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| Titel |
Ice hydrometeor profile retrieval algorithm for high-frequency microwave radiometers: application to the CoSSIR instrument during TC4 |
| VerfasserIn |
K. F. Evans, J. R. Wang, D. O'C Starr, G. Heymsfield, L. Li, L. Tian, R. P. Lawson, A. J. Heymsfield, A. Bansemer |
| 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 ; 5, no. 9 ; Nr. 5, no. 9 (2012-09-25), S.2277-2306 |
| Datensatznummer |
250003091
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| Publikation (Nr.) |
 copernicus.org/amt-5-2277-2012.pdf |
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| Zusammenfassung |
| A Bayesian algorithm to retrieve profiles of cloud ice
water content (IWC), ice particle size (Dme), and relative
humidity from millimeter-wave/submillimeter-wave radiometers is
presented. The first part of the algorithm prepares an a priori file
with cumulative distribution functions (CDFs) and empirical orthogonal
functions (EOFs) of profiles of temperature, relative humidity, three
ice particle parameters (IWC, Dme, distribution width), and
two liquid cloud parameters. The a priori CDFs and EOFs are derived
from CloudSat radar reflectivity profiles and associated ECMWF
temperature and relative humidity profiles combined with three cloud
microphysical probability distributions obtained from in situ cloud
probes. The second part of the algorithm uses the CDF/EOF file to
perform a Bayesian retrieval with a hybrid technique that uses Monte
Carlo integration (MCI) or, when too few MCI cases match the
observations, uses optimization to maximize the posterior probability
function. The very computationally intensive Markov chain Monte Carlo
(MCMC) method also may be chosen as a solution method. The radiative
transfer model assumes mixtures of several shapes of randomly oriented
ice particles, and here random aggregates of spheres, dendrites, and
hexagonal plates are used for tropical convection. A new physical model
of stochastic dendritic snowflake aggregation is developed. The
retrieval algorithm is applied to data from the Compact Scanning
Submillimeter-wave Imaging Radiometer (CoSSIR) flown on the ER-2
aircraft during the Tropical Composition, Cloud and Climate Coupling
(TC4) experiment in 2007. Example retrievals with error bars are shown
for nadir profiles of IWC, Dme, and relative humidity, and
nadir and conical scan swath retrievals of ice water path and average
Dme. The ice cloud retrievals are evaluated by retrieving
integrated 94 GHz backscattering from CoSSIR for comparison with the
Cloud Radar System (CRS) flown on the same aircraft. The rms difference
in integrated backscattering is around 3 dB over a 30 dB range. A
comparison of CoSSIR retrieved and CRS measured reflectivity shows that
CoSSIR has the ability to retrieve low-resolution ice cloud profiles in
the upper troposphere. |
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