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| Titel |
Cloud sensitivity studies for stratospheric and lower mesospheric ozone profile retrievals from measurements of limb-scattered solar radiation |
| VerfasserIn |
T. Sonkaew, V. V. Rozanov, C. Savigny, A. Rozanov, H. Bovensmann, J. P. Burrows |
| 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 ; 2, no. 2 ; Nr. 2, no. 2 (2009-11-04), S.653-678 |
| Datensatznummer |
250000575
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| Publikation (Nr.) |
 copernicus.org/amt-2-653-2009.pdf |
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| Zusammenfassung |
| Clouds in the atmosphere play an important role in reflection,
absorption and transmission of solar radiation and thus affect trace
gas retrievals. The main goal of this paper is to examine the
sensitivity of stratospheric and lower mesospheric ozone retrievals
from limb-scattered radiance measurements to clouds using the
SCIATRAN radiative transfer model and retrieval package. The
retrieval approach employed is optimal estimation, and the
considered clouds are vertically and horizontally homogeneous.
Assuming an aerosol-free atmosphere and Mie phase functions for
cloud particles, we compute the relative error of ozone profile
retrievals in a cloudy atmosphere if clouds are neglected in the
retrieval. To access altitudes from the lower stratosphere up to the
lower mesosphere, we combine the retrievals in the Chappuis and
Hartley ozone absorption bands. We find significant cloud
sensitivity of the limb ozone retrievals in the Chappuis bands at
lower stratospheric altitudes. The relative error in the retrieved
ozone concentrations gradually decreases with increasing altitude
and becomes negligible above approximately 40 km. The parameters
with the largest impact on the ozone retrievals are cloud optical
thickness, ground albedo and solar zenith angle. Clouds with
different geometrical thicknesses or different cloud altitudes have
a similar impact on the ozone retrievals for a given cloud optical
thickness value, if the clouds are outside the field of view of the
instrument. The effective radius of water droplets has a small
influence on the error, i.e., less than 0.5% at altitudes above the
cloud top height. Furthermore, the impact of clouds on the ozone
profile retrievals was found to have a rather small dependence on
the solar azimuth angle (less than 1% for all possible azimuth
angles). For the most frequent cloud types, the total error is below
6% above 15 km altitude, if clouds are completely neglected in the
retrieval. Neglecting clouds in the ozone profile retrievals
generally leads to a low bias for a low ground albedo and to a high
bias for a high ground albedo, assuming that the ground albedo is
well known. |
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