Impact of the planetary boundary layer processes on the turbulent length scales and heat fluxes at surface

The African Monsoon Multidisciplinary Analysis (http://www.amma-international.org) international project deals with the understanding of inter-annual variabilities of the West African Monsoon which lead during the last decades to extremely dry years with devastating environmental and socio-economic impacts. This project is necessarily a multi-scale analysis including large scale features such as Heat low or High level jets down to Boundary layer processes. Our study focuses on the boundary layer role in surface/deep convection interactions. Surface measurements of turbulence during the wet season of 2006 and aircraft measurements allowed both the study of temporal evolution near the surface and of the vertical structure of the PBL in term of turbulence. The relative roles of thermal convection controlled by the surface and entrainment processes between Monsoon and Harmattan layers are investigated through the study of rainy events impact on energy fluxes and on the integral scales of the scalars and their distributions. The long period of measurements also enabled to analyze the seasonal variation of this impact.