Sensitivity of simulated storm life span to ventilation parameterization in a cloud resolving model

Abstract

We perform a sensitivity study on the ventilation effect of large hydrometeors, namely, raindrops, snow aggregates, and hail in a cloud-resolving model. The ventilation effect could accelerate the heat and mass transfer rates between vapor and falling hydrometeors. It causes the falling hydrometeors to grow (in a supersaturated environment) and dissipate (in a subsaturated environment) faster than the stationary ones. The parameterizations of the ventilation effect on hydrometeors in a cloud model is critical as it could dramatically alter the structure and the lifespan of the simulated storm. Enhancing the ventilation coefficients of falling hydrometeors leads to a longer-lived storm featured by apparent storm splitting. The temporal evolution of hail density fluctuates greater than the default case (the control case) indicating both stronger deposition and sublimation in hail microphysical processes. However, both rainfall and hailfall become less intense than the control run. In contrast, reducing the ventilation effect causes moderate evaporation of raindrops as they fall through subsaturated air. Consequently, the concentration and precipitation rate of raindrops increase near the surface. Strong downdraft accompanying the heavy rainfall cuts off the low-level inflow of unstable moist air into the storm and results in early dissipation of the storm.