Evidence of two independent modes of convection at intraseasonal timescale in the West African summer monsoon

Abstract

Two main independent modes of convection at intraseasonal timescale in the West African summer monsoon are highlighted. One depicts a meridional dipole of convection over West Africa linked to a modulation of the latitude of the inter-tropical convergence zone (ITCZ); it is associated with a westward propagative signal of the convection over the Sahel, and to a modulation of cyclonic vorticity at these latitudes. The other one is characterized by a stationary uniform modulation of convection in the ITCZ without any significant modulation of its latitudinal location; it is associated with a modulation of the zonal wind component over the eastern equatorial Atlantic. The dominant periodicity of these two modes is around 15 days. It is necessary to take into account the relative parts of these two modes in order to accurately analyze the mechanisms involved in intraseasonal variability of the African monsoon. Copyright 2004 by the American Geophysical Union.