Radar Wind Profiler Joins ARM Mobile Facility Instrument Suite

 
Published: 15 May 2006

This spring, a 915 MHz radar wind profiler (RWP) was successfully installed at the ARM Mobile Facility (AMF) site in Niamey, Niger, West Africa, for the remainder of the 1-year RADAGAST field campaign which started in January. The RWP will provide information about wind speed, wind direction, and wind shear, and also enable measurements of the turbulence in the lower part of the troposphere. This may be a key variable in determining the vertical distribution of dust in the experimental domain. Gradients in the radar’s reflectivity spectrum may also help to provide continuous identification of the depth of the boundary layer in the summer months, when refractive gradients are likely to be maximized by low-level moisture.

Analysis of historical radiosonde data from Niamey showed the existence of significant stratification in the wind speed and direction profiles associated with the African Monsoon, the African Easterly Jet, and the “Harmattan” winds. Monthly composites of these data indicated strong directional and velocity shear in the lowest levels of the atmosphere, likely to be integrally involved with the associated cloud structures. Because these wind systems are critical components of the atmospheric structure above Niamey, the AMF science team determined they should be measured continuously during the AMF deployment.

As the latest addition to the baseline collection of AMF instruments, the RWP measures wind profiles from 2 to 5 km and virtual temperature profiles from 1 to 2 km by transmitting electromagnetic energy into the atmosphere and measuring the strength and frequency of back-scattered energy. The radar’s spectral recording capability will also significantly enhance researchers’ ability to interpret coincident data from the standard suite of AMF active remote sensors.