Interhemispheric Asymmetry of Field-Aligned Currents Determined by Principal Component Analysis of AMPERE-Iridium NEXT Magnetometer Data

While both polar ionospheric regions are closely coupled to the magnetosphere because of the geometry of the Earth's magnetic fields, the coupling is not necessarily symmetrical between hemispheres. An asymmetry exists between field aligned currents (FAC) in the northern and southern hemispheres. This asymmetry is believed to be caused by compound effects of multiple geophysical properties and conditions such as: the deviation of Earth's magnetic fields from a simple dipole field, the offset of magnetic and geographic poles, the Earth's orbital inclination, the Interplanetary Magnetic Field (IMF), and solar irradiance. Some of these causes are persistent over seasons and years, and some are highly changeable on minute timescales. Given the multiple cause and effect relationships that simultaneously operate at different time-scales, it is crucial to study this FAC asymmetry over the course of many years using satellite constellation observations.

Recently, years' worth of high accuracy magnetometer data obtained from the Iridium NEXT constellation have become available through the AMPERE program. Large volumes of data have been analyzed to determine FAC variability through principal component analysis implemented as nonlinear sequential regression. We have determined the global modes of FAC variability from the mean FAC patterns and have found the leading modes show prominent dayside signals in the local summer on both hemispheres. Conversely, in the local winter, the leading modes of FAC variability contain predominant features on the nightside. Furthermore, we have investigated how the magnitude of these modes change with different geophysical properties and conditions to decipher the causes of hemispheric asymmetries and symmetries in Earth's FAC structures.