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Naoko Sakaeda, Scott W. Powell, Juliana Dias, and George N. Kiladis

1. Introduction Intraseasonal variability in the atmosphere bridges an important time scale between climate and weather. A key phenomenon that occurs on intraseasonal time scales in the tropics is the Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 ). The MJO is known to influence a wide range of spatial and temporal weather and climate phenomena ( Lau and Waliser 2011 ), including the diurnal cycle of rain, which is the focus of this study. The diurnal cycle in precipitation is

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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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Weixin Xu, Steven A. Rutledge, Courtney Schumacher, and Masaki Katsumata

1. Introduction The Madden–Julian oscillation (MJO) ( Madden and Julian 1971 , 1972 ) has broad impacts on the global weather and climate [see Zhang (2005 , 2013) and references therein] such as monsoon rainfall variability, storm tracks, tropical cyclone frequency, tornado outbreaks, ENSO, intertropical convergence zone (ITCZ) convection, and extratropical climate modes. Despite decades of study, the MJO is still not well understood and therefore MJO prediction skill is limited, especially

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Adam Sobel, Shuguang Wang, and Daehyun Kim

1. Introduction Though the Madden–Julian oscillation (MJO) was first discovered over four decades ago ( Madden and Julian 1971 , 1972 ; Julian and Madden 1981 ), its basic dynamics remain unexplained to the collective satisfaction of the research community. There is no fundamental agreement on what kind of dynamical entity the MJO is. We have been pursuing the notion that the MJO is a moisture mode. At the broadest level, we mean by this a mode of variability that would not exist in any

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Douglas C. Stolz, Steven A. Rutledge, Weixin Xu, and Jeffrey R. Pierce

1. Introduction The discovery of 40–50-day oscillations in the zonal winds at 850 and 150 hPa in the tropical atmosphere over 45 years ago has incited a rich interest in researching and characterizing the Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 ) (important acronyms in this paper are also listed and defined in the appendix ). The MJO influences patterns of variability of lower- and upper-tropospheric winds, humidity, and temperature on 30–90-day time scales, and

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Emily M. Riley Dellaripa, Eric Maloney, and Susan C. van den Heever

theory predicted, nonlinear WISHE is still viable ( Sobel et al. 2010 ). Moisture is also integral to the moisture-mode hypothesis (e.g., Raymond 2001 ; Sobel and Maloney 2012 , 2013 ). Feedbacks among surface fluxes, radiation, and cloud processes can conspire to maintain free-tropospheric moisture and enhance convection against the drying and dissipating effects of vertical and horizontal advection (e.g., Sobel et al. 2001 ). Despite decades of research, most GCMs fail to simulate MJO events

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Matthew A. Janiga and Chidong Zhang

. Bechtold , P. , M. Köhler , T. Jung , F. Doblas-Reyes , M. Leutbecher , M. J. Rodwell , F. Vitart , and G. Balsamo , 2008 : Advances in simulating atmospheric variability with the ECMWF model: From synoptic to decadal time scales . Quart. J. Roy. Meteor. Soc. , 134 , 1337 – 1351 , doi: 10.1002/qj.289 . Benedict , J. J. , and D. A. Randall , 2007 : Observed characteristics of the MJO relative to maximum rainfall . J. Atmos. Sci. , 64 , 2332 – 2354 , doi: 10.1175/JAS

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

. Vitart , and G. Balsamo , 2008 : Advances in predicting atmospheric variability with the ECMWF model: From synoptic to decadal time-scales . Quart. J. Roy. Meteor. Soc. , 134 , 1337 – 1351 , https://doi.org/10.1002/qj.289 . 10.1002/qj.289 Bechtold , P. , N. Semane , P. Lopez , J.-P. Chaboureau , A. Beljaars , and N. Bormann , 2014 : Representing equilibrium and nonequilibrium convection in large-scale models . J. Atmos. Sci. , 71 , 734 – 753 , https://doi.org/10

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Weixin Xu and Steven A. Rutledge

.1175/1520-0493(1984)112<1782:TEOFAS>2.0.CO;2 . Bechtold , P. , M. Köhler , T. Jung , F. Doblas-Reyes , M. Leutbecher , M. J. Rodwell , F. Vitart , and G. Balsamo , 2008 : Advances in simulating atmospheric variability with the ECMWF model: From synoptic to decadal time-scales . Quart. J. Roy. Meteor. Soc. , 134 , 1337 – 1351 , doi: 10.1002/qj.289 . Bladé , I. , and D. L. Hartmann , 1993 : Tropical intraseasonal oscillations in a simple nonlinear model . J. Atmos. Sci. , 50 , 2922 – 2939 , doi

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Weixin Xu and Steven A. Rutledge

variability in the tropics and plays important roles at climate and weather system scales ( Zhang 2013 ). Despite decades of study, the MJO is not well understood and therefore MJO prediction skill is limited, especially for initiation over the Indian Ocean ( Bechtold et al. 2008 ; Kim et al. 2009 ; Vitart and Molteni 2010 ). Meanwhile, the MJO has been poorly simulated by several generations of general circulation models (GCMs) ( Lin et al. 2006 ; Hung et al. 2013 ). The representation of cumulus

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