LIMA (v2.0): A full two-moment cloud microphysical scheme for the mesoscale non-hydrostatic model Meso-NH v5-6

Abstract

A full two-moment microphysics parameterization of the LIMA scheme (with LIMA standing for Liquid Ice Multiple Aerosols and hereafter named LIMA v2.0) has been developed and successfully implemented in the Meso-NH cloud-resolving model. The novelty of the scheme is a set of prognostic equations of the number concentration of each precipitating ice category (snow/aggregates, graupel, and hail), in addition to the prediction of the mass mixing ratios. As a result, new microphysical conversion rates are introduced and explicitly computed using the size distributions of the hydrometeors. The new LIMA v2.0 scheme has been tested for an idealized deep convection case against the original LIMA scheme characterized by an empirical number-concentration–mixing-ratio relationship applied to the precipitating ice. Inclusion of number concentration equations for the snow/aggregates and graupel significantly alters the microphysical structure and dynamical evolution of the simulated supercell. When comparing to the results obtained with the previous version of LIMA, the new v2.0 of the scheme tends to increase the pristine ice mixing ratio; to decrease the other ice hydrometeors by slowing down the growing processes of snow/aggregates, graupel, and hail; and to enhance the feedbacks between raindrops and the ice-phase hydrometeors. This comparison also emphasizes the unreasonable diagnostic approach used to estimate the number concentration of precipitating ice particles in the previous version of the scheme. The new scheme is more efficient at producing earlier raindrops at ground level and reducing hail precipitation.