Surface current variability and wind influence in the northeastern Adriatic Sea as observed from high-frequency (HF) radar measurements

A network of HF radars operated in the northeastern Adriatic Sea in the period September 2007 to August 2008. Surface currents were collected with the purpose of studying the temporal and spatial modes of surface circulation in the area. Their dependence on local wind forcing was investigated using wind records from coastal stations and the mesoscale meteorological model ALADIN/HR. EOF decomposition, spectral and tidal analyses, and time-lagged correlation extracted the dominant features in the area and their time scales. The time-averaged flow presented a cyclonic circulation pattern with relatively weak currents and standard deviations comparable to average values. Three dominant current patterns were extracted by the EOF analysis, which accounted for about 70% of total variance. In the region, wind was the major source of current variability over a wide portion of frequencies, whereas tidal forcing was weak and limited to the semidiurnal and diurnal frequencies, representing 10%–20% of the total variance. The response to wind forcing was immediate with veering angles consistent with Ekman dynamics in the majority of the area. Coherence analyses revealed strong correlation within the sub-tidal and diurnal bands, the latter related to diurnal sea-breezes variability. The seasonal variability of the inertial motions was also observed in the area.