A comparison of X-band polarization parameters with in-situ microphysical measurements in the comma head of two winter cyclones

Finlon, Joseph A.

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https://hdl.handle.net/2142/89058 Copy

Description

Title

A comparison of X-band polarization parameters with in-situ microphysical measurements in the comma head of two winter cyclones

Author(s)

Finlon, Joseph A.

Issue Date

2015-12-07

Director of Research (if dissertation) or Advisor (if thesis)

• Rauber, Robert M.
• McFarquhar, Greg M.

Department of Study

Atmospheric Sciences

Discipline

Atmospheric Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• winter
• cyclone
• radar
• polarization
• cloud
• ice
• snow
• hydrometeor

Abstract

Since the advent of dual-polarization radar, methods of classifying hydrometeors by type from measured polarization variables have been developed. However, the deterministic approach of existing hydrometeor classification algorithms of assigning only one dominant habit to each volume does not properly consider the distribution of habits present in that volume. During the Profiling of Winter Storms (PLOWS) field campaign the NSF/NCAR C-130 aircraft, equipped with in-situ microphysical probes, made multiple passes through the comma head of two cyclones as the Mobile Alabama X-band (MAX) dual-polarization radar performed range-height indicator scans in the same plane as the C-130 flight track. On 14-15 February and 21-22 February 2010, 579 and 202 coincident data points, respectively, were identified when the plane was within 10 s (~1 km) of a radar gate. Using the axis ratio (α), sphericity (β), maximum dimension D, and projected area A of the in-situ imaged crystals, the habit of each particle was identified. For all particles that occurred for times within different binned intervals of radar reflectivity (ZHH) and of differential reflectivity (ZDR), the reflectivity-weighted contribution of each habit, and the frequency distributions of α and β were determined. Habits with less circular shapes (bullet rosettes and aggregates) had greater contributions to the reflectivity compared to other habits when ZHH > 7 dBZ and ZDR > 2 dB. The presence of bullet rosettes and aggregates for similar ZHH and ZDR supports previous studies that bullet rosettes are the favored crystal species for aggregate formation. While irregular particles made up 40% of the observed shapes, only 55% of the ZHH-ZDR bins had irregular particles contribute over 40% of the reflectivity. Additionally, over 88% of the bins did not have a single habit contribute over 75% to the reflectivity. These findings show the general lack of dominance of a given habit for a particular ZHH and ZDR, and suggest that determining the probability of specific habits in radar volumes may be more suitable than the deterministic methods currently used.

Graduation Semester

2015-12

Type of Resource

text

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http://hdl.handle.net/2142/89058

Copyright and License Information

Copyright 2015 Joseph Finlon

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