 |
| Titel |
On the relationship between the scattering phase function of cirrus and the atmospheric state |
| VerfasserIn |
A. J. Baran, K. Furtado, L.-C. Labonnote, S. Havemann, J.-C. Thelen, F. Marenco |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 2 ; Nr. 15, no. 2 (2015-01-30), S.1105-1127 |
| Datensatznummer |
250119356
|
| Publikation (Nr.) |
 copernicus.org/acp-15-1105-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| This is the first paper to investigate the relationship
between the shape of the scattering phase function of cirrus and the
relative humidity with respect to ice (RHi, using space-based solar
radiometric angle-dependent measurements. The relationship between
RHi and the complexity of ice crystals has been previously
studied using data from aircraft field campaigns and laboratory cloud
chambers. However, to the best of our knowledge, there have been no studies
to date that explore this relationship through the use of remotely sensed
space-based angle-dependent solar radiometric measurements. In this paper,
one case study of semi-transparent cirrus, which occurred on 25
January 2010 off the north-east coast of Scotland, is used to explore the
possibility of such a relationship. Moreover, for the first time, RHi
fields predicted by a high-resolution numerical weather prediction (NWP)
model are combined with satellite retrievals of ice crystal complexity. The
NWP model was initialised at midnight, on 25 January 2010, and the
mid-latitude RHi field was extracted from the NWP model at 13:00 UTC. At
about the same time, there was a PARASOL (Polarization and Anisotropy of Reflectance
for Atmospheric science coupled with Observations from a Lidar)
overpass, and the PARASOL swath covered the NWP-model-predicted RHi
field. The cirrus case was located over Scotland and the North Sea.
From the satellite channel based at 0.865 μm, the directionally
averaged and directional spherical albedos were retrieved between the
scattering angles of about 80 and 130°. An ensemble model of
cirrus ice crystals is used to predict phase functions that vary between
phase functions that exhibit optical features (referred to as pristine) and
featureless phase functions. For each of the PARASOL pixels, the phase
function that best minimised differences between the spherical albedos was
selected. This paper reports, for this one case study, an association
between the most featureless phase function model and the highest values of
NWP-predicted RHi (i.e. when RHi > 1.0). For pixels
associated with NWP-model-predicted RHi < 1, it was impossible
to generally discriminate between phase function models at the 5%
significance level. It is also shown that the NWP model prediction of the
vertical profile of RHi is in good agreement with dropsonde, in situ
measurements and independent aircraft-based physical retrievals of RHi.
Furthermore, the NWP model prediction of the cirrus cloud-top height and its
vertical extent is also found to be in good agreement with aircraft-based
lidar measurements. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|