Structure and Behavior of a Monsoon Cyclone over West Africa

D. E. Pedgley Department of Meteorology, Florida State University Tallahassee

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T. N. Krishnamurti Department of Meteorology, Florida State University Tallahassee

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Abstract

In this paper we present the results of a detailed synoptic compositing technique to determine the structure of a West African monsoon cyclone. The cyclone was in an early stage of development and was confined to the lower troposphere. Coastal weather along West Africa indicated the passage of this disturbance. This was noted from surface observations from ships of opportunity. A calculation of the meridional gradient of potential vorticity was carried out in the region of this disturbance. This calculation showed that the necessary condition for the existence of the combined barotropic-baroclinic instability was satisfied by these data. In order to go one step beyond the necessary conditions of this instability mechanism two very short range numerical prediction experiments are illustrated whose energetics confirm these results. Finally, we also present dynamic vertical motion distributions for this disturbance.

Abstract

In this paper we present the results of a detailed synoptic compositing technique to determine the structure of a West African monsoon cyclone. The cyclone was in an early stage of development and was confined to the lower troposphere. Coastal weather along West Africa indicated the passage of this disturbance. This was noted from surface observations from ships of opportunity. A calculation of the meridional gradient of potential vorticity was carried out in the region of this disturbance. This calculation showed that the necessary condition for the existence of the combined barotropic-baroclinic instability was satisfied by these data. In order to go one step beyond the necessary conditions of this instability mechanism two very short range numerical prediction experiments are illustrated whose energetics confirm these results. Finally, we also present dynamic vertical motion distributions for this disturbance.

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