Technologies of the Modernized US NWS

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

– 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

• 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.