Transcript Wind Profilers: General

Technologies of the Modernized US NWS
(National Weather System)
Today
• NWS technology includes the following:
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ASOS (completed topic)
AWIPS
Wind Profilers
NEXRAD
GOES I – M
• This lecture will focus on AWIPS and wind profilers
NEXRAD
• NEXt generation
RADar
• Known as WSR-88D
• Dual Doppler Radar
• It’s importance in
severe wx forecasting
recognized in early
1980s.
GOES Satellites
GOES I - M
• Geostationary Operational Environmental
Satellites (since 1975)
• Make Visible and Infrared Images of the
Earth Every Half Hour
• GOES I – M means GOES 8 through 12
• All have been launched, 8 & 10 are
operational (8 launched in 1994), 11/12 in
storage (in space), and 9 malfunctioned
AWIPS
• Advanced Weather
Interactive Processing
System
– Interactive wx
computer
– Core of the NWS
telecommunications
capability
– Used at all weather
forecast centres
(WFC).
AWIPS Components
• WFC Workstation
– Interprets and analyzes
data
– Helps prepare forecast
products for
transmission
– Stores, retrieves data
• Communications
System
– Collects data from
around world
– Data distributed among
AWIPS sites
– Distributes Info to the
public.
Wind Profilers
• Doppler radars used to measure vertical
profiles of horizontal wind speed and
direction from near the surface to the
tropopause (500 m to 16 km)
• Profiler Network
•
Deployed 1990-1992
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32 sites in central U.S., 3 in AK
How profilers work (1)
• Microwave (74 cm) pulses (404 MHz) are sent
along 3 beams (“beam swinging”)
•
One directly overhead
•
One tilted 15° from vertical to the east
•
One tilted 15° from vertical to the north
• 36 range gates (sampling heights) spaced 250 m
• Microwaves transmitted for 2 minutes on each
beam
• This long sampling time reduces noise in the data
404 MHz Antenna
Beam
Swinging
How Profilers Work (2)
• Two sampling modes operating for one
minute each in any direction
• High mode: longer pulse, increased
sensitivity by a factor of 40
- Samples from 7.5 km all the way to 16.25
km (36 gates)
• Low mode: samples every 250 m from 500
m to 9.25 km AGL (above ground level).
How profilers work (3)
• Beam pulses propagating through the atmosphere
do not have to strike clouds or precipitation
particles
• They are instead affected by clear air turbulence
• Radars detect air density changes induced by
turbulent mixing of air volumes having different
temperature and humidity.
• These T, q, gradients backscatter the radar energy,
returning some of it to the radar.
How profilers work (4)
• Turbulence induced T, q, gradients move with the
wind’s velocity and direction.
• They produce a doppler shift in the frequency of
the scattered radiation
• Doppler shift is used to calculate the wind speed
and direction
• Ten 6-minute measuring cycles generate the
hourly averages
• These profilers can even operate on cloudy days
with moderate rain
Wind Profiler Products
• Winds component velocities for u, v, ω
Vertical velocity ranges from +12 m/s
(sinking) to –12 m/s (rising)
• Thermal wind
• Wind Shear
• Cross-section
• Plan views of streamlines, relative vorticity
and horizontal divergence
Radio Acoustic Sounding System
(RASS)
• Is co-located with some profiler sites
• It is the simultaneous transmission of
acoustic- and micro-waves to deduce the
speed of sound as a function of altitude
• Helps estimate the virtual temperature as a
function of altitude from the measured
sound speed and vertical air motion
RASS
4 transducers per site
Sound emanates from
horn downward to the
dish and then upward.
Triangular shaped
features at top (earlier
photos) are noise
baffles called
thnadners.