CloudSat Level 2-C Precipitation Column Algorithm
Entry ID:
Cloudsat_2C-PRECIP-COLUMN
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Summary
Abstract:
[Source: CloudSat Level 2-C Precipitation Column Algorithm Product Process Description and Interface Control Document, http://www.cloudsat.cira.colostate.edu/ICD/2C-PRECIP-COLUMN/2C-PREC... ] The basis of the work is outlined in Haynes et al. [1], and all quantitative and mathematical details may be obtained from this source. An overview of the ... physical basis of the retrieval follows.
The algorithm makes use of path integrated attenuation (PIA) due to hydrometeors as a geophysical measurement. The method depends on the well-behaved relationship between the backscatter cross section of the ocean surface, σ0 , and the wind speed, V at the ocean surface. Higher wind speeds cause greater roughening of the ocean surface, resulting in increased scattering of microwave radiation away from the radar receiver and a lower resulting surface backscatter cross section. The sea surface temperature (SST) of the ocean surface also influences the backscatter cross section through variation of the index of refraction. A database of observations of the surface backscatter cross section under clear-sky conditions, σclr , provides a background reference for the state of the surface when hydrometeors are absent. When cloud or rain is present, the observed backscatter cross section is reduced by hydrometeor attenuation. This reduction allows calculation of PIA given knowledge of the wind speed at the ocean surface (derived from a numerical model) and, to a lesser extent, the SST [2].
The unattenuated radar reflectivity, Zu , near the surface is closely related to the presence of rain; the higher Zu the more likely precipitation is occurring. Zu is the sum of the measured reflectivity, the PIA, and a component due to gaseous attenuation, G (determined from the ECMWF-AUX temperature and moisture profile).
Multiple scattering within the precipitating column can be significant for rainfall exceeding a few millimeter per hour [3], so Monte Carlo modeling is used to simulate the relationship between rainfall and observed PIA for various vertical profiles of precipitation. A model of the melting layer is also incorporated into the Monte Carlo calculations to better represent the transition from snow to rain. This melting layer model aims to treat the attenuating characteristics of melting snowflakes. The model follows snow (modeled through the discrete dipole approximation) falling through a melting layer and melting into rain, assuming a constant lapse rate, Γe , of 6 ◦ C km−1 .
Liquid or mixed precipitation layers are considered to extend to the height of the lowest continuous cloud layer, HCT L , as determined from the 2B-GEOPROF cloud mask, capped by the height of the freezing level, Hf , from ECMWF-AUX. The effects of purely frozen precipitation on PIA are only considered when a core of 10 dBZ of greater reflectivity extends through the freezing level, Hsig . When such a core is absent, melting is considered to start at the freezing level itself. The combination of HCT L , Hf , and Hsig allow determination of the total depth of all precipitation, Dtot , and liquid precipitation, Dliq . 
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Geographic Coverage
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Spatial coordinates
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N: 90.0
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S: -90.0
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E: 180.0
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W: -180.0
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Data Set Citation
Dataset Originator/Creator:
NASA and Colorado State University, Cooperative Institute for Research in the Atmosphere, CloudSat Data Processing Center
Dataset Release Place:
Fort Collins, CO, USA
Dataset Publisher:
CloudSat Data Processing Center
Online Resource:
http://www.cloudsat.cira.colostate.edu/dataSpecs.php?prodid=93
Access Constraints
Most of the CloudSat data and products will be made available to the CloudSat Science Team and other authorized users in the general science community, via a web-based data server during the on-orbit phase, and all CloudSat products will be sent to the Langley DAAC after the end of the operational phase.
Use Constraints
Always cite the data originator if you use this data.
Data Set Progress
COMPLETE
Distribution
Distribution Media:
Online (HTTP)
Fees:
No Fee (Registration Required)
Personnel
Role:
TECHNICAL CONTACT
Email:
cloudsat at cira.colostate.edu
Contact Address:
CloudSat Data Processing Center
Cooperative Institute for Research in the Atmosphere
Colorado State University
City:
Fort Collins
Province or State:
CO
Postal Code:
80523-1375
Country:
USA
Role:
DIF AUTHOR
Phone:
301-614-5126
Fax:
301-614-5268
Email:
Scott.A.Ritz at nasa.gov
Contact Address:
NASA Goddard Space Flight Center
Global Change Master Directory
City:
Greenbelt
Province or State:
Maryland
Postal Code:
20771
Country:
USA
Creation and Review Dates
DIF Creation Date:
2009-10-28
Last DIF Revision Date:
2011-01-21
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