Papers in Meteorology and Geophysics
Online ISSN : 1880-6643
Print ISSN : 0031-126X
ISSN-L : 0031-126X
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A Three-Dimensional Tropical Cyclone Model with Parameterized Cumulus Convection
Masanori Yamasaki
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1986 Volume 37 Issue 4 Pages 205-234

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Abstract

   A three-dimensional tropical cyclone model is developed with a new parameterization of cumulus convection, based on the results from the non-parameterized model of Yamasaki (1977, 83). In order to simulate the important features and mechanisms of tropical cyclones obtained in the non-parameterized model, cloud water and rainwater are included as predicted variables. The effects of evaporation of rainwater and convective downdrafts are taken into account. Heating due to parameterized convection is assumed to depend on the vertical velocity at a low level and the degree of the conditional instability.
   Results from a numerical experiment indicate that the present model is capable of describing mesoscale convections which are pronounced in the non-parameterized model. Mesoscale convections behave in different ways, depending on the stage (or intensity) of a simulated tropical cyclone and on the location relative to the tropical cyclone center. Simulated spiral rainbands consist of mesoscale convections which form around the trailing edge of a rainband in many cases and move on the spiral band cyclonically towards the eyewall. In the case of spiral bands which are strongly affected by frictional inflow, mesoscale convections are maintained for a long period of time by successive formation of convective elements at the outer edge of the band in which warm moist air flows. The spiral bands do not behave like gravity waves. Most of the properties of mesoscale convections (including those at the pre-typhoon stage) and the tropical cyclone simulated in this study are similar to those obtained from the non-parameterized model. The essential aspects of the parameterization scheme which leads to such results and its shortcomings are also discussed.

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© 1986 by Japan Meteorological Agency / Meteorological Research Institute
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