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Brandon W. Kerns and Shuyi S. Chen

–Julian Oscillation, Kelvin wave, and equatorial Rossby wave . J. Atmos. Sci. , 64 , 4400 – 4416 . Molinari , J. , and D. Vollaro , 2000 : Planetary- and synoptic-scale influences on eastern Pacific tropical cyclogenesis. Mon. Wea. Rev., 128, 3296–3307 . Nakazawa , T. , 1988 : Tropical super clusters within intraseasonal variations over the western Pacific . J. Meteor. Soc. Japan , 66 , 823 – 839 . Ray , P. , and C. Zhang , 2010 : A case study of the mechanics of extratropical influence

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Yue Ying and Fuqing Zhang

1. Introduction The tropical atmosphere consists of weather systems spanning a wide range of spatial and temporal scales. At the planetary scale, the Madden–Julian oscillation (MJO) is found to be the dominant mode of intraseasonal variability with typical periods of 20–100 days ( Madden and Julian 1971 , 1972 ; Zhang 2005 ). The active phase of an MJO is characterized by enhanced deep convection and intense precipitation that propagates eastward at a speed around 5 m s −1 . Within the MJO

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Tim Li, Chongbo Zhao, Pang-chi Hsu, and Tomoe Nasuno

radiation (OLR), confirmed the planetary scale of the MJO ( Weickmann 1983 ; Murakami and Nakazawa 1985 ; Lau and Chan 1986 ; Li and Zhou 2009 ). Studies also show that the oscillation is more broadband than the original 40–50-day period identified by Madden and Julian (1971) and can span a range of 20–100 days (e.g., Krishnamurti and Subrahmanyam 1982 ; Annamalai and Slingo 2001 ; Lau and Waliser 2005 ; Zhang 2005 ; Li and Wang 2005 , Waliser 2006 ). As the most significant variability

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Simon P. de Szoeke, James B. Edson, June R. Marion, Christopher W. Fairall, and Ludovic Bariteau

wave-CISK propagate faster than the MJO, and the shortest waves are the most unstable to wave-CISK ( Hendon 2005 ). Frictional wave-CISK predicts slower waves destabilized by boundary layer moist static energy convergence. Convectively coupled equatorial Kelvin, Rossby, and inertia–gravity waves are observed with higher frequencies and smaller scales that do not match the planetary scale of the MJO ( Wheeler and Kiladis 1999 ). Quasi-equilibrium models assume that latent heating above precipitation

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

wave dynamics with a wave–conditional instability of the second kind (wave-CISK)-type parameterization of convective heating (e.g., Lau and Peng 1987 ). The most unstable wave in such a simplified system is normally at a small wavelength, which is different from the observed planetary-scale circulation associated with MJOs. To remedy the scale selection problem, Wang (1988) and Wang and Li (1994) added friction-induced boundary layer convergence in the wave-CISK framework. In the wave

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Ji-Hyun Oh, Xianan Jiang, Duane E. Waliser, Mitchell W. Moncrieff, Richard H. Johnson, and Paul Ciesielski

Bretherton 2001 ; Tung and Yanai 2002a , b ; Lin et al. 2005 ). Using Doppler radar data, Houze et al. (2000) identified strong midlevel inflow in the stratiform regions of mesoscale convective systems (MCSs) during the westerly onset and in regions of strong westerly winds associated with the Kelvin–Rossby wave pattern. They postulated that the mesoscale inflow transports easterly momentum downward, reducing the westerlies near the surface in the westerly onset region, while in the strong westerly

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Michael S. Pritchard and Christopher S. Bretherton

MJO and high-frequency tropical wave modes are discussed in section 5 and conclusions summarized in section 6 . 2. Model description The baseline code used for all simulations is the prototype version of SPCAM, version 3.0, as archived [ (rev. 80)] by the Center for Multiscale Modeling of Atmospheric Processes. The global scale is represented by a version of CAM that slightly predates the CAM3.0 release. Global dynamics are formulated spectrally, with a

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Jean-Philippe Duvel

1. Introduction The convectively active phase of a MJO event is a large-scale region covered by numerous synoptic-scale perturbations and convective systems of different sizes and durations. There are many examples showing how meso- to synoptic-scale convective systems may be organized in the active MJO phase (e.g., Nakazawa 1988 ; Chen et al. 1996 ; Katsumata et al. 2009 ). In particular, convective systems may be organized in large clusters possibly related to equatorial waves with periods

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

developed by W10 to properly treat the instrumental-noise issue. Turbulence can originate from static instabilities or from Kelvin–Helmholtz instabilities. These instabilities can be associated with gravity wave (GW) activity ( Cadet 1977 ; Barat 1983 ; Chao and Schoeberl 1984 ; Fritts and Dunkerton 1985 ; Fritts and Rastogi 1985 ; Fritts et al. 1988b ; Pavelin et al. 2001 ; Sharman et al. 2012 ; Fritts et al. 2016 ). This suggests the possibility of GWs playing a role in the formation of the

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George N. Kiladis, Juliana Dias, Katherine H. Straub, Matthew C. Wheeler, Stefan N. Tulich, Kazuyoshi Kikuchi, Klaus M. Weickmann, and Michael J. Ventrice

made in understanding and forecasting the MJO over the past four decades, it remains a significant outstanding problem in tropical meteorology (see Zhang et al. 2013 ). As discussed in detail by Straub (2013 , hereafter S13 ), one of the challenges faced by researchers studying the MJO has to do not only with tracking the disturbance through time, but simply defining it. This difficulty stems from the fact that the MJO is associated with strong planetary circulation anomalies, and similar

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