Event studies of high-latitude FACs with inverse and assimilative analysis of ampere magnetometer data

We present examples of high-latitude field-aligned current (FAC) and toroidal magnetic potential patterns in both hemispheres reconstructed at a 2-min cadence using an updated optimal interpolation (OI) method that ingests magnetic perturbation data provided by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) program. A solstice and an equinoctial event are studied to demonstrate the reconstructed patterns and to provide scientific insights into FAC response to different solar wind drivers.

For the 14 June 2011 high-speed stream event with mostly northward B-z driving, we found persistently stronger FACs in the Northern Hemisphere. Extreme interhemispheric asymmetry is associated with the interplanetary magnetic field (IMF) direction and large dipole tilt, consistent with earlier studies. FAC asymmetries seen during an isolated substorm can be attributed to dipole tilt.