 |
| Titel |
A new method for retrieval of the extinction coefficient of water clouds by using the tail of the CALIOP signal |
| VerfasserIn |
J. Li, Y. Hu, J. Huang, K. Stamnes, Y. Yi, S. Stamnes |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 6 ; Nr. 11, no. 6 (2011-03-29), S.2903-2916 |
| Datensatznummer |
250009529
|
| Publikation (Nr.) |
 copernicus.org/acp-11-2903-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
| A method is developed based on Cloud-Aerosol Lidar and Infrared Pathfinder
Satellite Observations (CALIPSO) level 1 attenuated backscatter profile data
for deriving the mean extinction coefficient of water droplets close to cloud
top. The method is applicable to low level (cloud top <2 km), opaque water
clouds in which the lidar signal is completely attenuated beyond about 100 m
of penetration into the cloud. The photo multiplier tubes (PMTs) of the
532 nm detectors (parallel and perpendicular polarizations) of the
Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) both exhibit a
non-ideal recovery of the lidar signal after striking a strongly
backscattering target (such as water cloud or surface). Therefore, the
effects of any transient responses of CALIOP on the attenuated backscatter
profile of the water cloud must first be removed in order to obtain a
reliable (validated) attenuated backscatter profile. Then, the slope of the
exponential decay of the validated water cloud attenuated backscatter
profile, and the multiple scattering factor are used for deriving the mean
extinction coefficient of low-level water cloud droplets close to cloud top.
This novel method was evaluated and compared with the previous method which
combined the cloud effective radius (3.7-μm) reported by MODIS
with the lidar depolarization ratios measured by CALIPSO to estimate the mean
extinction coefficient. Statistical results show that the extinction
coefficients derived by the new method based on CALIOP alone agree
reasonbably well with those obtained in the previous study using combined
CALIOP and MODIS data. The mean absolute relative difference in extinction
coefficient is about 13.4%. An important advantage of the new method is
that it can be used to derive the extinction coefficient also during
night time, and it is also applicable when multi-layered clouds are present.
Overall, the stratocumulus dominated regions experience larger day-night
differences which are all negative and seasonal. However, a contrary tendency
consisted in the global mean values. The global mean cloud water extinction
coefficients during different seasons range from 26 to 30 km−1, and the
differences between day and night time are all positive and small (about
1–2 km−1). In addition, the global mean layer-integrated
depolarization ratios of liquid water clouds during different seasons range
from 0.2 to 0.23, and the differences between day and night also are small,
about 0.01. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|