Atmos. Chem. Phys. Discuss., 8, 12253-12282, 2008
© Author(s) 2008. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Sensitivity of US air quality to mid-latitude cyclone frequency and implications of 1980–2006 climate change
E. M. Leibensperger, L. J. Mickley, and D. J. Jacob
School of Engineering and Applied Sciences, Harvard Univ., Cambridge, Massachusetts, USA

Abstract. We show that the frequency of summertime mid-latitude cyclones tracking across eastern North America at 40°–50° N (the southern climatological storm track) is a strong predictor of stagnation and ozone pollution episodes in the eastern United States. The NCEP/NCAR Reanalysis, going back to 1948, shows a significant long-term decline in the number of summertime mid-latitude cyclones in that track starting in 1980 (−0.15 a-1). The more recent but shorter NCEP/DOE Reanalysis (1979–2006) shows similar interannual variability in cyclone frequency but no significant long-term trend. A GISS general circulation model (GCM) simulation including historical forcing by greenhouse gases reproduces the cyclone trend seen in the NCEP/NCAR data. Such a long-term decrease in mid-latitude cyclone frequency over the 1980–2006 period would have offset by about a factor of 2 the ozone air quality gains from reductions in anthropogenic emissions in the northeastern United States. We find that if mid-latitude cyclone frequency had not declined, the northeastern US would have been largely compliant with the ozone air quality standard by 2001. Mid-latitude cyclone frequency is expected to decrease further over the coming decades in response to greenhouse warming and this trend needs to be considered in air quality management.

Citation: Leibensperger, E. M., Mickley, L. J., and Jacob, D. J.: Sensitivity of US air quality to mid-latitude cyclone frequency and implications of 1980–2006 climate change, Atmos. Chem. Phys. Discuss., 8, 12253-12282, doi:10.5194/acpd-8-12253-2008, 2008.
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