12C.6
The Deformation of Large Cloud Disturbance on Western Tropical Pacific
Atsushi Hamada, Kyoto University, Kyoto, Japan; and N. Nishi and H. Kida
During TOGA-COARE IOP (November 1992 - February 1993), zonally spread large cloud disturbance was divided simultaneously into two or three zonally elongated cloud band. We made case study with using GMS-TBB data and ECMWF global analysis.
More than ten cases of division were seen in the ITCZ of the western Pacific during TOGA-COARE IOP. The divided cloud bands were elongated zonally with the length of the order of 1000km. The life-cycle of division implies that this phenomenon synchronized with the diurnal cycle of the deep convective activity in the Tropics. Individual cumulonimbi making up the cloud band at first developed discretely in predawn to the morning, extended anvil clouds, and organized into one large cloud band. This cloud band had maximum horizontal extent in the afternoon and started dividing.
During division, the wind field was characterized by strong meridional divergence onto the basic wind in the upper troposphere. On the other hand, in the lower troposphere, prevailing wind did not seem to accompany with the division. Thus, it is implied that the extended cirriform clouds were blown away by strong divergence wind from cumulonimbi of the cloud band.
By using GMS-IR split window, a cloud classification technique was applied to the dividing cloud band. The result supported that the cloud lines separated to north and south were composed of cirriform clouds, not convective systems like squall lines. In the dividing stage, convective activity of remaining central region was already decaying.
A part of the cloud band had the characteristics of the equatorial trapped inertia-gravity waves with meridional mode n=1. But, the relation between the division of the cloud and this kind of wave is not sure now.
Session 12C, Monsoons and the intertropical convergenze zone I (Parallel with Sessions 12A and 12B)
Friday, 26 May 2000, 8:00 AM-9:45 AM
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