Orographic Impact on the Precipitation Microphysical Processes during HyMeX SOP-1

During, the first Special Observation Period (SOP-1) of the HyMeX campaign, in fall 2012, a specific observational network has been set-up in southern France with the aim to better understand the role and the impact of a complex terrain on the horizontal and vertical structure of rainfall and the associated microphysical processes. Based on two reference parameters of the drop size distributions (DSD) and the observed spectra for the IOP7a case study, it has been shown that the topography of the region has an impact on the rainfall structure at fine scale and that rainfall regimes also have an influence on the DSD. Those results have been generalized to the observation collected during the fall 2012 SOP period. In this presentation, we will focus on the microphysical processes being modified and on their modification by the underlying orography. A more detailed study based on the evolution of the shape of the DSD with regard to different rainfall regimes reveals that the coalescence mechanism seems dominant above the height of the local topography and for heavy rainfall. However, as we get closer to the ground, modifications of the observed DSD indicate that other microphysical processes such as break-up, evaporation or updraft effects might compete with the coalescence mechanism. Furthermore, these processes are affected by their direct environment with a more important break-up mechanism as the local terrain becomes more complex and the role of updraft and evaporation being more important over flatter terrain. Thus, the local orography and the rainfall regimes impact both the rainfall structure and the associated microphysical processes.