Impact of 4D-variational assimilation of WOCE hydrography on the meridional circulation of the Indian Ocean

Type Article
Date 2003-07
Language English
Author(s) Ferron Bruno, Marotzke Jochem
Affiliation(s) CNRS, IFREMER, UBO, UMR 6523,Lab Phys Oceans, Brest, France.
Southampton Oceanog Ctr, Sch Ocean & Earth Sci, Southampton, Hants, England.
Source Deep Sea Research Part II: Topical Studies in Oceanography (0967-0645) (Elsevier), 2003-07 , Vol. 50 , N. 12-13 , P. 2005-2021
DOI 10.1016/S0967-0645(03)00043-2
WOS© Times Cited 25
Keyword(s) Overturn, Oceanographic surveys, Hydrographic data, Ocean circulation
Abstract World Ocean Circulation Experiment (WOCE) hydrographic sections and a sea-surface climatology are combined with a ocean general circulation model through a 4D-variational method to analyze the meridional overturning of the Indian Ocean. The regional model is run with realistic surface forcings over year 1995 for which most of WOCE Indian Ocean sections were made. The assimilation controls the initial temperature and salinity fields, surface forcings and open-boundary velocities, temperature and salinity. When no observations are assimilated, the model shows that the deep (below 1000 m) meridional overturning is weak compared to observation-based estimates. This is a common feature of general circulation models. In contrast, after the assimilation, the model develops a deep overturning of 17 x 10(6) m(3) s(-1) at 32degreesS when a 10 x 10(6) m(3) s(-1) Indonesian Throughflow (ITF) is prescribed. The mass flux of bottom waters that moves northward below 3200 m is balanced by a southward mass flux of deep waters between 1000 and 3200 m. The deep overturning carries 10% of the total southward energy flux of 1.2 PW at 32degreesS. The intensity of this deep overturning changes only by +/-2 x 10(6) m(3) s(-1) When the annual mean ITF is zero or 30 x 10(6) m(3) s(-1). The upper circulation is less constrained by the assimilation because of the large temporal and spatial variability of this ocean and also because of limitations in the representation of the mixed layer physics during the assimilation process. Limitations in the physics of the model also are thought to be the source of the slow erosion of the deep overturning when the model is run for several years from its optimal state.
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