Resolute Bay Incoherent Scatter Radar observations of plasma structures in the vicinity of polar holes

Abstract

AbstractThe Resolute Bay Incoherent Scatter Radar North (RISR‐N) data collected between January 2012 and June 2013 are employed to identify and analyze 14 events with significant plasma density depressions (Ne<4 × 1010 m−3) in the winter polar cap ionosphere. The RISR‐N observations near a magnetic latitude (MLAT) of 85°N refer to the region poleward of the previously identified polar hole‐auroral cavity region 70°–80° MLAT where extremely low densities (down to 2 × 108 m−3 near 300 km in altitude) are found at times. Multipoint observations by RISR‐N are also characterized by multiple series of propagating local density enhancements (plasma structures) both well outside and in the vicinity of polar holes. A superposed epoch analysis of plasma density and convection reveals that the density depressions tend to reach their minimum near the reversal of the meridional convection component. The wavelet analysis of plasma density time series shows that the wave power is enhanced within the depressions and tends to peak near the density minimum. The plasma structures are more elongated at mesoscales (>150 km), with no apparent differences between structure shapes outside and inside low‐density regions. The structure propagation velocity is perpendicular to its elongation direction and consistent with that of the large‐scale plasma convection. The observations indicate that large‐scale density depressions can form under a variety of convection conditions and that plasma structuring processes outside the depressions may be responsible for their partial filling.