Dual-wavelength radar water vapor and cloud liquid water estimates: Verification and assimilation into a cloud model

Using simultaneous S and Ka band radar observations it is possible to retrieve a path integrated value of the water vapor content as well as range-resolved cloud liquid water content values using the differential attenuation properties of the two wavelengths. Recently the NCAR S-band dual polarimetric (S-Pol) radar has been upgraded to include simultaneous Ka-band radar measurements. The Ka band antenna is mounted on the side of the S-band antenna and the two radars have matched beam widths and range resolution.

In this paper we describe the methods to retrieve the vertical profiles of water vapor content and range resolved cloud liquid water content (LWC). Verification results will be shown from two field experiments: The Rain In Cumulus over the Ocean (RICO) experiment and the Refractivity Experiment For H2O Research And Collaborative operational Technology Transfer (REFRACTT06).

Experiments in assimilating the dual-wavelength radar water vapor profiles and cloud LWC retrievals into a cloud resolving model will be shown. The dual-wavelength radar retrieval of water vapor profiles can be updated much more frequently than operational soundings, which are taken every 12 hours. Thus dual-wavelength radar might have the capability to provide more timely humidity information in the pre-storm environment. Currently most numerical weather prediction models are not initialized with observations cloud LWC and must instead generate cloud it within the model. Cloud LWC is important to precipitation processes and storm morphology. Thus dual-wavelength LWC retrievals could provide a more accurate initial state for the models.