Statistical Evaluation of the Solar Wind Control of the Large-scale Birkeland Currents

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The magnetosphere and its coupling to the ionosphere is very complex and dynamic. Global-scale physics-based simulations using global magnetohydrodynamic (MHD) models are one of the principal tools used to study the system, and establishing the extent to which the simulations reproduce the behavior of the natural system is essential to assessing the state of our predictive capabilities. The global configuration and energy transport rate are reflected in the electric currents flowing along the lines of magnetic force between the magnetosphere and the ionosphere. These currents, referred to as Birkeland currents, can be observed using the magnetic perturbations observed by the Iridium communications satellites as well as other satellites such as those of the Defense Meteorological Satellite Program (DMSP), the Danish Oersted satellite and the German CHAMP (CHAllenging Minisatellite Payload) satellite. This project will quantitatively compare the observed current systems with the results of MHD simulations. There are two primary tasks. The first step is to determine the quantitative dependencies of the Birkeland current distributions and intensities on the controlling physical parameters, such as the interplanetary magnetic field carried by the solar wind and the ionospheric conductance generated by solar Extreme Ultraviolet (EUV) radiation. The second step will be to evaluate how well the simulations capture the dependencies of the currents on the system drivers. Magnetometer data from the constellation of more than 70 low-altitude, polar-orbiting Iridium satellites has been acquired since February 1999. Magnetic field observations from the DMSP, Oersted, and CHAMP satellites are also available during this time. Proven techniques are in place to derive the global Birkeland current distributions using all of these data. The project will use approximately 1000 intervals from 1999 to the present having stable solar wind conditions. In parallel with the data analysis effort, the project will use MHD simulations that include the effects of the ring current in the inner magnetosphere to model the currents. These simulations will be run at the Community Coordinated Modeling Center (CCMC) using the Space Weather Modeling Framework developed at the University of Michigan and Rice University. The comparison of the statistical model with the simulations will make it possible to determine quantitatively how well the simulations capture the dependence of the solar wind-magnetosphere-ionosphere interaction on the physical parameters.