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| Titel |
The effects of springtime mid-latitude storms on trace gas composition determined from the MACC reanalysis |
| VerfasserIn |
K. E. Knowland, R. M. Doherty, K. I. Hodges |
| 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. 6 ; Nr. 15, no. 6 (2015-03-31), S.3605-3628 |
| Datensatznummer |
250119591
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| Publikation (Nr.) |
 copernicus.org/acp-15-3605-2015.pdf |
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| Zusammenfassung |
| The relationship between springtime air pollution transport of ozone
(O3) and carbon monoxide (CO) and mid-latitude cyclones is explored for
the first time using the Monitoring Atmospheric Composition and Climate
(MACC) reanalysis for the period 2003–2012. In this study, the most intense
spring storms (95th percentile) are selected for two regions, the North
Pacific (NP) and the North Atlantic (NA). These storms (∼60 storms over
each region) often track over the major emission sources of East Asia and
eastern North America. By compositing the storms, the distributions of
O3 and CO within a "typical" intense storm are examined. We compare
the storm-centered composite to background composites of "average
conditions" created by sampling the reanalysis data of the previous year to
the storm locations. Mid-latitude storms are found to redistribute
concentrations of O3 and CO horizontally and vertically throughout the
storm. This is clearly shown to occur through two main mechanisms: (1)
vertical lifting of CO-rich and O3-poor air isentropically, from near the
surface to the mid- to upper-troposphere in the region of the warm conveyor
belt; and (2) descent of O3-rich and CO-poor air isentropically in the
vicinity of the dry intrusion, from the stratosphere toward the
mid-troposphere. This can be seen in the composite storm's life cycle as the
storm intensifies, with area-averaged O3 (CO) increasing (decreasing)
between 200 and 500 hPa. The influence of the storm dynamics compared
to the background environment on the composition within an area around the
storm center at the time of maximum intensity is as follows. Area-averaged
O3 at 300 hPa is enhanced by 50 and 36% and by 11 and
7.6% at 500 hPa for the NP and NA regions, respectively.
In contrast, area-averaged CO at 300 hPa decreases by 12%
for NP and 5.5% for NA, and area-averaged CO at 500 hPa
decreases by 2.4% for NP while there is little change over the NA
region. From the mid-troposphere, O3-rich air is
clearly seen to be transported toward the surface, but the downward transport
of CO-poor air is not discernible due to the high levels of CO in the lower
troposphere. Area-averaged O3 is slightly higher at 1000 hPa
(3.5 and 1.8% for the NP and NA regions, respectively). There is
an increase of CO at 1000 hPa for the NP region (3.3%)
relative to the background composite and a~slight decrease in area-averaged
CO for the NA region at 1000 hPa (-2.7%). |
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