Low-frequency modes in an equatorial shallow-water model with moisture gradients

Sukhatme, Jai (2014) Low-frequency modes in an equatorial shallow-water model with moisture gradients. In: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, 140 (683, B). pp. 1838-1846.

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Abstract

Motivated by observations of the mean state of tropical precipitable water (PW), a moist, first baroclinic mode, shallow-water system on an equatorial beta-plane with a background saturation profile that depends on latitude and longitude is studied. In the presence of a latitudinal moisture gradient, linear analysis of the non-rotating problem reveals large-scale, symmetric, eastward and westward propagating unstable modes. The introduction of a zonal moisture gradient breaks the east-west symmetry of the unstable modes. The effects of rotation are then included by numerically solving the resulting eigenvalue problem on an equatorial beta-plane. With a purely meridional moisture gradient, the system supports large-scale, low-frequency, eastward and westward moving neutral modes. Some of the similarities, and some of the discrepancies of these modes with intraseasonal tropical waves are pointed out. Finally, a zonal moisture gradient in the presence of rotation renders some of the aforementioned neutral modes unstable. In particular, according to observations of large-scale, low-frequency tropical variability, it is seen that regions where the background saturation profile increases (decreases) to the east favour eastward (westward) moving moist modes.

Item Type:	Journal Article
Publication:	QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY
Publisher:	WILEY-BLACKWELL,
Additional Information:	Copy right for this article belongs to the WILEY-BLACKWELL, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA.
Department/Centre:	Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited:	18 Oct 2014 06:54
Last Modified:	18 Oct 2014 06:54
URI:	http://eprints.iisc.ac.in/id/eprint/50040

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