Measurements of Differential Reflectivity in Snowstorms and Warm Season Stratiform Systems

Abstract

The organized behavior of differential radar reflectivity (ZDR) is documented in the cold regions of a wide variety of stratiform precipitation types occurring in both winter and summer. The radar targets and attendant cloud microphysical conditions are interpreted within the context of measurements of ice crystal types in laboratory diffusion chambers in which humidity and temperature are both stringently controlled. The overriding operational interest here is in the identification of regions prone to icing hazards with long horizontal paths. Two predominant regimes are identified: category A, which is typified by moderate reflectivity (from 10 to 30 dBZ) and modest 1ZDR values (from 0 to 13 dB) in which both supercooled water and dendritic ice crystals (and oriented aggregates of ice crystals) are present at a mean temperature of 2138C, and category B, which is typified by small reflectivity (from 210 to 110 dBZ) and the largest 1ZDR values (from 13 to 17 dB), in which supercooled water is dilute or absent and both flat-plate and dendritic crystals are likely. The predominant positive values for ZDR in many case studies suggest that the role of an electric field on ice particle orientation is small in comparison with gravity. The absence of robust 1ZDR signatures in the trailing stratiform regions of vigorous summer squall lines may be due both to the infusion of noncrystalline ice particles (i.e., graupel and rimed aggregates) from the leading deep convection and to the effects of the stronger electric fields expected in these situations. These polarimetric measurements and their interpretations underscore the need for the accurate calibration of ZDR.

Toward Exploring the Synergy Between Cloud Radar Polarimetry and Doppler Spectral Analysis in Deep Cold Precipitating Systems in the Arctic

“…The results of the first combined polarimetric and Doppler spectral radar measurements in precipitating deep Arctic clouds presented herein are generally in agreement with previous studies performed in midlatitude stratiform clouds using longer-wavelength radars operating at S, C, and X bands (e.g., Andrić et al, 2013;Bechini et al, 2013;Griffin et al, 2017;Kennedy & Rutledge, 2011;Moisseev et al, 2015;Schrom et al, 2015;Schrom & Kumjian, 2016;Thompson et al, 2014;Williams et al, 2015). All of these studies document notable enhancement of Z DR and/or K DP in the DGL although the Z DR and K DP signatures may not occur simultaneously and not be collocated.…”

How Does Riming Affect Dual‐Polarization Radar Observations and Snowflake Shape?

“…For cases with D Ze > 2 mm, Z dr decreases with the increase of Z e . This relation is expected and has been reported before (e.g., Vivekanandan et al, 1994;Williams et al, 2015).…”

Unsupervised classification of vertical profiles of dual polarization radar variables

“…Sinclair et al (2016) have shown that such observations can be used to test representation of the secondary ice production in numerical weather prediction models. Other dual-polarization observations that show notable features are high-Z DR regions surrounding the cores of snow-generating cells (Kumjian et al, 2014) and at the top of ice clouds which can be linked to the presence of planar crystals and further to the presence of supercooled liquid water, providing very favorable conditions for their growth at these temperatures (Williams et al, 2015;Oue et al, 2016).…”