Atmospheric Chemistry and Physics Discussions
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10.5194/acpd-7-12035-2007
http://www.atmos-chem-phys-discuss.net/7/12035/2007/
http://www.atmos-chem-phys-discuss.net/7/12035/2007/acpd-7-12035-2007.html
http://www.atmos-chem-phys-discuss.net/7/12035/2007/acpd-7-12035-2007.pdf
12035
12066
2007-08-14
Comparison between the first Odin-SMR, Aura MLS and CloudSat retrievals of cloud ice mass in the upper tropical troposphere
P. Eriksson
patrick.eriksson@chalmers.se
M. Ekström
B. Rydberg
D. L. Wu
R. T. Austin
D. P. Murtagh
Department of Radio and Space Science, Chalmers University of Technology, Gothenburg, Sweden
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA
Emerging microwave satellite techniques are expected to provide
improved global measurements of cloud ice mass. CloudSat, Aura MLS
and Odin-SMR fall into this category and first cloud ice retrievals
from these instruments are compared. The comparison is made for
partial ice water columns above 12 km, following the SMR retrieval
product. None of the instruments shows significant false cloud
detections and a consistent view of the geographical distribution of
cloud ice is obtained, but differences on the absolute levels exist.
CloudSat gives the lowest values, with an overall mean of 2.12 g/m<sup>2</sup>.
A comparable mean for MLS is 4.30 g/m<sup>2</sup>. This relatively high mean
can be an indication of overestimation of the vertical altitude of
cloud ice by the MLS retrievals. The vertical response of SMR has
also some uncertainty, but this does not affect the comparison
between MLS and CloudSat. SMR observations are sensitive to cloud
inhomogeneities inside the footprint and some compensation is
required. Results in good agreement with CloudSat, both in regard of
the mean and probability density functions, are obtained for a weak
compensation, while a simple characterisation of the effect
indicates the need for stronger compensation. The SMR mean was found
to be 1.89/2.62/4.10 g/m<sup>2</sup> for no/selected/strongest compensation,
respectively. Assumptions about the particle size distribution are a
consideration for all three instruments, and constitute the
dominating retrieval uncertainty for CloudSat. The comparison
indicates a retrieval accuracy of about 40% (3.1±1.2 g/m<sup>2</sup>).
This number is already very small compared to uncertainties of cloud
ice parametrisation in atmospheric models, but can be decreased
further through a better understanding of main retrieval error
sources.
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