A Study of a Non-Deepening Tropical Disturbance

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  • a Institute for Atmospheric Sciences, ESSA, Miami, Fla.
  • | b Florida State University, Tallahassee
  • | c National Center for Atmospheric Research, Boulder, Colo.
  • | d Florida State University, Tallahassee
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Abstract

Data for a 3-day period from an experimental region formed by 6 islands of the Windward Group in the West Indies, a research vessel in the tropical Atlantic, an instrumented aircraft, and TIROS VI and VII form the basis for the study of a synoptic-scale tropical disturbance. Detailed analysis coupled with careful integration of all the observations, make it possible to describe the structure of the system, and show it to be distinct from classically modelled travelling disturbances. Instead, the disturbance is shown to be uncorrelated with any low-level perturbation of wind direction; its evolution and its translation depend upon small in situ development and decay in the upper troposphere.

Examples of similar disturbances are shown as evidence that this is not an isolated system. Emphasis is placed upon the necessity of establishing dynamic and physical models of the flow field and their attendant cloud and rainfall patterns, as well as the role played by convective and mesoscale processes in the formation, maintenance and decay of such systems. To do this, carefully designed experiments based upon a selected island network and incorporating joint aircraft, oceanographic, and satellite programs are necessary.

Abstract

Data for a 3-day period from an experimental region formed by 6 islands of the Windward Group in the West Indies, a research vessel in the tropical Atlantic, an instrumented aircraft, and TIROS VI and VII form the basis for the study of a synoptic-scale tropical disturbance. Detailed analysis coupled with careful integration of all the observations, make it possible to describe the structure of the system, and show it to be distinct from classically modelled travelling disturbances. Instead, the disturbance is shown to be uncorrelated with any low-level perturbation of wind direction; its evolution and its translation depend upon small in situ development and decay in the upper troposphere.

Examples of similar disturbances are shown as evidence that this is not an isolated system. Emphasis is placed upon the necessity of establishing dynamic and physical models of the flow field and their attendant cloud and rainfall patterns, as well as the role played by convective and mesoscale processes in the formation, maintenance and decay of such systems. To do this, carefully designed experiments based upon a selected island network and incorporating joint aircraft, oceanographic, and satellite programs are necessary.

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