The Vorticity Budget of Synoptic-Scale Wave Disturbances in the Tropical Western Pacific

Richard J. Reed Dept. of Atmospheric Sciences, University of Washington, Seattle 98195

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Richard H. Johnson Dept. of Atmospheric Sciences, University of Washington, Seattle 98195

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Abstract

Composite fields of the large-scale variables determined from three months of observations at a triangular array of stations are used to determine the vorticity budget of easterly wave disturbances in the tropical western Pacific. The measurements reveal substantial imbalances which are largest in the disturbed or convectively active region of the waves. In this region there exists an apparent vorticity sink for the large-scale motions in the lower half of the troposphere and an apparent source in a relatively thin layer of the upper troposphere.

Cumulus modelling assumptions are employed to estimate vertical cloud mass flux and vertical profiles of cloud vorticity. It is concluded that the low-level sink and upper-level source can be attributed to the removal of vorticity-rich air from the lower layers and its deposition aloft by deep convection.

Abstract

Composite fields of the large-scale variables determined from three months of observations at a triangular array of stations are used to determine the vorticity budget of easterly wave disturbances in the tropical western Pacific. The measurements reveal substantial imbalances which are largest in the disturbed or convectively active region of the waves. In this region there exists an apparent vorticity sink for the large-scale motions in the lower half of the troposphere and an apparent source in a relatively thin layer of the upper troposphere.

Cumulus modelling assumptions are employed to estimate vertical cloud mass flux and vertical profiles of cloud vorticity. It is concluded that the low-level sink and upper-level source can be attributed to the removal of vorticity-rich air from the lower layers and its deposition aloft by deep convection.

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