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Tomoe Nasuno, Tim Li, and Kazuyoshi Kikuchi

horizontal advection was of the same order of magnitude as the net tendency in the middle troposphere ( Figs. 6b,c ). Thus, horizontal advection acted as a major source of middle-level moistening in the preconditioning period of the two MJO episodes when the drying tendency due to vertical advection was still pronounced in the free atmosphere ( Figs. 6a,b ). After the convective initiation, the vertical component became the major term of moistening, significantly exceeding the net tendency ( Figs. 6a

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Richard H. Johnson, Paul E. Ciesielski, James H. Ruppert Jr., and Masaki Katsumata

there is a dominance of each (cumulus, congestus, cumulonimbus) cloud type. However, the mechanisms by which the atmosphere is moistened during the initiation phase of the MJO are still not well understood and remain a matter of considerable debate (e.g., Waite and Khouider 2010 ; Hohenegger and Stevens 2013 ; Barnes and Houze 2013 ; Powell and Houze 2013 ; Yuan and Houze 2013 ). DYNAMO was designed to explore moistening processes and cloud populations within the MJO using multiple instrument

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James N. Moum, Simon P. de Szoeke, William D. Smyth, James B. Edson, H. Langley DeWitt, Aurélie J. Moulin, Elizabeth J. Thompson, Christopher J. Zappa, Steven A. Rutledge, Richard H. Johnson, and Christopher W. Fairall

Observations from 1 km beneath to 25 km above the sea surface reveal the complex interactions in Indian Ocean westerly wind bursts associated with the Madden–Julian oscillation. The Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 ) is a disturbance of the atmosphere over tropical oceans associated with surface westerly wind bursts, deep convection, and heavy precipitation. MJO convection typically initiates in the Indian Ocean, travels eastward at roughly 5 m s −1 along the

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Hungjui Yu, Paul E. Ciesielski, Junhong Wang, Hung-Chi Kuo, Holger Vömel, and Ruud Dirksen

1. Introduction Radiosonde data, with a long record of over 60 years and high vertical resolution (5–10 m), play an important role in helping us detect and quantify climate change and variability in the atmosphere ( Thorne et al. 2011 ). Unfortunately, its usage has been limited by radiosonde sensor–dependent systematic biases, which can vary substantially over space and time and introduce nonclimatic changes or inhomogeneities in historical data records from radiosonde measurements (e.g., Dai

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Sue Chen, Maria Flatau, Tommy G. Jensen, Toshiaki Shinoda, Jerome Schmidt, Paul May, James Cummings, Ming Liu, Paul E. Ciesielski, Christopher W. Fairall, Ren-Chieh Lien, Dariusz B. Baranowski, Nan-Hsun Chi, Simon de Szoeke, and James Edson

1. Introduction The Madden–Julian oscillation (MJO) is a low-frequency atmospheric anomaly traveling along the equatorial belt with a period of 30–60 days ( Madden and Julian 1971 , 1972 ). The MJO has a broad influence on the weather and climate systems by influencing the intraseasonal and interannual variability of atmosphere and ocean ( Lau and Waliser 2005 ; Zhang 2005 ). Numerous studies have characterized the large-scale environmental changes relative to MJO onset in terms of an

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Kai-Chih Tseng, Chung-Hsiung Sui, and Tim Li

period from early to middle November ( Fig. 6a ). The positive Q 2 here implies a drying (heating) effect by precipitating clouds. Contrary to recharging moisture by dominant nonprecipitating shallow convection in suppressed phase of MJO1, emerging precipitating convection discharges moisture in the suppressed phase of MJO2. This is supported by the relatively unstable atmosphere in the suppressed phase of MJO1 and a more neutral atmosphere in the suppressed phase of MJO2 ( Fig. 6d ), and the storm

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Shuguang Wang, Adam H. Sobel, Fuqing Zhang, Y. Qiang Sun, Ying Yue, and Lei Zhou

-scale structure of dynamical variables (temperature, zonal winds, humidity, and vertical motion) derived from the sounding network ( Johnson and Ciesielski 2013 ; Ciesielski et al. 2014 ), the cloud population observed from the ground-based precipitation radars (e.g., Zuluaga and Houze 2013 ; Powell and Houze 2013 ), the air and sea processes regulating the atmosphere–ocean interaction ( Moum et al. 2013 ), and the budget of moist static energy in the northern sounding array ( Sobel et al. 2014 , hereafter

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Weixin Xu and Steven A. Rutledge

occurrence is high in all MJO phases ( Fig. 7 ). We suggest that shallow convective cells play an important role in preconditioning the lower atmosphere for subsequent deep convection (especially during phases 7 and 8). During all phases, systems with echo tops reaching only the middle levels (5–8 km) contribute nearly equally to precipitation area compared to deep systems ( Figs. 11a,b ). A nonnegligible fraction (10%–15%) of rainfall comes from small systems across the MJO cycle, especially during the

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H. Bellenger, R. Wilson, J. L. Davison, J. P. Duvel, W. Xu, F. Lott, and M. Katsumata

. Rastogi , 1985 : Convective and dynamical instabilities due to gravity wave motions in the lower and middle atmosphere: Theory and observations . Radio Sci. , 20 , 1247 – 1277 , doi: 10.1029/RS020i006p01247 . 10.1029/RS020i006p01247 Fritts , D. C. , T. Tsuda , T. Sato , S. Fukao , and S. Kato , 1988a : Observational evidence of a saturated gravity wave spectrum in the troposphere and lower stratosphere . J. Atmos. Sci. , 45 , 1741 – 1759 , doi: 10

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Adam Sobel, Shuguang Wang, and Daehyun Kim

two, involving advection, are the most uncertain. The gross moist stability is difficult to estimate from observations, even in sign, and even in the climatological mean (e.g., Back and Bretherton 2006 ). Raymond and Fuchs (2009) obtain better MJO simulations in models whose gross moist stabilities are negative and infer that it is negative in the real atmosphere. Benedict et al. (2014) similarly found that stronger MJOs were simulated in models with small or negative values of the normalized

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