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Response of the Diurnal Cycle of Summer Rainfall to Large‐Scale Circulation and Coastal Upwelling at Hainan, South China
Author(s) -
Shi Rui,
Cai Qinbo,
Dong Lingyu,
Guo Xinyu,
Wang Dongxiao
Publication year - 2019
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd029528
Subject(s) - upwelling , sea breeze , climatology , environmental science , diurnal cycle , submarine pipeline , atmospheric instability , oceanography , atmospheric sciences , wind speed , geology
The modulation of coastal rainfall at Hainan by large‐scale circulation and coastal upwelling is studied using observations and numerical modeling. Tropical Rainfall Measuring Mission data show that the monthly mean rainfall off southern Hainan was considerably higher in August 2010 than in August 2011. The main cause of this difference is an intensification of offshore rainfall from midnight to early morning. Compared with the multiyear (2000–2017) average field, reanalysis data show that there is an apparent increase in atmospheric humidity in August 2010. During this time, a moderate El Niño was decaying and a new La Niña event was developing, so a significant adjustment of the large‐scale circulation was observed in the western Pacific. The resulting anomalous onshore wind depresses the development of upwelling, leading to a relatively warm sea surface temperature off the south coast of Hainan, which in turn enhances the land‐sea thermal contrast and land breeze at night. Decreases in upwelling intensity and asymmetric intensification of nocturnal and daytime offshore rainfall are confirmed not only in the summer of 2010 but also in the summer of 2003. Numerical simulations using the Weather Research and Forecasting model verify that the enhanced land breeze ultimately leads to pronounced coastal rainfall off southern Hainan at night. The results indicate that localized surface convergence associated with the sea and land breezes may be more important than the atmospheric humidity and convective instability in modulating the diurnal cycle of rainfall for tropical islands.