ELF and VLF Activity Associated with High Latitude Hole

Abstract

Based upon observations from a series of polar orbiting OGO satellites, the properties and structure of a “high latitude trough or hole” (HLT) or (HLH) in the topside ionosphere are summarized and correlated with the following terms, specifically in relation to ELF and VLF activity: (1) distinction from the midlatitude light ion trough (LIT) in H⁺, associated with the plasmapause; (2) a narrow, abrupt depletion in the concentrations of atomic ions H⁺, He⁺, O⁺, and N⁺; (3) molecular ion enhancements in NO⁺, O ⁺₂ , and N ⁺₂ ; (4) the > 30 keV electron trapping boundary; (5) the > 30 keV electron precipitation; (6)the electric field reversal; (7) the convective flow reversal; (8) the polar cap boundary. These observations are often well correlated with ELF and VLF activity, exhibiting enhancements in broadband auroral hiss, ELF noise and/or auroral kilometric radiation in the HLH region.