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