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The momentum constraints on the shallow meridional circulation associated with the marine ITCZ

Dixit, Vishal and Srinivasan, J (2017) The momentum constraints on the shallow meridional circulation associated with the marine ITCZ. In: METEOROLOGY AND ATMOSPHERIC PHYSICS, 129 (6). pp. 595-609.

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Official URL: http://doi.org/10.1007/s00703-016-0489-2

Abstract

Recent studies have shown that the shallow meridional circulation (SMC) coexists with the deep circulation in the marine ITCZ. The SMC has been assumed to be forced by strong meridional gradients of Sea Surface Temperature (SST) which affect the atmosphere under hydrostatic balance. In this paper, we present a new viewpoint that the shallow meridional circulation is a part of circulation that forms when the marine ITCZ is located away from the equator. To support this view, we have used reanalysis data over east Pacific ocean to show that the shallow meridional circulation is absent when the ITCZ is located near the equator while it is strong to the south of the ITCZ when the ITCZ is located away from the equator. To further support this view, we have conducted idealized aquaplanet experiments by shifting SST maximum polewards to simulate the observed contrast in the meridional circulation associated with near equatorial and off-equatorial ITCZ. The detailed momentum budget of the flow above the boundary layer shows that, to the south of an off-equatorial ITCZ, the dominant balance between the Coriolis force and the advection of relative vorticity by the mean flow leads to cancellation of the planetary rotational effects. As a result, the net rotational effects experienced by the diverging flow above the boundary layer are negligible and a shallow meridional flow along the pressure gradients is generated. This dominant balance does not occur in the aquaplanet GCM when the ITCZ forms near the equator.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the SPRINGER WIEN, SACHSENPLATZ 4-6, PO BOX 89, A-1201 WIEN, AUSTRIA
Department/Centre: Division of Mechanical Sciences > Divecha Centre for Climate Change
Depositing User: Id for Latest eprints
Date Deposited: 24 Nov 2017 10:17
Last Modified: 24 Nov 2017 10:17
URI: http://eprints.iisc.ac.in/id/eprint/58295

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