Mediterranean subsurface circulation estimated from Argo data
Milena Menna, Pierre Marie Poulain
OGS
(Abstract received 08/12/2009 for session A)
ABSTRACT
Data from 38 profiling floats, deployed as a part of the International Argo program since October 2003, are used to describe the subsurface Mediterranean currents for the period 2003-2009. These floats were programmed to execute 5-day cycles, to drift at a neutral parking depth of 350 m and measure temperature and salinity profiles from either 700 or 2000 m up to the surface. At the end of each cycle the Argo floats remain at the sea surface for about 6 hours, enough time to be localised and transmit the data to the Argos satellite system. The Argos positions are used to determine the float surface and subsurface displacements. The estimation of surface displacement involves the determination of the exact surfacing and diving times and the extrapolation in time of the Argos positions using a simple model based on linear displacement and inertial motion. The determination of subsurface displacement involves the use of the average vertical speed of the float and an approximation of current shear in the upper water column to evaluate the times and positions of the start and end of the subsurface drift. From these, the subsurface velocities at the 350 m parking depth, are estimated and finally used to compute pseudo-Eulerian circulation statistics. In the best sampled regions, the statistics show typical circulation pathways related to the motion of the Levantine Intermediate Water. Subsurface typical speeds can reach 15-20 cm/s and partial control of the currents by the continental shelf slope is evident.
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