Publication Date:
2008-06-24
Description:
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.
Electronic ISSN:
1680-7375
Topics:
Geosciences
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