Geoscience Reference
In-Depth Information
10
New Observations by Wind Profiling Radars
Masayuki K. Yamamoto
Research Institute for Sustainable Humanosphere (RISH), Kyoto University,
Japan
1. Introduction
Wind profiling radar, also referred to as “radar wind profiler”, “wind profiler”, and
“clear-air Doppler radar”, is used to measure height profiles of vertical and horizontal
winds in the troposphere. It receives signals scattered by radio refractive index
irregularities (clear-air echo) and measures the Doppler shift of the scattered signals
(Gage, 1990). Wind profiling radar measures wind velocities by steering its beam
directions or using spaced receiving antennas (e.g., Larsen & Röttger 1989; May, 1990).
The two methods are referred to as the Doppler beam swinging (DBS) technique and
spaced antenna (SA) technique, respectively. Owing to its capability to measure wind
velocities in the clear air with high height and time resolutions (typically a hundred to
several hundreds of meters and less than several minutes, respectively), it is used for
atmospheric research such as radio wave scattering, gravity waves, turbulence,
temperature and humidity profiling, precipitation system, and stratosphere-troposphere
exchange (STE) processes (Fukao, 2007; Hocking, 2011). Wind profiling radar is also
utilized for monitoring wind variations routinely. In USA and Japan, a nationwide
ultrahigh frequency (UHF) wind-profiling radar network is operated in order to provide
upper-air wind data to numerical weather prediction (Ishihara et al., 2006; Stanley et al.,
2004). In Europe, Cost Wind Initiative for a Network Demonstration in Europe
(CWINDE), now renamed as the Co-Ordinated Wind Profiler Network in Europe, is also
operated (Met Office, 2011).
For wind profiling radars, frequency range of 30-3000 MHz (i.e., very high frequency (VHF)
and UHF bands) is generally used because the energy spectrum of atmospheric turbulence
falls off rapidly with decreasing eddy size in the inertia subrange, and radar radio waves are
scattered only from turbulent eddies at the Bragg scale (i.e., half the radar wavelength). For
measurements from the ground to several thousand meters, UHF wind profiling radars are
widely used because their small antenna size enables their easy installation and their quick
switching time from transmission to reception is necessary for measurements near the
ground. Such UHF wind profiling radars are referred to as the boundary layer radars.
Because the minimum size of turbulent eddies increases exponentially with increasing
altitude (e.g., Hocking, 1985), frequencies near 50 MHz are used for clear-air radars which
measure the mesosphere, stratosphere and troposphere (MST radars) and those which
measure the stratosphere and troposphere (ST radars). In the chapter, measurement results
of VHF and UHF radars are presented.
