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Observed intra-seasonal to interannual variability of the upper ocean thermal structure in the southeastern Arabian Sea during 2002-2008

Gopalakrishna, VV and Durand, F and Nisha, K and Lengaigne, M and Boyer, TP and Costa, J and Rao, RR and Ravichandran, M and Amrithash, S and John, L and Girish, K and Ravichandran, C and Suneel, V (2010) Observed intra-seasonal to interannual variability of the upper ocean thermal structure in the southeastern Arabian Sea during 2002-2008. Deep-Sea Research Part I: Oceanographic Research Papers, 57 (6). pp. 739-754.

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Abstract

The southeastern Arabian Sea (SEAS), located in the Indian Ocean warm pool, is a key-region of the regional climate system. It is suspected to play an important role in the dynamics of the Asian summer monsoon system. The present study reports the salient features derived from a newly harvested observational dataset consisting of repeated fortnightly XBT transects in the SEAS over the period 2002-2008. The fortnightly resolution of such a multi-year record duration is unprecedented in this part of the world ocean and provides a unique opportunity to examine the observed variability of the near-surface thermal structure over a wide spectrum, from intra-seasonal to interannual timescales. We find that most of the variability is trapped in the thermocline, taking the form of upwelling and downwelling motions of the thermal stratification. The seasonal variations are consistent with past studies and confirm the role of the monsoonal wind forcing through linear baroclinic waves (coastally-trapped Kelvin and planetary Rossby waves). Sub-seasonal variability takes the form of anomalous events lasting a few weeks to a few months and occurs at two preferred timescales: in the 30-110 day band, within the frequency domain of the Madden-Julian oscillation and in the 120-180 day band. While this sub-seasonal variability appears fairly barotropic in the offshore region, the sign of the anomaly in the upper thermocline is opposite to that in its lower part on many occasions along the coast. Our dataset also reveals relatively large interannual temperature variations of about 1°C from 50 to 200. m depth that reflect a considerable year-to-year variability of the magnitude of both upwelling and downwelling events. This study clearly demonstrates the necessity for sustained long-term temperature measurements in the SEAS.

Item Type: Article
Additional Information: Copyright of this article belongs to Elsevier.
Uncontrolled Keywords: XBT data; Arabian Sea; Lakshadweep Sea; Interannual variability; Intra-seasonal variability; WICC
Subjects: Oceanography > oceanography
Depositing User: INCOIS Library
Date Deposited: 07 Dec 2013 23:47
Last Modified: 07 Dec 2013 23:47
URI: http://moeseprints.incois.gov.in/id/eprint/198

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