 |
| Titel |
Coupling aerosol-cloud-radiative processes in the WRF-Chem model: Investigating the radiative impact of elevated point sources |
| VerfasserIn |
E. G. Chapman, W. I. Gustafson, R. C. Easter, J. C. Barnard, S. J. Ghan, M. S. Pekour, J. D. Fast |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 9, no. 3 ; Nr. 9, no. 3 (2009-02-06), S.945-964 |
| Datensatznummer |
250006822
|
| Publikation (Nr.) |
 copernicus.org/acp-9-945-2009.pdf |
|
|
|
|
|
| Zusammenfassung |
| The local and regional influence of elevated point sources on summertime
aerosol forcing and cloud-aerosol interactions in northeastern North America
was investigated using the WRF-Chem community model. The direct effects of
aerosols on incoming solar radiation were simulated using existing modules
to relate aerosol sizes and chemical composition to aerosol optical
properties. Indirect effects were simulated by adding a prognostic treatment
of cloud droplet number and adding modules that activate aerosol particles
to form cloud droplets, simulate aqueous-phase chemistry, and tie a
two-moment treatment of cloud water (cloud water mass and cloud droplet
number) to precipitation and an existing radiation scheme. Fully interactive
feedbacks thus were created within the modified model, with aerosols
affecting cloud droplet number and cloud radiative properties, and clouds
altering aerosol size and composition via aqueous processes, wet scavenging,
and gas-phase-related photolytic processes. Comparisons of a baseline
simulation with observations show that the model captured the general
temporal cycle of aerosol optical depths (AODs) and produced clouds of
comparable thickness to observations at approximately the proper times and
places. The model overpredicted SO2 mixing ratios and PM2.5 mass, but
reproduced the range of observed SO2 to sulfate aerosol ratios,
suggesting that atmospheric oxidation processes leading to aerosol sulfate
formation are captured in the model. The baseline simulation was compared to
a sensitivity simulation in which all emissions at model levels above the
surface layer were set to zero, thus removing stack emissions.
Instantaneous, site-specific differences for aerosol and cloud related
properties between the two simulations could be quite large, as removing
above-surface emission sources influenced when and where clouds formed
within the modeling domain. When summed spatially over the finest resolution
model domain (the extent of which corresponds to the typical size of a
single global climate model grid cell) and temporally over a three day
analysis period, total rainfall in the sensitivity simulation increased by
31% over that in the baseline simulation. Fewer optically thin clouds,
arbitrarily defined as a cloud exhibiting an optical depth less than 1,
formed in the sensitivity simulation. Domain-averaged AODs dropped from 0.46
in the baseline simulation to 0.38 in the sensitivity simulation. The
overall net effect of additional aerosols attributable to primary
particulates and aerosol precursors from point source emissions above the
surface was a domain-averaged reduction of 5 W m−2 in mean daytime
downwelling shortwave radiation. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|