High-Resolution mapping of Bora winds in the Northern Adriatic Sea using synthetic aperture radar

Abstract

The Adriatic Sea is regularly subjected to strong Bora wind events from the northeast during winter. The events have a strong effect on the oceanography in the Adriatic, driving basin-scale gyres that determine the transport of biogeochemical material and extracting large amounts of heat. The Bora is known to have multiple surface wind jets linked to the surrounding orography and have been the focus of many studies, but the detailed spatial structure of these jets has not been possible to describe by in situ observations. Using high-resolution space-borne RADARSAT-1 Synthetic Aperture Radar (SAR) images collected during an active Bora period (Jan 23 - Feb 16, 2003), we created a series of high resolution (300 m) maps of the wind field. The obtained winds show reasonable agreement with several in situ wind observations, with an RMS wind speed error of 3.6 m/s, slightly higher than 2-3 m/s errors reported in previous studies. These SAR images reveal the spatial structure of the Bora wind in unprecedented detail, revealing several new features of the Bora. In the Senj region of Croatia, several images show rhythmic structure with wavelengths of 2-3 km that may reflect Bora pulsation seen at fixed locations by previous investigators. Along the Italian Coast, several images show a wide (20-30km) band of northwesterly winds that abruptly change to the northeasterly Bora winds further offshore. Meteorological model results suggest that these northwesterly winds are consistent with those of a barrier jet, forming along the Italian Apennine mountain chain.