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Yun-Lan Chen, Chung-Hsiung Sui, Chih-Pei Chang, and Kai-Chih Tseng

Abstract

This paper studies the influences of the Madden Julian Oscillation (MJO) on East Asian (EA) winter rainfall using the Singular Value Decomposition (SVD) approach. This method uses two-dimensional instead of the latitudinally-averaged variables in the commonly used Real-time Multivariate MJO (RMM) index. A comparison of the two approaches is made using the same OLR and zonal wind data over 37 boreal winter seasons of December – March. The SVD composite reveals a more conspicuous and coherent variation throughout the MJO cycle, while the RMM composite is more ambiguous. In particular, the SVD analysis identifies the convection anomalies over the Maritime Continent and the subtropical western Pacific (MCWP) as a major cause of enhanced rainfall in EA at RMM phases 8 and 1. This is at least one-eighth cycle earlier than the phases of convection development over Indian Ocean (IO) that were emphasized by previous studies. A linearized global baroclinic model is used to demonstrate the mechanism of MJO forcing on EA rainfall during various phases, with a focus on the MCWP cooling. The result shows that the anomalous MCWP cooling and the resultant low-level anticyclonic flow interact with the East Asian Jet, leading to an overall weakened EA winter monsoon circulation. The associated anomalous overturning circulation, with ascending motion and low-level horizonal moisture convergence in EA, contributes to the enhanced rainfall. This model result supports the interpretation of the SVD analysis, in that the MCWP-cooling induced anomalous meridional circulation is a more direct cause of enhanced EA rainfall than the IO-heating (or the IO-MCWP heating dipole) induced Rossby wave teleconnection.

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Beata Latos, Thierry Lefort, Maria K. Flatau, Piotr J. Flatau, Donaldi S. Permana, Dariusz B. Baranowski, Jaka A. I. Paski, Erwin Makmur, Eko Sulystyo, Philippe Peyrillé, Zhe Feng, Adrian J. Matthews, and Jerome M. Schmidt

the Philippines. This reached the central South China Sea on 22 January and is further investigated in section 3f . On 21 January a westerly low-level jet (LLJ) developed over the Java Sea. The peak strength at 850 hPa (about 24 m s −1 ) was observed at 0000 UTC 22 January, just west of Makassar. Fig . 4. Daily mean 850-hPa wind vectors and daily accumulated precipitation based on combined microwave-IR retrievals (shading, mm). The longest vector corresponds to a wind speed of 22 m s −1 . The

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Lei Song and Renguang Wu

of the East Asian trough. The southeastward flow to the rear of the East Asian trough favors the southward intrusion of cold air, leading to the invasion of cold events to eastern China ( Zhang et al. 1997 ; Jeong and Ho 2005 ; Takaya and Nakamura 2005a , b ; Bueh et al. 2011 ; Song et al. 2016 ; Song and Wu 2017 ). The development of the Siberian high and the East Asian trough is closely related to the Rossby wave trains propagating along the polar front jet and the subtropical jet

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Chen Li, Jing-Jia Luo, and Shuanglin Li

: Influence of El Niño Modoki on spring rainfall over south China . J. Geophys. Res. , 116 , D13102 , doi: 10.1029/2010JD015160 . 10.1029/2010JD015160 Findlater , J. , 1966 : Cross-equatorial jet streams at low levels over Kenya . Meteor. Mag. , 95 , 353 – 364 . Fu , C. , H. Diaz , and J. Fletcher , 1986 : Characteristics of the response of sea surface temperature in the central Pacific associated with warm episodes of the Southern Oscillation . Mon. Wea. Rev. , 114 , 1716 – 1739

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Ya Yang, Xiang Li, Jing Wang, and Dongliang Yuan

the equatorial and off-equatorial Rossby waves, have not been studied well. Existing studies (e.g., Meyers 1979 ; Qiu and Lukas 1996 ; Kessler 2006 ) used a 1.5-layer reduced gravity model to investigate the dynamics of the wind-forced low-frequency variability of the tropical Pacific Ocean circulation. In particular, Qiu et al. (2013) used a 1.5-layer ocean circulation model forced with annual cycle winds to produce alternating zonal jets in the Pacific basin. The dynamics are suggested to

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Chen Li, Jing-Jia Luo, Shuanglin Li, Harry Hendon, Oscar Alves, and Craig MacLachlan

-00072.1 . 10.1175/WAF-D-12-00072.1 Dee , D. P. , and Coauthors , 2011 : The ERA-Interim reanalysis: Configuration and performance of the data assimilation system . Quart. J. Roy. Meteor. Soc. , 137 , 553 – 597 , https://doi.org/10.1002/qj.828 . 10.1002/qj.828 Findlater , J. , 1966 : Cross-equatorial jet streams at low levels over Kenya . Meteor. Mag. , 95 , 353 – 364 . Findlater , J. , 1969 : A major low-level air current near the Indian Ocean during the northern summer . Quart. J. Roy

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James H. Ruppert Jr., Xingchao Chen, and Fuqing Zhang

Plateau during the warm season ( Wang et al. 2004 ; Bao et al. 2011 ), and likewise for many other continental regions downstream of mountain ranges (e.g., Laing et al. 2008 ). Many studies have argued that a key driver of this phenomenon is the mountain–plains solenoidal circulation ( Carbone and Tuttle 2008 ; Huang et al. 2010 ; Sun and Zhang 2012 ; Bao and Zhang 2013 ), and the nocturnal low-level jet in the case of the United States ( Stensrud 1996 ; Trier et al. 2014 ). These mechanisms

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Yan Zhu, Tim Li, Ming Zhao, and Tomoe Nasuno

, https://doi.org/10.1175/2010JCLI3833.1 . 10.1175/2010JCLI3833.1 Jiang , X. , and Coauthors , 2015 : Vertical structure and physical processes of the Madden–Julian oscillation: Exploring key model physics in climate simulations . J. Geophys. Res. , 120 , 4718 – 4748 , https://doi.org/10.1002/2014JD022375 . 10.1002/2014JD022375 Kang , W. , and E. Tziperman , 2018 : The MJO-SSW teleconnection: Interaction between MJO-forced waves and the midlatitude jet . Geophys. Res. Lett. , 45

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

westerly south of the equator ( Fig. 3b ). This low-level jet-like configuration results from the combined influences of the orientation and narrowing of the SCS toward the equator and the effects of a dynamic response to periodic midlatitude pressure forcing that behave like a dispersive group of equatorial Rossby meridional modes under surge conditions ( Chang et al. 2016 ). The southward intrusion of the higher MSLP and associated colder SST from northern SEA are conspicuous ( Fig. 3c ). Fig . 2

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Shijian Hu, Ying Zhang, Ming Feng, Yan Du, Janet Sprintall, Fan Wang, Dunxin Hu, Qiang Xie, and Fei Chai

( Nyadjro and Subrahmanyam 2016 ). Salinity and barrier-layer thickness in the eastern equatorial Indian Ocean show energetic subseasonal variation related to the Madden–Julian oscillations ( Drushka et al. 2014 ; Li et al. 2015 ). In the northern Indian Ocean, interannual variability of the Wyrtki jet and Bay of Bengal circulation exerts significant influence on salinity anomalies through freshwater exchange between the Bay of Bengal and the rest of the equatorial Indian Ocean that may be influenced

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