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

Abstract

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 ±30° 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 (∡(B,v)) 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 ∡(B,v) 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 ∡(B,v).