Spectral properties of sub-kilometer-scale equatorial irregularities as seen by the Swarm satellites

The faceplates on-board the Swarm satellites have provided high-resolution measurements of electron density at a frequency of 16 Hz along the satellite paths. The 16-Hz electron density data from Swarm were analyzed to determine the spectral characteristics of the F-region ionospheric irregularities at Swarm altitudes. The electron density data covered all geographic longitudes with quasi-dipole latitude limited between and the period considered was from October 2014 to October 2018, when the data was available. The Power Spectral Densities (PSDs) observed follows a power law. The values of spectral indices obtained showed a peak centered at around -2.5, located at the Equatorial Ionization Anomaly (EIA) belts. The spectral indices were found to be sensitive to irregularity amplitude. The local time distribution of the spectral indices also showed a peak within the time sector 20:00 LT - 22:00 LT and then decreased gradually after about 22:00 LT till 06:00 LT. The peak of the spectral index was also observed in the South American-Atlantic-African longitudes and it was generally low in the Asian-Pacific region. The angle between the Swarm satellite orbital path and the magnetic field (...) was also examined and it was observed that the highest percentage of occurrence of ionospheric irregularities and the peak in spectral index was obtained only when the was between 20° and 40°. The local turbulence is anisotropic with respect to the background magnetic field as indicated by a more negative spectral index for larger....