Potential of Using Scanning Polarimetric Cloud Radar Measurements for Identifying Habits of Ice Hydrometeors and Estimating Their Shapes

Sergey Matrosov University of Colorado
Gerald Mace University of Utah
Roger Marchand University of Washington
Matthew Shupe University of Colorado
Gannet Hallar Storm Peak Laboratory - Desert Research Institute
Ian McCubbin Desert Research Institute

Category: Cloud Properties

The ARM Mobile Facility 2 was deployed during the winter of 2010–11 near Steamboat Springs, Colorado for the Storm Peak Lab Cloud Property Validation Experiment (STORMVEX). This presentation deals with the preliminary analysis of the scanning W-band ARM cloud radar (SWACR) data, which were promising for identification of ice hydrometeor habits (e.g., planar crystals versus columnar crystals) and estimation of their shapes (e.g., mean aspect ratios). A slant 45-degree linear polarization was used with the SWACR during STORMVEX, and the slant linear depolarization ratio (SLDR) was the measured polarimetric radar parameter exhibiting sensitivity to particle habits/shapes. The range-height indicator (RHI) scans were used for habit/shape recognitions. The in situ particle observations, collocated with radar measurements, were conducted at the Storm Peak Lab, located at an altitude of 450 m and at a range of 2.4 km from the radar. Observed ice hydrometeor habits ranged from pristine and rimed dendrites/stellars to aggregates, irregulars, graupel, columns, plates and particle mixtures. SLDR trends as a function of the radar elevation angle were indicative of the predominant hydrometeor habit/shape. For planar particles, SLDRs increase from values near the cross-talk of -21.8 dB at zenith viewing to maximum values at slant viewing. These maximum values depend primarily on predominant aspect ratio and bulk density of hydrometeors. The highest observed SLDRs at slant viewing were about -8 dB for pristine dendrites, which had the smallest aspect ratio among observed planar crystals. The maximum SLDRs at slant viewing gradually decrease as planar particle mean aspect ratios increase (i.e., particles become more spherical) due to riming or/and aggregation. Unlike planar hydrometeors, columnar particles (e.g., columns, needles) did not exhibit pronounced SLDR trends with the elevation angle. A difference in SLDRs between zenith and slant viewing can be used for inferring predominant aspect ratios of planar hydrometeors if an assumption about bulk density is made. For columnar particles, SLDR offsets from the cross-talk value are indicative of aspect ratios. Collected data are also indicative of particles being oriented preferably with their major dimensions in the horizontal plane. Relatively simple oblate (for planar crystals) or prolate (for columnar crystals) spheroidal particle models were able to approximate SLDR changes with the elevation angle.

This poster will be displayed at ASR Science Team Meeting.