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| Titel |
Evaluation of stratocumulus cloud prediction in the Met Office forecast model during VOCALS-REx |
| VerfasserIn |
S. J. Abel, D. N. Walters, G. Allen |
| 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 ; 10, no. 21 ; Nr. 10, no. 21 (2010-11-10), S.10541-10559 |
| Datensatznummer |
250008882
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| Publikation (Nr.) |
 copernicus.org/acp-10-10541-2010.pdf |
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| Zusammenfassung |
| Observations in the subtropical southeast Pacific obtained during the
VOCALS-REx field experiment are used to evaluate the representation of
stratocumulus cloud in the Met Office forecast model and to identify key
areas where model biases exist. Marked variations in the large scale
structure of the cloud field were observed during the experiment on both
day-to-day and on diurnal timescales. In the remote maritime region the model
is shown to have a good representation of synoptically induced variability in
both cloud cover and marine boundary layer depth. Satellite observations show
a strong diurnal cycle in cloud fraction and liquid water path in the
stratocumulus with enhanced clearances of the cloud deck along the Chilean
and Peruvian coasts on certain days. The model accurately simulates the phase
of the diurnal cycle but is unable to capture the coastal clearing of cloud.
Observations along the 20° S latitude line show a gradual increase
in the depth of the boundary layer away from the coast. This trend is well
captured by the model (typical low bias of 200 m) although significant
errors exist at the coast where the model marine boundary layer is too
shallow and moist. Drizzle in the model responds to changes in liquid water
path in a manner that is consistent with previous ship-borne observations in
the region although the intensity of this drizzle is likely to be too high,
particularly in the more polluted coastal region where higher cloud droplet
number concentrations are typical. Another mode of variability in the cloud
field that the model is unable to capture are regions of pockets of open
cellular convection embedded in the overcast stratocumulus deck and an
example of such a feature that was sampled during VOCALS-REx is shown. |
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