Solar Wind-Magnetosphere Coupling Under Interim Steady Conditions

Abstract

Solar wind—magnetosphere coupling is an important driver of dynamics within the magnetosphere–ionosphere–thermosphere system, traditionally modeled using coupling functions. Most coupling functions assume the interaction is one-directional, that the solar wind conditions determine the energy that is transferred into the magnetosphere. To test this one-directional hypothesis, we use the Space Weather Modeling Framework to simulate nine 48-hr periods of idealized steady solar wind driving. The IMF inputs were varied every 2 hr, while the plasma conditions were held fixed for each of the nine intervals lasting 48 hr each. We calculate the energy flux through the magnetopause surface, including magnetopause motion effects. The energy transport through the open magnetopause is compared with two empirical coupling functions across all 2-hr intervals of steady solar wind driving. We find the energy input to the magnetosphere does not remain steady, as quantified by total variation, which has a median value of 1.36 TW. The variability results were binned according to a substorm indicator that combines signatures of dipolarization, plasmoid release, and substorm current wedge. Binning into substorm and non-substorm categories yielded different median variability values, but the substorm indicator failed to explain conditions of high variability in energy transport. Evaluation of energy injection results across all conditions suggests there may be a minimum energy state for a given solar wind condition. If such a minimum exists and can be reproduced, it may provide a basis for a new two-way solar wind–magnetosphere coupling function, including the effect of the state of the magnetosphere.