Major changes in Mediterranean Sea level variability from 7 years of TOPEX/Poseidon and ERS-1/2 data

Seven years of combined maps of TOPEX/Poseidon (T/P) and ERS-1/2 altimeter data are used to describe the surface circulation variability in the Mediterranean Sea. As described in the past, the Mediterranean Sea level variability is a complex combination of a wide range of spatial and temporal scales. However, this paper gives an improved estimation of sea level statistics (rms, annual, semiannual cycle). Moreover, the longer period (1993-1999) and the merging of T/P and ERS-1/2 altimeter data allows us to observe with a good accuracy the major changes that occurred in the Mediterranean Sea and, in particular, at basin and sub-basin scales. First, important interannual signals were found in the Ionian basin where the cyclonic circulation has clearly intensified since 1997. In the Levantine basin, although the lerapetra eddy exhibits a clear seasonal cycle, it is not always present during our period of observation. These interannual changes seem to be correlated with the variability of the Mid-Mediterranean Jet, which produces strong meanders. A new view of the circulation in the south of the basin is indeed suggested by considering that the eddies observed in the Mersa-Matruh and Shikmona areas represent meanders of the Mid-Mediterranean Jet rather than permanent structures as commonly described. Secondly, the seasonal cycle of the Alboran gyres is confirmed. Moreover, these gyres and the Ierapetra eddy constitute the most intense signals of the Mediterranean Sea variability. Finally, this descriptive study illustrates the need to continue monitoring the surface circulation in order to better understand the dynamics of the Mediterranean Sea. (C) 2002 Elsevier Science B.V. All rights reserved.