Some early results of the TerraSAR-X observations of the northeastern Adriatic bora wind are pres... more 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...
Quarterly Journal of the Royal Meteorological Society, 2015
This note examines two Adriatic bora events recorded in TerraSAR‐X (TS‐X) images taken in the win... more This note examines two Adriatic bora events recorded in TerraSAR‐X (TS‐X) images taken in the winters of 2011 (Case 1) and 2012 (Case 2). In Case 1, the TS‐X captured an image of a deep anticyclonic bora, whereas in Case 2 a shallow cyclonic bora was sampled. High‐resolution TS‐X images resolved the finer bora spatial structure to a scale of ≈1 km, which has not previously been reported in bora research. In particular, the structures in Case 2 appear to be driven by surface convective heat fluxes caused by substantial temperature differences between the relatively high sea surface temperature (SST) and the overflowing very cold air. The Weather Research and Forecasting (WRF) model simulations used to aid the analyses suggest that the very low upwind 2m temperature in Case 2 reinforced the orographic wave breaking by enhancing the cross‐mountain pressure gradient. The ensuing strong cross‐mountain flow was responsible for the appearance of secondary jets in the lee of Mount Velebit, ...
Satellite imagery can significantly aid classical oceanographic work by providing information on ... more Satellite imagery can significantly aid classical oceanographic work by providing information on temporal development of surface conditions, synoptically registered over large areal extents. The present paper is primarily focused on the two most often used remotely sensed fields: colour-pigment derived from the Coastal Zone Colour Scanner (CZCS) and temperature derived either from the Advanced Very High Resolution Radiometer (AVHRR) or the CZCS infrared channel. A brief review of a decade of classical oceanographic work is presented first. It demonstrates the researchers' bias towards general circulation problems, and the lack of mesoscale oriented studies. Analysis of papers on remote sensing and the Adriatic Sea reveals the prominence of algorithms and testing oriented works, and the largely indirect use of remotely sensed information. Among the latter group one can observe a similar bias towards general circulation problems as in classical studies. Moreover, wind-driven dynamics is treated convincingly, albeit not extensively. Lack of remote-sensing supported studies of the Adriatic mesoscale dynamics appears most surprising, considering the clear and numerous signatures the mesoscale processes seem to leave in the thermal and bio-optical surface fields. Lack of support for studies of periodic phenomena (e. g. inertia-period oscillations or tides) seems to be a consequence of inadequate temporal resolution of satellite sensors
A combination of recent intensive observations and simulations with two numerical models is used ... more A combination of recent intensive observations and simulations with two numerical models is used to revisit the issue of the northern Adriatic response to strong bora episodes. New observed and simulated data reinforce the view that an episode of strong bora wind provokes a double‐gyre (cyclonic, Trieste, and anticyclonic, Rovinj) response north of the Po Delta ‐ Pula line. During an intense bora episode, both measured and modeled statistics picture a downwind, highly polarized, and almost depth‐independent flow within the Trieste gyre NW arm. Its NE arm maintains a sharp polarization and strong depth dependence while exhibiting lower speeds, with models in good accord with observations. The current statistics for Rovinj gyre provide lower maximum and average speed values and less polarized but still rather depth‐independent flow, while exhibiting clockwise rotation. The north arm of the Senj gyre (positioned south of the Po Delta–Pula line) enjoys more lateral freedom, and exhibits...
From September 2002 to May 2003, fifteen bottom‐mounted, acoustic Doppler current profilers measu... more From September 2002 to May 2003, fifteen bottom‐mounted, acoustic Doppler current profilers measured currents of the northern Adriatic basin. Tidal fluctuations at all seven of the major Adriatic frequencies were synthesized from a response tidal analysis of these measurements. Most observed tidal current ellipses were nearly reversing, but near the bottom, tidal current ellipses all shortened and broadened, semidiurnal currents led upper water column currents, and diurnal tidal current ellipse orientations rotated counterclockwise toward the bottom. Theoretical solutions for a tidally forced, bottom Ekman layer with vertical eddy viscosity of the form Az = βz + k were least squares fit to the observations. Average values were β = 3 · 10−4 m/s and k = 5 · 10−4 m2/s. The value of k was important in matching tidal orientation and phase changes, and a nonzero β was important in matching tidal amplitude changes. The Navy Coastal Ocean Model (NCOM) and the Quoddy model were also compared...
A 2‐year deployment of high‐frequency radio current meters along the Italian coast of the northwe... more A 2‐year deployment of high‐frequency radio current meters along the Italian coast of the northwestern Adriatic is used to characterize the surface tidal currents. In the middle of the basin, the M2 and K1 currents oscillate along the basin axis, but become more circular toward the Italian coast. Comparisons with a 3‐D finite‐element nonlinear numerical model of the tides show a good agreement for phases in the middle of the basin, although modeled currents amplitudes are overestimated. However, modeled phases lag observed phases by up to 50° (1.7 hours) for M2 and 100° (6.7 hours) for K1, and modeled amplitudes are underestimated, in a 10–20 km wide strip along the Italian coast. This shallow (< 30 m deep) region is stratified by low‐salinity surface water from the Po, and laterally sheared by the Western Adriatic Current, both absent from the model but possibly affecting tidal propagation. The model may also incompletely parameterize the combined effects of bottom friction and ...
Sažetak Modelske simulacije jadranske temperature i saliniteta u 2008 godini uspoređene su s prio... more Sažetak 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 ...
ABSTRACT This is the first attempt to test the results of wind-induced current modelling for the ... more ABSTRACT This is the first attempt to test the results of wind-induced current modelling for the northern Adriatic (Kuzmić and Orlić 1987) using space-borne Coastal Zone Colour Scanner (CZCS) data. In particular, new remotely sensed empirical evidence has been sought for the previously studied effect of the spatially heterogeneous bura (gusty, katabatic wind of north-easterly direction) by observing changes in spectral reflectance of the northern Adriatic waters. To that end, an existing hydrodynamical model has been extended to include a simple two-dimensional random walk dispersion model. The CZCS measured radiance has been processed to estimate pigment concentration. Remotely sensed data corroborate mathematical model findings. Comparison of model-generated and sensor-collected information strongly suggests that bura-induced gyre is the mechanism responsible for particular spatial pattern change observed in the CZCS detected radiance and estimated pigment concentration.
Some early results of the TerraSAR-X observations of the northeastern Adriatic bora wind are pres... more 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...
Quarterly Journal of the Royal Meteorological Society, 2015
This note examines two Adriatic bora events recorded in TerraSAR‐X (TS‐X) images taken in the win... more This note examines two Adriatic bora events recorded in TerraSAR‐X (TS‐X) images taken in the winters of 2011 (Case 1) and 2012 (Case 2). In Case 1, the TS‐X captured an image of a deep anticyclonic bora, whereas in Case 2 a shallow cyclonic bora was sampled. High‐resolution TS‐X images resolved the finer bora spatial structure to a scale of ≈1 km, which has not previously been reported in bora research. In particular, the structures in Case 2 appear to be driven by surface convective heat fluxes caused by substantial temperature differences between the relatively high sea surface temperature (SST) and the overflowing very cold air. The Weather Research and Forecasting (WRF) model simulations used to aid the analyses suggest that the very low upwind 2m temperature in Case 2 reinforced the orographic wave breaking by enhancing the cross‐mountain pressure gradient. The ensuing strong cross‐mountain flow was responsible for the appearance of secondary jets in the lee of Mount Velebit, ...
Satellite imagery can significantly aid classical oceanographic work by providing information on ... more Satellite imagery can significantly aid classical oceanographic work by providing information on temporal development of surface conditions, synoptically registered over large areal extents. The present paper is primarily focused on the two most often used remotely sensed fields: colour-pigment derived from the Coastal Zone Colour Scanner (CZCS) and temperature derived either from the Advanced Very High Resolution Radiometer (AVHRR) or the CZCS infrared channel. A brief review of a decade of classical oceanographic work is presented first. It demonstrates the researchers' bias towards general circulation problems, and the lack of mesoscale oriented studies. Analysis of papers on remote sensing and the Adriatic Sea reveals the prominence of algorithms and testing oriented works, and the largely indirect use of remotely sensed information. Among the latter group one can observe a similar bias towards general circulation problems as in classical studies. Moreover, wind-driven dynamics is treated convincingly, albeit not extensively. Lack of remote-sensing supported studies of the Adriatic mesoscale dynamics appears most surprising, considering the clear and numerous signatures the mesoscale processes seem to leave in the thermal and bio-optical surface fields. Lack of support for studies of periodic phenomena (e. g. inertia-period oscillations or tides) seems to be a consequence of inadequate temporal resolution of satellite sensors
A combination of recent intensive observations and simulations with two numerical models is used ... more A combination of recent intensive observations and simulations with two numerical models is used to revisit the issue of the northern Adriatic response to strong bora episodes. New observed and simulated data reinforce the view that an episode of strong bora wind provokes a double‐gyre (cyclonic, Trieste, and anticyclonic, Rovinj) response north of the Po Delta ‐ Pula line. During an intense bora episode, both measured and modeled statistics picture a downwind, highly polarized, and almost depth‐independent flow within the Trieste gyre NW arm. Its NE arm maintains a sharp polarization and strong depth dependence while exhibiting lower speeds, with models in good accord with observations. The current statistics for Rovinj gyre provide lower maximum and average speed values and less polarized but still rather depth‐independent flow, while exhibiting clockwise rotation. The north arm of the Senj gyre (positioned south of the Po Delta–Pula line) enjoys more lateral freedom, and exhibits...
From September 2002 to May 2003, fifteen bottom‐mounted, acoustic Doppler current profilers measu... more From September 2002 to May 2003, fifteen bottom‐mounted, acoustic Doppler current profilers measured currents of the northern Adriatic basin. Tidal fluctuations at all seven of the major Adriatic frequencies were synthesized from a response tidal analysis of these measurements. Most observed tidal current ellipses were nearly reversing, but near the bottom, tidal current ellipses all shortened and broadened, semidiurnal currents led upper water column currents, and diurnal tidal current ellipse orientations rotated counterclockwise toward the bottom. Theoretical solutions for a tidally forced, bottom Ekman layer with vertical eddy viscosity of the form Az = βz + k were least squares fit to the observations. Average values were β = 3 · 10−4 m/s and k = 5 · 10−4 m2/s. The value of k was important in matching tidal orientation and phase changes, and a nonzero β was important in matching tidal amplitude changes. The Navy Coastal Ocean Model (NCOM) and the Quoddy model were also compared...
A 2‐year deployment of high‐frequency radio current meters along the Italian coast of the northwe... more A 2‐year deployment of high‐frequency radio current meters along the Italian coast of the northwestern Adriatic is used to characterize the surface tidal currents. In the middle of the basin, the M2 and K1 currents oscillate along the basin axis, but become more circular toward the Italian coast. Comparisons with a 3‐D finite‐element nonlinear numerical model of the tides show a good agreement for phases in the middle of the basin, although modeled currents amplitudes are overestimated. However, modeled phases lag observed phases by up to 50° (1.7 hours) for M2 and 100° (6.7 hours) for K1, and modeled amplitudes are underestimated, in a 10–20 km wide strip along the Italian coast. This shallow (< 30 m deep) region is stratified by low‐salinity surface water from the Po, and laterally sheared by the Western Adriatic Current, both absent from the model but possibly affecting tidal propagation. The model may also incompletely parameterize the combined effects of bottom friction and ...
Sažetak Modelske simulacije jadranske temperature i saliniteta u 2008 godini uspoređene su s prio... more Sažetak 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 ...
ABSTRACT This is the first attempt to test the results of wind-induced current modelling for the ... more ABSTRACT This is the first attempt to test the results of wind-induced current modelling for the northern Adriatic (Kuzmić and Orlić 1987) using space-borne Coastal Zone Colour Scanner (CZCS) data. In particular, new remotely sensed empirical evidence has been sought for the previously studied effect of the spatially heterogeneous bura (gusty, katabatic wind of north-easterly direction) by observing changes in spectral reflectance of the northern Adriatic waters. To that end, an existing hydrodynamical model has been extended to include a simple two-dimensional random walk dispersion model. The CZCS measured radiance has been processed to estimate pigment concentration. Remotely sensed data corroborate mathematical model findings. Comparison of model-generated and sensor-collected information strongly suggests that bura-induced gyre is the mechanism responsible for particular spatial pattern change observed in the CZCS detected radiance and estimated pigment concentration.
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