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Changing temperature inversion characteristics in the U.S. Southwest and relationships to large-scale atmospheric circulation

Bailey, A., T. Chase, J.J. Cassano, and D. Noone

2011, Journal of Applied Meteorology and Climatology, 50, 1307-1323, doi: 10.1175/2011JAMC2584.1.

Continental temperature inversions significantly influence air quality, yet little is known about their variability in frequency and intensity with time or sensitivity to dynamical changes with climate. Inversion statistics for six upper-air stations in the American Southwest are derived for the period 1994?2008 from radiosonde data reported by the Global Telecommunication System and National Climatic Data Center, which use different significant level standards. GTS data indicate low-level elevated inversions have increased in frequency at four of six sites, consistent with enhanced regional stagnation projected by models. NCDC data, in contrast, show remarkable declines in weak, near-surface inversions through 2001, indicating local surface conditions may counteract atmospheric dynamics in regulating inversion activity and air quality. To further test the sensitivity of inversion activity to climate, associations between wintertime inversion frequency and large-scale circulation are quantified using the self-organizing map technique. Twenty-four representative circulation patterns are derived from North American Regional Reanalysis 500-hPa geopotential height fields, and these patterns are correlated with inversion frequency at each site. Inversion activity in Salt Lake City, Utah and Albuquerque and Santa Teresa, New Mexico is found to correspond well with large-scale anticyclonic ridging, however sensitivities to large-scale circulation in Denver, Colorado and Flagstaff and Tucson, Arizona are weak. Denver stands out in exhibiting a higher percentage of near-surface inversions in winter than the other Southwestern sites. These findings indicate dynamical changes with climate will not uniformly influence inversions and hence urban air quality conditions in the American Southwest.