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 Z DR 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 Z DR 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 ρ HV 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 ρ HV aloft

Polarimetric Radar Signatures in Supercell Thunderstorms Z DR 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 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

0109 UTC – Sweep 4 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 Triple

Vertical Wind Calculation Downward integration Upward integration Variable Integration

Continuity _0106Z _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 / ρ HV 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 s -1 ) vertical vorticity Exhibited: –Cyclic updrafts –Velocity couplets aloft and at lowest scan elevations –Storm splitting Right and left movers Shedding updrafts –Z dr arcs –Lowering of ρ hv 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 ρ HV 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