2B-CWC-RO issues

2B-CWC-RO 007: Missing data in areas of thick cloud and precipitation

CloudSat DPC — 2007-04-30T21:31:09+01:00

Numerous areas of missing data are found where the Range_to_first_bin field in the 1B-CPR product cannot be accurately calculated.

See the associated 1B-CPR 007 issue.

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Planned resolution: R04 will use an improved 1B-CPR product

2B-CWC-RO 007: Assumption of constant number concentration & width parameter

CloudSat DPC — 2007-01-27T03:34:14+01:00

The liquid and ice cloud retrievals used in 2B-CWC-RO assume three-parameter distributions of cloud particles (lognormal for liquid, modified gamma for ice) and retrieve the distribution parameters directly by fitting to the measurements (radar) and a priori data. In order to reduce the number of unknowns to be retrieved, the current versions of the retrievals assume that two of the three parameters are constant with altitude (but their values are still retrieved): the number concentrations of particles and the distribution width parameters. This assumption is obviously more valid in some circumstances than others; it also prevents a priori data from varying with altitude. The next version of this algorithm should remove this assumption, allowing the algorithm to converge in more cases where the vertical variability is high.

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Planned resolution: Removed in R04 (product version 008)

2B-CWC-RO 007: Retrieval failure in regions of high Z (precipitation)

CloudSat DPC — 2007-01-27T03:29:22+01:00

The liquid and ice cloud retrievals used in 2B-CWC-RO assume distributions of cloud particles without substantial numbers of larger precipitation particles. The LWC retrieval in particular often fails (does not converge) for profiles containing high radar reflectivities (say, above 0 dBZe); this is most likely due to the presence of precipitation-sized particles, which the retrieval is unable to fit using the assumed distribution of cloud particles. Because the large precipitation particles dominate the radar signal, a more sophisticated retrieval (likely involving additional data streams) will be necessary to retrieve cloud properties in the presence of precipitation. Bits 0 and 1 in RO_CWC_Status indicate the failure of the LWC and IWC retrievals; bit 2 indicates possible precipitation in the profile (radar reflectivity > -15 dBZe).

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Planned resolution: TBD

2B-CWC-RO 007: Multi-phase cloud columns

CloudSat DPC — 2007-01-27T03:24:46+01:00

The 2B-CWC-RO algorithm has separate retrievals for liquid and ice clouds; the current algorithm does not attempt to retrieve both solid and liquid microphysical properties simultaneously in the same cloud column. Instead, separate retrievals are performed assuming that the entire cloud column is liquid-only and ice-only, and the two sets of results are combined into a composite profile according to a simple temperature relation (since we do not have an independent source of phase information). Ice-phase results are used for cold temperatures, liquid-phase results for warm temperatures, and a linear combination of the two are used in an intermediate temperature range, yielding an approximate mixed-phase solution. Future versions of the algorithm will likely take more sophisticated approaches to handling cloud columns with multiple phases based on limited information. The composite profile variable names all begin with "RO_"; the separate liquid-only and ice-only retrieval variable names begin with "LO_RO_" and "IO_RO_", respectively.

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Planned resolution: TBD

2B-CWC-RO 008: Radar forward model attenuation in liquid cloud

CloudSat DPC — 2011-09-22T01:39:57+01:00

The 2B-CWC-RO algorithm estimates liquid cloud properties using a radar forward model which includes the effects of attenuation by liquid cloud droplets. An error related to the calculation of the attenuation has been identified in the forward model. Due to a sign error, values for the two-way transmission in the forward model may be larger than 1.0. As a result, the forward-modeled attenuated reflectivity values can be larger than the unattenuated values.

An evaluation shows that effective radii and liquid water contents are typically underestimated by the retrieval as a result of the forward model error. These effects are most pronounced for those profiles containing dBZe > -15 (i.e., those profiles which likely contain precipitation).

This forward model is also used in the 2B-CWC-RVOD algorithm. The forward model is being corrected as part of the R05 product release. Note that this issue does not affect retrieved ice cloud properties.

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Planned resolution: TBD

2B-CWC-RO 008: Multi-phase cloud columns

CloudSat DPC — 2007-10-22T20:24:55+01:00

2B-CWC-RO 008: Retrieval failure in regions of high Z (precipitation)

CloudSat DPC — 2007-10-22T20:23:26+01:00