Utilization of statistical techniques to validate current systems in geospace simulations

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Monday, 3 February 2014
Hall C3 (The Georgia World Congress Center )
Michael Wiltberger, NCAR, Boulder, CO; and S. R. Sain, W. Kleiber, M. Heaton, and E. J. Rigler

Electric currents that flow within the magnetosphere, ionosphere, and between these two regions are very relevant to space weather. The predictive quality of a numerical model of this coupled system should therefore be tested against measurements, direct or indirect, of these currents.

Chains of ground-based magnetometers have typically been used to infer horizontal currents in the ionosphere at high latitudes, and large-scale magnetospheric currents at low latitudes. In truth, magnetic disturbance is the superposition of effects from both current regimes, especially at middle latitudes. It is difficult to reliably separate the influence of these two current systems in ground magnetic data, so we consider their cumulative effect in model output by integrating the Biot-Savart relationship over the entire magnetospheric volume.

Field-aligned currents (FACs) flowing between the magnetosphere and ionosphere are responsible for most of the energetic coupling between these two regimes, and are therefore of particular interest. FACs are difficult to detect from the ground, and almost impossible to isolate from other currents, but the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) uses magnetometers onboard the Iridium constellation of satellites to quantify the strength and location of these currents in situ.

All these current systems are organized more by magnetic latitude and local time than fixed geographic coordinates. Statistical “imputation” is used to map ground magnetic measurements at sampled locations to unsampled locations. This is only possible because Earth rotates ground stations through all local times, and because horizontal currents exhibit substantial correlation across significant length scales. AMPERE's observation platforms, on the other hand, are relatively fixed in magnetic coordinates, but a spherical harmonic fit is necessary to fill in between observations.

We asses the accuracy of modeled electric currents, or associated magnetic disturbance, for the Lyon-Fedder-Mobarry geospace model using object-based verification. We consider a variety of parameters, including the location, shape, and strength of these current systems. We start with a climatological view, considering different solar wind driving conditions and IMF directions, then progress to a more time-dependent analysis.