Atmospheric Ice Particle Shape Estimates from Polarimetric Radar Measurements and In Situ Observations

Journal Article · Fri Dec 01 00:00:00 EST 2017 · Journal of Atmospheric and Oceanic Technology

DOI:https://doi.org/10.1175/JTECH-D-17-0111.1· OSTI ID:1411985

Matrosov, Sergey Y. ^[1]; Schmitt, Carl G. ^[2]; Maahn, Maximilian ^[1]; de Boer, Gijs ^[1]

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1. Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, and NOAA/Earth System Research Laboratory, Boulder, Colorado
2. National Center for Atmospheric Research, Boulder, Colorado

A remote sensing approach to retrieve the degree of nonsphericity of ice hydrometeors using scanning polarimetric Ka-band radar measurements from a U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program cloud radar operated in an alternate transmission–simultaneous reception mode is introduced. Nonsphericity is characterized by aspect ratios representing the ratios of particle minor-to-major dimensions. The approach is based on the use of a circular depolarization ratio (CDR) proxy reconstructed from differential reflectivity ZDR and copolar correlation coefficient ρhυ linear polarization measurements. Essentially combining information contained in ZDR and ρhυ, CDR-based retrievals of aspect ratios are fairly insensitive to hydrometeor orientation if measurements are performed at elevation angles of around 40°–50°. The suggested approach is applied to data collected using the third ARM Mobile Facility (AMF3), deployed to Oliktok Point, Alaska. Aspect ratio retrievals were also performed using ZDR measurements that are more strongly (compared to CDR) influenced by hydrometeor orientation. The results of radar-based retrievals are compared with in situ measurements from the tethered balloon system (TBS)-based video ice particle sampler and the ground-based multiangle snowflake camera. The observed ice hydrometeors were predominantly irregular-shaped ice crystals and aggregates, with aspect ratios varying between approximately 0.3 and 0.8. The retrievals assume that particle bulk density influencing (besides the particle shape) observed polarimetric variables can be deduced from the estimates of particle characteristic size. Uncertainties of CDR-based aspect ratio retrievals are estimated at about 0.1–0.15. Given these uncertainties, radar-based retrievals generally agreed with in situ measurements. The advantages of using the CDR proxy compared to the linear depolarization ratio are discussed.

• Research Organization: Univ. of Colorado, Boulder, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER). Earth and Environmental Systems Science Division
• Grant/Contract Number: SC0013306
• OSTI ID: 1411985
• Alternate ID(s): OSTI ID: 1541862; OSTI ID: 1673380
• Journal Information: Journal of Atmospheric and Oceanic Technology, Journal Name: Journal of Atmospheric and Oceanic Technology Vol. 34 Journal Issue: 12; ISSN 0739-0572
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English

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