Role of angular momentum transports in tropical storm dissipation over tropical oceans
Date
1968-12
Authors
Wachtmann, Ronald F., author
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Abstract
The mean wind field is investigated around eleven tropical storms which dissipated over tropical waters south of 20° north latitude. Wind data at 850 mb and 200 mb are composited in a circular area of 12° latitude radius from the storm center for two periods in the life of these storms: (1) their intensification and mature stages, and (2) their dissipation stage. Vertical shears between these two levels are also composited. Wind data in the composites are converted to radial profiles of mean tangential wind for the two periods of storm life. These profiles are compared to similar profiles found in previous studies for intensifying tropical depressions and for mature tropical storms. The most significant differences are found in the low level wind field north of the storm centers. The broad easterly flow to the north of the intensifying tropical depressions is also found north of the dying storms during their intensification and mature stages. However, during the dissipation stage the easterly flow has weakened and become westerly over a part of the area. As a result, the mean tangential wind is significantly reduced at all radii thus reducing the import of relative angular momentum into the storm by the mean radial circulation. A deficiency in angular momentum results from a loss to the ocean greater than the import through the boundaries in at least some of the cases investigated. It is concluded that a lack of angular momentum import through the lateral boundaries may in some cases be an important factor in storm weakening or dissipation. Angular momentum import into storms at low latitudes is performed by the surrounding anticyclones at the outer radii. Maintenance and control of storm intensity is thus directly related to the position and intensity of these anticyclones.
Description
Originally published as author's thesis.
December 1968.
December 1968.
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Subject
Tropical meteorology