The Sensitivity of a Simulated Extratropical Mesoscale Convective System to Longwave Radiation and Ice-Phase Microphysics

Abstract

A two-dimensional, nonhydrostatic version of the Colorado State University Regional Atmospheric Modeling System (RAMS) was applied to the simulation of a midlatitude, continental mesoscale convective system. A control simulation was established that exhibited many features in common with observed MCSs. The sensitivity experiments revealed that the mesoscale circulations in the stratiform region were quite sensitive to longwave radiative cooling at stratiform anvil cloud top and heating at cloud base, and the presence of ice-phase precipitation processes and thermodynamics. Surface precipitation was little affected by radiational heating, however. Turning off melting of ice particles had little influence on the strength of simulated mesoscale and convective-scale downdrafts and the strength of the middle-level, rear-to-front flow. Melting had the greatest impact on the strength of the convective scale updrafts. These numerical experiments suggest that the strength of the middle-level, rear-to-front flow is primarily modulated by heating in the upper troposphere and by the strength of the low-level, convective scale “up-down” downdraft component.