The wind profiler is a ground based array of multiple beam Doppler radar units which measures and displays wind information up to an altitude of 16 km. This instrument is generally used to detect low level wind shear.
The wind profiler system consists of an array of Doppler Radar systems oriented to point upward. The "phased array" of 13 x 13 meter (40 ft by 40 ft) antennae are arranged in a array that looks like a chain link fence stretched out horizontally on stilts. This radar array operating at 404.37 MHz is used to sense the atmospheric wind profile from the surface up to an altitude of 16 km above the array on a nearly continuous basis.
A three-beam pattern in a sequence are generated, with one beam oriented vertically and the other two beams are oblique (that is, one is pointed to the north and one to the east).
Pulses of radar waves are emitted from the array in automated 6 minute cycles, repeated ten times each hour. The profiler system detects Doppler frequency shifts associated with the motions of atmospheric scattering agents along the direction of the radar beam. These motions are related to the fluctuations in atmospheric density caused by turbulent mixing of air with slightly different thermal and moisture properties. It is designed to operate even when clouds and precipitation are present. The returned signals are feed into a computer where they are converted to wind vectors. These data are processed at a Central Processing Facility where a finished hourly average of wind statistics is provided to users.
From a single profiler or the network, information is obtained about the horizontal and vertical distribution of winds. Thus, wind shear, turbulence and the location of jet streams can be located. Additional products related to divergence are produced by computers attached to the profiler unit.
Actually, only those wind shears that can be sensed must be at least 500 m from the surface.
The wind profilers cannot measure the vertical temperature or moisture profiles. Several Radio Acoustic Sounder Systems (RASS) have been deployed to generate atmospheric temperature profiles from the surface to an altitude of 6 km.
At present, the National Weather Service has installed a 30 station profiler network in the central United States as a demonstration project, called the Wind Profiler Demonstration Network (WPDN). NOAA FSL Profiler Network Map This network is meant to supplement the conventional radiosonde network, and would represent a tremendous improvement upon the twice daily radiosonde flights. Another wind profiler system is used at airports to monitor clear air turbulence and downbursts.
When the unit is operated in the Low mode, a fine height resolution (approximately 250 meter intervals) is available from 500 meters above the surface to approximately 9 km. In the High mode, a coarser altitude resolution is available to approximately 16 km.
The wind profiler data are routinely plotted upon a time-section chart. Temporal variations of wind conditions at various levels above the profiler can be graphically portrayed upon a vertical time section (or time series) chart. This type of chart provides a record of the profiler data for several hours at one particular site and affords the opportunity for further upper air analysis.
The vertical axis on this chart is altitude above the station. The exact vertical scale can be geographic altitude or pressure coordinates. The horizontal axis represents time progressing chronologically from left to right. Vertical lines may be drawn at equal time intervals.
Along each of these vertical lines, the typical wind shaft and wind arrow symbol is drawn at each level. This symbol is the same as found on a surface analysis and indicates the wind speed and wind direction.
Several atmospheric features can be detected from a wind profiler time section. Examples of what can be generated include the frontal structure and sequence during surface front passage.
Rapid changes in wind speed and/or wind direction over a vertical distance of the atmosphere at any time would indicate wind shear. Low level wind sheer may be associated with some convective activity, such as a thunderstorm, in the area. Upper tropospheric wind shear may be associated with the jet stream that may be found over the profiler.
Changes in the wind direction over time may also be seen. Frontal passages may be detected, with a change in the winds along a wind shift line accompanying the displacement of one air mass by another.
The manner in which the wind turns with height may indicate thermal advection. Winds turning in a clockwise direction with height would indicate warm advection, while winds turning in a counterclockwise direction with height suggests cold advection.
Last revision 9 June 1996© Copyright, 1996 Edward J. Hopkins, Ph.D. email@example.com
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