Satellite images of upwellings and cold filament dynamics as transient effects of violent air-sea interactions downstream from the island of Sardinia (western Mediterranean Sea)

Abstract

A systematic analysis of thermal satellite images of upwellings and cold filament dynamics downstream from the island of Sardinia (western Mediterranean Sea), covering the years 1984, 1985, 1989, 1990, 1993, and 1994, is discussed. For this sea the main transient atmospheric forcing comes from bursts of the mistral, a north-western wind which, downstream from Sardinia, affects a rather calm basin, the Tyrrhenian Sea. In early summer, particularly clear effects of atmospheric forcings such as gyres, upwellings, and cold filaments can be observed. Our analysis provides not only a systematic insight into these phenomena, but also some experimental evidence of a novel mechanism of cold filament formation and evolution. Indeed, in July 1989, a nice set of satellite images shows a cold filament rooted to the shallowest part of the wide shelf off Olbia, which meanders offshore for a few days under the effect of the mistral and of the general circulation. It is of interest to underline how stably the filament is rooted to the shelf so that in only one image it appears as an elongated straight segment. Also, the filament's potential vorticity is discussed in order to gain some insight into shelf water fluxes, detachment depths, and velocities relative to such phenomena. Copyright 1998 by the American Geophysical Union.