STEPSSevere Thunderstorm

Electrification and Precipitation Study

May-July 2000

STEPSSevere Thunderstorm

Electrification and Precipitation Study

May-July 2000Prof. Steven RutledgeDepartment of Atmospheric ScienceColorado State University

Radar NetworkRadar Network

Dual-Doppler Dual-Doppler and Tripleand TripleDopplerDopplerconfigurationsconfigurations

STEPS Ops CenterSTEPS Ops Center

CSU-CHILL National Radar Facility; 10 cm polarimetric/DopplerCSU-CHILL National Radar Facility; 10 cm polarimetric/Dopplerwww.chill.colostate.eduwww.chill.colostate.edu

STEPS Fixed Instrumentation: Triple-Doppler Network and LMA (VHF TOA)

STEPS Fixed Instrumentation: Triple-Doppler Network and LMA (VHF TOA)

At KGLD:At KGLD:

-NWSNWS

-T-28T-28

-NSSLNSSL

-Electric field Electric field balloonballoon

-Mobile Mobile mesonetmesonet

-MGLASSMGLASS

Storm swath of base reflectivities (2100-0251 UTC) with NLDN lightning data overlaid.

2130 UTC2130 UTC

2328 UTC2328 UTC

0110 UTC0110 UTC

0251 UTC0251 UTC

KGLDKGLD

Tessendorf et al., JAS, 2005

29 June Supercell• Inverted tripole• +CGs

3 June storm• Inverted dipole• No CGs

23 June storm Early: normal tripole, -CGs

Later, collapse: inverted tripole, +CGs

29 June

3 June

23 June

Q: Why did charge structures differ?A: Supercooled liquid watercontent.

+

+

Switching gears now, lets talk about polarimetric radar……

NWS Polarimetric upgrade!!

NWS Polarimetric upgrade!!

A really exciting opportunityfor the science communityas well!

The STSR architecture first developed on the CSU-CHILL radar in 1995. Proof of concept.

In STSR, H-V polarizations transmitted at the same time. Previously, alternate transmission of H,V used. Needed method to switch polarizations with so called “ferrite” switch—very unreliable.

The polarization variables..

The polarization variables..

In addition to Z and Doppler velocity..Zdr, differential reflectivity

Sensitive to particle shape and phasePower based measurement

Φdp, differential phase (Kdp)Sensitive to particle shape and phase

Phase based measurement

ρhv, correlation coefficientSensitive to particle shape and phase

Power based measurement

In addition to Z and Doppler velocity..Zdr, differential reflectivity

Sensitive to particle shape and phasePower based measurement

Φdp, differential phase (Kdp)Sensitive to particle shape and phase

Phase based measurement

ρhv, correlation coefficientSensitive to particle shape and phase

Power based measurement

hail

rainH

V

Zdr = 10 log10 (Zhh/Zvv)

Single particle Zdr expressed as dB

Plot from Herzegh and Jameson (1992)

Illustrates dependenceon both shape andphase, watervs. ice (dielectric)

see Lang et al. 2004 J. Atmos. Ocean. Tech.

Non-precipitation echo: insects (preferred flight direction)

Zdr values reach CHILL data system limit (+9 dB)

Large Z and Zdr when looking at long axis of insects, orientedwith mean wind.

Propagation Differential Phase, φdpPropagation Differential Phase, φdp

φdp is a phase based measurement, independent of power

Since the H wave encounters more dielectric compared to the V wave, the H wave moves more slowly than the V wave. H wave lags the V wave therefore in phase.

Φdp is then the phase difference (in degrees) between the H and V wave as these waves propagate out and back to the radar. This difference (degrees) will be > 0 for oblate particles (rain), zero for isotropic media (hail), and < 0 for prolate particles (e.g., oriented ice particles).

φdp is a phase based measurement, independent of power

Since the H wave encounters more dielectric compared to the V wave, the H wave moves more slowly than the V wave. H wave lags the V wave therefore in phase.

Φdp is then the phase difference (in degrees) between the H and V wave as these waves propagate out and back to the radar. This difference (degrees) will be > 0 for oblate particles (rain), zero for isotropic media (hail), and < 0 for prolate particles (e.g., oriented ice particles).

H

V

From A. Illingworth, Chapter 5, in Weather Radar (2003)P. Meischner, Editor (Springer)

Illustration of H and V waves propagating through oblate raindrops. A phase lag between H and V waves results since the H wave moves slightly more slowly thanthe V wave, in oblate media. For prolate media, the V wave lags the H wave. Phi dp(propagation differential phase) is a measure of this phase difference between H and V waves.

PPI display presentation of differential propagation phase

-20o diff. phase at near point

+15o ~8 km farther range

35o phase change in 8 km

Basic concept:

H, V return signal phase difference changes most rapidly in beam path segments where net differential forward scattering effects are large

Conversion to customary Kdp units:

(Bringi and Chandra (2001) Eq 7.17)

Kdp is product of rainwater content and deviation of mass-weighted mean axis ratio from one. (Alternatively, particles with mean axis ratio of one (tumbling hailstones) do not contribute to Kdp).

Kdp is phase measurement, not dependent on accurate radar reflectivity calibration (including partial beam blockage effects), Zdr offsets / drifts, etc.

From a physical perspective….

Kdp is only arrived at after “filtering” the range profile of φdp

Too little filtering introduces noise in rain estimates, too muchfiltering removes fine scale estimates of rain rate and rain ratelocal peaks.

Increasing rain rate

Rain rate estimation…

CHILL: Rainfall AccumulationOptimization Algorithm

CHILL: Rainfall AccumulationNEXRAD Z-R Algorithm

Icecontamination!

Engineering Parking Lot at Colorado State University: Flash Flood of 28 July 1997

CHILL observations of the Ft. Collinsflood led to research that caused theNWS in Denver to modify their algorithmsused to derive rainfall rates from NWS radar measurements

An Example from the Ft. Collins Flash Flood of 28 July 1997: Cumulative Rainfall

An Example from the Ft. Collins Flash Flood of 28 July 1997: Cumulative Rainfall

Gauge Survey

Z = ARb

Vertical structure of microphysical classification

Hydrometeor type classification results for 5 July storm from STEPS (data from CSU-CHILL)—Model Intercomparison

Squall line and HID usingpolarimetric variables

Co-polar H,V Correlation (ρhv)Co-polar H,V Correlation (ρhv)

The correlation coefficient is a measure of the shape variationsor irregularities in the radar resolution volume……

The correlation coefficient decreases when diverse particlestypes are present.

This diversity can be in phase of water, shape and size.

ρhv reduction to ~0.91 in a hail shaft: 7 June 1995 near Gilcrest, CO

CSU-CHILLdata

Negative Zdr;these valuesalso modeledfor larger, wethail. Mie effectsoperate to reduce ZH relativeto ZV, leading to negative Zdr. Foraxis ratios in rangeof 0.6 to 0.8.

hv reduced in hail area:

Mixed precip types; ρhvespecially reduced when Zrain=Zice

Diverse shapes

Ryzhkov et al. (2005)

REMOVING NON-MET ECHO:FUZZY LOGIC CLASSIFICATION (FHC)

Clutter/AP

Rain

Insects/Birds

Example from JPOLE of rain embedded in clutter/AP and biological scatterers

:

Primarily useful to characterize variability of scatterer characteristics within the pulse volume.

Drizzle / light rain > ~0.98

Convective (but no ice) rain > ~0.96

Hail / rain mixtures ~0.90

Bright band mixed rain and snow ~0.75

Tornado debris ~0.50 or less

Ground clutter ~0.6-0.8

Some winter storm applications…….

Bright band descendingto surface in rain/snowtransition

Vertical profile in asnowstorm.

Dual offset antenna: 2008Prof. Bringi leads a successful >$1MMRI proposal to acquire a new antenna

Offset feed design, first time be used on an S-band weather radar

Unprecedented performance has nowbeen demonstrated

Advances the Facility to a new level ofperformance

The new antenna set the stage for another major development…..

Dual-wavelength projectDual-wavelength project No other radar like

this in the world Will allow CHILL

to make impact on NWS gap-filling radar concept

Takes advantage of CASA second generation radar

Unique dual-frequency combination enables new science

CSU cost share dollars used to acquire critical components

Will be tested later in the spring….

No other radar like this in the world

Will allow CHILL to make impact on NWS gap-filling radar concept

Takes advantage of CASA second generation radar

Unique dual-frequency combination enables new science

CSU cost share dollars used to acquire critical components

Will be tested later in the spring….12/9/2010

Main Reflecto

r

Sub-Reflector

Feed Horn

CASA Magnetron

T/R Pkg

Dual-frequencyFeed Horn

CSU-CHILL Update 36