 Definition of Spectrum Width (σ v ) › 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 Reference: CRARP 24-06

 Spectrum width (σ v ) is one of three Doppler spectral moments collected by radar, i.e., Z, V, σ v  Legacy resolution of σ v – 1°, 0.25 km  Super Resolution of σ v – 0.5°, 0.25 km  Super Resolution → twice the legacy res.  σ v is typically a noisy product  Quality of σ v is dependent on S/N ratio

 σ v is not used too readily in radar operations  σ v compliments the other two Doppler spectral moments collected by RDA  σ v has utility in warning decision operations › hail › mesocyclone › tornado  σ v has utility in aviation operations › turbulence › frontal shear

 Spectrum width signal provides some additional interesting information about the TBSS ( lic/vol2-3/figure2.html) lic/vol2-3/figure2.html  Reflectivity TBSS may be obscured due to reflectivity display limitations  Spectrum width values associated with TBSS very large (OTO 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, Ref: Lindley et al., 2007: Preliminary Observations of Weak Three-Body Scatter Spikes Associated With Low-End Severe Hail, EJSSM, 2, 1-15

 In mature storms –σ v averages ~2ms-1 through mid-levels  Greater values of σ v associated with storm top  Greater values of σ v in the updraft/downdraft interface (core)  Lower values of σ v associated with BWER Ref: Melnikov et al., 2002: Spectrum Width from Echo Power Differences Reveal Meteorological Features, JOAT, 19,

 σ v integral in enhancing precipitation type detection in dual-pol systems due to the relation between DSD and σ v  σ v integral in enhancing precipitation type detection in dual-pol systems due to the relation between w(D) and σ v Ref: Moisseev et al., 2006: Dual Polarization Spectral Analysis for Retrieval of Effective Raindrop Size, JAOT, Ref: Shapiro, 2005: Drag Induced Transfer of Horizontal Momentum Between Air and Raindrops, JAS, 62,

 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,

 Observational study by WFO GID (based on legacy)  Paired σ v 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

Unfortunately, CS decommissioned with OB3 Combined threshold of σ v =6 ms-1 (12 kt) and CS =.0080 s-1 indicator of thunderstorms which produced tornadoes or damaging wind σ v ≥ 8 ms-1 (16 kt) and CS ≥ of.0090 s-1 better indicators of tornadic (?) circulations in the events examined

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

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

 JPOLE, 2003 (KOUN)  σ v by itself is not sufficient  Pairing with σ 2 s and P yields better results  TSS can be recognized by large σ v, low σ 2 s, and high P (PRIB) Ref: Yu et al., 2007: Characterization of Tornado Spectral Signatures Using Higher Order Spectra, JAOT,24,

Storm Relative VelocityReflectivitySpectrum Width Spectrum Flatness PRIB Ref: Yu et al., 2007: Characterization of Tornado Spectral Signatures Using Higher Order Spectra, JAOT,24,

 σ v compliments the other Doppler spectral moments  σ v alone will not provide a definitive answer in WDM  Observational studies have shown utility pairing σ v with WSR-88D base products and derived products  Numerical radar simulations support observational studies and visa versa  σ v will be helpful in delineating hydrometeor type with Dual-Pol  σ v will be integral in MDA and TDA for Dual-Pol

 Herald, P. and K. Drozd, 2006: USE OF COMBINED SHEAR AND SPECTRUM WIDTH IN TORNADO DETECTION, CRARP  Lemon, 1998: The Radar" Three Body Scatter Spike": An Operational Large Hail Indicator, WAF, 13,  Lindley et al., 2007: Preliminary Observations of Weak Three-Body Scatter Spikes Associated With Low-End Severe Hail, EJSSM, 2,  May et al., 2007: A Doppler Radar Emulator with Application to the Detectability of Tornadic Signatures, JAOT, 24,  Moisseev et al., 2006: Dual Polarization Spectral Analysis for Retrieval of Effective Raindrop Size, JAOT,  Shapiro, 2005: Drag Induced Transfer of Horizontal Momentum Between Air and Raindrops, JAS, 62,  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,