The Influence of the Polar Jet and Bermuda High on the Variability of Surface Ozone over the Eastern United States
Abstract:We investigated the meteorological drivers of daily variability of surface maximum daily 8-hour average (MDA8) ozone over 1980-2012 in summer and the implications of projected trends in these drivers over the 2000-2100 time horizon. We first applied Empirical Orthogonal Functions (EOF) analysis to 1980-2012 daily surface JJA ozone observations from the EPA Air Quality System and correlated the resulting EOFs with NCEP/NCAR Reanalysis meteorology. The first three leading EOF patterns describe (1) a broad decrease of ozone in the eastern US linked to a southward shift of the 500 hPa polar jet, (2) a north-south dipole pattern associated with the Bermuda High system when its western boundary extends along the East coast, and (3) an east-west dipole pattern linked to a westward shift of the Bermuda High, an enhanced low level jet in the Central Plains, and troughing of the polar jet in the Midwest. In the Midwest and Northeast, we found that the correlation between detrended JJA MDA8 ozone and polar jet frequency ranges between -0.75 and -0.86 over 1980-2012, depending on the time period selected. In the Southeast, the influence of Bermuda High on ozone variability depends on the location of its west edge. Westward movement increases the ozone only when the JJA Bermuda High west edge is located west of 87.5°W, while northward movement increases ozone in all years.
Using Coupled Model Intercomparison Project-Phase 5 (CMIP5) models, we found that the polar jet in the Northeast migrates poleward by ~1 degree and the Bermuda High west edge shifts westward by ~3 degree by 2100. The poleward shift of jet wind leads to a decrease of jet frequency in the Midwest and Northeast, resulting in a +2 ppbv increase of JJA ozone. This westward shift of the Bermuda High west edge enhances the Great Plains low level jet and strengthens the anticyclonic circulation in the Southeast. Our results imply that the climate penalty may increase JJA mean MDA8 ozone by 3-5 ppbv in the Southeast by 2100.