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Yan Liu, Zhe-Min Tan, and Zhaohua Wu

( Hayashi 1970 ; Lindzen 1974 ). The simplest form of the wave-CISK feedback is that large-scale atmospheric waves produce regions of low-level moisture convergence where vigorous convections develop; latent heat released by the convections induces upward motions and further strengthens low-level convergence. Numerical models with the convective parameterization (CP) based on the wave-CISK concept did reproduce the CCEWs with some success (e.g., Hayashi and Sumi 1986 ; Lau and Peng 1987 ), but they

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Ángel F. Adames and John M. Wallace

temperature and surface pressure and large variability in free-tropospheric moisture and precipitation ( Charney 1963 ; Sobel and Bretherton 2000 ). Held et al. (1993) noted that regions of precipitation are characterized by enhanced column-integrated water vapor and concluded that water vapor provides the “memory” necessary to ensure the development and maintenance of convection over an isolated region. Subsequent studies by Bretherton et al. (2004) , Holloway and Neelin (2009) , and Muller et al

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Samson Hagos, L. Ruby Leung, and Jimy Dudhia

(2005) , Lau and Waliser (2005) , and the references therein. One of the earliest theories proposed to explain large-scale intraseasonal variability is a mechanism often referred to as wave conditional instability of the second kind (wave-CISK; Lindzen 1974 ; Lau and Peng 1987 ). In this theory, convective heating and moisture convergence interact to create unstable modes. This theory has been refined to account for inconsistencies with observations such as the fact that the smallest wavelength

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Paul A. O’Gorman and Tapio Schneider

1. Introduction Studies of the Lagrangian moisture transport suggest that, sufficiently far away from regions of moist convection, large-scale processes significantly influence the relative humidity of the free troposphere. (e.g., Yang and Pierrehumbert 1994 ; Sherwood 1996 ; Salathé and Hartmann 1997 ; Pierrehumbert and Roca 1998 ; Dessler and Sherwood 2000 ). Galewsky et al. (2005) have shown that large-scale aspects of the relative humidity distribution in the free troposphere can be

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H. Bellenger, K. Yoneyama, M. Katsumata, T. Nishizawa, K. Yasunaga, and R. Shirooka

of several projects, including CINDY2011, DYNAMO, the Atmospheric Radiation Measurement Program (ARM) MJO Investigation Experiment (AMIE), and the Littoral Air–Sea Process (LASP) experiment. The observed increase of moisture in the lower troposphere prior to the triggering of the convectively active phase of the MJO ( Johnson et al. 1999 ; Kemball-Cook and Weare 2001 ; Benedict and Randall 2007 ; Thayer-Calder and Randall 2009 ; Riley et al. 2011 ; Cai et al. 2013 ) is one of the fundamental

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Ángel F. Adames and Yi Ming

GFDL’s atmospheric general circulation model (AM4.0). They found a strong coupling between anomalous precipitation and column moisture. By jointly analyzing the moisture and moist static energy budgets, they found that the moisture anomalies propagate because of horizontal advection of mean dry static energy (DSE) by the anomalous winds. Horizontal advection of DSE induces a moisture tendency by forcing ascent along the sloping isentropes of the monsoon region. The anomalous precipitation is

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Tao Feng, Jia-Yuh Yu, Xiu-Qun Yang, and Ronghui Huang

) . Because moist deep convection is, to a great extent, controlled by the buildup and removal of tropospheric moisture ( Sherwood 1999 ; Raymond 2000 ; Bretherton et al. 2004 ; Holloway and Neelin 2009 ), the total precipitable water was also found to be phase locked with TD-type disturbances in Part I . The maximum total precipitable water appears near the center of the disturbances, while the maximum tendency of total precipitable water leads the cyclonic vortex at one-quarter wavelength. Such

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Ángel F. Adames and Daehyun Kim

phenomena that are affected by it. However, in order to improve MJO simulation, a better understanding of the fundamental processes driving its dynamics is required. There is a growing body of theoretical work in which the MJO is considered to be a “moisture mode” ( Neelin and Yu 1994 ; Raymond 2000b , 2001 ; Sobel et al. 2001 ; Sobel and Gildor 2003 ; Fuchs and Raymond 2002 , 2005 , 2007 ; Sugiyama 2009a , b ; Majda and Stechmann 2009 ; Sobel and Maloney 2012 , 2013 , hereafter SM refers

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Masahiro Sugiyama

al. 2008 ). Deep convection, on the other hand, affects the tropospheric humidity budget in various ways. Such an interaction leads to a new kind of dynamical mode called the moisture mode (defined below). Theoretical papers on the moisture mode include Yu and Neelin (1994) , Sobel et al. (2001) , Fuchs and Raymond (2002 , 2005 , 2007) , and Bony and Emanuel (2005) , whereas Sobel and Bretherton (2003) and Grabowski and Moncrieff (2004) , for example, performed modeling studies. The

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Minoru Chikira

that the MJO can be explained as a moisture mode, which appears from a set of simplified equations and is characterized by the growth of convective activity through the amplification of moisture. The gross moist stability (GMS; Neelin and Held 1987 ), which was originally defined as the export of moist static energy (MSE) out of the column by a unit divergent circulation, becomes an important quantity in determining the stability of the mode. The mode occurs under the weak temperature gradient

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