Definition of Spectrum Width (σ v ) › Spectrum width is a measure of the velocity dispersion...

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A Relook at Spectrum Width in Warning Decision Operations 2009 WFO EAX Spring Severe Weather Seminar Suzanne

Transcript of Definition of Spectrum Width (σ v ) › Spectrum width is a measure of the velocity dispersion...

A Relook at Spectrum Width in Warning Decision Operations

2009 WFO EAX Spring Severe Weather SeminarSuzanne

Reference: CRARP 24-06

A Relook at Spectrum Width in Warning Decision Operations: Definition

Definition of Spectrum Width (σv )› Spectrum width is a measure of the

velocity dispersion within a sample volume or a measure of the variability of the velocity estimates

Large spectrum widths are related to turbulence intensity and to mean wind shear across the beam

A Relook at Spectrum Width in Warning Decision Operations: Definition

Spectrum width (σv ) is one of three Doppler spectral moments collected by radar, i.e., Z, V, σv

Legacy resolution of σv – 1°, 0.25 km Super Resolution of σv – 0.5°, 0.25 km Super Resolution → twice the legacy

res. σv is typically a noisy product Quality of σv is dependent on S/N ratio

A Relook at Spectrum Width in Warning Decision Operations

σv is not used too readily in radar operations σv compliments the other two Doppler

spectral moments collected by RDA σv has utility in warning decision operations

› hail › mesocyclone› tornado

σv has utility in aviation operations› turbulence› frontal shear

A Relook at Spectrum Width in Warning Decision Operations: Hail Detection

Spectrum width signal provides some additional interesting information about the TBSS (http://www.ejssm.org/ojs/public/vol2-3/figure2.html)

Reflectivity TBSS may be obscured due to reflectivity display limitations

Spectrum width values associated with TBSS very large (OTO 16-22 kts)› result of the presence of a

complex mixture involving both horizontal and vertical motions of the scatterers in this region)

Ref: Lemon, 1998: The Radar" Three Body Scatter Spike": An Operational Large Hail Indicator, WAF, 13, 327-340

Ref: Lindley et al., 2007: Preliminary Observations of Weak Three-Body Scatter Spikes Associated With Low-End Severe Hail , EJSSM,

2, 1-15

Ref: Melnikov et al., 2002: Spectrum Width from Echo Power Differences Reveal Meteorological Features, JOAT, 19, 1793-1810

A Relook at Spectrum Width in Warning Decision Operations: Hail Detection

In mature storms –σv averages ~2ms-1 through mid-levels

Greater values of σv associated with storm top

Greater values of σv in the updraft/downdraft interface (core)

Lower values of σv associated with BWER

A Relook at Spectrum Width in Warning Decision Operations: Hail Detection in Future

σv integral in enhancing precipitation type detection in dual-pol systems due to the relation between DSD and σv

σv integral in enhancing precipitation type detection in dual-pol systems due to the relation between w(D) and σv

Ref: Moisseev et al., 2006: Dual Polarization Spectral Analysis for Retrieval of Effective Raindrop Size, JAOT, 1682-1695

Ref: Shapiro, 2005: Drag Induced Transfer of Horizontal Momentum Between Air and Raindrops, JAS, 62, 2205-2219

A Relook at Spectrum Width in Warning Decision Operations: Mesocyclones and Tornadoes

Spectrum Width can be used to identify velocity contamination/distortion of interior storm features, i.e., mesocyclones

Spectrum width can be used to help identify such a distortion› The normal location of reflectivity cores

relative to mesocyclones will occasionally result in velocity pattern distortion

Ref: Lemon, 1998: The Radar" Three Body Scatter Spike": An Operational Large Hail Indicator, WAF, 13, 327-340

A Relook at Spectrum Width in Warning Decision Operations: Severe Local Storms, Tornadic Storms Observational study by WFO

GID (based on legacy) Paired σv with combined shear

(CS) derived product Combined Shear

› A derived product that quantifies radial and azimuthal shear

› Developed to provide measure of shear along frontal boundaries

› Complimentary product to Spectrum Width

› Default height for calculation ~1.5°

Reference: Herald, P. and K. Drozd, 2006: USE OF COMBINED SHEAR AND SPECTRUM WIDTH IN TORNADO DETECTION CRARP 24-06

A Relook at Spectrum Width in Warning Decision Operations: Mesocyclones and TVS

Unfortunately, CS decommissioned with OB3

• Combined threshold of σv =6 ms-1 (12 kt) and CS =.0080 s-1 indicator of thunderstorms which produced tornadoes or damaging wind• σv ≥8 ms-1 (16 kt) and CS ≥ of .0090 s-1 better indicators of tornadic (?) circulations in the events examined

A Relook at Spectrum Width in Warning Decision Operations: Mesocyclones and Tornadoes, 8-bit and Super-res

Ref: May & Biggerstaff et al., 2007: A Doppler Radar Emulator with Application to the Detectability of Tornadic Signatures, JAOT, 24,1973-1996

Control experiment for S-band radar with 1° beamwidth

S-band using smaller gate length, 125 m instead of 250 m (ala Super Res)

•SW values invof meso > 4 ms-1•SW values during tornado – 20 ms-1

A Relook at Spectrum Width in Warning Decision Operations: Mesocyclones and Tornadoes, 8-bit and Super-res: EAX example

A Relook at Spectrum Width in Warning Decision Operations: Mesocyclones and Tornadoes in Dual-Pol Future

Ref: Wang et al., :Spectral Analysis of Dual-Polarization Radar Signals in a Tornadic Supercell Storm

Ref: Yu et al., 2007: Characterization of Tornado Spectral Signatures Using Higher Order Spectra, JAOT,24, 1997-2013

A Relook at Spectrum Width in Warning Decision Operations: Mesocyclones and Tornadoes JPOLE, 2003 (KOUN) σv by itself is not

sufficient Pairing with σ2

s and P yields better results

TSS can be recognized by large σv , low σ2

s , and high P (PRIB)

A Relook at Spectrum Width in Warning Decision Operations: Future Supplements for Tornadic Detection

Storm Relative VelocityReflectivity Spectrum Width

Spectrum Width Spectrum FlatnessPRIB

Ref: Yu et al., 2007: Characterization of Tornado Spectral Signatures Using Higher Order Spectra, JAOT,24, 1997-2013

Summary

σv compliments the other Doppler spectral moments

σv alone will not provide a definitive answer in WDM

Observational studies have shown utility pairing σv

with WSR-88D base products and derived products Numerical radar simulations support observational

studies and visa versa σv will be helpful in delineating hydrometeor type

with Dual-Pol σv will be integral in MDA and TDA for Dual-Pol

References

Herald, P. and K. Drozd, 2006: USE OF COMBINED SHEAR AND SPECTRUM WIDTH IN TORNADO DETECTION, CRARP 24-06.

Lemon, 1998: The Radar" Three Body Scatter Spike": An Operational Large Hail Indicator, WAF, 13, 327-340.

Lindley et al., 2007: Preliminary Observations of Weak Three-Body Scatter Spikes Associated With Low-End Severe Hail , EJSSM, 2, 1-15.

May et al., 2007: A Doppler Radar Emulator with Application to the Detectability of Tornadic Signatures, JAOT, 24, 1973-1996.

Moisseev et al., 2006: Dual Polarization Spectral Analysis for Retrieval of Effective Raindrop Size, JAOT, 1682-1695.

Shapiro, 2005: Drag Induced Transfer of Horizontal Momentum Between Air and Raindrops, JAS, 62, 2205-2219.

Wang et al., Spectral Analysis of Dual-Polarization Radar Signals in a Tornadic Supercell Storm.

Yu et al., 2007: Characterization of Tornado Spectral Signatures Using Higher Order Spectra, JAOT,24, 1997-2013.