Daily ozonesondes were launched from 14 N. American sites during August 2006, providing the best set of free tropospheric ozone measurements ever gathered across the continent in a single season. The data reveal that the strongest regional-scale ozone enhancement is not in the lower troposphere, but in the upper troposphere above eastern North America, and centered over the southeastern USA. Recurring each year, the location and strength of the ozone maximum is influenced by the summertime upper tropospheric anticyclone that traps convectively lofted ozone and ozone precursors from anthropogenic sources, as well as ozone produced from lightning NOx, above the southeastern USA. The North American summer monsoon that flows northwards along the Rocky Mountains is embedded within the western side of the anticyclone and also marks the westernmost extent of the ozone maximum. Removing the influence from stratospheric intrusions, median ozone mixing ratios (78 ppbv) in the upper troposphere (> 6 km) above Alabama, near the center of the anticyclone, were nearly twice the level above the US west coast. Model simulations indicate lightning NOx emissions led to the production of 25-30 ppbv of ozone at 250 hPa above the southern USA during the study period.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 0322 Constituent sources and sinks;
- 0365 Troposphere: composition and chemistry;
- 0368 Troposphere: constituent transport and chemistry