Characteristics of mid‐latitude whistler ducts as deduced from ground‐based measurements

Abstract

Propagation characteristics of mid‐latitude whistlers, especially whistler duct characteristics, have been investigated based on measurements in August, 1994 at Dunedin, New Zealand(L=2.78) and in August, 1989 at Ceduna, Australia(L=1.93), both during local midnight. Polarization analyses have enabled us to locate whistlers which exited the ionosphere just above the observing station (LDF is defined in this way). The nose extension method was also applied to these whistlers (their Ln is estimated by this method). The following findings have emerged from the analyses; LDF ≃ Ln (at Dunedin) and LDF ≃ Ln‐0.43(at Ceduna). Our analysis suggests that mid‐latitude ducts are likely to extend down to the ionosphere at L ≈ 2.8. Ray tracing studies for realistic density profiles indicates that a whistler duct terminates at an altitude of about 3,500 ∼ 5,500 km at an L value of ∼1.9 with its enhancement factor being a few percent at least. These results may imply a strong variability of the latitudinal or temporal variations of mid‐latitude whistler ducts.

Real‐time imaging of density ducts between the plasmasphere and ionosphere

“…While the hypothesized existence of field-aligned density ducts accounts for a large body of experimental data [Ohta et al, 1996;Singh et al, 1998;Carpenter and Smith, 2001], it has not been previously possible to directly verify that large, cylindrical density structures greatly extended along the Earth's magnetic field lines exist, or to track their motions precisely and continuously over regional scales. Satellite in-situ observations [Sonwalkar et al, 1994] can only measure densities at single points, and cannot instantaneously probe the regional-scale density distribution.…”

“…The plasmasphere is a toroidal region within the Earth's magnetosphere that is filled with plasma from the ionosphere, which is a photoionized layer near the surface of the Earth [Goldstein, 2006]. The existence of field-aligned ducts in the plasmasphere is widely accepted as the explanation for ground-based detections of whistler-mode waves, which may be guided along such ducts [Ohta et al, 1996;Bakharev et al, 2010]. Wave-particle interactions that accelerate and precipitate particles into the atmosphere occur efficiently within these ducts, so their existence aids the removal of energetic particles from the magnetosphere and thereby influences global magnetospheric-ionospheric coupling and energetics [Sonwalkar , 2006].…”

Whistler‐Mode Waves Trapped by Density Irregularities in the Earth's Magnetosphere

“…Whistler‐mode waves were first discovered on the ground over a century ago (Preece, 1894), and were since frequently observed by ground‐based detections (Stenzel, 1999). The existence of Earth‐magnetosphere/ionosphere waveguide is widely accepted, which guides whistler‐mode waves to reach the ground (Ohta et al., 1996; Stenzel, 1999). The most common waveguides are field‐aligned density irregularities (also called density ducts) supported by theoretical and numerical works (Hanzelka & Santolík, 2019; Smith et al., 1960; Streltsov et al., 2006), which have been frequently detected by satellite‐based measurements (Carpenter et al., 2002; Darrouzet et al., 2009) and ground‐based imaging telescope (Loi et al., 2015).…”

Power spectrum analysis of ionospheric fluctuations with the Murchison Widefield Array

“…Field‐aligned density ducts are cylindrical enhancements/depletions in the plasmasphere with widths of 10–100 km [ Angerami , ; Ohta et al , ]. These can extend down to ionospheric altitudes [ Bernhardt and Park , ] and may form by the interchange of magnetic flux tubes under the influence of electric fields, e.g., those from thunderstorms [ Park , ; Walker , ].…”