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| Titel |
Aircraft millimeter-wave passive sensing of cloud liquid water and water vapor during VOCALS-REx |
| VerfasserIn |
P. Zuidema, D. Leon, A. Pazmany, M. Cadeddu |
| 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 ; 12, no. 1 ; Nr. 12, no. 1 (2012-01-05), S.355-369 |
| Datensatznummer |
250010439
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| Publikation (Nr.) |
 copernicus.org/acp-12-355-2012.pdf |
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| Zusammenfassung |
| Routine liquid water path measurements and water vapor path are valuable for
process studies of the cloudy marine boundary layer and for the assessment of
large-scale models. The VOCALS Regional Experiment respected this goal by
including a small, inexpensive, upward-pointing millimeter-wavelength passive
radiometer on the fourteen research flights of the NCAR C-130 plane, the
G-band (183 GHz) Vapor Radiometer (GVR). The radiometer permitted
above-cloud retrievals of the free-tropospheric water vapor path (WVP).
Retrieved free-tropospheric (above-cloud) water vapor paths possessed a
strong longitudinal gradient, with off-shore values of one to two mm and
near-coastal values reaching ten mm. The VOCALS-REx free troposphere was
drier than that of previous years. Cloud liquid water paths (LWPs) were
retrieved from the sub-cloud and cloudbase aircraft legs through a
combination of the GVR, remotely-sensed cloud boundary information,
and in-situ thermodynamic data. The absolute
(between-leg) and relative (within-leg) accuracy of the LWP retrievals at
1 Hz (~100 m) resolution was estimated at 20 g m−2 and
3 g m−2 respectively for well-mixed conditions, and 25 g m−2
absolute uncertainty for decoupled conditions where the input WVP
specification was more uncertain. Retrieved liquid water paths matched
adiabatic values derived from coincident cloud thickness measurements
exceedingly well. A significant contribution of the GVR dataset was the
extended information on the thin clouds, with 62 % (28 %) of the
retrieved LWPs <100 (40) g m−2. Coastal LWPs values were lower than
those offshore. For the four dedicated 20° S flights, the mean
(median) coastal LWP was 67 (61) g m−2, increasing to 166
(120) g m−2 1500 km offshore. The overall LWP cloud fraction from
thirteen research flights was 63 %, higher than that of adiabatic LWPs at
40 %, but lower than the lidar-determined cloud cover of 85 %, further
testifying to the frequent occurrence of thin clouds. |
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