Numerical simulations of microphysical processes involved during three MAP cases (IOP8, IOP2A and IOP3)

Numerical simulations of three MAP events (IOP2a, IOP3 and IOP8) have been performed with the MESO-NH model, run over three nested domains with horizontal grid increments of 32,8 and 2km. The simulations make use of an explicit microphysical scheme predicting the evolution of seven water species and including a four-class ice scheme (pristine ice, snow/aggregates, graupels, and hail categories).

These three MAP events are associated with different flow regimes: stable statification with blocked flow during IOP8, and unstable or potentially unstable conditions with flow over during IOP2a and IOP3.

In response to these different flow regimes, the numerical simulations exhibit a contrasted behaviour in the microphysical structure of the clouds. In the case of IOP8, cloud tops hardly reach the height of 5 km and the prominant microphysical processes are typical of stratiform clouds: coalescence below the freezing level, and vapor deposition above. In the case of IOP2a and IOP3, the cloud systems are much deeper and the contribution of ice microphysics is more important and more active. In both cases the dominant microphysical process above the freezing level is clearly the riming but only the case of IOP2a produces a thick layer of graupel and provides the conditions for the generation of hail in a significant amount. These results are in close agreement with the observations of the polarimetric radar S-Pol.