Diurnal Cycle of Tropical Deep Convection Examined Using High Space and TimeResolution Satellite Data

摘要

Infrared (IR) and visible (VIS) satellite data was used to examine the diurnalcycle of deep convection over a sector of the tropical west Pacific warm pool. Data were analyzed for 45 days of summer and for 65 days of winter. The synoptic backdrop was characterized by the monsoon trough. Convection was largely focused along the trough. December 1994 was characterized by an active phase of the intraseasonal oscillation (ISO) while January 1995 coincided with an inactive phase. Deep convective cloud was identified in IR imagery using brightness temperature (TBB) threshold techniques. Cloud forms associated with deep convection showed two distinct diurnal modes representing deep convection. The diurnal variation of cloud in these regimes was consistent for all time periods and for two tropical storms which occurred in the WP during December 1994. Three objective analysis techniques were developed to analyze the relation of tropical cloud cluster structure to the daily spatial and temporal variation of deep convection. Findings indicate that the diurnal cycle of deep convective cloud is driven by the internal variation of large clusters. Clusters that exist into or form during the night, grow spatially larger and more intense. Some results support direct radiative forcing of clouds and large scale clear region radiative destabalization as possible contributors to diurnal convective variability.