Physical factors contributing to severe convective storms

Description

Severe convective storms (SCS) comprise an extreme class of deep convective clouds that produce large hail, damaging winds and/or tornadoes, and torrential rainfall. SCS frequently causes as much annual property damage and more deaths than hurricanes in the U.S. Although there is good understanding about supercell and tornado dynamics, it is important to improve our fundamental understanding of how other environmental factors such as land-surface and aerosols on SCS can impact SCS properties. Wildfire and urbanization have been undergoing most significant changes on the surface of Earth. We have examined how changes in heat, land use, and aerosols, all of which result from wildfires and urbanizations, impact the SCS characteristics. We find that in a wildfire induced pyrocumulonimbus (pyroCb) event, both heat and aerosols increase low-level temperatures and mid-level thermal buoyancy significantly, causing strong convection. Both increase supercooled water available for to hail growth, which leads to larger hail size and enhanced lightning. The effect of heat is more significant than that of aerosol emissions. In a thunderstorm case occurring in Houston, we find that both Houston urban land and anthropogenic aerosols contribute drastically to strong convection and precipitation distribution over the region, with urban land contribution more significant. Urban anthropogenic aerosols from Houston enhance convective intensity and precipitation in a noticeable way through warm-phase invigoration induced by numerous but small aerosol particles. Over a long-term time period, our observational analysis suggests the annual variation of hail occurrence over the Southern Great Plains (SGP) are primarily attributed to variations of aerosols from Northern Mexico and SST temperature of the Gulf of Mexico.