The Field of Shock‐Generated Alfven Oscillations Near the Plasmapause

Abstract

A theoretical interpretation is given for magnetohydrodynamic (MHD) oscillations observed by the GOES and Cluster satellites on November 7, 2004 near the plasmapause (Zong et al., 2009, 2012, https://doi.org/10.1029/2009ja014393, https://doi.org/10.1029/2012ja018024), before and after an interplanetary shock passes through the magnetosphere (about 18:27 UT). It is shown that, after the shock front passage, the MHD oscillation spectra recorded by Cluster (C1) and GOES 12, located respectively inside and outside the plasmasphere, differ significantly. According to our interpretation, these differences are due to the shock wavefront affecting the plasmapause and exciting broadband resonant Alfven waves, thus significantly changing the MHD oscillation spectrum. A model in the form of a plasma cylinder was developed in order to study MHD oscillations in the dayside magnetosphere numerically. An analytical model is proposed for the source of resonant Alfven waves that has the form of two fast magnetosonic wave packets propagating along the plasmapause, resulting from the shock wave/plasmapause interaction. Numerically calculated parameters of Alfven waves excited by a source based on this model show a good agreement with the oscillation parameters observed by satellites.

Multispacecraft Observation of the Presubstorm Long‐Lasting Poloidal ULF Wave

“…Usually, Pc4–5 waves are associated with the MHD Alfvén waves (e.g., Dai et al., 2013), although sometimes they can be identified with the drift‐compressional modes (Mager et al., 2019; Rubtsov et al., 2018). According to previous studies, the dayside high‐ m Pc4–5 waves usually appear as a consequence of magnetic storms (Dai et al., 2015; Le et al., 2017), substorms (James et al., 2013; Zolotukhina et al., 2008), or interplanetary shocks (Leonovich et al., 2021; Zong et al., 2009).…”

Kinetic Alfven Waves Near a Dissipative Layer

“…The magnetic field components were calculated for Alfven oscillations in Leonovich et al., (2019), (2021) using the ideal MHD approximation. To regularize the singularity in the field of monochromatic oscillations at the resonance surface, the local decrement was taken into account.…”

“…The same holds for calculating the specific power the FMS wave loses near the resonance surface. We therefore will calculate the density of the flux [determined by the evaluation formula (Equation 27)] of energy carried by broadband KAWs assuming their amplitude to be approximately equal to the amplitude of broadband resonant Alfven waves calculated in Leonovich et al, 2019Leonovich et al, , (2021 in the ideal MHD approximation. / / is the energy of a single resonant electron.…”

“…A shock is by its nature a nonlinear FMS wave, which serves as a broadband source for resonant KAWs. The Alfven oscillation field was calculated in the above cylindrical magnetosphere model by Leonovich et al, (2019Leonovich et al, ( ), (2021.…”