Numerical Experiments of the Tropical Cyclone by Use of the Arakawa-Schubert Parameterization

[摘要] Several numerical experiments of axially symmetric tropical cyclones are performed by use of Arakawa-Schubert (1974)'s parameterization of cumulus convection. The main purpose of the study is to examine whether or not the development and structure of tropical cyclones can be simulated by their parameterization. The model includes five layers, four of which correspond to the free atmosphere and one to the mixed layer. According to the height of cloud top level, clouds are classified into three types; the tallest type (H-type), the middle type (M-type) and the lowest type (L-type). Their top heights are assumed to be 13km, 9km and 5km, respectively.The results of the numerical experiments indicate that the development of tropical cyclones can be simulated realistically by using their parameterization. Many features of the structure as well as evolution of a parameterized cumulus ensemble, are also well simulated. An eye and an eyewall are formed in the rapid developing stage when the tangential velocity near the center becomes strong. The eyewall is located around the radius of the maximum tangential velocity. Clouds in the eyewall are occupied by the H-type clouds in the later stage, although the M- and L-type clouds coexist with the H-type clouds in the early stage. In contrast to eyewall clouds, clouds in the outer region tend to have propagating nature.The effect of the surface friction is also investigated. The following results, which were obtained by Yamasaki (1977b) with a non-parameterized model, are confirmed with the present model: (1) Surface friction is indispensable to the formation of an eyewall and an eye. (2) Surface friction does not play an essential role to the development of a vortex at the stage when the vorticity is weak. The tropical cyclone simulated in this study is similar to that of Yamasaki (1977a) in many respects.Numerical experiments are also performed by changing the initial condition and the value of hM (moist static energy in the mixed layer). It is found that the initiation of rapid development sensitively depends on the magnitude of the cloud work function for the H-type.

[学科分类] 大气科学