M-I Coupling: An Observational and Modeling Study Under Conditions of Extreme Forcing

Boston College, Chestnut Hill MA

Investigators

Abstract

The investigators will study magnetosphere-ionosphere coupling through coordinated observational and modeling of the effects of the imposition of large polar-cap electric potentials on the M-I system. The focus will be on very large storms, i.e. superstorms, which exhibit highly unusual electrodynamic behavior. The evolution of the system and dissipation of energy are central to an understanding of how the coupled system proceeds from a highly energized state back to equilibrium. Previous studies have revealed during a detailed event study of a superstorm, that the observed Region 1 and 2 field-aligned currents (FACs), conductances and particle precipitation provided many surprises: the Region 2 FACs were amongst the largest ever observed in the ionosphere yet there was little magnetic signature on the ground; the conductances were many times larger than that predicted, and the measured precipitating electron flux consisted entirely of low-energy (E<200eV) particles. Similar behavior was manifest during other superstorms, which occurred during the recent solar maximum period. It is clear that the realm of behavior demonstrated during superstorms is beyond current understanding of M-I coupling. The investigators will study a series of superstorms in order to develop a qualitative and quantitative description of the electrodynamic properties of the ionosphere under conditions of unusually large polar-cap potential distributions. They will determine the evolution of electric fields, field-aligned currents and conductances during the course of several superstorms through direct observations of the plasma drifts, particle precipitation and magnetic perturbations. They will extend the database of observed plasma and magnetic measurements by using a global data-driven model of the ionosphere. They will also use a simplified version of the Rice Convection Model to consider the effect of the imposed polar-cap potential on magnetospheric convection. Guided by a model for magnetosphere-ionosphere coupling, the observations of the coupling currents and fields will provide a unified picture of the temporal and spatial evolution of the electrodynamic processes at work during the superstorm. Observations of plasmas and magnetic fields made by DMSP at 840 km altitude are limited to the local times sampled by the satellites, which are approximately 06-18 LT and 09-21 LT. While the sun-synchronous orbits allow continuous monitoring of these local time sectors, information on other local times and altitudes is lacking. Investigators will supplement the DMSP observations with global modeling of the ionosphere under conditions of extreme forcing. This research will lead to an improved understanding of M-I coupling processes, in particular the effects of large polar-cap potentials imposed on the ionosphere. It will yield quantitative ranges for electric fields, FACs, conductances and particle precipitation, which have never been reported systematically for magnetic storms. These parameters are essential for any detailed model of the evolution of the M-I system after the commencement of large magnetic activity. The study will be significant in modeling of energy balance and dissipation, the loci and time scales for these processes, all of which are central to the problem of M-I coupling.