Temporal and spatial variability of the surface temperature anomaly in the Levantine Basin of the Eastern Mediterranean

Abstract

In this study we use the monthly mean sea surface temperature (SST) fields (1985-1997), calculated by the National Oceanic and Atmospheric Administration (NOAA) Pathfinder project analysis of advanced very high resolution radiometer (AVHRR) data, to investigate the temporal and spatial variability of warm/cool anomalies in the Levantine Basin (LB). Wind data from European Remote Sensing Satellite-1/2 (ERS-1/2) over the LB are analysed and surface wind stress and wind stress curls are calculated. First, we employed an optimal interpolation scheme to build up a dataset for 1985-1997 on an 18 km 2 18 km grid. An ensemble mean SST field ( T ) has been established with a rather weak horizontal gradient (19.4° C south-east of Rhodes to 22.4° C southeast of the LB). Second, we performed a composite analysis to obtain the monthly averaged SST anomaly field ( T ) deviation from the ensemble mean. Three areas of evident SST anomalies were found: south of Rhodes, south-east of Crete and north-east of Cyprus. During the spring-to-summer transition (March to May), a small low anomaly is formed south-east of Crete ( T <-1.4° C in May), and a small high anomaly is formed south of Rhodes ( T >-0.4° C in May). During the autumn-to-winter transition (October to November), a small high anomaly forms south-east of Crete ( T >1.2° C in November), and a small low anomaly forms between Rhodes and Antalia Bay ( T <-0.2° C in November). Third, we performed an empirical orthogonal function (EOF) analysis on the residual T relative to T + T in order to obtain transient and interannual variations of the SST fields. EOF1 explains 73% of the total variance and represents the warm/cool anomaly pattern, with a maximum value in the region between the south of Rhodes and Cyprus and a minimum value off the western part of the Egyptian coast. EOF2 explains 6% of the total variance. A strong LB warm anomaly (1° C warmer) appears during August 1988, May 1994 and September-October-November 1994. A strong cool anomaly (1° C cooler) occurs during May 1987, November 1988, August 1989 and May 1992. The cross-correlation coefficient between wind stress curl from ERS-1/2 over the LB in the period from January 1992 to December 1997 and the SST anomaly were calculated, and it reveals the air-sea interaction in the LB.