Features of dominant mesoscale variability, circulation patterns and dynamics in the Strait of Sicily

Combining an intensive hydrographic data survey with a numerical primitive equation model by data assimilation, the main features of dominant mesoscal e to subbasin-scale variability in the Strait of Sicily (Mediterranean Sea) during the summer of 1996 are estimated, revealed and described, and sever al hydrographic and dynamical properties of the how and variabilities discu ssed. The feature identification is based on two independent real-time anal yses of the variability. One analysis "subjectively" evaluates and studies physical field forecasts and their variations. The other more "objectively" estimates and forecasts the principal components of the variability. The t wo independent analyses are found to be in agreement and complementary. The dominant dynamical variations are revealed to be associated with five feat ures: the Adventure Bank Vortex, Maltese Channel Crest, Ionian Shelfbreak V ortex, Messina Rise Vortex, and temperature and salinity fronts of the Ioni an slope. These features and their variations are found to have links with the meanders of the Atlantic Ionian Stream. For each feature, the character istic physical scales, and their deviations, are quantified. The predominan t circulation patterns, pathways and transformations of the modified Atlant ic water, Ionian water and modified Levantine intermediate water, are then identified and discussed. For each of these water masses, the ranges of tem perature, salinity, depth, velocity and residence times, and the regional v ariations of these ranges, are computed. Based on the estimated fields and variability principal components, several properties of the dynamics in the Strait are discussed. These include: general characteristics of the mesosc ale anomalies; bifurcations of the Atlantic Ionian Stream; respective roles of topography, atmospheric forcings and internal dynamics; factors control ling (strengthening or weakening) the vortices identified; interactions of the Messina Rise and Ionian Shelfbreak vortices; and, mesoscale dynamics an d relatively complex features along the Ionian slope. For evaluation and va lidation of the results obtained, in situ data, satellite sea surface tempe rature images and trajectories of surface drifters are employed, as well as comparisons with previous studies. (C) 2001 Elsevier Science Ltd. All righ ts reserved.