Interannual variability of summertime outgoing longwave radiation over the Maritime Continent in relation to East Asian summer monsoon anomalies

Abstract Defining the intensity of the East Asian summer monsoon (EASM) has been extremely controversial. This paper elaborates on the meanings of 25 existing EASM indices in terms of two observed major modes of interannual variation in the precipitation and circulation anomalies for the 1979–2006 period. The existing indices can be classified into five categories: the east–west thermal contrast, north–south thermal contrast, shear vorticity of zonal winds, southwesterly monsoon, and South China Sea monsoon. The last four types of indices reflect various aspects of the leading mode of interannual variability of the EASM rainfall and circulations, which correspond to the decaying El Niño, while the first category reflects the second mode that corresponds to the developing El Niño. The authors recommend that the EASM strength can be represented by the principal component of the leading mode of the interannual variability, which provides a unified index for the majority of the existing indices. This new index is extremely robust, captures a large portion (50%) of the total variance of the precipitation and three-dimensional circulation, and has unique advantages over all the existing indices. The authors also recommend a simple index, the reversed Wang and Fan index, which is nearly identical to the leading principal component of the EASM and greatly facilitates real-time monitoring. The proposed index highlights the significance of the mei-yu/baiu/changma rainfall in gauging the strength of the EASM. The mei-yu, which is produced in the primary rain-bearing system, the East Asian (EA) subtropical front, better represents the variability of the EASM circulation system. This new index reverses the traditional Chinese meaning of a strong EASM, which corresponds to a deficient mei-yu that is associated with an abnormal northward extension of southerly over northern China. The new definition is consistent with the meaning used in other monsoon regions worldwide, where abundant rainfall within the major local rain-bearing monsoon system is considered to be a strong monsoon.

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Interannual variability of the convective activities associated with the east asian summer monsoon obtained from tbb variability

Advances in Atmospheric Sciences ◽

10.1007/s00376-999-0005-4 ◽

1999 ◽

Vol 16 (1) ◽

pp. 77-90 ◽

Cited By ~ 12

Author(s):

Ren Baohua ◽

Huang Ronghui

Keyword(s):

Interannual Variability ◽

Summer Monsoon ◽

East Asian Summer Monsoon ◽

Asian Summer Monsoon ◽

East Asian ◽

Asian Summer

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Efficient transport of atmospheric microplastics onto the continent via the East Asian summer monsoon

Journal of Hazardous Materials ◽

10.1016/j.jhazmat.2021.125477 ◽

2021 ◽

Vol 414 ◽

pp. 125477

Author(s):

Xiaohui Wang ◽

Kai Liu ◽

Lixin Zhu ◽

Changjun Li ◽

Zhangyu Song ◽

...

Keyword(s):

Summer Monsoon ◽

East Asian Summer Monsoon ◽

Asian Summer Monsoon ◽

East Asian ◽

Asian Summer ◽

Efficient Transport

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Holocene variability of East Asian summer monsoon as viewed from the speleothem δ18O records in central China

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2021.116758 ◽

2021 ◽

Vol 558 ◽

pp. 116758

Author(s):

Yanjun Cai ◽

Xing Cheng ◽

Le Ma ◽

Ruixue Mao ◽

Sebastian F.M. Breitenbach ◽

...

Keyword(s):

Summer Monsoon ◽

East Asian Summer Monsoon ◽

Asian Summer Monsoon ◽

East Asian ◽

Central China ◽

Asian Summer

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Nonlinear, Intraseasonal Phases of the East Asian Summer Monsoon: Extraction and Analysis Using Self-Organizing Maps

Journal of Climate ◽

10.1175/jcli-d-11-00512.1 ◽

2012 ◽

Vol 25 (20) ◽

pp. 6975-6988 ◽

Cited By ~ 40

Author(s):

Jung-Eun Chu ◽

Saji N. Hameed ◽

Kyung-Ja Ha

Keyword(s):

Time Scales ◽

Summer Monsoon ◽

East Asian Summer Monsoon ◽

Asian Summer Monsoon ◽

East Asian ◽

Self Organizing Maps ◽

Dry Spell ◽

Asian Summer ◽

Upper Level ◽

Self Organizing

Abstract The hypothesis that regional characteristics of the East Asian summer monsoon (EASM) result from the presence of nonlinear coupled features that modulate the seasonal circulation and rainfall at the intraseasonal time scale is advanced in this study. To examine this hypothesis, the authors undertake the analysis of daily EASM variability using a nonlinear multivariate data classifying algorithm known as self-organizing mapping (SOM). On the basis of various SOM node analyses, four major intraseasonal phases of the EASM are identified. The first node describes a circulation state corresponding to weak tropical and subtropical pressure systems, strong upper-level jets, weakened monsoonal winds, and cyclonic upper-level vorticity. This mode, related to large rainfall anomalies in southeast China and southern Japan, is identified as the mei-yu–baiu phase. The second node represents a distinct circulation state corresponding to a strengthened subtropical high, monsoonal winds, and anticyclonic upper-level vorticity in southeast Korea, which is identified as the changma phase. The third node is related to copious rain over Korea following changma, which we name the postchangma phase. The fourth node is situated diagonally opposite the changma mode. Because Korea experiences a dry spell associated with this SOM node, it is referred to as the dry-spell phase. The authors also demonstrate that a strong modulation of the changma and dry-spell phases on interannual time scales occurs during El Niño and La Niña years. Results imply that the key to predictability of the EASM on interannual time scales may lie with analysis and exploitation of its nonlinear characteristics.

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The Variability of the Indian–East Asian Summer Monsoon Interface in Relation to the Spring Seesaw Mode between the Indian Ocean and the Central-Western Pacific

Journal of Climate ◽

10.1175/jcli-d-15-0839.1 ◽

2016 ◽

Vol 29 (13) ◽

pp. 5027-5040 ◽

Cited By ~ 7

Author(s):

Jie Cao ◽

Shu Gui ◽

Qin Su ◽

Yali Yang

Keyword(s):

Indian Ocean ◽

Summer Monsoon ◽

East Asian Summer Monsoon ◽

General Circulation ◽

Asian Summer Monsoon ◽

East Asian ◽

Western Pacific ◽

Observational Analysis ◽

Westerly Winds ◽

Asian Summer

Abstract The interannual zonal movement of the interface between the Indian summer monsoon and the East Asian summer monsoon (IIE), associated with the spring sea surface temperature (SST) seesaw mode (SSTSM) over the tropical Indian Ocean (TIO) and the tropical central-western Pacific (TCWP), is studied for the period 1979–2008. The observational analysis is based on Twentieth Century Reanalysis data (version 2) of atmospheric circulations, Extended Reconstructed SST data (version 3), and the Climate Prediction Center Merged Analysis of Precipitation. The results indicate that the IIE’s zonal movement is significantly and persistently correlated with the TIO–TCWP SSTSM, from spring to summer. The results of two case studies resemble those obtained by regression analysis. Experiments using an atmospheric general circulation model (ECHAM6) substantiate the key physical processes revealed in the observational analysis. When warmer (colder) SSTs appear in the TIO and colder (warmer) SSTs occur in the TCWP, the positive (negative) SSTSM forces anomalous easterly (westerly) winds over the Bay of Bengal (BOB), South China Sea (SCS), and western North Pacific (WNP). The anomalous easterly (westerly) winds further result in a weakened (strengthened) southwest summer monsoon over the BOB and a strengthened (weakened) southeast summer monsoon over the SCS and WNP. This causes the IIE to shift farther eastward (westward) than normal.

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