Diurnal Variations of Satellite-Measured TBB Areal Distribution and Eye Diameter of Mature Typhoons

Abstract

Geostationary Meteorological Satellite (GMS) observations of diurnal variations of cirrus canopy and eye diameter in mature northwest Pacific typhoons are presented. The variations in cirrus canopy are quantitatively determined by the areal distribution of equivalent black body temperatures (TBB) (10.5-12.5μm, window channel) in the ranges: TBB_??_-70°C, -70°C, <TBB_??_-50°C, -50°TBB_??_30 and -30°TBB_??_0°C. The coldest region has a sharp maximum at 0600-0730LST and a minimum at 1800-2100LST. The maxima in the warmer cloud tops occur some hour later at 1500-1800LST and 2100LST, respectively, as rising the TBB thresholds. Satellite observed eye diameter exhibits a wedge-shaped morning minimum and a plateau-shaped afternoon-evening maximum. The time lagged diurnal variation of areal extent of warmer cirrus clouds, and the out of phase variation of eye diameter compared to the coldest cirrus clouds, is explained as a result of outward and inward expansion of cirrus following an early morning peak in eyewall and spiral band convections.
When a typhoon passes over or near to large islands, the total cirrus canopy is reduced in size and a second afternoon peak in areal coverage develops.