Fine-scale numerical analysis of the sensitivity of the HyMeX IOP16a Heavy Precipitating Event to the the turbulent mixing length parametrization

The Mediterranean region is an area affected by heavy precipitating event, frequently exceeding more than 150mm in 24 hours, mostly during fall season. These events are often associated with major and devastating flash floods, life-threatening for the local population. However, it is still difficult to predict the exact location and intensity of such heavy precipitation events. One major goal of the HyMeX program, which the 1^st special observation period (SOP1) took place in autumn 2012, is to improve our ability to predict such high-impact weather events and their consequences.

The goal of this study is to better understand offshore deep convection during the intense observation period IOP16a, on the 26/10/2012. The major initiation and maintenance mechanisms for this case study are the low level convergence between a moist and unstable south-easterly low-level jet and a south westerly flow. The existence of a low-level cooling in the north-western part of the system also appears to be involved in the development of the mesoscale convective system.

Sensitivity experiments were performed with the mesoscale non-hydrostatic french model to examine the impact of an increasing horizontal resolution, ranging from 2.5km to 500m and 150m, to avoid the grey-zone of the turbulence. Sensitivity to mixing length formulation is also assessed in this study. Special attention will be paid to microphysical processes and dynamics of the convective system. The HyMeX SOP1 observation dataset enables to assess the quality of the numerical simulations.