Geoscience Reference
In-Depth Information
1
Doppler Radar for USA Weather Surveillance
Dusan S. Zrnic
NOAA, National Severe Storms Laboratory
USA
1. Introduction
Weather radar had its beginnings at the end of Word War II when it was noticed that storms
clutter radar displays meant to reveal enemy aircraft. Thus radar meteorology was born.
Until the sixties only the return power from weather tracers was measured which offered
the first glimpses into precipitation structure hidden inside clouds. Possibilities opened up
to recognize hail storms, regions of tornadoes (i.e., hook echoes), the melting zone in
stratiform precipitation, and even determine precipitation rates at the ground, albeit with
considerable uncertainty.
Technology innovations and discoveries made in government laboratories and
universities were quickly adopted by the National Weather Service (NWS). Thus in 1957
the Miami Hurricane Forecast Center commissioned the first modern weather radar
(WSR-57) the type subsequently installed across the continental United States. The radar
operated in the 10 cm band of wavelengths and had beamwidth of about 2
o
. In 1974 more
radars were added: the WSR-74S operating in the band of 10 cm wavelengths and WSR-
74C in the 5 cm band.
Development of Doppler radars followed, providing impressive experience to remotely
observe internal motions in convective storms and infer precipitation amounts. Thus
scientists quickly discovered tell tale signatures of kinematic phenomena (rotation, storm
outflows, divergence) in the fields of radial velocities.
After demonstrable successes with this technology the NWS commissioned a network of
Doppler radars (WSR-88D=Weather Surveillance Radars, year 1988, Doppler), the last of
which was installed in 1997. Much had happened since that time and the current status
pertinent to Doppler measurements and future trends are discussed herein.
The nineties saw an accelerated development of information technology so much so that,
upon installation of the last radar, computing and signal processing capabilities available to
the public were about an order of magnitude superior to the ones on the radar. And
scientific advancements were still coming in strong implying great improvements for
operations if an upgrade in processing power were to be made. This is precisely what the
NWS did by continuing infusion of the new technology into the system. Two significant
upgrades have been made. The first involved replacement of the computer with distributed
workstations (on the Ethernet in about 2002) for executing algorithms for precipitation
estimation, tornado detection, storm tracking, and other. The second upgrade (in 2005)
