severe weather seminar spring 2011 pat.spoden@noaa.gov

Operational Use of Spectrum Width

Severe Weather Seminar

Spring 2011

Pat.spoden@noaa.gov

What is Spectrum Width?

• One of the 3 base moments available with WSR-88D

• Measures the variability of movement within a bin

• With super-high resolution, there is much we can see

• Not available on the web – GR software only – Color scales important, as always

Spectrum Width

• Spectrum Width depicts a measure of velocity dispersion. It provides a measure of the variability of the mean radial velocity estimates due to wind shear, turbulence, and/or the quality of the velocity samples. It is used to estimate turbulence associated with boundaries, thunderstorms, mesocyclones.

Spectrum Width

Low Spectrum Width High Spectrum Width

Both situations can be helpful…

Low Spectrum Width

• Depicts a smooth flow• Supercell• May 2, 2010

Low Spectrum Width

Low, or smoothvalues

Low Spectrum Width

Rear FlankDowndraft

Low Spectrum Width

Tornado is now“cutoff” and soon dissipates

Damage Map

Tornado RFD wind damage

High Spectrum Width

Distant Supercell

May 2, 2010

EF0 Tornado in northern Butler

Image from 10-15mintues prior to touchdown

High Spectrum Width

Other Uses

• TBSS – Three Body Scatter Spike

1949 @ 9.9 (19,500 ft)

August 14, 2010

-Signature seen5-10 minutesprior to 65-70mph microburst.

1954 Cross Section

• It is not always clear nor easy to locate the true “leading edge.”

• Strong winds can push storms upshear which may complicate the matter

Next Question

Where is the “leading edge”

??

• Use Spectrum Width or Velocity productSolutions

Where is the “leading edge?”

Where you thought?

Another way to help spot interfaces and mesovortices – use SPECTRUM WIDTH!

Spectrum Width

• Depicts turbulence within the range bin.• Low values suggest “smooth flow”

– RFDs, inflow

• High values suggest turbulent flow– Boundaries– Potential of tornadic signatures with weak

rotation