Numerical Study of the Initiation Over Mountainous Area of a Squall Line Associated with an Easterly Wave

Squall Lines (SL) are among the most important meteorological events in the west african monsoon area. Explicit simulations, in addition with observations, are necessary to allow us to progress in our understanding about SL. Then, explicit resolution of African SL have been performed and interesting results about internal dynamics and thermodynamics have been found (Redelsperger and Lafore, 1988; Caniaux et al., 1992). However, the initition stage of african SL has been weakly studied. Moreover, explicit resolution of SL is generally achieved with an homogeneous initial state and added perturbation.

Here in the first phase of our work, the meso-NH atmospheric system simulation is used to simulate the genesis and the propagation of a Squall Line observed on 21-22 August 1992 on Infrared Images METEOSAT during Hapex-Sahel Experiment in Niger. Explicit simulations initialized by ECMWF re-analysis and fine orography are performed. First, to allow a better boundary layer, we perform explicit simulations starting at sunrise with an resolution of 5 km. Second, we use these simulations to force and initialize simulations with finer resolution (2.5 km). The Meso-NH model is able to simulate explicitly a SL, starting only with large scale fields, without any initial artifices. Trigger area, structure and intensities found are closed to satellite imagery and ground stations measurements.

The second phase will consist to simulate the entire lifetime of the SL and to study interactions between the system and the AEW present in ECMWF re-analysis.