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Eric D. Skyllingstad and Simon P. de Szoeke

, convectively forced cold pools appear as cool and slightly drier air masses beneath convective systems, with wind gusts enhancing surface fluxes as they spread laterally. They have been observed in association with convection at many scales ranging from precipitating trade wind cumulus ( Zuidema et al. 2012 ) to mesoscale convective complexes ( Young et al. 1995 ). In midlatitudes, cold pool boundaries are known to trigger new convection and are often implicated in the development of severe storms

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Brandon W. Kerns and Shuyi S. Chen

when the data are updated with new swaths. Also, moderate changes in midlevel moisture with the boundary layer and upper levels remaining moist are not easily distinguished in terms of TPW. For these reasons, the evolution of TPW is most useful at determining strong gradients between moist (>~55 mm) and dry air (<~45 mm) masses, where there are large gradients of moisture through a deep layer of the atmosphere. Fortunately, these sharp moisture gradients are common ( Zhang et al. 2003 ). 3

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Nick Guy and David P. Jorgensen

phenomena (e.g., El Niño–Southern Oscillation, North Atlantic Oscillation, Indian Ocean dipole); discussed further in Lau and Waliser (2005) and Zhang (2005) . Given the extensive impact of the MJO on global circulations, it is important to correctly simulate the MJO in forecast and climate models. However, current model simulations do not represent the MJO well ( Lin et al. 2006 ; Benedict and Randall 2009 ). This is due in part to an incomplete understanding of convective dynamics and

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

truncation of T1279, a reduced Gaussian grid (equivalent to 16-km global grid spacing), and 91 vertical levels (denoted as T1279L91). Persisted SST anomalies are used as the lower boundary condition. Forecasts from 12 to 240 h with an interval of 12 h initialized at 0000 and 1200 UTC from 1 October 2011 to 31 January 2012 were evaluated in this study. Table 2. List of operational forecast products. All forecasts were initialized daily at 0000 and 1200 UTC. The other ECMWF forecast component is the

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Tomoe Nasuno, Tim Li, and Kazuyoshi Kikuchi

presented in Fig. 4 . Subsidence and negative moisture anomalies at the beginning of the preconditioning periods ( Figs. 4a,b ) transitioned into upward motion with positive moisture anomalies 2–3 days before the date of convective initiation. In the boundary layer (950–1000 hPa), upward motion and warm anomalies started during the early preconditioning stage ( Figs. 4a,c ). These precursor signals were consistent with those in the climatological MJO ( Zhao et al. 2013 ), but with a slower evolution of

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