Water vapor and liquid water estimates using simultaneous S and Ka band radar measurements

Using simultaneous S and Ka band observations it is possible to retrieve a path integrated value of the water vapor content as well as cloud liquid water content values using the atmospheric attenuation properties of the two frequencies. 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 propose a new method to retrieve the path integrated water vapor content using the differential atmospheric absorption of the two frequencies. The cloud liquid water content is also retrieved by using differential absorption through drops assuming 100% relative humidity in the cloud.

Extensive simultaneous dual frequency radar measurements were recently obtained during the Rain In Cumulus over the Ocean (RICO) experiment using S-Pol-Ka. The trade wind cumuli observed with S-Pol-Ka during RICO are ideal for testing water vapor and cloud water content retrievals. The small convective cells distributed throughout the radar domain offer numerous paths for both retrieval of vapor and liquid water. The radar observations were in coordination with in-cloud aircraft measurements, dropsondes, upsondes and surface measurements, which will be used for comparison and validation.