[Picture shows radar images of reflectivity, velocity, and spectrum width with the data field extending to the WNW in a pattern characteristic of a hail signature]
Notes:
This commonly observed signature (i.e., the radially extended data fields
in the WNW direction) is commonly called a “Hail Signature”, or “Hail Spike” because
it often appeared when hail shafts are present. Dr. Dusan Zrnic provided
the correct explanation of this signature. Although it is often associated
with hail, hail is not a necessary ingredient. Forward scatter from high
reflectivity regions (commonly associated with intense rain rates and/or
hail) and backscatter from the ground are involved in constructing this
signature. Because precipitation is involved twice in scattering, and the
ground once, it is called by Dr. Zrnic as three body scattering. The next
slide depicts the three body scattering process.