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Ocean Science An interactive open-access journal of the European Geosciences Union
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.
09 Jun 2008
Review status
This discussion paper is a preprint. A revision of the manuscript for further review has not been submitted.
North Indian Ocean variability during the Indian Ocean dipole
J. Brown1, C. A. Clayson1, L. Kantha2, and T. Rojsiraphisal3 1Geophysical Fluid Dynamics Institute, Florida State University, Tallahassee, Florida, USA
2Department of Aerospace Engineering Sciences, University of Colorado, Boulder,\newline Colorado, USA
3Department of Mathematics, Burapha University, Thailand
Abstract. The circulation in the North Indian Ocean (NIO henceforth) is highly seasonally variable. Periodically reversing monsoon winds (southwesterly during summer and northeasterly during winter) give rise to seasonally reversing current systems off the coast of Somalia and India. In addition to this annual monsoon cycle, the NIO circulation varies semiannually because of equatorial currents reversing four times each year. These descriptions are typical, but how does the NIO circulation behave during anomalous years, during an Indian Ocean dipole (IOD) for instance? Unfortunately, in situ observational data are rather sparse and reliance has to be placed on numerical models to understand this variability. In this paper, we estimate the surface current variability from a 12-year hindcast of the NIO for 1993–2004 using a 1/2° resolution circulation model that assimilates both altimetric sea surface height anomalies and sea surface temperature. Presented in this paper is an examination of surface currents in the NIO basin during the IOD. During the non-IOD period of 2000–2004, the typical equatorial circulation of the NIO reverses four times each year and transports water across the basin preventing a large sea surface temperature difference between the western and eastern NIO. Conversely, IOD years are noted for strong easterly and westerly wind outbursts along the equator. The impact of these outbursts on the NIO circulation is to reverse the direction of the currents – when compared to non-IOD years – during the summer for negative IOD events (1996 and 1998) and during the fall for positive IOD events (1994 and 1997). This reversal of current direction leads to large temperature differences between the western and eastern NIO.

Citation: Brown, J., Clayson, C. A., Kantha, L., and Rojsiraphisal, T.: North Indian Ocean variability during the Indian Ocean dipole, Ocean Sci. Discuss.,, in review, 2008.
J. Brown et al.
Interactive discussionStatus: closed (peer review stopped)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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RC S68: 'Review', Anonymous Referee #1, 11 Jul 2008 Printer-friendly Version 
RC S82: 'Discuss the past literatures carefully', Anonymous Referee #3, 18 Jul 2008 Printer-friendly Version 
J. Brown et al.
J. Brown et al.


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