Impact of penetrative solar radiation on the diagnosis of water mass transformation in the Mediterranean Sea
Résumé
We applied a revised diagnosis of water mass formation and mixing to a 1/8° resolution ocean model of the Mediterranean Sea. The diagnosis method used and presented by Iudicone et al. (2008) is similar to that developed by Walin (1982) and applied to the Mediterranean Sea by Tziperman and Speer (1994), to which we added a penetrative solar radiation. Both the prognostic model and the diagnostic method were in agreement with respect to the solar flux parameterization. Major changes were observed in the yearly budget of water mass transformation when the penetrative solar radiation is taken into account in the diagnosis. Annual estimates of water mass formation rates were decreased by a factor of two, with values within the range [-3.7 Sv, 1.5 Sv] compared to [-6 Sv, 3 Sv]. This decrease resulted from a lower seasonal variation when penetrative solar radiation was included. This can be explained by the fact that the solar radiation flux acted over a wider range of seawater density leading to lower net values over a given density interval. The major impact of the penetrative solar radiation occurred during spring and summer. Newly formed dense water was then transformed into lighter water with a rate reaching a value about 50% of that of the water mass formation rate in winter. Another consequence was that mixing processes which counteract formation rate in yearly budget of water mass formation rates, were overestimated. We showed that, in spring and summer, about a third of the transformation took place below the surface layer.
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