Trace Gas Removal by Deep Convective Storms

Yang, Q., Pacific Northwest National Laboratory

Cloud Processes

Cloud Life Cycle

Bela MM, MC Barth, OB Toon, A Fried, CR Homeyer, H Morrison, KA Cummings, Y Li, KE Pickering, DJ Allen, Q Yang, PO Wennberg, JD Crounse, JM St. Clair, AP Teng, D O'Sullivan, L Huey, D Chen, X Liu, DR Blake, NJ Blake, EC Apel, RS Hornbrook, F Flocke, T Campos, and G Diskin. 2016. "Wet scavenging of soluble gases in DC3 deep convective storms using WRF-Chem simulations and aircraft observations." Journal of Geophysical Research: Atmospheres, 121(8), 10.1002/2015jd024623.

Science

Deep convective storms have a large impact on the climate by sending atmospheric trace gases high into the atmosphere where they participate in particle formation and ozone formation that affect the amount of sunlight, or radiative energy, that passes through the atmosphere to Earth’s surface. Understanding how storms, or convective systems, transport trace-gas concentrations to the upper atmosphere will help scientists understand how ozone and aerosols affect the climate.

Impact

Researchers found that scavenging efficiencies of all trace gases (a measurement that reflects the efficiency of trace gases being removed from the atmosphere in various ways), except for nitric acid, are highly sensitive to their ability to be retained by ice (ice retention fraction), which will help guide model representation of the trace-gas wet-removal processes. The study also provides insight into how wet removal of trace gases varies among storms.

Summary

Researchers, including a Department of Energy scientist from Pacific Northwest National Laboratory, examined wet scavenging (removal through rain, snow, and ice) of soluble trace gases in storms observed during the Deep Convective Clouds and Chemistry (DC3) field campaign in 2012 using both observations and model simulations. They found significant differences in scavenging efficiencies among storms for different trace-gas species. The research observed more scavenging of nitric acid and less removal of methyl hydrogen peroxide in storms with higher maximum flash rates, an indication of more graupel (soft hail) mass. Graupel is associated with mixed-phase (clouds with both rain and snow) scavenging and lightning production of nitrogen oxides, processes that may explain the observed differences in nitric acid and methyl hydrogen peroxide scavenging.