Spatial distribution of ionospheric plasma and field structures in the high‐latitude F region

Abstract

Ion density and velocity measurements from the Dynamics Explorer 2 (DE 2) spacecraft are used to obtain the average magnetic local time versus invariant latitude distribution of irregularities in the high‐latitude F region ionosphere. To study the small‐scale structure and its relationship to background conditions in the ionosphere, we have formed a reduced database using 2‐s (≈ 16 km) segments of the ion density and velocity data. The background gradients associated with each 2‐s segment and the spectral characteristics, such as power at 6 Hz (≈ 1.3 km) and spectral index, are among the reduced parameters used in this study. The relationship between the observed plasma structure and its motion is complex and dependent on the externally applied fields as well as locally generated plasma structure. The evolution of plasma structures also depends critically on the conductivity of the underlying ionosphere. Observations indicate an enhancement of irregularity amplitudes in two spatially isolated regions in both the ion density and the velocity. Convective properties seem to play a more important role in winter hemisphere where smaller‐scale structures axe maintained outside the source regions. ΔV irregularity amplitudes are enhanced in the cusp and the polar cap during northward interplanetary magnetic field regardless of season. The power in ΔV is usually higher than that associated with local polarization electric fields, suggesting that the observed structure in ΔN/N is strongly influenced by ΔV structure applied to large density gradients.