Dual-polarimetric and multi-Doppler analysis of a High Plains supercell
Darren Clabo
Nick Guy
Nathan Hitchens
Outline
• Introduction
• Background
• Dual-polarimetric Doppler analysis
• Multi-Doppler analysis
• Summary
Introduction
Soundings
DNR
LBF
RIW
Surface Observations
Storm Information
• Initiation: 2337 UTC on 4 June 2009– First reflectivity seen aloft (8.81 km) at 2326
UTC on 4 June 2009
• Last radar scan by CSU-CHILL at 0112 UTC on 5 June 2009
1km Visible Satellite
Storm initiation
CSU-CHILL Reflectivity
CoCoRaHS Reports
SHAVE Reports
Background
Supercell Model
Klemp (1987)
Polarimetric Radar Signatures in Supercell Thunderstorms
Kumjian and Ryzhkov (2008)
Polarimetric Radar Signatures in Supercell Thunderstorms
• ZDR arc signature– Usually found on the
right southern edge of the forward flank downdraft
– Shallow (1-2 km in depth)
– Effect of size sorting of raindrops resulting from vertical increase in speed and veering of storm-relative winds
Kumjian and Ryzhkov (2008)
Polarimetric Radar Signatures in Supercell Thunderstorms
• Hail signature– Low ZDR value (near 0) due
to chaotic orientation of tumbling hailstones
Kumjian and Ryzhkov (2008)
Polarimetric Radar Signatures in Supercell Thunderstorms
• Inflow signature– Vigorous low-level inflow into supercells may contain
nonmeteorological scatterers (e.g. grass, leaves, dust)
– Results in lower values of ρHV
Kumjian and Ryzhkov (2008)
Polarimetric Radar Signatures in Supercell Thunderstorms
• Updraft signature– Light debris may be ingested into updraft from
inflow and a lack of hydrometeors may exist
– Results in low ρHV aloft
Polarimetric Radar Signatures in Supercell Thunderstorms
• ZDR columns– High values associated with
updrafts indicative of large raindrops or water-coated hailstones
– Narrow (4-8 km wide)– Increasing values
associated with updraft intensification, and thus storm intensification
Kumjian and Ryzhkov (2008)
Radar Coverage
• Dual-polarized, S-band– CSU-CHILL
• Single-polarized, S-band– CSU-PAWNEE– Denver NEXRAD (KFTG)– Cheyenne NEXRAD
(KCYS)
Vorticity Evolution
.00E+000
.20E-002
.40E-002
.60E-002
.80E-002
.10E-001
.12E-001
234000 236000 238000 240000 242000 244000 246000 248000 250000 252000 254000
Time (UTC)
Vo
rtic
ity
(s-1
)
< 4.99 km 5.00 - 5.99 km 6.00 - 6.99 km > 7.00 km
• Vorticity calculated using the tangential shear between two points corresponding to the maximum inbound and outbound velocities not more than 10 km apart in an area thought to contain the updraft– Updraft denoted by bounded weak echo region aloft
• Red line denotes minimum vertical vorticity for a mesocyclone as described by the synthesis of Bunkers et al. (2009)
Storm
undergoing
new updraft
growth
Dual-Polarimetric Doppler Analysis
2352 UTC - Base
2352 UTC – Sweep 4
0013 UTC - Base
0013 UTC – Sweep 4
0020 UTC - Base
0020 UTC – Sweep 4
0046 UTC – Sweep 4
0049 UTC - Base
0049 UTC – Left Split
0053 UTC - Base
0053 UTC – Sweep 4
0106 UTC - Base
0106 UTC – Sweep 4
0109 UTC – Base
Updraft Updraft
Updraft Updraft
0109 UTC – Sweep 4
Updraft Updraft
Updraft Updraft
Multi-Doppler Analysis
Multi-Doppler Analyses
• Radar data edited in SOLOII– Removal of egregious data
• Interpolated to Cartesian grid via REORDER software package
• Dual- and Multi-Doppler analyses performed with CEDRIC software package– Extremely finicky!
Radar Ranges
Multi-Doppler Analyses
Quad
Dual Dual
Triple
Vertical Wind CalculationDownward integration Upward integration
Variable Integration
Continuity
090605_0106Z 090605_0109Z
Vertical Structure
1.50 km
3.0 km
Vertical Structure
4.50 km
6.5 km
Vertical Structure
8.0 km
10.0 km
Vertical Wind / ρHV relationship
ρHV
ZDR
Summary
Dual-Polarimetric Analysis• Storm consisted of three distinct right-moving updrafts, though
possibly more– Cyclonic rotation– New cells formed on flanking line
• Two distinct left moving updrafts– Anticyclonic
• Storm exhibited supercellular characteristics through most of its lifetime– Persistence and depth of significant (> 0.3 x 10-2 s-1) vertical vorticity
• Exhibited: – Cyclic updrafts– Velocity couplets aloft and at lowest scan elevations– Storm splitting
• Right and left movers• Shedding updrafts
– Zdr arcs– Lowering of ρhv in mesocyclone center
Multi-Doppler Analysis
• Continuity with previous scan time suggests results are robust for instantaneous analysis
• Tri-Doppler analysis produces “best” results due to beam propagation characteristics and over-determined solutions
• Variable integration technique produced best results• Vertical structure shows
– Poor agreement at extreme lower upper and levels– Reasonable results when compared to radar analysis
• Unclear whether ρHV is possibly correlated to calculated vertical wind
Acknowledgements
• Special thanks to our mentors:– Wen Chau Lee– Pat Kennedy– Tammy Weckwerth
• Also thanks to….– NCAR, ASP, and the colloquium organizers– Mike Bell– Tracy Emerson– Group 10b
“This is indicative of a deep psychological problem.”
– Pat Kennedy
0011 UTC – TBSS
0011 UTC – TBSS2
0008 UTC – Sweep 5
0017 UTC - TBSS
0037 UTC - TBSS
0031 UTC – Sweep 2
Velocity Fields