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| Titel |
Transport pathways of CO in the African upper troposphere during the monsoon season: a study based upon the assimilation of spaceborne observations |
| VerfasserIn |
B. Barret, P. Ricaud, C. Mari, J.-L. Attié, N. Bousserez, B. Josse, E. Flochmoën, N. J. Livesey, S. Massart, V.-H. Peuch, A. Piacentini, B. Sauvage, V. Thouret, J.-P. Cammas |
| 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 ; 8, no. 12 ; Nr. 8, no. 12 (2008-06-26), S.3231-3246 |
| Datensatznummer |
250006228
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| Publikation (Nr.) |
 copernicus.org/acp-8-3231-2008.pdf |
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| Zusammenfassung |
| The transport pathways of carbon monoxide (CO) in the African Upper
Troposphere (UT) during the West African Monsoon (WAM) is investigated
through the assimilation of CO observations by the Aura Microwave Limb
Sounder (MLS) in the MOCAGE Chemistry Transport Model (CTM). The assimilation
setup, based on a 3-D First Guess at Assimilation Time (3-D-FGAT) variational
method is described. Comparisons between the assimilated CO fields and
in situ airborne observations from the MOZAIC program between Europe
and both Southern Africa and Southeast Asia show an overall good agreement
around the lowermost pressure level sampled by MLS (~215 hPa). The 4-D
assimilated fields averaged over the month of July 2006 have been used to
determine the main dynamical processes responsible for the transport of CO in
the African UT. The studied period corresponds to the second AMMA (African
Monsoon Multidisciplinary Analyses) aircraft campaign. At 220 hPa, the CO
distribution is characterized by a latitudinal maximum around 5° N
mostly driven by convective uplift of air masses impacted by biomass burning
from Southern Africa, uplifted within the WAM region and vented predominantly
southward by the upper branch of the winter hemisphere Hadley cell. Above
150 hPa, the African CO distribution is characterized by a broad maximum over
northern Africa. This maximum is mostly controlled by the large scale UT
circulation driven by the Asian Summer Monsoon (ASM) and characterized by the
Asian Monsoon Anticyclone (AMA) centered at 30° N and the Tropical
Easterly Jet (TEJ) on the southern flank of the anticyclone. Asian pollution
uplifted to the UT over large region of Southeast Asia is trapped within the
AMA and transported by the anticyclonic circulation over Northeast Africa.
South of the AMA, the TEJ is responsible for the tranport of CO-enriched air
masses from India and Southeast Asia over Africa. Using the high time
resolution provided by the 4-D assimilated fields, we give evidence that the
variability of the African CO distribution above 150 hPa and north of the WAM
region is mainly driven by the synoptic dynamical variability of both the AMA
and the TEJ. |
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