Professor Jiannan Tu
University of Massachusetts, Lowell, Center for Atmospheric Research (UMLCAR)
Title: Inductive-Dynamic Magnetosphere-Ionosphere Coupling via MHD waves
Seminar Tuesday, Nov. 5, 2013 at Boston College ISR
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 (Ampere's and Faraday's laws) and with
photochemistry included. This inductive-dynamic approach we use is fundamentally different from
those in previous 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 selfconsistent 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 Alfven 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.