Properties of Convective Outflow during the Tracking Aerosol Convection interactions ExeRiment (TRACER) campaign

Convective updraft and downdraft dynamics have a significant effect on water, heat, momentum, and aerosol fluxes within the convective system. Through these processes, these clouds play a critical role in the Earth’s climate system. However, despite their importance, they remain poorly understood and difficult to measure, resulting in confusion concerning the microphysics of convective clouds. The TRacking Aerosol Convection interactions ExpeRiment (TRACER) campaign was designed to collect data to better understand the evolution of convective clouds along with their properties as they initiate, propagate, and decay. We use observations from TRACER to quantify the impact of downdraft outflow from isolated convective cells on boundary layer thermodynamics, aerosol properties and trace gas concentrations. Outflow events were identified by first using radar observations to find convective cells passing near the main TRACER observation site. For the times when convective cells were in the vicinity, we analyzed surface meteorological and water vapor isotopic composition data to identify downdraft outflow. Convective downdraft signatures included a decrease in equivalent potential temperature, an increase in wind speed, a shift in wind direction, and isotopic depletion of water vapor. We identify more than fifty instances of convective outflow measured at the TRACER site. For these cases we quantify the perturbation the concentrations of trace gases and aerosol properties towards understanding the contribution of downward convective transport to the surface layer budgets. This analysis will be used to improve model simulations of deep convection by constraining vertical transport between the free troposphere and boundary layer.