Evidence of two regimes of easterly waves over West Africa and the tropical Atlantic

Synoptic‐scale easterly waves at 700 hPa have been studied over West Africa and the tropical Atlantic for the summers of 1979–1995. Spectral analyses (Fast Fourier and Wavelet Transforms) of 700 hPa meridional wind component along 17.5°N enable to point out two band‐periods, between 3 and 5 days and between 6 and 9 days. An example of each wave is shown. Composite analysis confirms the evidence of two such regimes of easterly waves during summer over West Africa and the tropical Atlantic. The 6–9‐day wave regime differ from the 3–5‐day wave regime by larger anticyclonic cells originated from the Libyan and the Azores areas, and by more northern tracks.