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