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| Titel |
Sensitivity analysis of the potential impact of discrepancies in stratosphere–troposphere exchange on inferred sources and sinks of CO2 |
| VerfasserIn |
F. Deng, D. B. A. Jones, T. W. Walker, M. Keller, K. W. Bowman, D. K. Henze, R. Nassar, E. A. Kort, S. C. Wofsy, K. A. Walker, A. E. Bourassa, D. A. Degenstein |
| 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. 20 ; Nr. 15, no. 20 (2015-10-23), S.11773-11788 |
| Datensatznummer |
250120116
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| Publikation (Nr.) |
 copernicus.org/acp-15-11773-2015.pdf |
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| Zusammenfassung |
| The upper troposphere and lower stratosphere (UTLS)
represents a transition region between the more dynamically active
troposphere and more stably stratified stratosphere. The region is
characterized by strong gradients in the distribution of long-lived tracers,
whose representation in models is sensitive to discrepancies in transport. We
evaluate the GEOS-Chem model in the UTLS using carbon dioxide (CO2) and
ozone (O3) observations from the HIAPER (The High-Performance
Instrumented Airborne Platform for Environmental Research) Pole-to-Pole
Observations (HIPPO) campaign in March 2010. GEOS-Chem CO2/O3
correlation suggests that there is a discrepancy in mixing across the
tropopause in the model, which results in an overestimate of CO2 and an
underestimate of O3 in the Arctic lower stratosphere. We assimilate
stratospheric O3 data from the Optical Spectrograph and InfraRed Imager
System (OSIRIS) and use the assimilated O3 fields together with the
HIPPO CO2/O3 correlations to obtain an adjustment to the modeled
CO2 profile in the Arctic UTLS (primarily between the 320 and 360 K
isentropic surfaces). The HIPPO-derived adjustment corresponds to a sink of
0.60 Pg C for March–August 2010 in the Arctic. Imposing this adjustment
results in a reduction in the CO2 sinks inferred from GOSAT observations
for temperate North America, Europe, and tropical Asia of 19, 13, and
49 %, respectively. Conversely, the inversion increased the source of
CO2 from tropical South America by 23 %. We find that the model also
underestimates CO2 in the upper tropical and subtropical troposphere.
Correcting for the underestimate in the model relative to HIPPO in the
tropical upper troposphere leads to a reduction in the source from tropical
South America by 77 %, and produces an estimated sink for tropical Asia
that is only 19 % larger than the standard inversion (without the imposed
source and sink). Globally, the inversion with the Arctic and tropical
adjustment produces a sink of −6.64 Pg C, which is consistent with the
estimate of −6.65 Pg C in the standard inversion. However, the standard
inversion produces a stronger northern land sink by 0.98 Pg C to account
for the CO2 overestimate in the high-latitude UTLS, suggesting that this
UTLS discrepancy can impact the latitudinal distribution of the inferred
sources and sinks. We find that doubling the model resolution from
4° × 5° to 2° × 2.5°
enhances the CO2 vertical gradient in the high-latitude UTLS, and
reduces the overestimate in CO2 in the extratropical lower stratosphere.
Our results illustrate that discrepancies in the CO2 distribution in the
UTLS can affect CO2 flux inversions and suggest the need for more
careful evaluation of model errors in the UTLS. |
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