Relationship between large-scale ionospheric field-aligned currents and electron/ion precipitations: DMSP observations

Chao Xiong,Jan Rauberg,Claudia Stolle,Patrick Alken

doi:10.1186/s40623-020-01286-z

Abstract

In this study, we have derived field-aligned currents (FACs) from magnetometers onboard the Defense Meteorological Satellite Project (DMSP) satellites. The magnetic latitude versus local time distribution of FACs from DMSP shows comparable dependences with previous findings on the intensity and orientation of interplanetary magnetic field (IMF) By and Bz components, which confirms the reliability of DMSP FAC data set. With simultaneous measurements of precipitating particles from DMSP, we further investigate the relation between large-scale FACs and precipitating particles. Our result shows that precipitation electron and ion fluxes both increase in magnitude and extend to lower latitude for enhanced southward IMF Bz, which is similar to the behavior of FACs. Under weak northward and southward Bz conditions, the locations of the R2 current maxima, at both dusk and dawn sides and in both hemispheres, are found to be close to the maxima of the particle energy fluxes; while for the same IMF conditions, R1 currents are displaced further to the respective particle flux peaks. Largest displacement (about 3.5°) is found between the downward R1 current and ion flux peak at the dawn side. Our results suggest that there exists systematic differences in locations of electron/ion precipitation and large-scale upward/downward FACs. As outlined by the statistical mean of these two parameters, the FAC peaks enclose the particle energy flux peaks in an auroral band at both dusk and dawn sides. Our comparisons also found that particle precipitation at dawn and dusk and in both hemispheres maximizes near the mean R2 current peaks. The particle precipitation flux maxima closer to the R1 current peaks are lower in magnitude. This is opposite to the known feature that R1 currents are on average stronger than R2 currents.

Highlights

Auroral field-aligned currents (FACs), known as Birkeland currents, are an important transport mechanism for energy and momentum between the magnetosphere and ionosphere and are of fundamental importance for understanding the solar wind–magnetosphere–ionosphere–thermosphere coupling (e.g., Milan et al 2017)
In “Justification of FACs derived from Defense Meteorological Satellite Project (DMSP) Section”, we show one example of the Swarm observations to compare with DMSP data, and the altitude and local time evolution of Swarm A has been added, here marked in green
The main findings can be summarized as: 1. FACs derived from DMSP magnetic data have been compared with Swarm satellite observations and evaluated against earlier studies

Summary

Introduction

Auroral field-aligned currents (FACs), known as Birkeland currents, are an important transport mechanism for energy and momentum between the magnetosphere and ionosphere and are of fundamental importance for understanding the solar wind–magnetosphere–ionosphere–thermosphere coupling (e.g., Milan et al 2017). By comparing FACs derived from single- and dual-satellite of Swarm, Lühr et al (2015) found that at the auroral latitudes, the large-scale FAC signatures are consistent between the two approaches, but discrepancies commonly appear poleward of 75o magnetic latitude (MLAT). Filamentary FAC signatures are captured by the dual-satellite approach at poleward auroral oval under northward IMF condition, but are missed by the single-satellite technique. Another application of a multi-satellite approach to calculate FACs is the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) project (e.g., Anderson et al 2000; Green et al 2009; Korth et al 2010). Twodimensional average configurations of FACs are derived at cadences of less than an hour from magnetic measurements of 66 Iridium satellites

Discussion

Conclusion