Insights into riming and aggregation processes as revealed by aircraft, radar, and disdrometer observations for a 27 April 2011 widespread precipitation event

Abstract

This study presents aircraft spiral ascent and descent observations intercepting a transition to riming processes during widespread stratiform precipitation. The sequence is documented using collocated scanning and profiling radar, including longer-wavelength dual polarization measurements and shorter-wavelength Doppler spectra. Riming regions are supported using aircraft measurements recording elevated liquid water concentrations, spherical particle shapes, and saturation with respect to water. Profiling cloud radar observations indicate riming regions during the event as having increasing particle fall speeds, rapid time-height changes, and bimodalities in Doppler spectra. These particular riming signatures are coupled to scanning dual polarization radar observations of higher differential reflectivity (Z DR ) aloft. Reduced melting layer enhancements and delayed radar bright-band signatures in the column are also observed during riming periods, most notably with the profiling radar observations. The bimodal cloud radar Doppler spectra captured near riming zones indicate two time-height spectral ice peaks, one rimed particle peak, and one peak associated with pristine ice needle generation and/or growth between À4°C and À7°C also sampled by aircraft probes. This pristine needle population gives a partial explanation for the enhanced Z DR we observe near this rimed particle region. The riming signatures aloft and radar measurements within the melting level are weakly lag correlated (r~0.6) with smaller median drop sizes at the surface, as compared with later times when aggregation of larger particle sizes was believed dominant.

Global Positioning System precipitable water vapour (GPS‐PWV) jumps before intense rain events: A potential application to nowcasting

“…Figure shows that the disdrometer time series is consistent with the 95th percentile time series, although differences are expected due to the different areas covered by each instrument, and besides, the total precipitation from the disdrometer is always larger than that measured by radar and a rain gauge because large droplets were not filtered as suggested by Giangrande et al . ().…”

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

“…Schrom et al () suggested a polarimetric technique to separate contributions from aggregates and dendrites in the DGL of midlatitude winter storms. Polarimetric signatures of the secondary ice mixed with aggregated and rimed snow in layers with temperature around −5°C were found by cloud and precipitation radar measurements in high‐latitude deeper snow clouds (Oue, Kumjian, Lu, Verlinde, et al, ; Sinclair et al, ), midlatitude mesoscale convective systems (Giangrande, Toto, Bansemer, et al, ; Kumjian et al, ), and midlatitude snowstorms (Kumjian & Lombardo, ). However, combining polarimetric measurements with the analysis of Doppler spectra yields a much better chance to identify and separate different types of ice, and to quantify their amounts if their corresponding fall velocities are associated with separate peaks in the Doppler spectrum.…”

Quantifying the effect of riming on snowfall using ground‐based observations

“…Dual‐polarization radar observations are often used to identify ice precipitation regions affected by riming [e.g., Straka et al , ; Liu and Chandrasekar , ; Chandrasekar et al , ; Giangrande et al , ]. Accurate identification of such regions would improve our understanding of precipitation processes as well as improve aviation safety [ Ellis et al , ], among other applications.…”