Numerical Investigations of Interhemispheric Asymmetry due to Ionospheric Conductance. Issue 7 (8th July 2020)

• Record Type: Journal Article
• Authors: Lysak, R. L.; Song, Y.; Waters, C. L.; Sciffer, M. D.; Obana, Y.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 7(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-07-08
• Subjects: ULF waves -- quarter wave modes -- magnetoseismology -- magnetosphere‐ionosphere coupling; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA027866
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Due to differences in solar illumination, a geomagnetic field line may have one foot point in a dark ionosphere while the other ionosphere is in daylight. This may happen near the terminator under solstice conditions. In this situation, a resonant wave mode may appear, which has a node in the electric field in the sunlit (high conductance) ionosphere and an antinode in the dark (low conductance) ionosphere. Thus, the length of the field line is one quarter of the wavelength of the wave, in contrast with half‐wave field line resonances in which both ionospheres are nodes in the electric field. These quarter waves have resonant frequencies that are roughly a factor of 2 lower than the half‐wave frequency on the field line. We have simulated these resonances using a fully three‐dimensional model of ULF waves in a dipolar magnetosphere. The ionospheric conductance is modeled as a function of the solar zenith angle, and so this model can describe the change in the wave resonance frequency as the ground magnetometer station varies in local time. The results show that the quarter‐wave resonances can be excited by a shock‐like impulse at the dayside magnetosphere and exhibit many of the properties of the observed waves. In particular, the simulations support the notion that a conductance ratio between day and night foot points of the field line must be greater than about 5 for the quarter waves to exist. Key Points: Quarter‐wave modes can be excited on magnetic field lines with one foot point in a sunlit ionosphere and the other foot points in darkness These wave modes are strongly coupled with cavity resonances in the plasmasphere and magnetosphere The quarter‐wave modes are found when the ratio of Pedersen conductances between the sunlit and dark ionospheres is greater than 5