Polarimetric radar and aircraft observations of saggy bright bands during MC3E

Abstract

Polarimetric radar observations increasingly are used to understand cloud microphysical processes, which is critical for improving their representation in cloud and climate models. In particular, there has been recent focus on improving representations of ice collection processes (e.g., aggregation and riming), as these influence precipitation rate, heating profiles, and ultimately cloud life cycles. However, distinguishing these processes using conventional polarimetric radar observations is difficult, as they produce similar fingerprints. This necessitates improved analysis techniques and integration of complementary data sources. The Midlatitude Continental Convective Clouds Experiment (MC3E) provided such an opportunity. Quasi-vertical profiles of polarimetric radar variables in two MC3E stratiform precipitation events reveal episodic melting layer sagging. Integrated analyses using scanning and vertically pointing radar and aircraft measurements reveal that saggy bright band signatures are produced when denser, faster-falling, more isometric hydrometeors (relative to adjacent times) descend into the melting layer. In one case, strong circumstantial evidence for riming is found during bright band sagging times. A bin microphysical melting layer model successfully reproduces many aspects of the signature, supporting the observational analysis. If found to be a reliable indicator of riming, saggy bright bands could be a proxy for the presence of supercooled liquid water in stratiform precipitation, which may provide important information for mitigating aircraft icing risks and for constraining microphysical models.

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

“…The signature of needle and/or columnar crystals in a temperature range from À8 to À3°C, where ice particles seeded in the MPL and secondary ice formation via the Hallett-Mossop ice multiplication mechanism (Hallett & Mossop, 1974) could be active, is often observed in Arctic mixed-phase clouds in linear depolarization ratio measurements . Similar signatures were observed in midlatitude winter storms and convective systems (e.g., Giangrande, Toto, Bansemer, et al, 2016;Kumjian et al, 2016;Kumjian & Lombardo, 2017;Sinclair et al, 2016;Zawadzki et al, 2001). Kumjian et al (2016) observed K DP enhancements produced by needle and columnar crystals in secondary ice formation regions.…”

“…Similar signatures were observed in midlatitude winter storms and convective systems (e.g., Giangrande, Toto, Bansemer, et al, 2016;Kumjian et al, 2016;Kumjian & Lombardo, 2017;Sinclair et al, 2016;Zawadzki et al, 2001). Kumjian et al (2016) observed K DP enhancements produced by needle and columnar crystals in secondary ice formation regions. In the present study, similar slightly enhanced K DP values at Ka band are found at altitudes below 1 km in the 29 April case (Figure 1b).…”

“…Schrom et al (2015) 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 À5°C were found by cloud and precipitation radar measurements in high-latitude deeper snow clouds Sinclair et al, 2016), midlatitude mesoscale convective systems Kumjian et al, 2016), and midlatitude snowstorms (Kumjian & Lombardo, 2017). 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.…”

Inadvertent Localized Intensification of Precipitation by Aircraft

“…Even though we argue that LIP has an anthropogenic cause, the reported phenomenon demonstrates how cloud-to-precipitation processes work in mixed-phase clouds and what processes may be responsible for the intensification of precipitation occurring under natural conditions. It demonstrates that aggregation growth of snowflakes and ice phase cloud seeding are important processes in multilayer clouds, as discussed in, for example, Moisseev et al (2015) and Schrom and Kumjian (2016), augmenting the analysis presented by Verlinde et al (2013), Moisseev et al (2017), Kumjian et al (2016Kumjian et al ( , 2014, and Giangrande et al (2016) discussing the importance of riming.…”

Cloud‐resolving model intercomparison of an MC3E squall line case: Part I—Convective updrafts

“…The squall‐line MCS case simulated in this study occurred on 20 May 2011, during the Midlatitude Continental Convective Clouds Experiment (MC3E) [ Petersen and Jensen , ; Jensen et al ., ], which was supported by both the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM) and NASA's Global Precipitation Measurement mission ground validation program in north‐central Oklahoma from 22 April to 6 June 2011. Detailed ground‐based and aircraft cloud dynamical and microphysical observations are available for this case [ Mather and Voyles , ; Jensen et al ., ], which has been a focus of several recent studies [e.g., Tao et al ., , ; Giangrande et al ., ; Fan et al ., ; Kumjian et al ., ; Marinescu et al ., ; Van Lier‐Walqui et al ., ; Saleeby et al ., ; Fridlind et al ., ]. Section 2 includes a more detailed description of the case and the relevant observations used in this study.…”