Influence of Environmental Instability and Cold Pools on Mountain-Crossing Mesoscale Convective Systems

Abstract

This study employs idealized large-eddy simulations with the Cloud Model 1, coupled with observations from the Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign, to investigate the role of environmental instability and cold pool characteristics on mesoscale convective system (MCS) behavior during mountain crossings. The control simulation initialized with a sounding from a CACTI MCS event reproduces a commonly observed mountain-crossing life cycle, with windward intensification, leeward weakening with rain shadow, and downstream redevelopment. Sensitivity simulations that systematically vary convective available potential energy (CAPE) highlight the sensitivity of crossing behavior to ambient instability. Lower base-state CAPE (1000–1500 J kg −1 ) yields noncrossing MCSs, moderate CAPE (1750–2250 J kg −1 ) supports discrete propagations, and higher CAPE (2500–3000 J kg −1 ) enables smooth translations across the mountain. Cold pool intensity, which is strongly influenced by base-state CAPE, and the resulting lift fosters these crossing behaviors. Stronger cold pools weaken over the lee slope but remain sufficient to initiate lee-side convection. Weaker cold pools decay in the lee and fail to support storms downstream of the mountain. Sensitivity simulations systematically modify cold pool characteristics within each base-state CAPE environment. Regardless of cold pool intensity, crossing behavior remains dictated by the base-state CAPE. Further, cold pools with similar intensities produced differing crossing behaviors.