permette la messa a punto di un modello statistico in grado di sintetizzare l'andamento dei dati mediante un'espressione di probabilità comprendente pochi parametri. In prima approssimazione la serie temporale dei dati è stata considerata ciclostazionaria. Inoltre è stato scelto di caratterizzare ogni giorno con precipitazione misurabile mediante tre variabili: la quantità di acqua precipitata, q, il numero di giorni secchi che hanno preceduto il giorno con pioggia, d,il numero d'ordine del giorno considerato entro ogni anno. Il modello ipotizzato è bivariato in q e d. La distribuzione di probabilità della variabile q segue una distribuzione gamma, mentre quella della variabile d approssima una distribuzione di Polya. La rappresentazione della probabilità tramite una distribuzione di Polya non è unica. Si è trovato che tale probabilità può essere espressa da un modello ad urna la cui composizione cambia ogni giorno.

1984 - Urn model for daily hydric precipitation [Abstract in Atti di Convegno]
Morelli, Sandra; Santangelo, Renato
abstract

The aim of this paper is to present a statistical model which could exploit further dynamical information, capable to give a better forecast of daily hydric precipitation. The two variables, amount of water (q) and number of dry days which precede the wet day (d), appeared reasonably independent. The statistical distribution of q is well fitted by a Gamma distribution. Each day is considered wet or dry according to the result of a drawing from an urn. The composition of the urn changes day to day as in the contagious models.

1980 - Search of single long period oscillations in the daily temperatures [Articolo su rivista]
Cecchi, Rodolfo; Marseguerra, Marzio; Morelli, Sandra; Santangelo, Renato
abstract

Long-period oscillations have been searched in the time series of the daily minimum, mean and maximum temperatures measured in Modena, Italy, during the years 1869–1976. By assuming only one oscillation present, the amplitude and its statistical uncertainty have been estimated by means of a fitting procedure which takes into account the stochastic variability of the daily temperatures. The period of the long-term oscillations has been chosen to be an integer number of years (from 2 up to 36). This choice and the fit performed over a suitable number of years (the maximum possible multiple of the period) ensure a numerical stable solution and a negligible correlation between the long-period oscillation and the annual and seasonal oscillations present in the time series. The instrumental uncertainty of the long-period amplitude has been also evaluated. Within the overall uncertainty, no reliable evidence exists on single long-period oscillations. Sono state cercate oscillazioni singole a lungo periodo nella serie temporale formata dalle temperature minime, medie e massime, misurate giornalmente a Modena durante gli anni 1869–1976. Nell'ipotesi di un'unica oscillazione sono state stimate l'ampiezza dell'oscillazione e la sua incertezza statistica mediante un procedimento di approssimazione che teneva conto della variazione stocastica delle temperature giornaliere. Come periodo delle oscillazioni a lungo termine si è scelto un numero intero di anni compreso fra 2 e 36. L'approssimazione è stata effettuata su un numero di anni che era il massimo multiplo del periodo compatibile con i dati disponibili. Con tali scelte le soluzioni risultano numericamente molto stabili. Inoltre le correlazioni fra i diversi parametri stimati in ciascuna approssimazione risultano trascurabili. È stato anche valutato l'effetto dell'errore sistematico di misure sull'ampiezza dell'oscillazione a lungo periodo. Dai risultati non emergono prove affidabili sull'esistenza di oscillazioni singole a lungo termine entro la risoluzione statistica e sistematica del presente studio. Проводится поиск осцилляций с большим периодом во временной последователвности суточных минимальных, средних и максимальных температур, измеренных в Модене, Италии, в течение 1869–1976 г. г. Предполагал, что существует только одна осцилляция, оценивается амплитуда и статистическая неопределенность, оспользуя процедуру подгонки, которая учитывает стохастическое изменение суточных температур. Период продолжителяной осцилляции выбирается равным целому числу лет (от 2 до 36). Этот выбор и проведенная подгонка соответствующего числя лет (максимально возможное кратное периоду) обеспечивают численное устойчивое решение и позволяйт пренебречь корреляцией между осцилляцией с большим периодом и ежегодными и сезонными осцилляциями, присутствующми во временной последовательности. Оценивается инструментальная неопределенность амплитуды осцилляции с большим периодом. С учетом полной неопределенности не обнаружено нодежного подтверждения отдельных осцилляциь с большим периодом.

1979 - Evidence of an anthropogenic climatic change in the daily temperatures of Modena,Italy [Articolo su rivista]
Marseguerra, Marzio; Morelli, Sandra; Saltini, Gianfranco Matteo; Santangelo, Renato
abstract

The daily minimum, mean and maximum temperatures, measured in Modena, Italy, in the years 1869–1976 have been analysed in order to detect possible long-term trends. An increasing trend appears to be present both in the minimum and in the mean temperature with a reasonable confidence level. The presence of a trend in the maximum temperatures instead is questionable. The trends have been estimated by means of a procedure which provides also the statistical uncertainty of the parameter representing the trend. The uncertainty due to the errors of the measuring instruments has been also evaluated. The trends do not show any clear seasonal pattern. The overall behaviour of the trends (for the three daily temperatures) and the lack of a seasonal pattern can be explained by a «greenhouse» effect due to the increasing town. The experimental results and the explanation suggested are quite consistent with similar results and conclusions found elsewhere. Sono state analizzate le temperature giornaliere minime, medie e massime misurate nella città di Modena nel periodo 1869–1976, at fine di mettere in evidenza eventuali tendenze a lungo termine. Nelle temperature giornaliere minime e medie esiste una tendenza all'aumento con un ragionevole livello di affldabilità. Viceversa è più dubbia la presenza di una tendenza nelle temperature giornaliere massime. Il parametro che rappresenta la tendenza a lungo termine è stato stimato mediante una procedura che permette di ottenere la sua varianza. Oltre alla parte statistica è stata stimata anche l'incertezza causata dagli errori strumentali. Le tendenze a lungo termine stimate non risentono di effetti stagionali. Il comportamento delle tendenze a lungo termine (caratterizzate dall'aumento in due sole temperature giornaliere) e la mancanza di effetti stagrionali può essere spiegata da un effetto «serra» causato dall'accrescimento della città. I risultati sperimentali e la spiegazione che è proposta sono compatibili con analoghi risultati e conclusioni già trovati altrove. Чтобы определить возможные долгосрочные тенденции, анализируются ежедневные минимальные, средние и максимальные температуры, измеренные в Модене (Италия) в период 1869–1976 г.г. Обнаружена тенденция увеличения минимальных и средних температур. Однако наличие тенденции для максимальной температуры является сомнительным. Указанные тенденции установлены с помощью процедуры, которая дает также статистическую неопределенность параметра, характеризующего тенденцию. Также оценивалась неопределенность, обусловловленная ошибками аппаратуры измерений. Тенденции не обнаруживают каких-либо ясных сезонных характеристик. Общее поведение тенднций (для трех ежедневных температур) и отсутствие сезонных особенностей может быть объяснено с помощью эффекта, обусловленного растущими городами. Полученные экспериментальные результаты и предложенное объяснение сотласуются с аналотичными результатами и выводами, полученными ранее.

1979 - Quantitative estimation of climatic changes in the daily temperatures [Articolo su rivista]
Marseguerra, Marzio; Menziani, Marilena; Morelli, Sandra; Pugnaghi, Sergio; Santangelo, Renato
abstract

In geophysical time series, such as daily temperatures, trends may be present due to global or to anthropogenic climatic changes. In this paper the quantitative estimation of the trend and of its statistical uncertainty is obtained by means of a fitting procedure, provided the stochastic behaviour of the time series has been previously determined, and the time random part of the time series is stationary. Moreover a detailed discussion on the reliability of the results is presented. The method has been tested with positive results on the minimum daily temperatures measured in Modena, Italy, since 1869.

1979 - Search of long term periodicities in the daily temperatures. [Abstract in Rivista]
Cecchi, Rodolfo; Marseguerra, Marzio; Morelli, Sandra; Santangelo, Renato
abstract

The long records of the daily minimum, mean and maximum temperatures measured in Modena since 1868, have been analyzed in order to detect long term periodicities with a fitting procedure which provides also the statistical uncertanty of the stimated amplitudes. From the values of the amplitudes and their overall uncertainties no striking evidence exists of long term amplitudes with high confidence level.

1978 - Absolute estimation of radon daughter concentrations in air by alfa-spectrometry [Articolo su rivista]
Aprilesi, Giancarlo; A., Loria; Magnoni, Gaetano; Marseguerra, Marzio; Morelli, Sandra; Rivasi, Maria Rosa
abstract

A method for the estimation of the concentration of radon daughter in air is given. The method is based on alfa spectrometric counting measurements performed either during or after the dust collection with an electrostatic precipitator. The relations between measured counts and concentrations in air of the collected nuclides (RaA, RaB and RaC) are obtained assuming a constant collection rate and a linear collection rate model. It turns out that the less sophisticated model gives more satisfactory estimations of the parameters.

1978 - Statistical forecasting of daily temperatures using short records of previous temperatures [Articolo su rivista]
Balestri, Lorenzo; Cecchi, Rodolfo; Marseguerra, Marzio; Morelli, Sandra; Rivasi, Maria Rosa; Santangelo, Renato
abstract

From previous analysis of the daily minimum, meam and maximum temperatures in Modena, Italy, over more than 100 years, it has already been demonstres that each time series may be well represented by the sum of a seasonal deterministic function and a stationary gaussian stochastic signal. The latter was found to be autocorrelated and well represented by an autoregressive, moving-average process of order 2 and 1 respectively, AR(2)-MA(1). In this paper, starting from subrecords of daily temperatures, taken from the whole record available in Modena, long-term and short-term predictions have been compared with the actually measured values. The positive results obtained by using the previous model suggest that such statistical forecasting can be performed also in other locations of similar climatic behavior, even if only short records of daily temperatures are available.

1977 - Le falde acquifere della pianura di Reggio Emilia: 2°-Idrochimica [Capitolo/Saggio]
Pellegrini, Maurizio; Colombetti, Alessandro; Morelli, Sandra; Zavatti, Adriano
abstract

Nella presente nota vengono descritte alcune caratteristiche chimiche delle acque sotterranee della Provincia di Reggio Emilia (Pianura Padana, Italia settentrionale) e precisamente: residuo fisso a 105°C, grado idrotimetrico e concentrazione dello ione ferro. A tal fine si è esaminato il chimismo delle acque dei fiumi e si sono prese in considerazione circa 5200 analisi relative ad acque provenienti da pozzi di diversa profondità, fino a 90 m. Dopo aver suddiviso i pozzi in tre classi di profondità (0-30; 30-60; 60-90 m), si è proceduto ad una rielaborazione matematica delle analisi con un metodo, qui descritto, che ha scarsi precedenti in letteratura e che consiste innanzitutto in una interpolazione bidimensionale dei dati al fine di ottenere i valori nei nodi di un prefissato reticolo regolare, poichè i dati a disposizione possedevano una distribuzione molto irregolare. Si sono poi tracciate, utilizzando il programma PLOFOU, le curve delle concentrazioni dei tre parametri considerati, relativamente ai tre intervalli di profondità fissati, ottenendo così nove carte. Mentre per lo ione ferro non si sono ottenuti risultati significativi o riferibili a condizioni idrogeologiche particolari, per gli altri due parametri sono state evidenziate una stretta dipendenza delle acque sotterranee da quelle superficiali e aree preferenziali di infiltrazione, fatto questo assai importante ai fini della protezione territoriale. La nota, infine, descrive l'andamento dell'interfaccia tra le acque salate e quelle dolci, che si mantiene a profondità variabili da 100 a 600 m, seguendo all'incirca le forme strutturali del substrato marino di età calabriana e pre-quaternaria, notevolmente dislocato.

1977 - Statistical forecasting of daily temperatures [Abstract in Rivista]
Balestri, Lorenzo; Cecchi, Rodolfo; Marseguerra, Marzio; Morelli, Sandra; Rivasi, Maria Rosa; Santangelo, Renato
abstract

The behaviour of the daily minimum, mean and maximum temperatures was already found to be given by the sum of a deterministic function of the day and a stationary normal process with zero mean. Its standard deviations for the three temperatures observed in the period 1892-1974 are given. This is a measure of the error in the long term prediction of daily temperatures. The normal process is found to be well represented by an autoregressive- moving average process.

1977 - Stochastic behaviour of the daily minimum mean and maximum temperature in Modena,Italy [Articolo su rivista]
Aprilesi, Giancarlo; Marseguerra, Marzio; Morelli, Sandra; Rivasi, Maria Rosa; Saltini, Gianfranco Matteo; Santangelo, Renato
abstract

The minimum, mean and maximum daily temperature measured in Modena, Italy, since 1892 can be well represented by the sum of a deterministic and a fluctuating signal. The deterministic signal is given by a constant plus the first three harmonics having a fundamental period of one year: a total of seven constant parameters (four amplitudes and three phases). The fluctuating term is stationary and has a first-order probability density function which is normal with zero mean. The autocovariance of the fluctuating signal is well fitted by the sum of two decreasing exponentials for time lags up to 30 days. Since the second exponential is much smaller in amplitude and much slower, the autocovariance is approximated by a single decreasing exponential for time lags up to 7–10 days. Therefore the process is Markovian only initially.

1976 - Stochastic behaviour of daily minimum, mean and maximum temperatures in Modena, Italy. [Abstract in Rivista]
Aprilesi, Giancarlo; Marseguerra, Marzio; Morelli, Sandra; Rivasi, Maria Rosa; Saltini, Gianfranco Matteo; Santangelo, Renato
abstract

A stochastic model, mostly non-parametric, has been developed for the analysis of the daily temperatures in view of their forecasting and of studies of climatic changes.As an example the minimum, mean and maximum daily temperatures in Modena, Italy, since 1892, have been analyzed.

1975 - Concentrazione di SO2 nell'area urbana di Modena [Articolo su rivista]
Aprilesi, Giancarlo; Balestri, Lorenzo; Cecchi, Rodolfo; Magnoni, Gaetano; Morelli, Sandra; Rivasi, Maria Rosa
abstract

E' in corso lo studio di una serie di dati relativi alla concentrazione di SO2 nell'area urbana di Modena. In questa fase preliminare si è cercato di verificare l'esistenza ed il tipo di correlazioni tra concentrazione dell'inquinante e parametri meteorologici per mezzo di un semplice modello matematico. Per la città di Modena i valori della concentrazione, anche se mediati su tempi lunghi (1 mese), risultano indipendenti dalla velocità media del vento, mentre mostrano, a parità di intensità di emissione (Q), una certa correlazione con la temperatura, almeno durante la stagione fredda.

1975 - Dati di nevosità registrati dall'Osservatorio Geofisico di Modena (1830-1975) [Articolo su rivista]
Aprilesi, Giancarlo; Balestri, Lorenzo; Cecchi, Rodolfo; Morelli, Sandra; Rivasi, Maria Rosa; Santangelo, Renato
abstract

Sono state riorganizzate in forma sistematica e divulgate le misure di precipitazione nevosa a Modena dal 1830 al 1975 (data della pubblicazione). I dati di nevosità sono caratterizzati dalla data e dalla altezza raggiunta al suolo dalla "neve asciutta". Per la interpretazione di alcuni casi controversi, sono stati consultati testi e manoscritti di archivio. E' stata, inoltre, effettuata una iniziale analisi statistica.

1975 - Le precipitazioni nevose a Modena dal 1830 al 1975 [Articolo su rivista]
Aprilesi, Giancarlo; Balestri, Lorenzo; Cecchi, Rodolfo; Morelli, Sandra; Rivasi, Maria Rosa; Santangelo, Renato
abstract

Le precipitazioni nevose registrate a Modena fin dal 1830 sono messe a disposizione per lo studio dei cambiamenti climatici. I dati sono raggruppati entro ciascuna "stagione fredda" al fine di ottenere una maggiore significatività statistica ed eliminare quasi completamente ogni correlazione temporale. La stagione fredda corrisponde all'inverno attorniato da quei mesi vicini durante i quali a Modena può nevicare. Precisamente vengono presentati in una tabella il numero di giorni di neve e la quantità di neve "asciutta" precipitata. La neve asciutta, misurata in centimetri, viene definita come la neve che si è depositata al suolo senza fondersi. Vengono inoltre mostrate e discusse alcune distribuzioni ricavate dai parametri riportati nella tabella. Vengono anche date altre informazioni riguardanti le nevicate più precoci e più tardive, le nevicate più cospicue e più intense e altri fenomeni eccezionali associati alle precipitazioni nevose.

1975 - Valori normali della temperatura a Modena (1892-1974) [Articolo su rivista]
Aprilesi, Giancarlo; Balestri, Lorenzo; Cecchi, Rodolfo; Morelli, Sandra; Rivasi, Maria Rosa; Saltini, Gianfranco Matteo; P., Tavoni
abstract

Avendo creato presso l'Osservatorio Geofisico dell'Università di Modena un banco dati meteorologico, comprendente, alla data della pubblicazione, osservazioni dal 1892 al 1974, è stato possibile l'aggiornamento dei valori normali la cui ultima elaborazione risaliva al 1943.

1973 - Trapping levels in anthracene crystals by thermally stimulated currents [Articolo su rivista]
Garofano, Torquato; Morelli, Sandra
abstract

Thermally stimulated current (T.S.C.) measurements in anthracene crystals indicate the presence of various trapping levels. By regulating the excitation time and the excitation temperature we could isolate a monomolecular T.S.C. signal withE = (0.53 ± 0.03) eV and ϕ = 0.6.108 s-1 and determine the sign of the trapped carriers. The results obtained support the hypothesis that a level is involved which is strictly connected with the crystal lattice and presumably associated with chemical impurities contained in the crystal. Misure di correnti termicamente stimolate (T.S.C.) in cristalli di antracene hanno permesso di accertare la presenza di vari livelli di intrappolamento. Regolando tempo e temperatura di irraggiamento è stato possibile isolare un segnale di T.S.C. monomolecolare conE = (0.53 ± 0.03) eV e ϕ = 0.6 . 108 s-1. È stato inoltre accertato il segno dei portatori intrappolati. I risultati ottenuti avvalorano l’ipotesi che si tratti di un livello strettamente connesso con il reticolo cristallino, presumibilmente associate ad impurezze chimichc contenute nell’interno del cristallo. Измерения термическ и стимулированного т ока в кристаллах антрацена указывает на присутствие разли чных уровней ловушек. Регулируя время возбуждения и темпер атуру возбуждения, мы можем изолировать си гнал мономолекулярного т ермически стимулиро ванного тока сЕ= (0.53 ± 0.03) эВ и ϕ=0.6·108 сек-1 и кроме то го определить знак за хваченных носителей. Полученны е результаты подтвер ждают гипотезу, что им еется один уровень, тесно связанный с кри сталлической решетк ой и, вероятно, с химиче скими примесями, содержащимися внутр и кристалла.