ASPECTS OF TIME SEASONAL AND MESOSCALE VARIABILITIES OF THE NORTHERN CURRENT IN THE WESTERN MEDITERRANEAN-SEA INFERRED FROM THE PROLIG-2 AND PROS-S EXPERIMENTS

This paper presents a study of the Northern Current, which is a major component of the circulation in the western Mediterranean Sea. Our ana lysis is based on a monthly CTD survey (PROS-6 experiment), and on 12 current-meter time series collected at three depths on four moorings ( PROLIG-2 experiment) from May to December 1985. These data support the fact that the mesoscale activity of the Northern Current smoothly dec reases in spring-summer and then rapidly increases in early autumn. Fr om the first period to the second, the fluctuations become more isotro pic, their time and space scales become smaller and they have a more r educed vertical extent. The mesoscale phenomena are characterized by t wo main fluctuation bands: at all depths, a 10-20-d band only appears in the direction of the mean flow while a 3-6 d band mainly appears in a perpendicular direction, being polarized anticlockwise at some dist ance from the coast. The phase speeds are generally equal to or lower than similar to 10 km/d in both bands. These values compare rather wel l with those deduced from previous analyses of hydrological data and b aroclinic instability models, We hypothesize that the fluctuations at 10-20 d are pulses of the mean flow while those at 3-6 d are current m eanders that are more intense in autumn than in spring-summer.