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A Two-Layer Quasi-Geostrophic Model of Summer Trough Formation in the Australian Subtropical Easterlies

C. B. FandryCSIRO Division of Oceanography, G.P.O. Box 1538, Hobart, Tasmania, Australia 7001

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L. M. LeslieAustralian Numerical Meteorology Research Centre, G.P.O. Box 5089AA, Melbourne, Victoria, Australia 3001

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Abstract

A dominant feature of the low-level easterly wind flow in the Australian subtropics during summer is the trough development that occurs on both the western and eastern sides of the continent. This phenomenon is investigated analytically with a two-level model. A generalized solution is derived from the steady-state quasi-geostrophic equations governing uniform flow over arbitrarily shaped orography. The model solutions indicate that orography acting alone is of only marginal importance in producing the western trough. However, the high east coast orography is of significance in the formation of the eastern trough.

Land-sea temperature contrast is parameterized in terms of equivalent orography with localized surface heating being mathematically equivalent to an orographic depression. The solutions including orography and surface heating acting together simulate well the lower layer flow over the Australian subtropics.

Abstract

A dominant feature of the low-level easterly wind flow in the Australian subtropics during summer is the trough development that occurs on both the western and eastern sides of the continent. This phenomenon is investigated analytically with a two-level model. A generalized solution is derived from the steady-state quasi-geostrophic equations governing uniform flow over arbitrarily shaped orography. The model solutions indicate that orography acting alone is of only marginal importance in producing the western trough. However, the high east coast orography is of significance in the formation of the eastern trough.

Land-sea temperature contrast is parameterized in terms of equivalent orography with localized surface heating being mathematically equivalent to an orographic depression. The solutions including orography and surface heating acting together simulate well the lower layer flow over the Australian subtropics.

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