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| Titel |
A comprehensive numerical study of aerosol-cloud-precipitation interactions in marine stratocumulus |
| VerfasserIn |
Y.-C. Chen, L. Xue, Z. J. Lebo, H. Wang, R. M. Rasmussen, J. H. Seinfeld |
| 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. 18 ; Nr. 11, no. 18 (2011-09-21), S.9749-9769 |
| Datensatznummer |
250010093
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| Publikation (Nr.) |
 copernicus.org/acp-11-9749-2011.pdf |
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| Zusammenfassung |
| Three-dimensional large-eddy simulations (LES) with detailed bin-resolved
microphysics are performed to explore the diurnal variation of marine
stratocumulus (MSc) clouds under clean and polluted conditions. The
sensitivity of the aerosol-cloud-precipitation interactions to variation of
sea surface temperature, free tropospheric humidity, large-scale divergence
rate, and wind speed is assessed. The comprehensive set of simulations
corroborates previous studies that (1) with moderate/heavy drizzle, an
increase in aerosol leads to an increase in cloud thickness; and (2) with
non/light drizzle, an increase in aerosol results in a thinner cloud, due to
the pronounced effect on entrainment. It is shown that for higher SST,
stronger large-scale divergence, drier free troposphere, or lower wind speed,
the cloud thins and precipitation decreases. The sign and magnitude of the
Twomey effect, droplet dispersion effect, cloud thickness effect, and cloud
optical depth susceptibility to aerosol perturbations (i.e., change in cloud
optical depth to change in aerosol number concentration) are evaluated by LES
experiments and compared with analytical formulations. The Twomey effect
emerges as dominant in total cloud optical depth susceptibility to aerosol
perturbations. The dispersion effect, that of aerosol perturbations on the
cloud droplet size spectrum, is positive (i.e., increase in aerosol leads to
spectral narrowing) and accounts for 3% to 10% of the total cloud
optical depth susceptibility at nighttime, with greater influence in heavier
drizzling clouds. The cloud thickness effect is negative (i.e., increase in
aerosol leads to thinner cloud) for non/light drizzling cloud and positive
for a moderate/heavy drizzling clouds; the cloud thickness effect contributes
5% to 22% of the nighttime total cloud susceptibility. Overall, the
total cloud optical depth susceptibility ranges from ~0.28 to 0.53 at
night; an increase in aerosol concentration enhances cloud optical depth,
especially with heavier precipitation and in a more pristine environment.
During the daytime, the range of magnitude for each effect is more variable
owing to cloud thinning and decoupling. The good agreement between LES
experiments and analytical formulations suggests that the latter may be
useful in evaluations of the total cloud susceptibility. The ratio of the
magnitude of the cloud thickness effect to that of the Twomey effect depends
on cloud base height and cloud thickness in unperturbed (clean) clouds. |
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