Determination of the parameters of travelling ionospheric disturbances in the high-latitude ionosphere using CUTLASS coherent scatter radars

A multi-frequency experiment at thermospheric heights using skip observations (METSO) has been designed for the co-operative UK twin located auroral sounding system (CUTLASS) radars for studying travelling ionospheric disturbances (TIDs). This mode uses both frequency and azimuthal scanning to build a two-dimensional phase map of the wave field independently in the two fields of view. On February 21, 2004, a superposition of three disturbances was observed and their parameters have been determined by a two-dimensional least-squares fitting method. Two of the disturbances were found to be consistent with models of TIDs caused by acoustic gravity waves (AGWs) from a point source: a medium-scale Earth-reflected mode and a large-scale direct mode. The propagation directions of the third disturbance, on the other hand, were found to differ in the two fields of view in a way inconsistent with a single point source, but rather a longitudinally extended one. All the waves were found to originate north of the radars.