Utilizing riometry to observe gravity waves in the sunlit mesosphere

The novel use of imaging riometers to observe mesospheric gravity waves is described. Imaging riometers respond to changes in the absorption of cosmic radio noise in the ionospheric D-region which enables them to detect the compression and rarefaction of the atmosphere at ∼90 km altitude generated by the passage of gravity waves. A considerable advantage of this method is that, unlike conventional techniques which rely on imaging faint optical emissions from the airglow layer at ∼87 km altitude, riometers remain operative under daylit, moonlit or cloudy conditions. This is particularly important for research into gravity wave forcing of mesospheric temperature at polar latitudes in summer when continuous 24-hour daylight prevails. An example in which the same wave event is characterized in co-located airglow imager and imaging riometer shows good agreement between the two instruments.