Opažanja sjeveroistočno-jadranske bure pomoću satelita TerraSAR-X: rani rezultati

Some early results of the TerraSAR-X observations of the northeastern Adriatic bora wind are presented in this paper. TerraSAR-X is a German X-band radar satellite launched in 2007 that carries phased array X-band synthetic aperture radar (SAR) operating in different polarizations and providing multiple imaging modes. SAR backscatter can be used to derive wind fields at spatial resolution that no other instrument can provide. Terrain-induced jet and wake patterns are particularly conductive to the SAR-instrument examination. Bora, a cold and dry downslope wind blowing from north-easterly directions on the eastern side of the Adriatic Sea, exhibits such a response. Since bora is primarily winter wind and the town of Senj is known for frequent and severe bora episodes we focus on TerraSAR-X scenes collected in the winters of 2011 and 2012 over an area with Senj roughly in its center. Recently developed XMOD2 geophysical model function is used for wind magnitude derivation, whereas the WRF model was employed to estimate the wind direction. The selected TerraSAR-X scenes have captured representative bora events exhibiting rich details in bora-induced jet and wake patterns on the lee of the Dinaric Alps. The details registered in the normalized radar cross section response strongly suggest the need for still higher resolution numerical simulations in order to properly model the orographic impact on and the fine details in the surface wind field. Comparisons with both research and operational modeling results indicate that the currently used geophysical model function may benefit from enlarging the matchup data base with samples of severe winds.U radu su prikazani rani rezultati detekcije bure na sjeveroistočnoj strani Jadrana pomoću satelita TerraSAR-X. TerraSAR-X je njemački satelit lansiran 2007. godine koji nosi „phased- array“ radar sintetičke aperture (SAR) s mogućnošću rada uz različite polarizacije i uz više načina snimanja. Povratno zračenje instrumenta SAR može se iskoristiti za određivanje polja vjetra uz prostorno razlučivanje koje ne omogućuje ni jedan drugi instrument. Područja niskih mlaznih struja i zavjetrinske tišine, uzrokovana terenom, posebno su podatni za ispitivanja pomoću instrumenta SAR. Bura - hladan, suh i jak planinski vjetar koji puše iz sjeverno istočnih smjerova na istočnoj strani Jadranskog mora, izaziva spomenuti odziv. Kako je bura primarno zimski vjetar a senjsko područje poznato po čestim epizodama olujne bure, rad je fokusiran na TerraSAR-X scene registrirane tijekom zima 2011. i 2012. godine u širem području približno centriranom na Senj. Nedavno razvijena geofizička modelska funkcija XMOD2 korištena je za određivanje brzine vjetra a WRF model za procjenu njegova smjera. Odabrane TerraSAR scene pokrivaju reprezentativne epizode bure te pokazuju bogatstvo detalja u daljinskim zapisima niskih mlaznih struja i zavjetrinskih struktura koji nastaju na jadranskoj strani Dinarida. Detalji zabilježeni u odzivnom normaliziranom radarskom presjeku uvjerljivo sugeriraju potrebu još boljeg prostornog razlučivanja u numeričkim simulacijama da bi se ispravno modeliralo orografski utjecaj i detalje pripovršinskog polja vjetra. Usporedbe s rezultatima, kako istraživačkog tako i operativnog modeliranja, ukazuju da bi proširenje baždarne baze podataka uzorcima olujnog i orkanskog vjetra moglo poboljšati geofizičku modelsku funkciju

SEVERE NORTH-EASTERN ADRIATIC BURA EVENTS AND CIRCULATION IN GREATER KVARNER REGION

In this paper we explore onset and duration of several severe Bura events, focusing on the circulation that such events impose in the greater Kvarner region. Three periods, better documented meteorologically and/or oceanographically, were selected for modelling and analysis: 5-9 November 1999, 8-15 February 2003, and 12-16 November 2004. In the performed simulations the wind emerged as the dominant driving force with important coastal and bathymetric constrains, The modelled barotropic response to the selected Bura events is characterized by a multitude of cyclonic and anticyclonic circulation cells, strongly controlled by the rich insular topology, lateral geometry, and bottom topography. The high resolution finite-element mesh of the model has allowed for the first time to resolve the intricacies of numerous sub-basins and channels, and to elucidate the interplay of laterally heterogeneous wind stress and bottom topography. The important aspect of the heat loss and surface cooling triggered by Bura episodes has been also addressed to the extent the model and data limitations allowed

Usporedba ALADIN i IFS Modela brzine vjetra preko Jadrana

The wind output from atmospheric models is instrumental in forcing the oceanic models. Here we consider the wind output from the ALADIN and IFS models and compare it with the results of scatterometer and altimeter estimates of wind speed over the Adriatic Sea, as well as with the field data from 18 meteorological stations and a gas rig platform. A five-year period from 2008 to 2012 is considered in the comparison. Our principal conclusion is that, overall, both atmospheric models, when compared to the altimeter data, give very similar statistical results, with a scatter index of 0.33 and 0.35 for IFS and ALADIN respectively. More specifically, the ALADIN appears to be better in the Northern Adriatic whereas the IFS seems superior in the Southern Adriatic. A possible explanation of this difference could be that the higher spatial resolution of ALADIN is crucial in resolving the bora wind impact over the Northern Adriatic.Vjetar dobiven atmosferskim modelima je instrumentalan u prisiljavanju oceanskog modela. U ovom radu razmotrit će se vjetra dobiven Aladin i IFS modelima te će se usporediti s rezultatima skat -erometrijske i altimetrijske procjene brzine vjetra iznad Jadranskog mora, kao i s 18 meteoroloških postaja i plinske platforme u razdoblju 2008-2012. Glavni zaključak je da oba atmosferska modela, u usporedbi s podacima altimetrije, daju vrlo slične statističke rezultate, s indeksom raspršenja 0,33 za IFS i 0,35 za ALADIN. Čini se da ALADIN daje bolje rezultate za sjeverni Jadran, a IFS za južni Jadran. Moguće objašnjenje te razlike može biti veća prostorna rezolucija ALADIN-a koja je presudna u rješavanju utjecaja bure na sjevernom Jadranu

Predikcija površinske temperature i slanosti Jadranskog mora: novije iskustvo u modeliranju

Oceanographic model simulations of the Adriatic temperature and salinity fields for the year 2008 were compared against coastal Conductivity Temperature Depth (CTD) observations and satellite detected Sea Surface Temperature (SST) in order to evaluate the model hindcasting skills. To that end, the Regional Ocean Modeling System (ROMS) configured with horizontal resolution of 2 km and forced with 8 km resolution output from the atmospheric model ALADIN (Aire Limitée Adaptation Dynamique développement Inter-National), was applied to the Adriatic Sea. Temperature and salinity CTD measurements collected along the eastern Adriatic coast, within the framework of the Adriatic Sea Monitoring Program, exhibits correlation with model in the temperature field between 0.75 and 0.95, depending on the season/cruise, while for salinity those values are between 0.32 and 0.78. Comparison of the modeled and daily derived satellite SST for the whole 2008 year was made on each data pixel. Results show that the hindcasts are characterized with small model-to-data RMSE, namely with values in the North Adriatic 0.90 °C, in the Middle Adriatic 0.79 °C and in the South Adriatic 0.80 °C. There is a high correlation between modeled and satellite SST data with values in a range of 0.44 to 0.92, depending on month and region, with a value of 0.99 for all time records and in any of three regions.Modelske simulacije jadranske temperature i saliniteta u 2008 godini uspoređene su s priobalnim CTD mjerenjima i satelitski detektiranim površinskim temperaturama mora u cilju vrednovanja prediktivnih sposobnosti modela u priobalnom moru. S tim ciljem je Regional Ocean Modeling System (ROMS), forsiran atmosferskim modelom ALADIN (Aire Limitée Adaptation Dynamique développement Inter-National) uz razlučivanje od 8 km, primijenjen na Jadransko more uz horizontalno razlučivanje od 2 km. Mjerenja temperature i saliniteta pomoću CTD sonde, obavljena u istočno-jadranskom priobalju u okviru Programa monitoringa Jadranskog mora, imaju visoku korelaciju s modelom u temperaturnom polju s vrijednostima između 0.75 i 0.95, ovisno o godišnjem dobu/krstarenju, dok za polje saliniteta vrijednosti su između 0.32 i 0.78. Usporedba s daljinski detektiranim podacima o površinskoj temperaturi mora (SST), za cijelu 2008. godinu, napravljena je za svaki pojedinačni pixel s podacima. Rezultati usporedbi pokazuju da aposteriorne simulacije (hindcasts) za cijelu 2008 godinu imaju malu RMS pogrešku, u sjevernom Jadranu 0.90 °C, u području srednjeg Jadrana 0.79 °C, te južnog Jadrana 0.80 °C. Koeficijent korelacije između modeliranih i satelitski dobivenih površinskih temperatura mora ima vrijednosti između 0.44 i 0.92, ovisno o mjesecu i području Jadrana, dok za sve vrijednosti u vremenu iznosi 0.99 za bilo koje područje