A Synthesis of Polarimetric and Dual-Frequency Radar Observations of Winter Storms for Estimating Ice Water Content

The millimeter-wavelength polarimetric radars (e.g., Ka band, W-band) have been recently used for high-spatiotemporal resolution observations of ice precipitation clouds in wide communities and have been expected to be used to improve qualitative estimates of precipitation amount. Although the ice water content (IWC) estimates from centimeter-wavelength radars (e.g., S band) have been established and evaluated in the previous studies, those using millimeter-wavelength radars have still large uncertainties. This study illustrates a synergy between the centimeter-wavelength operational radar network and millimeter-wavelength radar observations for IWC retrievals using columnar vertical profiles (CVP) from the NEXRAD (S-band) polarimetric radar at Upton, NY (KOKX) and quasi-vertical profiles (QVP) from the Ka-band Scanning Polarimetric Radar (KASPR) at Stony Brook, NY, for snowstorms along the U.S. Northeast Coast. This methodology revealed the possibility for estimation of the dual-wavelength ratio DWRS/Ka without the need for matching the radar beams and synchronizing scanning strategies for the two non-collocated radars and the validity of a Rayleigh assumption in the use of KASPR specific differential phase (KDP) for the IWC retrievals.

This study proposes two IWC relations for Ka-band radar measurements: one as a function of the total number of particles in a unit volume Nt and reflectivity (IWC(Nt,Z)) and the other as a function of KDP, reflectivity, and the degree of riming frim (IWC(KDP,Z,frim)). They are derived from the S-band radar IWC relations with a Rayleigh scattering assumption, incorporating the relationship between DWRS/Ka and the mean volume diameter Dm. Both relations show good promise for accurate estimation of IWC. Generally, IWC(Nt,Z) with the particle size distribution (PSD) shape parameter μ=-0.5 works well for cases where dense aggregates dominate, and an exponential PSD assumption works efficiently for one case where less dense aggregates dominate. For IWC(KDP,Z,frim), optimization of frim is rather important. This study sheds light on the millimeter-wavelength polarimetric radar IWC estimation using non-collocated dual-wavelength radar characteristics.