Diagnostic and prognostic numerical studies of LIW formation

We use a hierarchy of diagnostic and prognostic numerical methods to investigate the formation mechanisms of Levantine Intermediate Water (LIW), determine the formation sites and estimate its annual formation rates. Although the three methods are different and use different hydrological/atmospheric forcing data, all of them reach the same qualitative and quantitative results: under mean climatological conditions the LIW is formed during winter in the Rhodes cyclonic gyre with an annual formation rate of 1.0 Sv. The preferred formation site is mainly controlled by the preconditioning of the hydrology, i.e., the presence of the Rhodes gyre, rather than the spatial distribution of surface forcing, which plays a significant role only during extreme meteorological episodes. The interannual variability experiments show that during severe winters, the formation rate is not increased significantly but instead, deep waters are formed in the center of the gyre, and the LIW formation area is extended towards the northeast Levantine. During mild winters, the formation rate is reduced considerably (< 0.6 Sv) and waters with lower density are being formed. (C) 1998 Elsevier Science B.V. All rights reserved.