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| Titel |
Methodology for evaluating lateral boundary conditions in the regional chemical transport model MATCH (v5.5.0) using combined satellite and ground-based observations |
| VerfasserIn |
E. Andersson, M. Kahnert, A. Devasthale |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 8, no. 11 ; Nr. 8, no. 11 (2015-11-19), S.3747-3763 |
| Datensatznummer |
250116668
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| Publikation (Nr.) |
 copernicus.org/gmd-8-3747-2015.pdf |
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| Zusammenfassung |
| Hemispheric transport of air pollutants can have a significant
impact on regional air quality, as well as on the effect of air pollutants on
regional climate. An accurate representation of hemispheric transport in
regional chemical transport models (CTMs) depends on the specification of the
lateral boundary conditions (LBCs). This study focuses on the methodology for
evaluating LBCs of two moderately long-lived trace gases, carbon monoxide (CO) and
ozone (O3), for the European model domain and over a 7-year period,
2006–2012. The method is based on combining the use of satellite
observations at the lateral boundary with the use of both satellite and in
situ ground observations within the model domain. The LBCs are generated by
the global European Monitoring and Evaluation Programme Meteorological Synthesizing Centre – West (EMEP MSC-W) model; they are evaluated at the lateral boundaries by
comparison with satellite observations of the Terra-MOPITT (Measurements Of Pollution In The Troposphere) sensor (CO)
and the Aura-OMI (Ozone Monitoring Instrument) sensor (O3). The LBCs from the global model lie well
within the satellite uncertainties for both CO and O3. The
biases increase below 700 hPa for both species. However, the
satellite retrievals below this height are strongly influenced by the a
priori data; hence, they are less reliable than at, e.g. 500 hPa.
CO is, on average, underestimated by the global model, while
O3 tends to be overestimated during winter, and underestimated during
summer. A regional CTM is run with (a) the validated monthly climatological
LBCs from the global model; (b) dynamical LBCs from the global model; and (c)
constant LBCs based on in situ ground observations near the domain boundary.
The results are validated against independent satellite retrievals from the
Aqua-AIRS (Atmospheric InfraRed Sounder) sensor at 500 hPa, and against in situ ground observations
from the Global Atmospheric Watch (GAW) network. It is found that (i) the use
of LBCs from the global model gives reliable in-domain results for O3
and CO at 500 hPa. Taking AIRS retrievals as a reference, the
use of these LBCs substantially improves spatial pattern correlations in the
free troposphere as compared to results obtained with fixed LBCs based on
ground observations. Also, the magnitude of the bias is reduced by the new
LBCs for both trace gases. This demonstrates that the validation methodology
based on using satellite observations at the domain boundary is sufficiently
robust in the free troposphere. (ii) The impact of the LBCs on ground
concentrations is significant only at locations in close proximity to the
domain boundary. As the satellite data near the ground mainly reflect the a
priori estimate used in the retrieval procedure, they are of little use for
evaluating the effect of LBCs on ground concentrations. Rather, the
evaluation of ground-level concentrations needs to rely on in situ ground
observations. (iii) The improvements of dynamic over climatological LBCs
become most apparent when using accumulated ozone over threshold 40 ppb (AOT40) as a metric. Also, when focusing on
ground observations taken near the inflow boundary of the model domain, one
finds that the use of dynamical LBCs yields a more accurate representation of
the seasonal variation, as well as of the variability of the trace gas
concentrations on shorter timescales. |
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