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Fei Liu and Bin Wang

1. Introduction The Madden–Julian oscillation (MJO), named after its discoverers ( Madden and Julian 1971 , 1972 , 1994 ), features an equatorially trapped, slowly eastward-propagating (about 5 m s −1 ), planetary-scale baroclinic circulation cell in the Eastern Hemisphere ( Knutson and Weickmann 1987 ; Wang and Rui 1990 ; Hendon and Salby 1994 ; Maloney and Hartmann 1998 ; Kiladis et al. 2005 ; Zhang 2005 ). The MJO circulation comprises equatorial Kelvin waves and Rossby waves, and

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Danyang Wang, Jun-Ichi Yano, and Yanluan Lin

1. Introduction The tropical atmospheric Madden–Julian oscillation (MJO) is an eastward-propagating wavelike entity associated with strong convective activity ( Zhang 2005 ). For this reason, the MJO is often considered an equatorial wave strongly coupled with convection (e.g., Emanuel 1987 ; Yano and Emanuel 1991 ; Fuchs and Raymond 2007 ; Raymond and Fuchs 2007 , 2009 ; Majda and Stechmann 2009 ). Recently, Yano and Tribbia (2017) proposed an alternative theory that explains the MJO

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Pallav Ray and Chidong Zhang

1. Introduction The mechanism of initiation of the Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 ) remains a challenging problem for research. This is highly relevant to operational forecast of the MJO, since the MJO is connected to a variety of events around the globe [see references in Lau and Waliser (2005) and Zhang (2005) ]. The time scale of the MJO relates to the subseasonal predictability and affects medium- and extended-range weather forecasts in both the tropics

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Yanzhen Chi, Fuqing Zhang, Wei Li, Jinhai He, and Zhaoyong Guan

strengthening of the mean southerly wind due to the reversal of zonal land–sea thermal contrast ( Qi et al. 2008 ; Zhao et al. 2007 ; Zhu et al. 2012 ). Through all of this debate on mechanism, there is not yet a consensus criterion for defining the EASSM onset. In recent years, the impacts of intraseasonal oscillations in convective activity, such as the Madden–Julian oscillation (MJO) ( Madden and Julian 1971 ), on the EASM has attracted a lot of attention ( Wen et al. 2004 ; Ding and Chan 2005 ; Zhou

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Jennifer Gahtan and Paul Roundy

1. Introduction The Madden–Julian oscillation (MJO; Zhang 2005 ) is typically characterized by equatorial eastward-propagating circulative and deep convective anomalies on intraseasonal temporal and planetary zonal scales. While circulation signals extend globally, MJO deep convection is mainly restricted to tropical warm pool regions, such that convective onset often occurs over the western Indian Ocean. Though discharge–recharge-type hypotheses suggest that the moistening required for onset

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Paul E. Roundy

1. Introduction The tropical atmosphere organizes moist deep convection over a broad range of spatial and temporal scales. The Madden–Julian oscillation (MJO) dominates variability in convection on intraseasonal time scales of roughly 30–100 days ( Madden and Julian 1994 ; Zhang 2005 ). Rainfall associated with the local active convective phase of the MJO (hereafter, active MJO) is in turn organized into smaller-scale wave modes and mesoscale convective systems. Convectively coupled Kelvin

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Bin Wang and Fei Liu

1. Introduction The Madden–Julian oscillation (MJO) features an equatorially trapped, planetary-scale baroclinic circulation cell ( Madden and Julian 1971 , 1994 ) coupled with a multiscale convective complex ( Nakazawa 1988 ) and propagates eastward slowly (about 5 m s −1 ) in the Eastern Hemisphere ( Knutson and Weickmann 1987 ). The MJO circulation comprises equatorial Kelvin and Rossby waves and shows a quadrupole vortex horizontal structure when the MJO convection is located over the

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Katherine Thayer-Calder and David A. Randall

1. Introduction The Madden–Julian oscillation (MJO), an intraseasonal oscillation of convection and winds in the tropical Indian and western Pacific Oceans, is a very large, generally equatorial, eastward-propagating region of active convection, followed and/or preceded by an equally large eastward-moving region of clearer skies and suppressed convection ( Madden and Julian 1972 , 1994 ). The MJO spans 50 to 100 degrees longitude, or zonal wavenumbers 1 to 5, and its speed generally varies

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James J. Benedict and David A. Randall

1. Introduction The Madden–Julian oscillation (MJO), an eastward-moving couplet of convectively active and suppressed atmospheric conditions in the Indian and west Pacific Ocean regions, is the leading mode of tropical variability on 30–60-day (intraseasonal) time scales. Since its discovery in the early 1970s ( Madden and Julian 1971 ), a host of observational, theoretical, and modeling studies have gradually improved our understanding of the MJO but have also revealed its many complexities (e

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Fei Liu and Bin Wang

1. Introduction The Madden–Julian oscillation (MJO), named after its discoverers ( Madden and Julian 1971 ), features an equatorially trapped, slowly eastward-propagating (about 5 m s −1 ), planetary-scale baroclinic circulation cell in the Eastern Hemisphere ( Knutson and Weickmann 1987 ; Wang and Rui 1990a ; Hendon and Salby 1994 ; Maloney and Hartmann 1998 ; Kiladis et al. 2005 ; Zhang 2005 ). The MJO circulation comprises equatorial Kelvin waves and Rossby waves and exhibits a

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