This study represents a multi-scale simulation of the sahelian weather system in late summer. It focuses on the modelisation of the squall line observed on 21-22 August 1992 during HAPEX-Sahel experiment and its interactions with large scale features in the West African Monsoon region. A 24-hours explicit simulation of the life cycle of this convectve event is achieved taking account the large scale dynamics thanks to the use of grid-nesting technique.

Comparisons of model-synthetic and Meteosat infrared radiances indicate that the simulated scenario of convection developpement and structures are realistic. Also, the simulated arc-shaped structure and surface signature fit well to observations. Its formation is a result of three mechanisms: thermal forcing over Air Mountains, monsoon advection from the south and convection induced by the density current. The simulated squall line at mature stage exhibits not only the 2D conceptual model structures but also a strong 3D structure with a generation of dipole of counter rotating vorticities. This dipole may reinforce the barotropic instability on the north flank of the AEJ.

The simulated squall line has a strong impact at large scale: the monsoon flow is reinforced farther than 500 km south of the convective system; the AEJ is weakened and strenghened ahead and behind the squall line, respectiveley; the TEJ is intensified to the southwest of the convective system up to 700 km, which can explain the two-branches structure of the TEJ. Comparison with ERA-15 analysis reveals a similar behaviour for the TEJ and the monsoon flow and both analysis and simulations show that the AEJ core propagates westward faster with convective activity.