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Eli Tziperman
and
Artur Hecht

Abstract

A finite difference linear inverse model is applied to hydrographic data from six summer and fall cruises in a small area (250 × 200 km) of the eastern Mediterranean sea. The temperature and salinity equations are used to form a linear set of equations for the reference geostrophic velocities and the mixing coefficients, which are then solved by singular value decomposition.

Advection by the horizontal velocities is the dominant process affecting the temperature and salinity fields in the region, and the model successfully resolves the horizontal velocities. Mixing and vertical advection are smaller by an order of magnitude, and the model cannot fully resolve the mixing coefficients and vertical velocities.

The six velocity fields calculated from the data indicate a very strong variability that makes it difficult to identify a repeating summer or fall circulation patterns on the scale of the region covered by the data.

An appendix contains the details of a new procedure for including linear inequalities in the solution of a rank deficient system of linear equations.

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Artur Hecht
,
Nadia Pinardi
, and
Allan R. Robinson

Abstract

Hydrographic measurements in the southeastern Levantine basin are analyzed, and the climatological water masses of the region and their seasonal variations are identified. We observe the formation of the salty and warm Levantine Surface Water Layer (LSW); we characterize the subsurface Atlantic Water Layer (AW); and we describe the properties of the thermocline waters, called Levantine Intermediate Waters (LIW). The baroclinic dynamical modes are computed for the climatological stratification parameters. The empirical orthogonal function (EOF) analysis of the vertical shear profiles shows that considerable energy is contained in the second EOF at the thermocline and deep levels. Maps of the baroclinic streamfunction field referred to 700 meters are displayed: 16 instantaneous flow field realizations show an intense mesoscale eddy file never revealed before in the region. The space scales of the eddies are about 100 km and a smaller scale (60–70 km) variability is also evident. The eddies are present, e.g., stationary for over a season, and there are periods in which only a single eddy center is present embedded in an almost quiescent flow. The velocities in the strong jets at the border of the eddies are of the order of 20–40 cm −1 at the upper thermocline levels. The water mass analysis of this eddy field shows that the AW and LIW salinity properties are distributed in filaments and patches: the maximum salinity cores of LIW are trapped in the anticyclones found in the region. An event of salinity ventilation (down to 200 m) is described that seems to involve the homogenization of the salinity properties but not convective mixing of the density structure. The traditional picture of the basin currents is compared with the mesoscale flow analyzed here, and we speculate upon possible mechanisms of water mass transport.

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