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| Titel |
Estimating drizzle drop size and precipitation rate using two-colour lidar measurements |
| VerfasserIn |
C. D. Westbrook, R. J. Hogan, E. J. O'Connor, A. J. Illingworth |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 3, no. 3 ; Nr. 3, no. 3 (2010-06-09), S.671-681 |
| Datensatznummer |
250001113
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| Publikation (Nr.) |
 copernicus.org/amt-3-671-2010.pdf |
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| Zusammenfassung |
A method to estimate the size and liquid water content of drizzle drops using
lidar measurements at two wavelengths is described. The method exploits the
differential absorption of infrared light by liquid water at 905 nm and
1.5 μm, which leads to a different backscatter cross section for
water drops larger than ≈50 μm. The ratio of backscatter
measured from drizzle samples below cloud base at these two wavelengths (the
colour ratio) provides a measure of the median volume drop diameter D0.
This is a strong effect: for D0=200 μm, a colour ratio of
≈6 dB is predicted. Once D0 is known, the measured
backscatter at 905 nm can be used to calculate the liquid water content
(LWC) and other moments of the drizzle drop distribution.
The method is applied to observations of drizzle falling from stratocumulus
and stratus clouds. High resolution (32 s, 36 m) profiles of D0, LWC and
precipitation rate R are derived. The main sources of error in the
technique are the need to assume a value for the dispersion parameter μ
in the drop size spectrum (leading to at most a 35% error in R) and the
influence of aerosol returns on the retrieval (≈10% error in R
for the cases considered here). Radar reflectivities are also computed from
the lidar data, and compared to independent measurements from a colocated
cloud radar, offering independent validation of the derived drop size
distributions. |
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