Abstract
In this study, the atmospheric moisture transport involved in the East Asian summer monsoon (EASM) water cycle is examined. Observational estimates are contrasted with the Met Office Unified Model (MetUM) climate simulations to evaluate the model’s ability to capture this transport. We explore the role of large circulation in determining the regional water cycle by analyzing key systematic errors in the model. MetUM exhibits robust errors in its representation of the summer Asian-Pacific monsoon system, including dry biases in the Indian peninsula and wet biases in the tropical Indian Ocean and tropical West Pacific. Such errors are consistent with errors in the atmospheric moisture convergence in the area. Diabatic heating biases in the Maritime Continent domain are shown, via nudging sensitivity experiments, to play a crucial role in remotely forcing the model circulation and moisture transport errors in the East Asian area. We also examine changes in the regional water cycle in response to interannual variability of the West Pacific subtropical high (WPSH). It is shown by water budget analysis that, although the model in general is not able to faithfully reproduce the response on a month to month basis, it gives comparable seasonal trends in regional moisture convergence and precipitation associated with shifts of the WPSH.
Highlights
The East Asian boreal summer climate is dominated by the East Asian summer monsoon (EASM), which brings southwesterly surface winds to the region, accompanied by heavy rain, and a generally hot and humid climate [1]
We examine changes in the regional water cycle in response to interannual variability of the West Pacific subtropical high (WPSH)
We investigate the effects that the interannual variability of the WPSH, one of the main components of the EASM, has in the East Asian water cycle
Summary
The East Asian boreal summer climate is dominated by the East Asian summer monsoon (EASM), which brings southwesterly surface winds to the region, accompanied by heavy rain, and a generally hot and humid climate [1]. The EASM is thought to have three main components that are highly coupled, the East Asian Meiyu (China), Changma (Korea), Baiu (Japan) rain front, the western Pacific subtropical high (WPSH), and the western Pacific intertropical convergence zone [2,3,4,5]. The rain belt of the East Asian summer monsoon undergoes two northward jumps. From May to June, the precipitation advances from southern China to the Yangtze River valley and, from June to July, the rainband jumps farther to the northern parts of East Asia. The rain belt brings an important water resource to highly populated economic centres in the world. The Meiyu rainfall provides nearly 45% of summer precipitation over the Yangtze River valley [6,7,8]. Droughts and floods associated with the monsoon variability have cause extensive social and economic impacts on the region [1]
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