VHF radars (similar to that at Davis) are also known as Mesosphere-Stratosphere-Troposphere (MST) radars. They are able to detect reflections from turbulent structures in the clear air in the mesosphere, the stratosphere and the troposphere.

Measurements of wind speed and direction

The strongest radar reflections that the radar detects come from the lower part of the atmosphere (the troposphere and the lower stratosphere). As a result, the radar is able to measure the wind speed and direction in this part of the atmosphere all year round.

Wind measurements rely on turbulent patches that move with the atmosphere. The sophisticated antenna array installed at Davis can form a narrow radar beam through which to track the turbulence. The so-called 'Doppler shift' gives the speed with which the air is moving toward or away from you along the beam. It can be used to build a three dimensional picture of the wind pattern above the radar.

The presence of enhanced reflections from the mesosphere during the summertime (Polar Mesosphere Summer Echo or PMSE) extends the reach of the radar into the upper part of the middle atmosphere. VHF radars are also capable of detecting meteor trails in the upper mesosphere and lower thermosphere. These trails are formed when small particles of meteoric dust fall to earth and create short-lived ionised trails. For a short time, these trails are very good VHF radar reflectors. The movement of the trail towards or away from the radar, along with the direction from which the reflection is coming, allow the wind pattern to be determined. The result is a measurement of the wind an amazing 100 km away. A smaller group of antennas, known as 'the meteor array' is used for measurements from meteor trails.

Momentum fluxes

The amount of momentum that is being transported vertically through the atmosphere by atmospheric gravity waves is an important parameter in determining the global circulation of the atmosphere. The narrow radar beams that can be formed using this radar can be configured to measure this parameter at the heights where it is possible to measure winds.