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

Abstract

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 (GTS) and National ClimaticData Center (NCDC), which use different significant level standards. GTS data indicate that low-level elevated inversions have increased in frequency at four of six sites, consistent with enhanced regional stagnation projected bymodels. NCDCdata, 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 largescale circulation are quantified using the self-organizingmap technique. Twenty-four representative circulation patterns are derived from North American Regional Reanalysis (NARR) 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 inwinter than the other southwestern sites. These findings indicate that dynamical changes with climate will not uniformly influence inversions and hence urban air quality conditions in the American Southwest. © 2011 American Meteorological Society.