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Impact of interannual atmospheric forcing on the Mediterranean Outflow Water variability in the Atlantic Ocean
Alexandra Bozec, Eric Chassignet, Susan Lozier
COAPS/FSU
(Abstract received 05/05/2009 for session X)
ABSTRACT
Several questions remain unanswered about the role and importance of the Mediterranean Overflow Water (MOW) for the Atlantic Ocean circulation and the global thermohaline circulation. Of particular interest is the temporal variability of the MOW in the Atlantic Ocean found by Potter and Lozier (2004) and the mechanism(s) responsible for such variability on interannual and decadal scales. The source of this variability has been attributed to changes in the source water (i.e. Mediterranean Sea Water), changes in the entrained North Atlantic Central Water (NACW), or both. The analysis of the variability of the Mediterranean Sea Water (Lozier and Sindlinger, 2008) and of the NACW in the Gulf of Cadiz, using HYDROBASE profiles, on the period 1955-1995, show that the variability of these water masses can not be responsible for the variability of the MOW in the Atlantic. Here, we test the impact of an interannual atmospheric forcing on the spatial pattern of the MOW tongue. We use a 1/3º Atlantic configuration of the HYbrid Coordinate Ocean Model (HYCOM) with the Price and Yang (1998) marginal sea boundary condition for the Mediterranean outflow. Three experiments of 59 years are performed using a constant MOW outflow (T=11ºC, S=36.2psu and Tr=4Sv): one forced by the ERA15 climatology wind-stress and buoyancy forcing, one forced by the ERA15 buoyancy forcing but the NCEP 1948-2006 wind-stress and the last one forced by the NCEP1948-2006 wind-stress and buoyancy forcing. Only the simulation forced by the interannual wind and buoyancy forcing reproduces the MOW trend observed in the Atlantic showing that the MOW decadal variability is driven by the variability of the atmosphere during the 1955-1995 period. Furthermore, we find a westward extension of the MOW tongue during the 1980-2000 period compared with the 1950-170 period that coincides with a retraction of the Labrador Sea water from the central Atlantic Ocean.
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2009 LOM Workshop, Miami, Florida Jume 1 - 3, 2009