Thursday, October 07, 2010

A Three-Body Scatter Spike Due To Large Hail Observed By Phoenix Radar

A radar-observed reflectivity spike extending from the far side of an intense thunderstorm was shown by Lemon (1998) to be the result of three-body scattering by large hail in the core of the storm. A very distinct example of such a spike observed by the Green Bay WI radar is shown in top image (snipped from Kurimski, 2010). A schematic (middle image) illustrating how the energy in the radar beam is scattered into the ground and then, eventually, bounced back to the radar receiver (also snipped from Kurimski, but originally in earlier work by Lemon) with the time delay from hail-to-ground-to-hail-to-radar producing the false echo extending out of the far side of the storm echo. Such severe hail signatures are very robust, and they are usually seen associated with central US thunderstorms. However, a rare example occurred here in Arizona on Tuesday afternoon. The bottom image shows the KIWA (NWS Phoenix) radar 0.5 degree reflectivity at 2335 UTC. The KIWA radar is just off the lower right of the image and the three-body scatter spike produced by the hail in the echo core (violet to white portion of echo) extends west-northwest out of the far side (left side) of the echo core. Storms producing large hail are quite rare in Arizona, and this is the only example of this radar signature that I've seen in Arizona.
Lemon, L. R., 1998: The Radar "Three-Body Scatter Spike": An Operational Large-Hail Signature. Wea. Forecasting, 13, 327-340.
Kurimski, P. G., 2010: Radar Observations of a Rare "Triple" Three-Body Scatter Spike. Nat. Wea. Digest, 34, August 2010. This paper can be viewed on-line at:

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