Case studies of the propagation characteristics of auroral TIDS with EISCAT CP2 data using maximum entropy cross-spectral analysis

In this paper case studies of propagation characteristics of two TIDs are presented which are induced by atmospheric gravity waves in the auroral F-region on a magnetic quiet day. By means of maximum entropy cross-spectral analysis of EISCAT CP2 data, apparent full wave-number vectors of the TIDs are obtained as a function of height. The analysis results show that the two events considered can be classi®ed as moderately large-scale TID and mediumscale TID, respectively. One exhibits a dominant period of about 72 min, a mean horizontal phase speed of about 180m/s (corresponding to a horizontal wavelength of about 780 km) directed south-eastwards and a vertical phase speed of 55m/s for a height of about 300 km. The other example shows a dominant period of 44min, a mean horizontal phase velocity of about 160m/s (corresponding to a horizontal wavelength of about 420 km† directed southwestwards, and a vertical phase velocity of about 50m/s at 250 km altitude.