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CLIVAR MADDEN–JULIAN OSCILLATION WORKING GROUP:

1. Introduction The Madden–Julian oscillation ( Madden and Julian 1971 , 2005 ) is the dominant component of intraseasonal variability in the tropical atmosphere. It is characterized by eastward-propagating, equatorially trapped, baroclinic oscillations in the tropical wind field. During a typical MJO event, a positive convection/rainfall anomaly develops over the western Indian Ocean, while convection tends to be suppressed further east over the western Pacific. Over the course of the

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Liping Deng, Sally A. McFarlane, and Julia E. Flaherty

1. Introduction The Madden–Julian oscillation (MJO) ( Madden and Julian 1972 , 1994 ) is a dominant mode of intraseasonal (30–90 days) variability in the tropical atmosphere. Its characteristics and structure have been well documented by previous studies (e.g., Kiladis et al. 2005 ; Lau and Waliser 2005 ; Zhang 2005 ; Wu et al. 2007 ; Jiang et al. 2009 ; Zhang et al. 2010 ). The organization and evolution of tropical convection is a major component of the MJO and generally includes

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Fei Liu and Bin Wang

1. Introduction The Madden–Julian oscillation (MJO), as a significant driver of global circulation with a period of 30–90 days, is characterized by a zonal planetary scale and slow eastward propagation (5 m s −1 ) over the tropical Indian and western Pacific Oceans ( Zhang 2005 ). The MJO has different spectral characteristics from the moist Kelvin waves, since its frequency is nearly independent of wavelength, whereas the frequency of the moist Kelvin waves increases with wavenumber linearly

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Daehyun Kim, Jong-Seong Kug, and Adam H. Sobel

1. Introduction The Madden–Julian oscillation (MJO) is the dominant mode of intraseasonal variability in the tropics ( Madden and Julian 1972 ). A few distinct characteristics of the MJO are its vast horizontal scale (wavenumber 1–3), the time scale shorter than a season but longer than a month (30–60-day period), and the eastward propagation. The MJO interacts with many short-term weather and climate phenomena ( Takayabu et al. 1999 ; Maloney and Hartmann 2000 ; Wheeler and McBride 2005

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Traute Crueger, Bjorn Stevens, and Renate Brokopf

1. Introduction The Madden–Julian oscillation (MJO) is the dominant mode of intraseasonal variability in boreal winter and/or spring in the equatorial tropics. Discovered by Madden and Julian (1971 , 1972 , 1994 ), its salient features are coherent eastward propagating patterns of enhanced and suppressed convection over the Indian Ocean, the Indo-Pacific warm pool, and the western Pacific Ocean. Because it describes an envelope of convective activity, and hence precipitation, the MJO is

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Philip J. Klotzbach

1. Introduction The Madden–Julian oscillation (MJO) ( Madden and Julian 1972 ) is a large-scale mode of tropical variability that propagates around the globe on an approximately 30–60-day time scale. As it does so, it alters large-scale fields known to impact tropical cyclone (TC) activity, such as vertical wind shear, vertical motion, relative vorticity, and low- and midlevel moisture. Gray (1979) was one of the first to note that TCs tend to cluster in time, with active periods of one to

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Philip J. Klotzbach

1. Introduction The Madden–Julian oscillation (MJO) is a globally propagating mode of tropical atmospheric intraseasonal variability ( Madden and Julian 1972 , 1994 ). Associated with this convectively driven mode of variability are large-scale variations in upper- and lower-level winds, vertical motion, atmospheric moisture content, and sea surface temperatures ( Fig. 1 ). This global wave tends to propagate eastward at approximately 5 m s −1 , circling the globe in approximately 40–50 days

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David J. Raymond and Željka Fuchs

1. Introduction The Madden–Julian oscillation (MJO) is notoriously difficult for global models to simulate ( Lin et al. 2006 ). Furthermore, there is no universally accepted theory of this phenomenon. Zhang (2005) describes the essential characteristics of the MJO in his comprehensive review. These can be summarized briefly as follows: (i) The MJO is a global-scale, convectively coupled, eastward-moving disturbance with roots in the tropics. The convective aspects are most obvious in the

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Guosen Chen and Bin Wang

1. Introduction The slow eastward propagation of convective anomalies over the Indo-Pacific warm pool region is the most fundamental feature of the Madden–Julian oscillation (MJO) ( Madden and Julian 1972 ). Explanation of this slow eastward propagation is a central issue in studies of the MJO. The observed MJO eastward propagation speed exhibits a broad range from about 2 to 9 m s −1 ( Knutson et al. 1986 ; Zhang and Ling 2017 ). Understanding what accelerates or retards the MJO propagation

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Brandon O. Wolding and Eric D. Maloney

1. Introduction Despite four decades of research, no consensus currently exists as to what method is “best” for objectively assessing the state, either past or present, of the Madden–Julian oscillation (MJO) ( Straub 2013 ). This lack of consensus results from the diverse needs of the various user groups, differing views of the pertinent features that describe the MJO, and the advantages and disadvantages of the numerous techniques used to assess the MJO. Most MJO indices result from the

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