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See Yee Lim
,
Charline Marzin
,
Prince Xavier
,
Chih-Pei Chang
, and
Bertrand Timbal

Abstract

TRMM rainfall data from 1998–2012 are used to study the impacts and interactions of cold surges (CSs) and the Madden–Julian oscillation (MJO) on rainfall over Southeast Asia during the boreal winter season from November to February. CSs are identified using a new large-scale index. The frequencies of occurrences of these two large-scale events are comparable (about 20% of the days each), but the spatial pattern of impacts show differences resulting from the interactions of the general flow with the complex orography of the region. The largest impact of CSs occurs in and around the southern South China Sea as a result of increased low-level convergence on the windward side of the terrain and increased shear vorticity off Borneo that enhances the Borneo vortex. The largest impact of the MJO is in the eastern equatorial Indian Ocean, sheltered from CSs by Sumatra. In general CSs are significantly more likely to trigger extreme rainfall. When both systems are present, the rainfall pattern is mainly controlled by the CSs. However, the MJO makes the environment more favorable for convection by moistening the atmosphere and facilitating conditional instability, resulting in a significant increased rainfall response compared to CSs alone. In addition to the interactions of the two systems in convection, this study confirms a previously identified mechanism in which the MJO may reduce CS frequency through opposing dynamic structures.

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Chih-Pei Chang
,
Richard H. Johnson
,
Kyung-Ja Ha
,
Daehyun Kim
,
Gabriel Ngar-Cheung Lau
,
Bin Wang
,
Michael M. Bell
, and
Yali Luo
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Chih-Pei Chang
,
Michael Ghil
,
Hung-Chi Kuo
,
Mojib Latif
,
Chung-Hsiung Sui
, and
John M. Wallace
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Bin Wang
,
Michela Biasutti
,
Michael P. Byrne
,
Christopher Castro
,
Chih-Pei Chang
,
Kerry Cook
,
Rong Fu
,
Alice M. Grimm
,
Kyung-Ja Ha
,
Harry Hendon
,
Akio Kitoh
,
R. Krishnan
,
June-Yi Lee
,
Jianping Li
,
Jian Liu
,
Aurel Moise
,
Salvatore Pascale
,
M. K. Roxy
,
Anji Seth
,
Chung-Hsiung Sui
,
Andrew Turner
,
Song Yang
,
Kyung-Sook Yun
,
Lixia Zhang
, and
Tianjun Zhou

Abstract

Monsoon rainfall has profound economic and societal impacts for more than two-thirds of the global population. Here we provide a review on past monsoon changes and their primary drivers, the projected future changes, and key physical processes, and discuss challenges of the present and future modeling and outlooks. Continued global warming and urbanization over the past century has already caused a significant rise in the intensity and frequency of extreme rainfall events in all monsoon regions (high confidence). Observed changes in the mean monsoon rainfall vary by region with significant decadal variations. Northern Hemisphere land monsoon rainfall as a whole declined from 1950 to 1980 and rebounded after the 1980s, due to the competing influences of internal climate variability and radiative forcing from greenhouse gases and aerosol forcing (high confidence); however, it remains a challenge to quantify their relative contributions. The CMIP6 models simulate better global monsoon intensity and precipitation over CMIP5 models, but common biases and large intermodal spreads persist. Nevertheless, there is high confidence that the frequency and intensity of monsoon extreme rainfall events will increase, alongside an increasing risk of drought over some regions. Also, land monsoon rainfall will increase in South Asia and East Asia (high confidence) and northern Africa (medium confidence), decrease in North America, and be unchanged in the Southern Hemisphere. Over the Asian–Australian monsoon region, the rainfall variability is projected to increase on daily to decadal scales. The rainy season will likely be lengthened in the Northern Hemisphere due to late retreat (especially over East Asia), but shortened in the Southern Hemisphere due to delayed onset.

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Bin Wang
,
Michela Biasutti
,
Michael P. Byrne
,
Christopher Castro
,
Chih-Pei Chang
,
Kerry Cook
,
Rong Fu
,
Alice M. Grimm
,
Kyung-Ja Ha
,
Harry Hendon
,
Akio Kitoh
,
R. Krishnan
,
June-Yi Lee
,
Jianping Li
,
Jian Liu
,
Aurel Moise
,
Salvatore Pascale
,
M. K. Roxy
,
Anji Seth
,
Chung-Hsiung Sui
,
Andrew Turner
,
Song Yang
,
Kyung-Sook Yun
,
Lixia Zhang
, and
Tianjun Zhou
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Yali Luo
,
Renhe Zhang
,
Qilin Wan
,
Bin Wang
,
Wai Kin Wong
,
Zhiqun Hu
,
Ben Jong-Dao Jou
,
Yanluan Lin
,
Richard H. Johnson
,
Chih-Pei Chang
,
Yuejian Zhu
,
Xubin Zhang
,
Hui Wang
,
Rudi Xia
,
Juhui Ma
,
Da-Lin Zhang
,
Mei Gao
,
Yijun Zhang
,
Xi Liu
,
Yangruixue Chen
,
Huijun Huang
,
Xinghua Bao
,
Zheng Ruan
,
Zhehu Cui
,
Zhiyong Meng
,
Jiaxiang Sun
,
Mengwen Wu
,
Hongyan Wang
,
Xindong Peng
,
Weimiao Qian
,
Kun Zhao
, and
Yanjiao Xiao

Abstract

During the presummer rainy season (April–June), southern China often experiences frequent occurrences of extreme rainfall, leading to severe flooding and inundations. To expedite the efforts in improving the quantitative precipitation forecast (QPF) of the presummer rainy season rainfall, the China Meteorological Administration (CMA) initiated a nationally coordinated research project, namely, the Southern China Monsoon Rainfall Experiment (SCMREX) that was endorsed by the World Meteorological Organization (WMO) as a research and development project (RDP) of the World Weather Research Programme (WWRP). The SCMREX RDP (2013–18) consists of four major components: field campaign, database management, studies on physical mechanisms of heavy rainfall events, and convection-permitting numerical experiments including impact of data assimilation, evaluation/improvement of model physics, and ensemble prediction. The pilot field campaigns were carried out from early May to mid-June of 2013–15. This paper: i) describes the scientific objectives, pilot field campaigns, and data sharing of SCMREX; ii) provides an overview of heavy rainfall events during the SCMREX-2014 intensive observing period; and iii) presents examples of preliminary research results and explains future research opportunities.

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