Diurnal variation of convective activity over the tropical western pacific

Abstract

Diurnal variations of convective activities in the tropical western Pacific are examined by using 3-hourly geostationary meteorological satellite data acquired over a 9-year period (1980-1989). Large diurnal variations of convection exist over continents, large islands and their adjacent sea regions such as the Indochina Peninsula, the Tibetan Plateau, North Australia and the maritime continent regions. Large diurnal variations are also found over the Bay of Bengal and the South China Sea. Although the diurnal variation is less pronounced over the open oceanic regions east of 150°E than over the maritime continent regions, moderate amplitudes of diurnal variations are observed over the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ). Features of the diurnal variation vary with the seasons and it is enhanced during seasons in which mean convective activities become strong. Over continents and large islands, the convection attains its maximum intensity in late afternoon to evening, probably due to strong surface heating during daytime. Over sea areas in the vicinity of large islands, the maximum convective activity generally occurs in the morning. It is suggested that the interaction between land-sea circulations and large-scale environmental flows may produce a diurnal cycle in the offshore convection. There exist large amplitudes of diurnal variations over the head of the Bay of Bengal during the Indian summer monsoon season with the maximum amplitude in the afternoon. The diurnal cycle of convection becomes predominant during summer and fall over the South China Sea, with the maximum convective activity near local noontime. The convection over the ITCZ and the SPCZ has a maximum intensity in the morning, in general, but a secondary maximum of convection occurs in the afternoon. The Fourier analysis of the second component (semi-diurnal variation) suggests that there exist semi-diurnal variations of convection over the ITCZ and the SPCZ with maximum peaks around 3-4 LST and 15-16 LST.