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| Titel |
Assessing regional scale predictions of aerosols, marine stratocumulus, and their interactions during VOCALS-REx using WRF-Chem |
| VerfasserIn |
Q. Yang, W. I. Jr. Gustafson, J. D. Fast, H. Wang, R. C. Easter, H. Morrison, Y.-N. Lee, E. G. Chapman, S. N. Spak, M. A. Mena-Carrasco |
| 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 ; 11, no. 23 ; Nr. 11, no. 23 (2011-12-02), S.11951-11975 |
| Datensatznummer |
250010231
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| Publikation (Nr.) |
 copernicus.org/acp-11-11951-2011.pdf |
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| Zusammenfassung |
| This study assesses the ability of the recent chemistry version (v3.3) of
the Weather Research and Forecasting (WRF-Chem) model to simulate boundary
layer structure, aerosols, stratocumulus clouds, and energy fluxes over the
Southeast Pacific Ocean. Measurements from the VAMOS
Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) and
satellite retrievals (i.e., products from the MODerate resolution Imaging
Spectroradiometer (MODIS), Clouds and Earth's Radiant Energy System
(CERES), and GOES-10) are used for this assessment. The Morrison double-moment microphysics scheme is
newly coupled with interactive aerosols in the model. The 31-day (15 October–16 November 2008) WRF-Chem simulation with aerosol-cloud interactions
(AERO hereafter) is also compared to a simulation (MET hereafter) with fixed
cloud droplet number concentrations in the microphysics scheme and simplified cloud and aerosol
treatments in the radiation scheme. The well-simulated aerosol quantities
(aerosol number, mass composition and optical properties), and the inclusion
of full aerosol-cloud couplings lead to significant improvements in many
features of the simulated stratocumulus clouds: cloud optical properties and
microphysical properties such as cloud top effective radius, cloud water
path, and cloud optical thickness. In addition to accounting for the aerosol
direct and semi-direct effects, these improvements feed back to the
simulation of boundary-layer characteristics and energy budgets.
Particularly, inclusion of interactive aerosols in AERO strengthens the
temperature and humidity gradients within the capping inversion layer and
lowers the marine boundary layer (MBL) depth by 130 m from that of the MET
simulation. These differences are associated with weaker entrainment and
stronger mean subsidence at the top of the MBL in AERO. Mean
top-of-atmosphere outgoing shortwave fluxes, surface latent heat, and
surface downwelling longwave fluxes are in better agreement with
observations in AERO, compared to the MET simulation. Nevertheless, biases
in some of the simulated meteorological quantities (e.g., MBL temperature
and humidity) and aerosol quantities (e.g., underestimations of accumulation mode
aerosol number) might affect simulated stratocumulus and energy fluxes over
the Southeastern Pacific, and require further investigation. The
well-simulated timing and outflow patterns of polluted and clean episodes
demonstrate the model's ability to capture daily/synoptic scale variations
of aerosol and cloud properties, and suggest that the model is suitable for
studying atmospheric processes associated with pollution outflow over the
ocean. The overall performance of the regional model in simulating mesoscale
clouds and boundary layer properties is encouraging and suggests that
reproducing gradients of aerosol and cloud droplet concentrations and
coupling cloud-aerosol-radiation processes are important when simulating
marine stratocumulus over the Southeast Pacific. |
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