Principal component analysis of Birkeland currents determined by the Active Magnetosphere and Planetary Electrodynamics Response Experiment

TL;DR

This study applies principal component analysis to Birkeland current data to identify coherent patterns related to geomagnetic activity, revealing the dominant current systems and their modulation by seasonal and substorm processes.

Contribution

It introduces PCA as a tool to analyze Birkeland currents, highlighting the main current patterns and their dependence on geomagnetic and seasonal factors.

Findings

Region 1 and 2 currents are most reproducible

Cusp currents are seasonally modulated

No single pattern characterizes substorm current wedges

Abstract

Principal component analysis is performed on Birkeland or field-aligned current (FAC) measurements from the Active Magnetosphere and Planetary Electrodynamics Response Experiment. Principal component analysis (PCA) identifies the patterns in the FACs that respond coherently to different aspects of geomagnetic activity. The regions 1 and 2 current system is shown to be the most reproducible feature of the currents, followed by cusp currents associated with magnetic tension forces on newly reconnected field lines. The cusp currents are strongly modulated by season, indicating that their strength is regulated by the ionospheric conductance at the foot of the field lines. PCA does not identify a pattern that is clearly characteristic of a substorm current wedge. Rather, a superposed epoch analysis of the currents associated with substorms demonstrates that there is not a single mode of response, but a complicated and subtle mixture of different patterns.