Radar Observations of Dendritic Growth Zones in Colorado Winter Storms
Open Access
- Author:
- Schrom, Robert Stephen
- Graduate Program:
- Meteorology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 31, 2015
- Committee Members:
- Matthew Robert Kumjian, Thesis Advisor/Co-Advisor
- Keywords:
- radar
microphysics
meteorology - Abstract:
- X-band polarimetric radar observations of winter storms in northeastern Colorado on 20-21 February, 9 March, and 9 April 2013 are examined. These observations were taken by the Colorado State University-University of Chicago-Illinois State Water Survey (CSU-CHILL) radar during the Front Range Orographic Storms (FROST) project. The polarization radar moments of reflectivity factor at horizontal polarization (ZH), differential reflectivity (ZDR), and specific differential phase (KDP) exhibit a range of signatures at different times near the -15° C temperature level favored for dendritic ice crystal growth. Generally, KDP is enhanced in dendritic ice crystal growth region with ZDR decreasing and ZH increasing towards the ground, suggestive of aggregation (or riming). The largest ZDR values (~3.5-5.5 dB) are found during periods of significant low-level upslope flow. Convective features observed when the upslope flow was weaker have the highest KDP (> 1.5 deg km-1) and ZH (> 20 dBz) values. Vertically-pointing observations of radial velocity (VR) taken by NCAR’s X-band polarimetric radar (NCAR-XPOL) are analyzed along with the polarimetric observations from the CSU-CHILL radar. The magnitude of VR is found to decrease towards the ground near the -15 °C temperature level, indicating a decrease in the mean particle fall speed. ZH increases towards the ground in this region, indicating an increase in the mean particle size. These signatures are found to be consistent with the growth and subsequent aggregation of dendrites. Electromagnetic scattering calculations using the Generalized Multi-particle Mie (GMM) method are used to determine whether these radar signatures are consistent with dendrites. Particle size distributions (PSDs) are retrieved for a variety of cases using these scattering calculations and the corresponding radar observations. The PSDs are found to be reasonably consistent with previous observations of ice particle size distributions. Observations of enhanced KDP, decreasing ZDR, and increasing ZH towards the ground may therefore be useful in identifying regions of rapidly collecting dendrites and thus increased surface snowfall rates.