Diurnal Variations in Summer Monsoon Precipitation over Thailand and Its Vicinity Observed from Ten Years of TRMM Data
Atsamon Limsakul1,*, Usa Humphries2, Angkool Wangwongchai2, Thanet Chitsuphaphan2 and Prungchan Wongwises3,4
1Environmental Research and Training Center, Technopolis, Klong5, Klong Luang, Pathumthani 12120 Thailand
2Department of Mathematics, King Mongkut’s University of Technology Thonburi, Bang Mod, Thung Khru, Bangkok 10140 Thailand
3The Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology Thonburi,
Bang Mod, Thung Khru, Bangkok 10140 Thailand
4Center of Excellence on Energy Technology and Environment, Ministry of Education, Thailand
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Abstract: On the basis of Empirical Orthogonal Function (EOF) and harmonic analysis, spatial patterns of diurnal cycles of precipitation during a rainy season over Thailand and its vicinity were examined using 3-hourly, 0.25° TRMM data for the time period 2000-2009. Results revealed that the leading two EOFs and harmonics could explain most of diurnal precipitation variations. The first EOF and harmonic represent the diurnal cycle with an afternoon-evening peak and amplitude of 30-88% of the climatological mean. This dominant feature reflects land-sea difference in the atmospheric response to solar radiation forcing, representing potential instability forced by the surface heat flux, insolation and long-wave radiative cooling during the day and night. Whereas, the second EOF and harmonic denote the semidiurnal cycle, with nocturnal and early morning maxima and amplitude of 10-33% of the climatological mean. The secondary sub-daily cycle represents a complementary local variation, and is associated with mesoscale dynamics of convective systems and its interactions with local thermally induced circulations. The findings from this study provide evidence to broaden the understanding of local climate, and to validate certain parameterizations in numerical models as well as to improve weather forecast accuracy. However, further analysis should relate and simulate the identified diurnal variations to large-scale atmospheric circulation modes . This future work may lead to better understand the mechanisms of diurnal precipitation variations under a recent widening of the tropical belt and an anthropogenically warmed climate.
Keywords: Diurnal variation, Precipitation, Empirical Orthogonal Function, Harmonic, Thailand.
