A Linear Model Study of Cross-Equatorial Flow Forced by Summer Monsoon Heat Sources

Keith D. Sashegyi Science.applications International Corporation, McLean, VA 22102

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John E. Geisler Department of Meteorology, University of Utah, Salt Lake City, UT 84112

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Abstract

A linear model of the steady response of a stratified fluid to isolated heat sources on a sphere is developed. The model is used to examine the response to diabatic heating associated with summer monsoon precipitation in India and to low-level diabatic heating along the northeast coast of Africa. In a laterally unbounded, spherical domain, the summer monsoon heat source forces a cross-equatorial meridional cell that is about half as strong as the main response feature, which is a cell oriented zonally and situated on the west side of the source. The imposition of a meridional wall concentrates the cross-equatorial flow in the meridional cell into a western boundary current. For representative summer monsoon heating the northward transport in this simple East African Jet is comparable to what is observed. The cross-equatorial flew pattern forced by low-level, diabatic heating along the African coast consists of a western boundary current near the equator that turns into a geostrophically balanced sea breeze in low latitudes away from the equator. The northward mass flux in this locally forced jet is about an order of magnitude smaller than that which is forced by the summer monsoon heat source.

Abstract

A linear model of the steady response of a stratified fluid to isolated heat sources on a sphere is developed. The model is used to examine the response to diabatic heating associated with summer monsoon precipitation in India and to low-level diabatic heating along the northeast coast of Africa. In a laterally unbounded, spherical domain, the summer monsoon heat source forces a cross-equatorial meridional cell that is about half as strong as the main response feature, which is a cell oriented zonally and situated on the west side of the source. The imposition of a meridional wall concentrates the cross-equatorial flow in the meridional cell into a western boundary current. For representative summer monsoon heating the northward transport in this simple East African Jet is comparable to what is observed. The cross-equatorial flew pattern forced by low-level, diabatic heating along the African coast consists of a western boundary current near the equator that turns into a geostrophically balanced sea breeze in low latitudes away from the equator. The northward mass flux in this locally forced jet is about an order of magnitude smaller than that which is forced by the summer monsoon heat source.

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