CloudSat Reflectivity-Height Histogram Data Product

Roger Marchand (University of Washington)

 

Description:

Launched in late April 2006, the CloudSat satellite carries on board a 94 GHz cloud radar. The satellite has for much (but not all) of its life been orbiting in formation with other NASA spacecraft in the A-Train, in a sun synchronous orbit with an equator crossing time of 0130/1330 local time on the ascending/descending node. The radar is near-nadir pointing (it does not scan) and probes the vertical structure of clouds and precipitation with a 1.4 km across-track by 1.8 km along-track footprint along the direction of flight, essentially creating a cross-section or curtain of observed radar reflectivity. The radar has a range resolution of approximately 480 m, and the return power is oversampled with a range gate spacing of about 240 m (http://cloudsat.atmos.colostate.edu).

The CloudSat Reflectivity-Height Histogram product (also known by the CMIP variable name cfadDbze94) contains 2D histograms (joint distributions) of the CloudSat observed radar reflectivity factor (in dBZe) with altitude above mean sea level, as depicted in the figure to the left. The data are monthly composites and stored on a simple 2 x 2 degree fixed latitude by longitude grid, and using a vertical (altitude) grid with 480 m vertical spacing. The product is generated from the Level 2 GEOPROF product (Marchand et al. 2008, DOI: 10.1175/2007JTECHA1006.1).

 

Example of plot:

cfaddBZe_example_Roger.png

 

Data access:

Details on the histogram construction and dataset variables are given in the Data Description and Quality Statement. This most recent version of the histogram product was produced in March 2019 (and is based on GeoProf version P1 R05). These data are available HERE via ftp. (Older versions of the data are available in the parent directory).

The radar had an estimated minimum detectable signal of about -30.5 dBZe at the start of the mission, with a sensitivity that is now approaching -26 dBZ. The impact of sensitivity changes is generally small. Nonetheless, a "constant sensitivity" version of these data (more suitable for trend and variability studies) is in development but is not yet available.

More importantly, users should be aware that on April 17th 2011, CloudSat suffered a battery anomaly that resulted in CloudSat being out of the A-Train for a period of about 1 year. ONLY data collected while CloudSat was in the A-Train are included in the present dataset. CloudSat is no longer in the A-Train and will not return. Users interested in data collected during periods outside the A-Train should contact Roger Marchand.

Further, since the 2011 battery anomaly the CloudSat radar has only be able to operate during daylight conditions. The current Version 5 dataset includes data subset by day and night conditions, and includes a variety of data flags to help users navigate how to use the data. Details are given in the Data Description and Quality Statement (link above) and we strongly encourage users to read this document.

 

Contact:

Please contact Roger Marchand if you have any question or comments about CloudSat dataset.