Effect of Brief Northward Turning in IMF Bz in an MHD Simulation

Abstract:

While the solar wind is typically highly variable, most MHD simulation studies use idealized steady state conditions to study the magnetosphere-ionosphere coupling. To better understand the effect of variable solar wind conditions, we have conducted a variety of numerical experiments using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic simulation. The solar wind input into the LFM simulation has been configured to contain an interplanetary magnetic field (IMF) that starts at a steady southward IMF and suddenly turns northward for a brief period of time before turning back into a steady southward IMF. The height of the brief northward turning and the period of northward turning has been varied for each simulation run. Classically, the period of northward will greatly reduce energy dissipation in the ionosphere. When the northward IMF is flipped back to southward, the reduced dissipation lingers and causes the period of southward immediately following the northward IMF turning to also have less dissipation. With larger northward IMF magnitudes, the dissipation during southward is also correspondingly lower. We will present a detailed analysis of the magnetic topology for the period of southward immediately following the northward IMF turning and discuss a possible cause for this reduction in energy dissipation.