Precipitation and Evolution Sensitivity in Simulated Deep Convective Storms: Comparisons between Liquid-Only and Simple Ice and Liquid Phase Microphysics*

Abstract

Weisman and Klemp suggested that their liquid-only, deep convective storm experiments should be repeated with a liquid-ice microphysics scheme to determine if the solutions are qualitatively the same. Using a three-dimensional, nonhydrostatic cloud model, such results are compared between three microphysics schemes: the “Kessler” liquid-only scheme (used by Weisman and Klemp), a Lin–Farley–Orville-like scheme with liquid and ice parameterization (Li), and the same Lin–Farley–Orville-like microphysics scheme but with only liquid processes turned on (Lr). Convection is simulated using a single thermodynamic profile and a variety of shear profiles. The shear profiles are represented by five idealized half-circle wind hodographs with arc lengths (U_s) of 20, 25, 30, 40, and 50 m s⁻¹. The precipitation, cold pool characteristics, and storm evolution produced by the different schemes are compared. The Kessler scheme produces similar accumulated precipitation over 2 h compared to Lr for all shear regimes. Although Kessler's rain evaporation rate is 1.5–1.8 times faster in the lower troposphere, rain production is also faster via accretion and autoconversion of cloud water. In addition, nearly ∼40% more accumulated precipitation occurs in Li compared to Lr. This can be attributed primarily to increased precipitation production rates and enhanced low-level precipitation fluxes in Li for all shear regimes. Differences in the amount of precipitation reaching ground and the low-level cooling rates also cause differences in storm cold pools. For the U_s = 25 shear regime, microphysics cases with colder low-level outflow are shown to be associated with temporarily weaker (Li) or shorter-lived (Kessler) supercells as compared to cases with warmer outflow (Lr). This is consistent with a previous study showing that the cold pool has a greater relative impact on the storm updraft compared to dynamic forcing for weaker shear.