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| Titel |
Influence of synoptic patterns on surface ozone variability over the eastern United States from 1980 to 2012 |
| VerfasserIn |
L. Shen, L. J. Mickley, A. P. K. Tai |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 19 ; Nr. 15, no. 19 (2015-10-01), S.10925-10938 |
| Datensatznummer |
250120068
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| Publikation (Nr.) |
 copernicus.org/acp-15-10925-2015.pdf |
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| Zusammenfassung |
| We investigate the effect of synoptic-scale weather patterns on observed
maximum daily 8-hour average (MDA8) surface ozone over the eastern United
States during 1980–2012 in summer (June–August, JJA). Zonally averaged, the
relative standard deviation (SD) of daily MDA8 JJA ozone shows a bimodal
structure, with peaks at 28–32 and 40–45° N,
and we show that those regions are most influenced by the
variability in daily weather. We apply empirical orthogonal functions (EOFs)
to understand the causes of this structure. The first three leading EOF
patterns explain 53 % of the total variance in detrended surface ozone,
displaying (1) a widespread response of ozone in the eastern United States
associated with north–south movement of jet wind latitude, (2) a north–south
pattern linked to the Bermuda High system when its west boundary is located
along the east coast, and (3) an east–west pattern characteristic of a
westward extension of the Bermuda High and an enhanced Great Plains low
level jet (GPLLJ). The northern peak of ozone relative SD can be explained
by polar jet activity, while the southern peak appears related to
variability in the Bermuda High and GPLLJ. We define a new metric polar jet
frequency as the total number of days the jet traverses the Midwest and
northeast each summer. In the Midwest and northeast, we find that the
correlation coefficient r between detrended mean JJA MDA8 ozone and the polar
jet frequency ranges between −0.76 and −0.93 over 1980–2012 depending on the
time period selected, suggesting that polar jet frequency could provide a
simple metric to predict ozone variability in future climate regimes. In the
southeast, the influence of the Bermuda High on mean JJA MDA8 ozone depends
on the location of its west edge. For those summers when the average
position of the west edge is located west of ~ 85.4°
W, a westward shift in the Bermuda High west edge increases ozone in the
southeast by ~ 1 ppbv deg−1 in longitude. For all
summers, a northward shift in the Bermuda High west edge increases ozone
over the entire eastern United States by 1–2 ppbv deg−1 in latitude.
None of the synoptic patterns identified in this study show a significant
trend from 1980 to 2012, confirming that the observed ozone decrease over
the eastern United States during this time period is mainly caused by
emission controls. Our work underscores the impact of synoptic patterns on
ozone variability and suggests that a combination of changing local and
synoptic meteorology together with trends in background ozone will determine
the influence of climate change on US ozone air quality in future decades.
The observed relationships of US surface ozone and synoptic circulations
in this study can also be used to validate models of atmospheric chemistry. |
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