S-Band Radar Dual-Polarization Observations of Winter Storms
P. C. Kennedy and S. A. Rutledge CSU-CHILL Radar Facility
CSU-CHILL Data Overview
• 3 dB beamwidth ~1o
• Alternating H, V transmit polarization• 11 cm wavelength• Scan rates 6-10 os-1 PPI and 1 os-1 RHI• Wang and Chandrasekar (2009) Kdp• Data collected when significant winter
precipitation expected within ~100 km of Greeley, CO
20 Dec 2006 1419 UTC 3.5o PPI data
Temperatures from 12 UTC DNR sounding
Reflectivity (dBZ) Kdp (o km-1 x 10)
20 Dec 2006 1442 UTC 3.5o PPI data
Reflectivity (dBZ) Kdp (o km-1 x 10)
20 Dec 2006 1504 UTC 3.5o PPI data
Reflectivity (dBZ) Kdp (o km-1 x 10)
20 Dec 2006 1504 UTC 3.5o PPI data
Unfolded radial velocity (ms-1); multi-day KDEN closure starts ~22 UTC
20 Dec 2006 1502 UTC 156.8 o RHIAggregation reflectivity profile; max Kdp layer aloft
Reflectivity (dBZ) Kdp (o km-1)
Storm 2: 18 March 2003
Kdp (0 km-1 x 10) at 4.2o PPI as heavy snow period starts at KFCL
Rings are -10, -15, -20 o C from LBF 12 UTC sounding
1844 UTC 2004 UTC
Height profiles extracted from RHI scan data in the two storms
Kdp max near -15 o C level; polarimetric traces imply aggregation with descent
T-Matrix simulations of Kdp generation from ice particles
Lo and Passarelli (1982) DSD: 0.2 to 2.0 mm diameter “dendrites”
“Aggregated” particle population: Kdp=.09 o km-1; Zdr=0.3 dB; Zh=19 dBZ
Summary
• Several 10th’s of a o km-1 Kdp values observed at S-Band in major winter storms (see also Trapp et al 2001.)
• Kdp values maximize near the -15o C ambient temperature level
• Scattering model results suggest that suitable populations of dendritic crystals can generate observed Kdp magnitudes (in situ obs needed)
• Positive Kdp areas near -15 o C level may be an indication of active dendritic particle growth
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