A Tropical Cyclone Model with Parameterized Vertical Partition of Released Latent Heat

Abstract

As a continuation of the previous study (Yamasaki, 1968), several numerical experiments for the development of tropical cyclones are performed with a time-dependent vertical partition of released latent heat. This partition ratio is expressed in terms of the large scale temperature field and, the pseudo-wet-bulb potential temperature (θsw) of cumulus clouds.
First experiment is made with the constant θsw. The result shows that the warm core formation begins in the upper layer. When the stratification becomes less unstable in the upper layer, the heat partition ratio to the lower layer is increased and thereby a rapid development occurs. At the mature stage the stratification becomes moist neutral near the center. The results of other experiments reveal that the growth rate of computed tropical cyclones is sensitive to the initial static stability. It is also found that the radial profile of the tangential velocity assumed at the initial time is an important factor not only to the growth rate but also to the formation of eye.
Finally, a case is discussed in which surface air temperature is kept to be a constant value and surface air is always saturated with water vapor. In this case the deepening of the surface pressure induces the increase of θsw and in turn the increase of θsw induces further deepening of the surface pressure. It is, however, shown that there exist an upper limiting value of θsw and a lower limiting one of the surface pressure. The limiting values are dependent on surface air temperature.