Interhemispheric and Seasonal Differences of Field-Aligned Currents Characterized by Principal Component and Multivariate Alteration Detection of AMPERE-Iridium NEXT Magnetometer Data

Ionospheric conductivity is known to modulate field-aligned currents (FAC) and exhibits a pronounced seasonal dependence, leading to an asymmetry between the hemispheres in the magnetosphere-ionosphere system. This asymmetry is influenced not only by ionospheric conductivity but also by other factors such as the deviation of Earth's magnetic fields from a simple dipole, the offset of magnetic and geographic poles, Earth's orbital inclination, and the Interplanetary Magnetic Field (IMF). Some of these causes of asymmetry persist over seasons and years, while others change quickly. Therefore, gaining a comprehensive understanding of this asymmetry requires a thorough investigation of satellite observations over many years. The Iridium NEXT constellation has provided years worth of high-accuracy magnetometer data through the AMPERE program, which has allowed us to analyze the variability of FAC using Principal Component Analysis (PCA) implemented as a nonlinear sequential regression.
We have identified global modes of FAC variability, which show different patterns on the day side during local summer and the night side during local winter. Additionally, we have investigated how the magnitudes of these modes change with different geophysical properties and conditions to better understand the causes of hemispheric asymmetries and symmetries in Earth's FAC structures. To further investigate these underlying modes, we employed Multivariate Alteration Detection (MAD), resulting in a grid-point by grid-point quantification of hemispheric asymmetries.