Downwelling along the Northeastern Coasts of the Eastern Mediterranean

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  • 1 Israel Institute for Biological Research, Department of Mathematics, Ness-Ziona, Israel
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Abstract

The most prominent winter storms in the eastern part of the Eastern Mediterranean are known as Cyprus cyclones. The surface wind speed is between 15–30 m s−1, and about five such cyclones occur in a typical winter. The cyclone radius is between 500 and 1500 km. The evolution of the sea structure under such atmospheric forcing is examined with a two-dimensional numerical model in the vertical cross section perpendicular to the shore line. Two distinct regions result in the sea. A downwelling zone near the coast, about 100 km wide, and a horizontally homogeneous zone in the open sea, where vertical mixing is the important dynamical process. In the open sea the final profiles turn out to be similar to those observed in the Levantine Intermediate Water (LIW) in their formation region. We suggest that the LIW forms in the region under the influence of these Cyprus cyclones.

In the downwelling zone the 14°–17°C isotherms decline by more than 250 m. This water has the same T-S properties as the water in the anticyclonic eddies found along the Asia Minor coast and other parts of the Eastern Mediterranean. A very deep mixed layer is obtained, deeper than 300 m. The water in the downwelling zone near the sea surface is warmer by 0.50°–1°C than in the open sea. This last result is observed in winter IR satellite images.

The downwelling rate increase with increasing wind stress and decreasing horizontal eddy coefficient. This rate is not influenced by the evolution in the mixing layer.

Along the coast in the downwelling front a prominent jet developed. The scale of the jet is proportional to the square root of the horizontal eddy coefficient.

Abstract

The most prominent winter storms in the eastern part of the Eastern Mediterranean are known as Cyprus cyclones. The surface wind speed is between 15–30 m s−1, and about five such cyclones occur in a typical winter. The cyclone radius is between 500 and 1500 km. The evolution of the sea structure under such atmospheric forcing is examined with a two-dimensional numerical model in the vertical cross section perpendicular to the shore line. Two distinct regions result in the sea. A downwelling zone near the coast, about 100 km wide, and a horizontally homogeneous zone in the open sea, where vertical mixing is the important dynamical process. In the open sea the final profiles turn out to be similar to those observed in the Levantine Intermediate Water (LIW) in their formation region. We suggest that the LIW forms in the region under the influence of these Cyprus cyclones.

In the downwelling zone the 14°–17°C isotherms decline by more than 250 m. This water has the same T-S properties as the water in the anticyclonic eddies found along the Asia Minor coast and other parts of the Eastern Mediterranean. A very deep mixed layer is obtained, deeper than 300 m. The water in the downwelling zone near the sea surface is warmer by 0.50°–1°C than in the open sea. This last result is observed in winter IR satellite images.

The downwelling rate increase with increasing wind stress and decreasing horizontal eddy coefficient. This rate is not influenced by the evolution in the mixing layer.

Along the coast in the downwelling front a prominent jet developed. The scale of the jet is proportional to the square root of the horizontal eddy coefficient.

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