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Edward K. Vizy and Kerry H. Cook

, a temporal compositing technique is used in addition with synoptic analysis. For each wave, the location of the 700-hPa vortex center is used to determine when the vortex passes the 15° and 25°W meridians (i.e., into and out of the boxed area in Fig. 1 ), which we call the Cape Verde region. Atmospheric fields (i.e., geopotential height, temperature, winds, vertical velocity, relative humidity, precipitation) are averaged over this period to establish the environmental conditions in the Cape

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Jonathan Zawislak and Edward J. Zipser

, 3-hourly 0.25° × 0.25° gridded rain rates are available from the level-3 TRMM algorithm, 3B42. The algorithm adjusts rain rates derived from geosynchronous IR observations with TRMM estimated surface rain and hydrometeor structure. c. NCEP GDAS description The Global Data Assimilation System, run by NCEP and obtained from the University Corporation for Atmospheric Research (UCAR) Data Support Center, analysis is utilized to track 700- and 925-hPa vorticity maxima and the 700-hPa wave trough. The

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Robert Cifelli, Timothy Lang, Steven A. Rutledge, Nick Guy, Edward J. Zipser, Jon Zawislak, and Robert Holzworth

1. Introduction A significant fraction of rainfall in the Sahel region of West Africa occurs during the West African monsoon season (July–September). A substantial portion is associated with mesoscale convective systems (MCSs). Indeed, Mathon et al. (2002) have shown that over 90% of the annual rainfall in parts of the central Sahel is associated with organized convection during boreal summer. Over West Africa and the eastern Atlantic, African easterly waves (AEWs) occur on a time scale of 3

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Joël Arnault and Frank Roux

1. Introduction This work has two objectives: 1) to propose an energy budget adapted from Lorenz’s (1955 , hereafter L55) analysis in order to precisely quantify the growth of an African easterly wave (AEW) in a limited domain and 2) to apply this energy budget to the AEW that spawned Hurricane Helene (2006). AEWs are wavelike disturbances observed in West Africa during the summer months. They have wavelengths of 3000–5000 km and periods of 3–5 days. Their amplitude is maximum at the level

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Zhuo Wang, M. T. Montgomery, and T. J. Dunkerton

layer. Tropical easterly waves usually reach their maximum intensity around 600–700 hPa (the jet level) over the central and eastern Atlantic, while the ITCZ is confined mostly within the atmospheric boundary layer. It is plausible that convergence within the ITCZ enhances the low-level vorticity associated with the easterly wave and creates a deeper pouch structure extending to lower levels below the jet maximum. Since a convectively active pouch obtains moisture mainly from the boundary layer, a

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Oreste Reale, William K. Lau, Kyu-Myong Kim, and Eugenia Brin

1. Introduction African easterly waves (AEWs) have been recognized as prominent weather-producing events of northern tropical Africa (e.g., Burpee 1974 ; Asnani 2005 ) and have been extensively studied from observational and modeling perspectives (e.g., Hsieh and Cook 2005 ; Kiladis et al. 2006 ). However, the development of AEWs into tropical depressions remains one of the most challenging problems in the prediction and modeling of Atlantic tropical cyclones. Investigations of tropical

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Syed Ismail, Richard A. Ferrare, Edward V. Browell, Gao Chen, Bruce Anderson, Susan A. Kooi, Anthony Notari, Carolyn F. Butler, Sharon Burton, Marta Fenn, Jason P. Dunion, Gerry Heymsfield, T. N. Krishnamurti, and Mrinal K. Biswas

limit (∼30°N and 38°W) of National Oceanic and Atmospheric Administration (NOAA) research aircraft that were conducting coordinated Saharan Air Layer Experiment (SALEX) research missions from Barbados ( Zipser et al. 2009 ). The study of African easterly waves (AEWs; Thorncroft and Hoskins 1994a , b ) and the potential development of AEWs into major Atlantic hurricanes is of great interest because nearly 85% of intense (or major) hurricanes have their origins as AEWs ( Landsea 1993 ). Seven AEWs

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Wei Zhong, Da-Lin Zhang, and Han-Cheng Lu

unity. The mixed-wave concept implied above refers to the coexistence of two or more different types of waves in a dynamical system. In fact, the atmospheric flows at any instant may consist of many types of wave motions at different scales because of the presence of compressibility, gravity ( g ), earth rotation (  f  ), and curvature ( β ) ( Holton 2004 ). But most mixed waves are simply linear superimposition of their associated eigenfrequencies because their restoring forces can be clearly

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Zhuo Wang, M. T. Montgomery, and T. J. Dunkerton

1. Introduction This is the second of a two-part study examining the numerically simulated formation of Atlantic Hurricane Felix (2007) in a cloud-representing framework. In Part I of this study ( Wang et al. 2010 , hereafter Part I ) the simulation commenced during the wave stage of the precursor African easterly wave disturbance. Analysis of the real-case simulation pointed to a bottom-up development process within the parent wave’s cyclonic “cat’s eye” recirculation flow (or the wave

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Wallace Hogsett and Da-Lin Zhang

different stages of storm development. They found that the KE budgets are determined primarily by the mean flow, although the contribution of eddies is not negligible. Wang (2002a) also examined the inner-core energetics of a simulated TC vortex and found that the maximum eddy KE, located in the lower levels near the radius of maximum wind (RMW), appears to be associated with vortex–Rossby waves (VRWs). Although VRWs have been hypothesized to be active in the inner core of TCs ( Montgomery and

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