Inductive‐dynamic magnetosphere‐ionosphere coupling via MHD waves

Abstract

In the present study, we investigate magnetosphere-ionosphere/thermosphere (M-IT) coupling via MHD waves by numerically solving time-dependent continuity, momentum, and energy equations for ions and neutrals, together with Maxwell's equations (Ampère's and Faraday's laws) and with photochemistry included. This inductive-dynamic approach we use is fundamentally different from those in previous magnetosphere-ionosphere (M-I) coupling models: all MHD wave modes are retained, and energy and momentum exchange between waves and plasma are incorporated into the governing equations, allowing a self-consistent examination of dynamic M-I coupling. Simulations, using an implicit numerical scheme, of the 1-D ionosphere/thermosphere system responding to an imposed convection velocity at the top boundary are presented to show how magnetosphere and ionosphere are coupled through Alfvén waves during the transient stage when the IT system changes from one quasi steady state to another. Wave reflection from the low-altitude ionosphere plays an essential role, causing overshoots and oscillations of ionospheric perturbations, and the dynamical Hall effect is an inherent aspect of the M-I coupling. The simulations demonstrate that the ionosphere/thermosphere responds to magnetospheric driving forces as a damped oscillator.

A two‐dimensional global simulation study of inductive‐dynamic magnetosphere‐ionosphere coupling

“…An interesting feature, which has been discussed in our previous study [Tu et al, 2014], is that v , as well as B (data not shown), is produced even though the ionosphere is pushed at the top boundary only in the antisunward direction (i.e., only v z is imposed at the top boundary). This is essentially a result of the dynamic Hall effect.…”

“…During periods of southward interplanetary magnetic field (IMF) the solar wind and magnetospheric convection drives a two-cell ionospheric convection in the high latitude, while more complicated ionospheric convection patterns occur if the IMF directs to the north. Indeed, our previous one-dimensional numerical simulations [Song et al, 2009;Tu et al, 2011Tu et al, , 2014 have clearly shown the dynamic processes of the M-I coupling via the MHD waves, particularly the Alfvén waves. The field-aligned currents or electric potential mapping from the magnetosphere have long been used to represent the electrodynamics coupling between the magnetosphere and ionosphere [e.g., Vasyliūnas, 1970, Wolf , 1970Richmond, 1995].…”

“…In our previous simulation studies, we have explored the transient responses of the ionosphere-thermosphere to the imposed magnetospheric convection in one-dimensional geometry [Song et al, 2009;Tu et al, 2011Tu et al, , 2014, which led to the appreciation of the importance of the wave reflection from the low-altitude ionosphere in causing the overshoots and oscillations of the ionosphere perturbations. In our previous simulation studies, we have explored the transient responses of the ionosphere-thermosphere to the imposed magnetospheric convection in one-dimensional geometry [Song et al, 2009;Tu et al, 2011Tu et al, , 2014, which led to the appreciation of the importance of the wave reflection from the low-altitude ionosphere in causing the overshoots and oscillations of the ionosphere perturbations.…”

North–South Asymmetries in Earth’s Magnetic Field

“…In reality the ionosphere responds to changes in magnetospheric convection in a finite time (e.g., Song et al 2009;Tu et al 2014), since the magnetosphere must overcome the inertia of the ionosphere/thermosphere system before a steady state is reached. The inertia may well be different between hemispheres, due to both seasonal variations and differences in the Earth's magnetic field as discussed in Sect.…”

Semiannual and solar activity variations of daytime plasma observed by DEMETER in the ionosphere‐plasmasphere transition region

“…Besides the photochemical reactions, the plasma spatial distributions are changed by neutral wind drag and/or electromagnetic forces [ Anderson , ; Murphy et al ., ; Balan et al ., ; Denton et al ., ; Luan and Solomon , ; Wang et al ., ]. Meanwhile, the plasma motions are also influenced by magnetosphere‐ionosphere coupling processes [ Song et al ., , ; Song and Vasyliūnas , ; Tu et al ., ]. The ionospheric ions may outflow into the magnetosphere [ Yu and Ridley , ] and therefore influence some dynamic processes in the magnetosphere [ Li et al ., ; Yu and Ridley , ].…”