Interaction of African monsoon and the large-scale atmospheric circulation and oceans on intraseasonal, interannual and multidecadal timescales

Recent studies have identified intraseasonal variability in the African monsoon system (Sultan and Janicot, 2003; and Mathews, 2004), and a relationship between African variability, the large-scale system and the South Asian monsoon (Hoyos and Webster, 2004; and Collins and Webster, 2005). We explore the African intraseasonal and interannual variability and its physical forcing by the large-scale atmosphere and ocean-atmosphere interactions using the operational ECMWF 1˚x1˚ reanalysis atmospheric circulation data and Reynolds sea surface temperature data. A key aspect of this study will be the separation of forcing and response of the African monsoon into timescales from intraseasonal to multidecadal climate change. For this, we use two statistical tools, multivariate singular spectral analysis and wavelet analysis. Intraseasonal and interannual variable signals may be compared through correlation or composites relative to African climate variability or sea surface temperature variability. To determine the forcing of the African monsoon system by anthropogenic climate change in the 20th century, we make use of a set of coupled global GCM runs made under the auspices of the IPCC. Because sea surface temperature and large-scale atmospheric circulation are forced by atmospheric composition in these model simulations, the response of the African monsoon to multidecadal anthropogenic climate change may be assessed. As a first step, the ability of these GCMs to simulate the large-scale circulation associated with African climate variability is evaluated.