1,721,113 research outputs found
Meteorological impact of realistic Terra Nova Bay polynyas
No full textThe 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
Il banco dati meteorologico ed i modelli di previsione statistica dell'Osservatorio Geofisico di Modena
No full textL'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
Modeled surface heat fluxes over Terra Nova Bay polynya
No full textPolynyas 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
An upgraded version of the Eta Model applied to Antarctic case studies
No full textUpgrades 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-
Modelli statistici di serie storiche.
No full textSono 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
Analisi di sondaggi meteorologici e dati di previsione di modelli a circolazione generale
No full textSono 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
A modeling study of an Antarctica polynya event.
No full textAn 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
Simulation of a katabatic wind event at Terra Nova Bay
No full textIn 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
Direct and total irradiance: measurement, calculation and comparison with Lowtran 6 and Lowtran 7 predictions
No full textThe 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
Surface-Atmosphere Interactions during a Polynya Event at Terra Nova Bay (Antarctica).
No full textNumerical 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 image
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