Radar System Proposal
Eureka, CA
December through February
Pink Team: Robb Ellis, Kurt Korte, Matthew Miller
Objectives: The objective of this project was to design a
radar observing system to optimally observe precipitation
near Eureka, CA for the months of December through
February
Radar Climatology: Eureka is located on the northern California coast. It has
a maritime climate with a rainy season spanning from October through April.
Winter storms typically move in from the Gulf of Alaska, riding the prevailing
northwest winds. These storms are strong frontal systems accompanied by a
strong upper level jet and a strong upper level low. Theses storms have
ample moisture drawn from the Pacific Ocean. Radar Observations indicate
that the precipitation is widespread, but shallow. This indicates that the
storms typically bring in stratiform clouds with a precipitation level below
three kilometers. There is a constant bright-band on the radar due to
perpetual, low wintertime melting layer. The melting layer signature is a
common winter feature and leads to an overestimation of radar derived
precipitation. Literature has pointed out that there are problems in
observing this shallow West Coast precipitation via NWS radar due to the
low-level confinement of the precipitation and the high physical elevation of
the radar installations. Overshooting by even the lowest level scans leads to
much of the near surface precipitation to go unobserved.
Avg.
Avg. In
Avg. Storm Avg. Storm
Avg. Storm Avg. Storm
Avg. Radar
Freezing
Storm
Motion
Evolutio
Height
Area
Echo
Level
Airflow
Speed
n Time
m
2.3
Km
7.75
Km2
25000
Km/Hr
35
Km/Hr
30
Hr.
1
DBz
25
Design Objectives: The large areas of the winter storms prompt for a large range for the radar specifications. We choose
to have a maximum range of 250km so that the entire storm area can be observed. Radar climatology indicated that the
average maximum storm height was below 8km. Therefore, a scan strategy optimized to capture features below 8km was
developed. A large antenna size was chosen to allow for a narrow beam width to facilitate the capture of storm features
are far away from the radar was reasonable. Because the winter storms are fairly uniform in structure over time with a
slow evolution speed, a volume scan time goal of 6 to 12 minutes was chosen.
System Design and Specifications: We chose to use an S-band radar in order to achieve maximum range and to minimize
attenuation effects from transmitting through a long path length filled with moderate precipitation. Due to the uniformity
and widespread nature of the winter storms in question, we choose a single doppler radar sited near the coast at an
elevation of 762 meters.
Wavelength: 10cm
Antenna Beamwidth: 0.82º (assuming k=70º)
Antenna Diameter: 8.53m
The antenna diameter was chosen to minimize beamwidth and as a cost control measure due to it's widespread use in
existing radar systems.
Due to the normally homogeneous nature of the stratiform precipitation found off the northern California coast in the
winter, the added expense of dual polarization radar and other technologies were unjustifiable.
Scan Strategy 1: The following scan strategy was
developed to best observe the stratiform
precipitation that moves into the Eureka area
from the ocean. The 0º base scan level was
chosen to view more of the precipitation below
the melting layer to prevent the overestimation
of precipitation due to bright band
contamination. The elevation of the radar site
prevents ground contamination of the return
signal when used over the ocean. On the VCP plot
presented to the right the average melting height
and the average storm top height are show by the
red dotted line and blue solid line respectively.
Range of elevation angles: min. angle=0º, max.
angle= 19.5º
Number of angles to be scanned in the volume=11
Scan Rate=7.6875 º/s
PRF=600Hz
Nyquist Velocity=15m/s
Maximum Unambiguous Range=250Km
Scan Strategy 2: The following
scan strategy was developed to
best observe the orographic
precipitation enhancement by
the mountains to the west of
Eureka. On the VCP plot
presented to the left the
average melting height and the
average storm top height are
show by the red dotted line and
blue solid line respectively.
Range of elevation angles: min.
angle=0º, max. angle=19.5 º
Number of angles to be scanned
in the volume=11
Scan Rate=10.98 º/s
PRF=854.143Hz
Nyquist Velocity=21.43m/s
Maximum Unambiguous
Range=175Km
Strengths and Weaknesses: The scan strategies illustrated above have been designed with two types of storm structures in
mind. The first scan strategy was designed to observe shallow stratiform precipitation over the ocean with an elevated
radar. The second scan strategy was devised for observing the orographic enhancement of precipitation over the windward
slope of the mountains that lie to the east of Eureka. S-band radar was chosen to minimize attenuation effects that may
occur due to the long path lengths of the radar signal. Static, non-meteorological echoes occurring from the nearby
mountains will have to be filtered by the signal processor of the radar. Due to the elevation of the radar site, sea spray
should not pose a problem by creating false echoes.
Acknowledgements: The Pink Team would like to thank each other. We would also like to thank Dr. Yuter and Catherine
Spooner and guidance and code.
References:
Westrick, K. J., C. F. Mass, and B. A. Colle, 1999: The Limitations of the WSR-88D Radar Network for
Quantitative Precipitation Measurement over the Coastal Western United States. Bull. Amer.
Meteor. Soc., 80, 2289-2298.
Rinehart, R. E., 2004: Radar for Meteorologists. Rinehart Publishing, 482pp.