Geoscience Reference
In-Depth Information
Fig. 6. (a) Doppler velocity spectra at different ranges made with a radar with a very large
Nyquist interval. The arrow points to the tornado. The spectrum is bi-model. (b) a
simulation of the spectra. (c) and (d) are simulated measured spectra made with different
Nyquist intervals. The spectrum overlaps and is aliased. In (c) the spectra is bi-modal still,
would produce a radial velocity estimate near zero with a very broad variance. In (d), the
mean is still zero, the spectra is uni-modal with a smaller variance.
6. Global survey
This section provides a necessarily brief global survey of various convective weather radar
processing systems. In fact, there are only a few NHMS' that actually provide a severe
weather warning service. The systems are presented in a sequence that approximately
matches when they were developed and the reader can follow the progression of the system
and philosophical developments.
6.1 RADAP - II, U.S.A.
The first radar processing system for severe weather was RADAP-II and it was built in the
1970's (Winston and Ruthi, 1986) and it followed from D/RADEX (Breidenbach et al, 1995;
Saffle, 1976) within the National Weather Service. They used VIL (vertically integrated liquid
water) and a significant innovation was the introduction of a SWP (Severe Weather
Probability) product. They were using probabilistic and uncertainty concepts then! There were
many innovations with RADAP-II but its deployment was curtailed due to the development of
the Doppler upgrade called the WSR-88D (Crum and Alberty, 1993; Lemon et al, 1977; Wilson
