The West African region has been characterised by significant interannual rainfall variability this century: the Sahelian region in particular has experienced a recent long-running drought, in contrast to the too much wetter decades of the 1950s. The social and economic impacts of this can be tragic. Since the Sahel receives most of its rain during the boreal summer season, there is an urgent need for seasonal predictions of rainfall.
Major contributors to the Sahelian rainfall variability are mesoscale convective systems and easterly waves. Such systems can not be well captured by the coarse resolution general circulation models (GCMs). To diagnose the nature of individual weather systems and their variability, a hierarchy of models of various spatial resolution are required.
An ensemble of seasonal cycle integrations has been done using the UKMO Unified Model together with its Limited Area Model (LAM). These models are characterised by the same vertical resolution (30 layers) but by different horizontal resolution ranging from 2 degrees (GCM) to 0.44 degrees (LAM). The sensitivity of the West African monsoon to model resolution will be shown by the comparison of these models'results, focusing on the convection and the easterly waves