Travelling ionospheric disturbances (TIDs) and tides observed by a super-resolution HF direction finding system

In this paper, the occurrence of tides, large-scale travelling ionospheric disturbances (LSTIDs) and medium-scale travelling ionospheric disturbances (MSTIDs) at mid-latitudes is investigated with respect to different geomagnetic conditions described by the K-index. As measurement system a high-frequency (HF) super-resolution direction-finding system has been used. An ionospherically refracted HF wave is affected by tilts and wave-like variations of the height of the ionosphere and its propagation is deviated from the great circle path. The temporal evolution of the deviation of the measured bearing and the respective power spectrum has been analyzed to detect the occurrence of TIDs and tides. During dusk and dawn, expected deviations of the bearing due to tides were found in agreement with the gradient of TEC in the respective TECmaps. At daytime, LSTIDs could generally be related to magnetic storms. Rarely they occurred as special events when the magnetosphere was extremely quiet (K<2). At nighttime, LSTIDs were found more often regardless of the K-index. MSTIDs passed in all measurements during all geomagnetic conditions at any time of the day or night. The power spectrum of the temporal evolution of the bearing showed characteristic shapes depending on whether LSTIDs were present or not. Parameters are defined which detect the occurrence of LSTIDs in the power spectrum.