The interannual and intraseasonal variability of the frequency, intensity and structure of African Easterly Waves is investigated. NCEP reanalysis data is used to enable waves from dry years in West Africa (1982-85) to be contrasted with those from wet years (1958-61). Wavelet analysis is applied to time series of grid points at 15N 0E at both 600mb and 925mb . The modulus of the wavelet transform describes an annual cycle of wave magnitude. A line representing the 99% confidence level delineates the summer wave season. Substantial changes in the strength and frequency of the waves are also evident within the season. Composites of the modulus from wet and dry years are used to identify systematic differences in the annual cycle between the two regimes.
The structure of the waves are examined by producing vertical cross-sections of the zonally averaged eddy kinetic energy. These revealed the location of the maximum wave amplitude in relation to the African Easterly Jet (AEJ). The cross-sections were produced for periods representing the early and late parts of the wave season. In addition composites of the cross sections were made for wet and dry years. Some interannual and intraseasonal differences in wave characteristics appear to be due to variations in the jet that alter the influence of different wave generating mechanisms