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James H. Ruppert Jr. and Richard H. Johnson

1. Introduction The Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 ) dominates tropical intraseasonal (20–90 day) variability and influences global weather (e.g., tropical cyclone frequency, monsoon onset and variability, ENSO, and midlatitude storm tracks) through myriad tropical–extratropical teleconnections ( Zhang 2005 , 2013 ). Through these teleconnections the MJO acts as a “bridge” between weather and climate ( Zhang 2013 ), thereby holding a critical key to our

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Michael S. Pritchard and Christopher S. Bretherton

1. Introduction The Madden–Julian oscillation (MJO) has been hypothesized to be a “moisture mode.” Moisture is especially fundamental to the dynamics of tropical convective disturbances because equatorial scalings of the primitive equations include latent heating active at leading order and weak temperature gradient balance ( Sobel et al. 2001 ). Energetic thermodynamic feedbacks can thus occur between moisture anomalies and their effect through deep convection on circulations, evaporative

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Hyodae Seo, Aneesh C. Subramanian, Arthur J. Miller, and Nicholas R. Cavanaugh

1. Introduction The Madden–Julian oscillation (MJO) is the dominant form of intraseasonal variability in Earth’s atmospheric system. Characterized by large-scale, eastward-propagating, equatorially trapped, baroclinic oscillations in the tropical wind field at periods of 30–90 days ( Madden and Julian 1971 , 1994 ), the MJO has predictability time scales of 10–30 days, far beyond the usual time scales of weather prediction (e.g., Hendon et al. 2000 ; Waliser et al. 2003 ). Although the MJO

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Tomoe Nasuno, Tim Li, and Kazuyoshi Kikuchi

1. Introduction The Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 ) is a prominent tropical disturbance that has a broad impact on the global weather and climate ( Zhang 2013 ; Gottschalck et al. 2010 ). The MJO is related to a wide variety of tropical and extratropical ocean and atmosphere phenomena, ranging from local to global spatial scales and diurnal to interannual time scales. Therefore, it is an important target of extended-range weather forecasting. However

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Wen-wen Tung, Dimitrios Giannakis, and Andrew J. Majda

1. Introduction The Madden–Julian oscillation (MJO; e.g., Madden and Julian 1971 , 1972 ) is an eastward-propagating, planetary-scale envelope of organized convective activity in the tropics. Characterized by gross features in the 20–90-day intraseasonal time range and zonal wavenumbers 1–4, it dominates tropical variability in subseasonal time scales. Moreover, through tropical–extratropical interactions, it influences global weather and climate variability, fundamentally linking short

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Nick Guy and David P. Jorgensen

1. Introduction A dominant component of intraseasonal tropical variability is the Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 ), characterized by an eastward-moving envelope of organized, deep convection (and precipitation) and westerly winds. The MJO has been shown to influence monsoon systems (e.g., Asia, Africa, and Australia), tropical cyclones in all cyclone basins, midlatitude weather (e.g., rainfall and temperature variability), and other atmospheric and ocean

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Samson M. Hagos, Zhe Feng, Casey D. Burleyson, Chun Zhao, Matus N. Martini, and Larry K. Berg

1. Introduction Despite decades of work, simulating the Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 ) in climate models and understanding the instabilities that drive it remain a significant challenge. However, some progress has been reported in recent years. For example, Hung et al. (2013) found that, in general, models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) perform better than those that participated in phase 3 of CMIP (CMIP3) in

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Weixin Xu and Steven A. Rutledge

1. Introduction The Madden–Julian oscillation (MJO), first discovered by Madden and Julian (1971 , 1972) , is widely known as a remarkable coupled convective–wind tropical disturbance that usually develops in the Indian Ocean (IO) and slowly propagates eastward with an intraseasonal cycle of 30–60 days ( Weickmann et al. 1985 ; Rui and Wang 1990 ; Sui and Lau 1992 ; Salby and Hendon 1994 ; Wheeler and Hendon 2004 ; Zhang 2005 ). The MJO is the most dominant mode of intraseasonal

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Ji-Eun Kim, Chidong Zhang, George N. Kiladis, and Peter Bechtold

1. Introduction During the Dynamics of the Madden–Julian Oscillation (DYNAMO) 1 field campaign ( Yoneyama et al. 2013 ), two quadrilateral sounding arrays were formed with six sites (two ships and four islands) over the equatorial central Indian Ocean ( Fig. 1 ). Intensive sounding observations (eight per day) were taken during the special observing period (SOP) of 1 October–15 December 2011 from the arrays, which were reduced to triangles for short periods of ship port calls and after the SOP

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Kunio Yoneyama, Chidong Zhang, and Charles N. Long

A field campaign in the Indian Ocean region collected unprecedented observations during October 2011–March 2012 to help advance knowledge of physical processes of the MJO—especially its convective initiation—and improve its prediction. View from Addu Atoll showing a mix of convective and cirroform clouds. From time to time, the tropical atmosphere feels the pulses of extraordinary strong deep convection and rainfall that repeat every 30–90 days. They come from the Madden–Julian oscillation (MJO

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