梅雨前線上の中間規模雲cluster

Abstract

Observation features and evolution process of a long-lived medium-scale cloud cluster have been analyzed in Part I of the present paper. Thermal and kinematic fields and heat budget of this cloud cluster are investigated in Part II. The special attention is given in its formation and developing stages over the Continental China region.The following results were obtained.1). A cloud cluster developed in the uniform unstable tropical air over the Continent. Thermal fields in and around the cloud cluster exhibited local variations due to convections and 3-dimensional moisture advection.2). Kinematic fields in the cloud cluster over the Continent also showed particular localized features. That is, medium-scale cyclonic circulation in the lower troposphere, anticyclonic circulation in the upper layer and upward motion are found. They indicated time variations throughout the formation and developing stages.3). An apparent moisture sink in the lower tropospere and an apparent heat source in the upper troposphere existed in the cloud cluster. The both quantities reached the maxima at the time when observed rainfall reached the maximum (∼80mm/6 hour).4). Calculated rainfall (vertically integrated apparent moisture sink) showed similar time variation to that in the observed rainfall: The calculated rainfall amount showed a variation of about one day period, that was consistent with the observed variation analyzed in Part I of the present paper.5). Thermal and kinematic fields in and around the cloud cluster investigated in this study, which developed in the uniform unstable air over the Continent, showed similar features to those of medium-scale cloud clusters frequently developed in the Baiu front (subtropical baroclinic zone) over the Japan Islands and the Pacific Ocean, in spite of different environmental situations.The present study indicates that the cloud cluster transformed into a frontal depression under the influence of a short wave trough in the subtropical baroclinic zone. It is conjectured that in the atmosphere without baroclinicity the cloud cluster remained as a cloud cluster without transforming into a depression, even though a large amount of heat was released and redistributed through convections.