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Tomoe Nasuno, Tim Li, and Kazuyoshi Kikuchi

or precipitation have been proposed ( Gottschalck et al. 2013 , hereafter G13 ; Ling et al. 2013 , 2014 ; Kiladis et al. 2014 ). One of the most distinctive indicators of the MJO convective initiation is the equatorial concentration of convection ( Ling et al. 2013 ). The effects of local, possibly higher-frequency perturbations on convective initiation need further inspection, along with the large-scale dynamics. Regarding the origin of MJO initiation, there are two categories of hypotheses

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David M. Zermeño-Díaz, Chidong Zhang, Pavlos Kollias, and Heike Kalesse

1. Introduction In the tropics, shallow cumulus clouds (herein called shallow clouds) are the most populous cloud type ( Lau and Wu 2003 ; Masunaga and Kummerow 2006 ) and produce about 20% of the total rainfall ( Short and Nakamura 2000 ). They are embryos for tropical deep convective disturbances in different time scales ( Mapes et al. 2006 ). Diabatic heating and moistening effects from shallow clouds have been suggested to be particularly important to the Madden–Julian oscillation (MJO

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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

circulations are at times not accompanied by an organized convective signal ( Weickmann and Berry 2009 ). In addition, when present, the convective signal is not a discrete entity, but rather appears in satellite imagery as planetary-scale “envelope” of intermittent higher-frequency convective activity that is not necessarily systematically organized ( Dias et al. 2013 ). It is also well known that the location and behavior of MJO convection is strongly dependent on the seasonal cycle, enough so that

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

a. Sounding observations The DYNAMO sounding network was composed of two quadrilateral arrays—one north and one south of the equator—referred to as the northern and southern sounding arrays or NSA and SSA, respectively ( Fig. 1 ). Details of the sounding systems, observing characteristics, and quality-control procedures are contained in Ciesielski et al. (2014a) . Incorporated into our analyses are corrections for flow distortion and island heating effects by the mountainous island of Sri Lanka

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

. Miller , 2009 : Seasonal effects of Indian Ocean freshwater forcing in a regional coupled model . J. Climate , 22 , 6577 – 6596 , doi: 10.1175/2009JCLI2990.1 . Seo , K.-H. , and W. Wang , 2010 : The Madden–Julian oscillation simulated in the NCEP Climate Forecast System Model: The importance of stratiform heating . J. Climate , 23 , 4770 – 4793 , doi: 10.1175/2010JCLI2983.1 . Seo , K.-H. , W. Wang , J. Gottschalck , Q. Zhang , J.-K. E. Schemm , W. R. Higgins , and A

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

, it has been noted that the westerly wind events (WWEs) associated with the MJO can impact El Niño–Southern Oscillation (ENSO) ( Zhang 2005 ; Hendon et al. 2007 ; Seiki and Takayabu 2007 ). Despite considerable effort made toward improving the prediction skill of the MJO, critical challenges still remain for current general circulation models (GCMs) to more accurately represent the MJO and, in particular, its initiation over the IO. Dominated by seasonally changing monsoon flow, the IO is a

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Michael S. Pritchard and Christopher S. Bretherton

simulation and linearly interpolated to the model's internal calendar day. To limit effects of α to the equatorial zone, after synthesis of the full velocities U and from their spherical harmonic subcomponents on the global Gaussian grid, the hybrid auxiliary velocity is calculated as That is, transitions smoothly via a smooth Heaviside approximation in latitude ϕ from the vortically perturbed velocity field (equatorward of a critical latitude ϕ 0 ) to the actual velocity field (poleward of

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Xiouhua Fu, Wanqiu Wang, June-Yi Lee, Bin Wang, Kazuyoshi Kikuchi, Jingwei Xu, Juan Li, and Scott Weaver

). Through upscale/downscale impacts and tropical–extratropical teleconnections, the MJO modulates the weather and climate activities over the globe ( Donald et al. 2006 ; Zhang 2013 ). The recurrent nature of the MJO with a period of 30–60 days also offers an opportunity to bridge the forecasting gap between medium-range weather forecast (~1 week) and seasonal prediction (~1 month and longer) (e.g., Waliser 2005 ; Fu et al. 2008a ; Brunet et al. 2010 ; Hoskins 2013 ). However, most global research

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Aurélie J. Moulin, James N. Moum, and Emily L. Shroyer

08411 . 10.1029/JC091iC07p08411 Pujiana , K. , J. N. Moum , and W. D. Smyth , 2018 : The role of subsurface turbulence in redistributing upper-ocean heat, freshwater, and momentum in response to the MJO in the equatorial Indian Ocean . J. Phys. Oceanogr. , 48 , 197 – 220 , . 10.1175/JPO-D-17-0146.1 Seo , H. , S.-P. Xie , R. Murtugudde , M. Jochum , and A. J. Miller , 2009 : Seasonal effects of Indian Ocean freshwater forcing in a

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Jian Ling, Peter Bauer, Peter Bechtold, Anton Beljaars, Richard Forbes, Frederic Vitart, Marcela Ulate, and Chidong Zhang

episodes before January 2012 to a period with a much dryer troposphere. This shift of humidity regime is part of the seasonal cycle over the Indian Ocean and is related to the Asian winter monsoon when dry air from the northern extratropics pushes its way into the tropics and seasonal precipitation moves southward across the equator ( Yoneyama et al. 2013 ; Gottschalck et al. 2013 ). The HRES forecast captured this shift almost precisely up to a lead time of 10 days. Fig . 13. As in Fig. 12 , but for

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