Diurnal variability of cloudiness over East Asia and the western Pacific ocean as revealed by GMS during the warm season

Abstract

Diurnal variations of cloudiness over East Asia and the western Pacific are investigated for the warm season of 1987, based on GMS-3 IR data at every three hours. The domain chosen for the present analysis is between latitude 50°N and 20°S and longitude 90°E and 160°E. The main results obtained are: (1) Diurnal variations of cloudiness result from superposition of large diurnal-cycle and small semidiurnal-cycle variations. Amplitude and phase of the diurnal-cycle variation are much different over land and ocean. Semidiurnal-cycle variations over land and ocean are almost in phase with maxima at 0300 ∼ 0500 LT and 1500 ∼ 1700 LT, and have similar amounts of amplitude. (2) A systematic phase delay of diurnal-cycle variation appears to the east of the Tibetan Plateau. A maximum of cloudiness appears near dusk over the Tibetan Plateau and at midnight in the Sichuan Basin. Phase speed of the variations is almost the same as in the eastward phase propagation of the diurnal-cycle variation of precipitation frequency east of the Rocky Mountains in the United States. Eastward movement of cloud clusters generated over the Tibetan Plateau, as well as locally induced convections, should be taken into account to understand the behavior of diurnal variation of cloudiness to the east of the Plateau. (3) The eastward phase delay of the diurnal-cycle variation to the east of the Tibetan Plateau is obscured during mid-summer. This may be caused by locally induced active convections intensified near dusk to the east of the Plateau, and seasonal disappearance of upper westerly flow passing over the Plateau.