Statistical Analysis of the Electron Density Gradients in the Polar Cap F Region Using the Resolute Bay Incoherent Scatter Radar North

Abstract

AbstractElectron density gradients in the polar F region ionosphere are essential for the structuring processes through the gradient‐drift instability (GDI). The information about the typical strength of gradients is important for the theoretical studies and modeling of the GDI waves, but rarely available because of significant experimental challenges in evaluation of the gradients, particularly at small scales and in 3‐D. In this study, multipoint density measurements of the Resolute Bay Incoherent Scatter Radar North working in a special high‐spatial‐resolution mode are employed to address the above question in a systematical manner. The 3‐D gradient vectors as well as their horizontal and vertical components are estimated for the first time and analyzed statistically utilizing a large Resolute Bay Incoherent Scatter Radar North data set. Statistical analysis of the gradient strength shows that the vertical components of the gradient strength vectors are larger than their horizontal counterparts, especially in the lower portion of the F region (below 220 km). The sharpness of the density gradients reveals a significant increase around magnetic midnight due to a decreased effect of the solar smoothing. Further, sharp density gradients occur during magnetically quiet times, possibly because of the presence of the polar holes and reduced plasma precipitation. The peak of occurrence for the horizontal components of the gradient strength vectors occurs at 0.5 × 10−6 m−1, whereas 15.5% of horizontal gradients exceeds 10−5 m−1. These gradients are strong enough for a direct generation of GDI waves at decameter scale (i.e. in linear regime), which implies that nonlinear turbulent cascade is not necessarily required for at least some GDI waves.