Driving magnetosphere-ionosphere coupling in upper-atmosphere models with observed field-aligned currents from the AMPERE mission

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Friday, November 2, 2012

Geomagnetic field-aligned currents from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) satellite mission are used to drive the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM).

Comparison between simulated and observed image
Comparison between simulated (dashed) and observed (solid) ground magnetic perturbations at College, Alaska.
Observed field-aligned currents image
Observed field-aligned currents in the northern hemisphere from AMPERE, compared with the currents calculated from the TIEGCM when the sum of northern and southern AMPERE currents are used to drive the electrodynamics

We present a comparison between ground magnetic signatures computed by the model and observations at four different geomagnetic observatories, for different magnetic disturbance levels. Results show the ability of the model to pick up the gross features of the magnetic variations, improving its performance with increasing disturbance level and from low to high latitudes. During geomagnetically quiescent conditions a baseline noise of about 5 nT is evident in reconstructed ground magnetic field signatures, which we attribute to the baseline noise level in the AMPERE currents. For variations shorter than about 30 min the modeled signals are often significantly lower than observed by a factor up to 3 to 4, possibly reflecting localized ionization structures not captured in the TIEGCM conductance modules, or missing small-scale and rapid temporal variations in auroral currents. While the observed horizontal field variations are reflected in the model, the vertical component is consistently underestimated, possibly indicating errors in the estimates for ground induction currents. Comparison with the standard version of the TIEGCM is also carried out, showing that time variations shorter than 6 h and down to the 10 min resolution of the AMPERE data (which do not appear in the standard version of TIEGCM) are now reflected in the AMPERE-driven model.

Reference: Marsal, S., A.D. Richmond, A. Maute, and B.J. Anderson (2012), Forcing the TIEGCM model with Birkeland currents from the Active Magnetosphere and Planetary Electrodynamics Response Experiment, J. Geophys. Res., 117, A06308, doi:10.1029/2011JA017416.