Effect of Stratospheric Intrusions on Tropospheric and Boundary Layer Ozone in the NASA SEAC4RS Campaign

The NASA Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS) field campaign occurred in the south central U.S. during August and September of 2013 with a complement of surface, aircraft, and satellite measurements to further understand atmospheric chemistry in the troposphere and stratosphere. Flights on the NASA DC8 and ER2 from Houston were augmented by a network of six coordinated ozonesonde launching stations (SEACIONS) that included St. Louis, Houston, and Huntsville. Stratospheric intrusion events were studied to investigate the impact on free troposphere and boundary layer ozone. Relative humidity profiles from the AIRS (Atmospheric InfraRed Sounder) satellite instrument, confirmed the presence of stratospheric intrusions when dry stratospheric air was co-located with ozone-rich, nitrogen dioxide deficient, and carbon monoxide deficient air as measured by the ozonesondes and aircraft instruments. The Goddard Earth Observing System Model Version 5 (GEOS-5) was run with stratospheric tracers to determine the quantitative impact of stratosphere-to-troposphere transport (STT) on the ozone budget. Case studies through the campaign are presented to show the variability and impact of the stratospheric intrusions that occurred. Overall stratospheric intrusion events during this period increased free tropospheric ozone by 20-40 ppb, including just above the boundary layer. However, they generally had no noticeable effect on the boundary layer composition.