8B.6
An idealised two-dimensional framework to study convection over West Africa
S. D. Wright, CNRM, Toulouse, France; and J. P. Lafore and J. L. Redelsperger
For the region of West Africa, a region where deep, active convection is universal in the rainy season, the diurnal cycle of land-based convection is basically a response to the radiative forcing with an increase in the surface temperature leading to instabilities, convection and convective precipitation. However, before analysing the local diurnal cycle, the large-scale dynamical forcing in this region has to be to simulated, i.e. the Hadley cells, and hence this is a multi-scale problem. This has been achieved within an idealised framework using the meso-scale model Méso-NH. Here the aim is not to simulate real cases, but to define idealised cases that contain the basic ingredients of the reality. Hence, a two-dimensional, vertical-meridional domain has been taken between 30° south and 30° north. From land-use data, idealised surface conditions have been employed along with a soil-vegetation scheme connected with a water cycle, a sub-grid condensation scheme, a radiation scheme and a convective scheme. During a simulation time of 10 days a basic large-scale equilibrium is obtained and contained within this equilibrium the convection is visible. This idealised approach is then used to gain budget diagnostics about the instability, turbulence, radiation, surface fluxes and large-scale forcing and is crucial to gain an improved understanding of the key underlying physics. This allows us to examine the sensitivity of the atmosphere in West Africa to any of the underlying physical properties that have been parameterised within the numerical model. It will be shown that using this idealised approach such phenomena as the African Easterly Jet, the Tropical Easterly Jet, the monsoon flux and the Hadley circulation are present within the simulated fields as well as the local diurnal cycle dependent on latitude, i.e. the diurnal cycle takes a different form over the ocean, the Sahel and Sahara regions.
Session 8B, Large-Scale Dynamics and Convection III (Parallel with Sessions 8A, 8C, and 8D)
Wednesday, 1 May 2002, 9:15 AM-10:30 AM
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