THE NUMERICAL PREDICTION OF HURRICANE MOVEMENT WITH A TWO-LEVEL BAROCLINIC MODEL

Akira Kasahara The University of Chicago

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Abstract

A steering method of predicting hurricane movement is formulated based upon a two-level baroclinic model. The upper steering-flow field is constructed from the pressure-weighted mean of the 200- and 500-mb steering-height fields, and the lower steering field is constructed from the pressure-weighted mean of the 700- and 1000-mb steering-height fields. Here, the steering flow of a hurricane is defined as the residual field after eliminating the vortex pattern from the total-flow field.

The evolutions of the upper and lower steering flows are predicted simultaneously by solving the two-level steering-flow vorticity equations. Based upon those steering-flow forecasts, the movement of a hurricane is predicted with the use of an equation which is derived from a solution of two vortex vorticity equations. A side condition is imposed that the upper and lower vortex patterns should move with the same velocity in the corresponding steering flows.

Ten cases of predicting the movement of hurricane “Betsy” (August 1956) up to 48 hr are presented. A preliminary comparison of the forecasts with those obtained from the barotropic model is also made.

Abstract

A steering method of predicting hurricane movement is formulated based upon a two-level baroclinic model. The upper steering-flow field is constructed from the pressure-weighted mean of the 200- and 500-mb steering-height fields, and the lower steering field is constructed from the pressure-weighted mean of the 700- and 1000-mb steering-height fields. Here, the steering flow of a hurricane is defined as the residual field after eliminating the vortex pattern from the total-flow field.

The evolutions of the upper and lower steering flows are predicted simultaneously by solving the two-level steering-flow vorticity equations. Based upon those steering-flow forecasts, the movement of a hurricane is predicted with the use of an equation which is derived from a solution of two vortex vorticity equations. A side condition is imposed that the upper and lower vortex patterns should move with the same velocity in the corresponding steering flows.

Ten cases of predicting the movement of hurricane “Betsy” (August 1956) up to 48 hr are presented. A preliminary comparison of the forecasts with those obtained from the barotropic model is also made.

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