Diurnal variations of circulation and precipitation in the vicinity of the Tibetan Plateau in early summer |
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| Authors: | K C Chow Johnny C L Chan |
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| Institution: | (1) CityU-IAP Laboratory for Atmospheric Sciences, Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China;(2) Atmospheric Research Center, HKUST Fok Ying Tung Graduate School, Hong Kong University of Science and Technology, Nansha IT Park, Nansha, Guangzhou, China |
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| Abstract: | A regional climate model (RCM) has been applied to simulate the diurnal variations of the Asian summer monsoon during the
early summer period. The ERA40 reanalysis data and the TRMM precipitation data are used to evaluate the performance of the
model. The 5-year simulations show that the RCM could simulate well the diurnal cycle of the monsoon circulation over the
region. A strong diurnal variation of circulation over the Tibetan Plateau (TP) can be observed at the 500-hPa level, with
strong convergence and upward motion in the late afternoon. The diurnal variation of the 500-hPa relative vorticity over the
TP associated with the corresponding diurnal variation of convergence may lead to the formation of a prominent plateau-scale
cyclonic circulation over the TP during the evening to midnight period. The simulated diurnal variation of precipitation over
land is generally better than that over the ocean, particularly over the regions close to the TP such as the Bangladesh region
in the southern flank of the TP, where the well-known nocturnal maximum in precipitation is well captured by the RCM. However,
the late-afternoon maximum in precipitation over the Southeast Asia region is not well simulated by the RCM. The model results
suggest that the diurnal variation of precipitation over the southern flank of the TP is associated with the strong diurnal
variation in the circulation over the TP. |
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| Keywords: | Diurnal variation Tibetan Plateau Asian summer monsoon |
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