Optimal estimates of rain profiles using multiple wavelength radar measurements at ARM SGP Central Facility

The US Department of Energy Atmospheric Radiation Measurement (ARM) program facilities now host continuous multiple wavelengths radar measurements with matched beams. Thanks to the recent reconfiguration and improved signal processing of the UHF wind profiler in a precipitation mode, triple wavelength (UHF, Ka- and W-band) profiles of rain events are now available at the Southern Great Plains (SGP) site.

Against common expectations, millimetre wavelength cloud radars are very good sensors of precipitation through its attenuation. Indeed, rain attenuation has a closer link to rain rate than precipitation radar reflectivity has. However, Rayleigh reflectivity profiles by precipitation radar are still needed as a non-attenuated reference. The key step in this methodology is to disentangle the contributions to the measured dual wavelength ratios provided by rain attenuation and by non-Rayleigh effects which can be of the same order of magnitude for cloud radars. The triple wavelength measurements available at SGP are ideal for this project and provide enough independent measurements for the retrieval of the full drop size distribution characteristics. These retrievals are made through an adaptive optimal estimation framework capable of providing results also for the dual-wavelength portion of the profiles, i.e., when the W-band signal is fully attenuated. The results will be compared to the retrievals from the well-known W-band spectral technique based on the location of Mie oscillations.