Abstract
Abstract. The evolution of the upper thermocline on a section across the eastern Mediterranean was recorded bi-weekly through a series of XBT transects from Piraeus, Greece to Alexandria, Egypt, extending from October 1999 to October 2000 on board Voluntary Observing Ships in the framework of the Mediterranean Forecasting System Pilot Project. The data acquired provided valuable information on the seasonal variability of the upper ocean thermal structure at three different regions of the eastern Mediterranean: the Myrtoan, Cretan and Levantine Seas. Furthermore, the horizontal distance (~12 miles) between successive profiles provides enough spatial resolution to analyze mesoscale features, while the temporal distance between successive expeditions (2–4 weeks) allows us to study their evolution. Sub-basin scale features are identified using contemporaneous sea surface temperature satellite images. The cross-transect geostrophic velocity field and corresponding volume fluxes for several sub-basin scale features of the Levantine Sea are estimated by exploiting monthly q / S diagrams from operational runs of the Princeton Ocean Model in use at NCMR. A southwestward transport in the proximity of the southeast tip of Crete was estimated between 1–3 Sv. The transport increases after the winter formation of dense intermediate water in the Cretan Sea strengthens the pressure gradient across the Cretan Straits. The Mersah-Matruh anticyclone was identified as a closed gyre carrying about 2–6 Sv. This feature was stable throughout the stratified period and disappeared from our records in March 2000. Finally, our data reveal the existence of an eastward-flowing coastal current along the North African coast, transporting a minimum of 1–2 Sv. Key words. Oceanography: physical (eddies and mesoscale processes; currents; marginal and semi-closed seas)
Highlights
The Mediterranean Forecasting System Pilot Project (MFSPP) was an international effort supported by the 4th Frame-work Programme of the European Commission, aiming to develop the main observing and modelling components of an operational forecasting system able to produce weekly to monthly forecasts of ecosystem variability (Pinardi and Flemming, 1998)
The eastern Mediterranean was covered by 4 routes: the Greek National Center for Marine Research (NCMR) was responsible for a transect joining the harbors of Piraeus, Greece and Alexandria, Egypt
Before examining the evolution of the thermocline along the Piraeus – Alexandria transect throughout the MFSPP experiment, a satellite SST image obtained on 23 October 1999 (Fig. 2), during the first crossing of the transect, was used to identify sub-basin scale features responsible for the isothermal displacements recorded by the XBT transects (Fig. 3)
Summary
The Mediterranean Forecasting System Pilot Project (MFSPP) was an international effort supported by the 4th Frame-. The MMJ’s track appears to be determined by the presence of a series of permanent sub-basin scale features: the Cretan cyclone to the SW of the island of Crete, the Rhodes cyclonic gyre SE of Rhodes Island, and the large Mersah-Matruh anticyclone occupying a major part of the southern Levantine basin. Some semipermanent and recurrent eddies revealed by the POEM project were identified: the most important of them are the Ierapetra anticyclone appearing south of Crete (between the Cretan and Rhodes cyclones) and the Shikmona gyre south of the island of Cyprus at the easternmost part of the eastern Mediterranean. Discussion of the results and conclusions are presented in the last section of this work
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