CLaSP Special Seminar - Dr. Mary Barth
Date: April 25, 2017
Time: 3:30 pm - 5:00 pm
Location: Room 2424, Space Research Building
Our guest for this CLaSP Special Seminar is Dr. Mary Barth, Senior Scientist in NCAR's Atmospheric Chemistry Observations and Modeling (ACOM) Laboratory and Mesoscale and Microscale Meteorology (MMM) Laboratory and head of the Regional and Process Modeling Group.
Title: "Thunderstorms and Atmospheric Composition: A Meeting of Cloud Physics, Dynamics, Lightning, and Chemistry"
Abstract: Upward motions in thunderstorms transport trace gases and aerosols from the boundary layer to the upper troposphere and lower stratosphere. Along the way, many complicated processes occur, including lightning and its production of nitrogen oxides (NOx), scavenging by precipitation, and chemical reactions. The consequence of these processes is high-altitude plumes of photochemically-active chemistry that produce ozone in the UTLS region where ozone acts as a greenhouse gas. To advance our understanding of how thunderstorms affect tropospheric composition, the Deep Convective Clouds and Chemistry (DC3) field campaign was conducted over the central United States in May and June 2012. Examples of lightning-NOx production, scavenging efficiencies, ozone production, and stratosphere-troposphere exchange from the DC3 campaign will be presented.
Highlights of these analyses include the higher than expected scavenging of methyl hydrogen peroxide resulting in low mixing ratios of peroxides (100-300 pptv) and high formaldehyde mixing ratios (1000-1500 pptv) in the convective outflow plumes. These results suggest that formaldehyde may be the primary HOx source in the convective outflow plumes that then reacts with lightning-generated NOx to produce 10-15 ppbv ozone during the day following convection. However, another source of upper troposphere ozone is cloud-scale stratosphere-troposphere exchange caused by the thunderstorm dynamics. DC3 measurements often found stratospheric ozone alongside storm anvils, even wrapping around the anvil in one case, bringing high ozone concentrations into the upper troposphere. Thus, both in situ chemical production and cloud-scale mixing processes must be considered to understand ozone sources in the upper troposphere.
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