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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 .

Related URL

Link: GET DATA

Description: Order CloudSAT data.

Geographic Coverage

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Spatial coordinates

N: 90.0

S: -90.0

E: 180.0

W: -180.0

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

Location Keywords

GEOGRAPHIC REGION > GLOBAL

Science Keywords

ATMOSPHERE > PRECIPITATION > HYDROMETEORS

ATMOSPHERE > PRECIPITATION > PRECIPITATION AMOUNT

ISO Topic Category

CLIMATOLOGY/METEOROLOGY/ATMOSPHERE

Platform

CLOUDSAT

Instrument

CLOUDSAT-CPR > CLOUDSAT CLOUD PROFILING RADAR

Project

EOS > Earth Observing System

CLOUDSAT > Cloud Satellite

ESSP > NASA Earth System Science Pathfinder

Quality Please check the data issues page:
http://www.cloudsat.cira.colostate.edu/dataIssues.php

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

Originating Center

CloudSat Data Processing Center

Data Center

CloudSat Data Processing Center, Cooperative Institute for Research in the Atmosphere, Colorado State University

Data Center URL: http://www.cloudsat.cira.colostate.edu/

Data Center Personnel
Name: CLOUDSAT DATA PROCESSING CENTER 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

Distribution

Distribution Media: Online (HTTP)

Fees: No Fee (Registration Required)

Personnel

CLOUDSAT DATA PROCESSING CENTER

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

SCOTT A. RITZ

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

Publications/References

Please view the NASA CloudSat Publications page:
http://cloudsat.atmos.colostate.edu/publications

Creation and Review Dates

DIF Creation Date: 2009-10-28

Last DIF Revision Date: 2011-01-21

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