The Properties of Typhoon-Scale Disturbances Produced by Arakawa-Schubert Parameterization

[摘要] In order to obtain a theoretical base of formation and development of a tropical cyclone, properties of unstable waves produced by cumulus convection which is expressed by a parameterization scheme proposed by Arakawa and Schubert (1974) are investigated by a linear analysis.The model used is a four-layer model containing three layers of the free atmosphere and one mixed layer. Thus three cloud types such as the highest type (H), the middle type (M) and the lowest type (L) are defined. The following seven combinations may be considered; (HML), (HM), (HL), (ML), (H), (M) and (L), depending on the co-existence of these cloud types.Among these seven, the combination which is accompanied by a large scale disturbance is uniquely determined as an eigen solution for almost all cases if the basic field and the scale of the disturbance are specified. In general, the mode (H), the mode (HM) and the mode (HML) appear in turn with increasing wavelength. The mode which becomes most unstable depends on the vertical distribution of temperature and water vapour of the basic field.The typhoon-scale disturbance whose preferred scale is less than a few hundred kilometers and growth rate is in a range of 10-610-5sec-1 belongs to eigher the mode (H) or the mode (HM). These modes can be unstable as the lower layer of basic field becomes conditionally unstable and humid. The convective heating in the lower layer plays an essential role for the typhoon-scale disturbance to become unstable.Finally, a comparison is attempted between the typhoon-scale disturbance mentioned above and the typhoon mode of Ooyama (1964).

[学科分类] 大气科学