Interpretation of dynamical processes in the upwelling area off northwest Africa using simulated and remotely sensed data

摘要

Dynamical processes in the upwelling area off northwest (NW) Africa are studied. Three remote sensing data sets are analysed to evaluate the time and space scales and to conclude the dynamics of upwelling events. The remote sensing data have been gathered by the Coastal Zone Color Scanner (CZCS) during October 1981-1987, the Advanced Very High Resolution Radiometer (AVHRR) during June-July, 1987, and the Geodetic Satellite (GEOSAT) radar altimeter during 1987. Striking upwelling features along the coast off NW Africa, so-called filaments, are oriented normal to the coast with a life time ranging from days to weeks and spatial scales between 10-200 km. Due to collinear track analysis of GEOSAT altimeter data the filament of Cap Ghir at 30/spl deg/N was detected, concluding that this filament is a mainly barotropic quasi stationary signal. Therefore, two-dimensional vorticity dynamics was used to investigate the source of those filaments. In addition, the horizontal temperature structure of a vertically stratified circulation model, forced with transient wind fields, was analysed for the interpretation of surface signatures. Cold surface temperature signatures extending seaward, can be explained by conservation of potential vorticity due to the topography and with time scales according to the wind forcing.