Westward Movement and Splitting of an Equatorial Cloud Cluster Associated with Tropical Large-Scale Vortices

[摘要] During the intensive observing period (IOP) of TOGA-COARE, a significant westward-moving cloud cluster was observed in the equatorial Pacific from 10 to 13 November 1992. Although cloud activity in this region was less intense in November than that of other periods of the IOP, an eastward-propagating super cluster was still observed. The westward-moving cloud cluster was considered to be a hierarchic component of the super cluster. The cloud cluster moved westward against the prevailing westerly caused by a westward-propagating large-scale vortex and split into two clusters. One part of the cloud cluster continued to move westward and the other part was almost stationary in the zonal direction.In order to clarify mechanisms of the westward movement and splitting of the cloud cluster and its relationship with large-scale disturbances, a numerical simulation experiment and sensitivity tests were performed. The experiment simulated the westward movement and the splitting of the cloud cluster. The large-scale vortex intensified the westerly in the equatorial region. The cloud cluster developed where latent heat flux from the sea was enhanced by the strong westerly. Consequently, the westward-moving part of the cloud cluster moved with the westward-propagating vortex. The remaining part of the cloud cluster was associated with stationary twin cyclones and was, therefore, stationary in the zonal direction.On the basis of the data analyses and results of the numerical modelings, we conclude that the development and westward movement of the cloud cluster of the present paper were caused by the westward-propagating large-scale vortex and that the splitting of the cloud cluster is attributed to the different phase velocities of the westward-propagating vortex and the stationary twin cyclones.

[学科分类] 大气科学