Ionospheric Tidal Waves Observed From Global Ionosphere Maps: Analysis of Total Electron Content

The monthly, seasonal, yearly, and latitudinal variations of ionosphere tidal waves are studied based on the total electron content (TEC) data from global ionosphere maps. We use two-dimensional (longitudinal, -180 degrees E to 180 degrees E; and time, 10 days) Fourier transform of TEC variations along different latitude to obtain all wave modes for the period from 18 November 2002 to 15 October 2014. The wave modes can be classified as westward propagating (eastward propagating and standing) waves with 85.8-97.3% (2.3-10.0% and 0.4-4.2%) of total power. The wave modes are found to consist of migrating waves with power 75-94% and nonmigrating waves with 5.8-25%. The migrating waves are dominated by diurnal migrating tide (DW1, 69.9-89.4%), semidiurnal migrating tide (SW2, 0.5-4.3%), and terdiurnal migrating tide (TW3, 0.2-1.9%). Also, the total wave power and powers of DW1 and SW2 peak along magnetic latitude 10 degrees N and decrease with increasing magnetic latitude. The power of TW3 peaks along the magnetic equator and decreases with increasing magnetic latitude. We also found that the wave powers of DW1 and SW2 obtained from TEC data are very similar to the wave powers obtained from the ionospheric density with a profile of sech(2) solitary wave. The observed migrating amplitudes are stronger in equinoxes and weaker in solstices. For the nonmigrating tides, we simultaneously identify the wave modes and wave powers, which contribute to wave-1, wave-2, wave-3, wave-4, and wave-5 peak structures in the local time frame. The total wave power associated with TEC variations increases with solar activity (sun spot number).