We thank the two reviewers for their comments and suggestions, which greatly helped to improve the manuscript. Stephanie Leroux was supported by the French Ministry of “Enseignement superieur et Recherche.” This work is part of the AMMA project. AMMA (African Monsoon Multidisciplinary Analyses) was built by an international scientific group and is currently funded by a large number of agencies, especially from France, the UK, the U.S., and Africa. It has been the beneficiary of a major financial contribution from the European Community’s Sixth Framework Research Programme. Detailed information on scientific coordination and funding is available on the AMMA International Web site (http://www.amma-international.org).
Burpee, R., 1972: The origin and structure of easterly waves in the lower troposphere of North Africa. J. Atmos. Sci., 29 , 77–90.
Carlson, N., 1969: Synoptic histories of three African disturbances that developed into Atlantic hurricanes. Mon. Wea. Rev., 97 , 256–276.
Charney, J., , and M. Stern, 1962: On the stability of internal baroclinic jets in a rotating atmosphere. J. Atmos. Sci., 19 , 159–172.
Cornforth, R. J., , B. J. Hoskins, , and C. D. Thorncroft, 2009: The impact of moist processes on the African easterly jet–African easterly wave system. Quart. J. Roy. Meteor. Soc., 135 , 894–913.
Dickinson, M., , and J. Molinari, 2000: Climatology of sign reversals of the meridional potential vorticity gradient over Africa and Australia. Mon. Wea. Rev., 128 , 3890–3900.
Duvel, J-P., 1990: Convection over tropical Africa and the Atlantic Ocean during northern summer. Part II: Modulation by easterly waves. Mon. Wea. Rev., 118 , 1855–1868.
Fink, A. H., , and A. Reiner, 2003: Spatiotemporal variability of the relation between African easterly waves and West African squall lines in 1998 and 1999. J. Geophys. Res., 108 , 4332. doi:10.1029/2002JD002816.
Fjortoft, R., 1950: Application of integral theorems in deriving criteria for stability for laminar flows and for baroclinic circular vortex. Geophys. Publ., 17 , 1–52.
Grist, J., , S. Nicholson, , and A. Barcilon, 2002: Easterly waves over Africa. Part II: Observed and modeled contrasts between wet and dry years. Mon. Wea. Rev., 130 , 212–225.
Hall, N., , G. Kiladis, , and C. Thorncroft, 2006: Three dimensional structure and dynamics of African easterly waves. Part II: Dynamical modes. J. Atmos. Sci., 63 , 2231–2245.
Hsieh, J-S., , and K. H. Cook, 2005: Generation of African easterly wave disturbances: Relationship to the African easterly jet. Mon. Wea. Rev., 133 , 1311–1327.
Hsieh, J-S., , and K. H. Cook, 2007: A study of the energetics of African easterly waves using a regional climate model. J. Atmos. Sci., 64 , 421–440.
Hsieh, J-S., , and K. H. Cook, 2008: On the instability of the African easterly jet and the generation of African waves: Reversals of the potential vorticity gradient. J. Atmos. Sci., 65 , 2130–2151.
Kanamitsu, M., , W. Ebisuzaki, , J. Woollen, , S-K. Yang, , J. J. Hnilo, , M. Fiorino, , and G. L. Potter, 2002: NCEP–DOE AMIP-II Reanalysis (R-2). Bull. Amer. Meteor. Soc., 83 , 1631–1643.
Kiladis, G., , C. Thorncroft, , and N. Hall, 2006: Three-dimensional structure and dynamics of African easterly waves. Part I: Observations. J. Atmos. Sci., 63 , 2212–2230.
Leroux, S., , N. Hall, , and G. Kiladis, 2009: A climatological study of transient-mean flow interactions over West Africa. Quart. J. Roy. Meteor. Soc., in press.
Mekonnen, A., , C. D. Thorncroft, , and A. R. Aiyyer, 2006: Analysis of convection and its association with African easterly waves. J. Climate, 19 , 5405–5421.
Nicholson, S. E., , A. I. Barcilon, , and M. Challa, 2008: An analysis of West African dynamics using a linearized GCM. J. Atmos. Sci., 65 , 1182–1203.
North, G. R., , T. L. Bell, , R. F. Cahalan, , and F. J. Moeng, 1982: Sampling errors in the estimation of empirical orthogonal functions. Mon. Wea. Rev., 110 , 699–706.
Paradis, D., , J-P. Lafore, , J-L. Redelsperger, , and V. Balaji, 1995: African easterly waves and convection. Part I: Linear simulations. J. Atmos. Sci., 52 , 1657–1679.
Reed, R., , D. Norquist, , and E. Recker, 1977: The structure and properties of African wave disturbances as observed during Phase III of GATE. Mon. Wea. Rev., 105 , 317–333.
Thorncroft, C., 1995: An idealized study of African easterly waves. III: More realistic basic states. Quart. J. Roy. Meteor. Soc., 121 , 1589–1614.
Thorncroft, C., , and B. Hoskins, 1994a: An idealized study of African easterly waves. I: A linear view. Quart. J. Roy. Meteor. Soc., 120 , 953–982.
Thorncroft, C., , and B. Hoskins, 1994b: An idealized study of African easterly waves. II: A nonlinear view. Quart. J. Roy. Meteor. Soc., 120 , 983–1015.
Thorncroft, C., , and K. Hodges, 2001: African easterly wave variability and its relationship to Atlantic tropical cyclone activity. J. Climate, 14 , 1166–1179.
Thorncroft, C., , N. Hall, , and G. Kiladis, 2008: Three dimensional structure and dynamics of African easterly waves. Part III: Genesis. J. Atmos. Sci., 65 , 3596–3607.