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Summertime buildup and decay of lightning NOx and aged thunderstorm outflow above North America
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
Department of Regional and Global Pollution Issues, Norwegian Institute for Air Research, Kjeller, Norway
NASA Langley Research Center, Hampton, Virginia, USA
Science System and Applications, Inc., Hampton, Virginia, USA
Department of Chemistry and Department of Earth and Planetary Science, University of California, Berkeley, California, USA
Department of Chemistry and Department of Earth and Planetary Science, University of California, Berkeley, California, USA
Department of Chemistry and Department of Earth and Planetary Science, University of California, Berkeley, California, USA
Department of Chemistry and Department of Earth and Planetary Science, University of California, Berkeley, California, USA
Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania, USA
Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania, USA
Laboratory for Air Pollution/Environmental Technology, Materials Science and Technology, EMPA, Dübendorf, Switzerland
Boeing Company, Seattle, Washington, USA
This study explores the upper tropospheric anticyclone above eastern North America and its influence on the summertime buildup and decay of lightning NOx (LNOx) and thunderstorm outflow. LNOx transport is simulated with a particle dispersion model that releases a LNOx tracer from the locations of millions of cloud-to-ground lightning flashes during May–September 2004 and 2006. On average, upper tropospheric zonal flow in May transitions to a closed anticyclone above northern Mexico and the southern United States in July that strengthens in August and rapidly decays in September. Concentrations of the LNOx tracer reach a maximum above the southern United States and Gulf of Mexico in July and August. Fourteen study sites across North America exhibit high day-to-day variability of the LNOx tracer in the upper troposphere during summer, with the sites most heavily influenced by the North American summer monsoon having the greatest background concentrations. During late spring and September the western sites have low concentrations with little variability. In general, the west coast sites plus Barbados have the most aged thunderstorm outflow, while the east coast sites have the least aged outflow. More than 80% of summertime upper tropospheric NOx above the eastern United States is produced by lightning. To produce the best available observation-based view of upper troposphere NOx above North America, measurements from six aircraft campaigns are combined in a single composite plot. The modeled upper tropospheric NOx matches the general continental-scale distribution of NOx in the composite plot, supporting the dominant role of LNOx in the simulations.
Received 18 April 2008; accepted 8 October 2008; published 9 January 2009.
Citation: (2009), Summertime buildup and decay of lightning NOx and aged thunderstorm outflow above North America, J. Geophys. Res., 114, D01101, doi:10.1029/2008JD010293.
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