Variable sea level and strait flows in the Mediterranean: a theoretical study of the response to meteorological forcing

Abstract

Changes in atmospheric pressure over the Mediterranean are thought to account for a significant part of low frequency sea level changes and associated flow through the Strait of Gibraltar. However, Crepon's (1965) examination of sea level data suggested that both sea level in the Western Mediterranean and inflow through the Strait were in phase with minus the atmospheric pressure, in apparent contradiction to mass conservation. This apparent paradox can be resolved if allowance is made for flow through the Strait of Sicily in response to different sea levels in the Eastern and Western Mediterranean basins. A two-basin, two-strait model is developed, using a simple approximate formula for strait flow that is likely to be adequate for the 10 day periodicity that is emphasized. The phase difference between flow through the Strait of Gibraltar and sea level in the Western basin becomes fairly small if allowance is made for the eastward propagation of atmospheric pressure systems, but a significantly non-inverse-barometer response of sea level in the Eastern Mediterranean is predicted for periods of several days. The effect on Mediterranean sea level of low frequency wind-induced set-up on the continental shelf outside the Strait of Gibraltar is estimated to be less than the effect of atmospheric pressure. The great need is for a statistical study of data on sea level in the Eastern Mediterranean, and of flow through the two straits, in relationship to the large-scale low frequency weather patterns.