Ka/W-band SACR-2 Spectral and polarimetric measurements of Arctic mixed-phase clouds at the NSA Oliktok site

Description

Mixed-phase clouds produce a variety of ice particle shapes through depositional growth, aggregation, and riming over the Arctic. Our understanding about microphysics of the mixed-phase clouds is insufficient. The second generation Ka- and W-band ARM scanning cloud radars (Ka/W-SACR2) were installed at the NSA Oliktok site in 2015. The SACR2 can transmit and receive H and V polarizations, observing full polarimetric variables at two different radar frequencies (Ka and W). The SACR2 measurements are expected to improve our ability to distinguish ice habits and the microphysical processes responsible for their production and growth. First light observations from the SACR2 were recorded during the October-November Calibration, Grooming and Alignment (CGA) activity of the radar group. During selected RHI scans, the SACR2 collected Doppler spectra with the single polarimetry mode (H transmit/H&V receive) and moments with full polarimetry mode during mixed-phase cloud evens. The Doppler spectra at both Ka and W band indicated the presence of a liquid layer coexisting with faster-falling snow particles at 2.2-2.8 km altitudes. The liquid cloud signature was consistent in elevation angle at a constant altitude. The liquid-cloud signatures from zenith pointing radars, which fall speeds are ~0 m s-1, are sometimes contaminated by clutter noise. The Doppler spectra from RHI measurements can improve detecting liquid-cloud layers. Doppler spectra of dual wavelength ratio (Ka/W, DWR) near the cloud top (~3.3 km altitude) showed an elevation dependency for slower-falling particles, while differential reflectivity (ZDR) also showed an elevation dependence which has higher ZDR values (>2.5 dB) at lower elevation angles and approaches 0 dB at vertical incidence. These signatures suggest the presence of plate-like crystals. The W-band radar observed specific differential phase shift (KDP) approximately 2.6 times larger than Ka-band KDP in large reflectivity regions. We would like to discuss about these signatures of polarimetric variables and DWR and microphysics using scattering calculations.