Technologies of the Modernized US NWS
(National Weather System)
Today
" NWS technology includes the following:
 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 " Communications
System
 Interprets and analyzes
data
 Collects data from
around world
 Helps prepare forecast
products for
 Data distributed among
transmission
AWIPS sites
 Stores, retrieves data
 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
" 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, É
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.