Properties of Convective Outflow from Isolated Cells Observed during TRACER

Deep convective clouds play an important role in the atmospheric circulation. Sometimes referred to as atmospheric “elevators” because of their role in transporting moisture, heat, momentum, particles, and gases through different layers of the atmosphere, they are characterized by strong updrafts and downdrafts, often accompanied by heavy precipitation. Despite these clouds’ influence on the local weather and global climate, their dynamics are not well captured by computational models. Inaccurate forecasting and modeling of deep convection poses a risk to life, property, and infrastructure on both regional and global scales. This work uses data collected during the U.S. Department of Energy Atmospheric Radiation Measurement facility’s TRacking Aerosol Convection Interactions ExpeRiment (TRACER), which took place from October 2021 through September 2022 in southeastern Texas near Houston. This region is uniquely well-suited for studying deep convection and its interactions with aerosols owing to the frequent occurrence of isolated convective clouds along with diverse natural and anthropogenic aerosol sources.

Our analysis focuses on identifying the times during the intensive operational period (June to September 2022) when the main TRACER ground-based observation site in La Porte, TX was influenced by downdraft-generated convective outflow from isolated cells. Outflow events were identified using scanning and vertically pointing radar observations identifying both convective cells passing near the site and those passing directly over the site. For the times when convective cells were in the vicinity of the La Porte site, we analyzed surface measurements of meteorological variables (temperature, humidity, and winds) and water vapor isotopic composition (deuterium and oxygen-18). Convective outflow signatures typically included a decrease in equivalent potential temperature, an increase in wind speed, a shift in wind direction, and isotopic depletion of water vapor molecules containing deuterium or oxygen-18. Through visual inspection of the time series of these quantities, we identify more than fifty instances of convective outflow measured at the La Porte site. For these cases we further analyze the concentrations of trace gases, including ozone, and aerosol characteristics such as the size distribution, composition, hygroscopicity, and optical properties towards understanding the contribution of downward convective transport to the surface layer budgets of these atmospheric constituents. Further planned analysis includes the use of vertical sounding profiles of environmental ozone and equivalent potential temperature, which are both approximately conserved under pseudoadiabatic processes, to estimate the originating height of the downdraft and the entrainment of environmental air. This analysis will enable improved model simulations of deep convection by constraining vertical transport.