Northern preference for terrestrial electromagnetic energy input from space weather

I P Pakhotin,J K Burchill,K Xie,I R Mann,D J Knudsen

doi:10.1038/s41467-020-20450-3

I P Pakhotin, J K Burchill + Show 3 more

Open Access

https://doi.org/10.1038/s41467-020-20450-3

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Journal: Nature Communications	Publication Date: Jan 8, 2021
Citations: 32	License type: open-access

Affiliation: University of Alberta, University of Calgary

Abstract

Terrestrial space weather involves the transfer of energy and momentum from the solar wind into geospace. Despite recently discovered seasonal asymmetries between auroral forms and the intensity of emissions between northern and southern hemispheres, seasonally averaged energy input into the ionosphere is still generally considered to be symmetric. Here we show, using Swarm satellite data, a preference for electromagnetic energy input at 450 km altitude into the northern hemisphere, on both the dayside and the nightside, when averaged over season. We propose that this is explained by the offset of the magnetic dipole away from Earth’s center. This introduces a larger separation between the magnetic pole and rotation axis in the south, creating different relative solar illumination of northern and southern auroral zones, resulting in changes to the strength of reflection of incident Alfvén waves from the ionosphere. Our study reveals an important asymmetry in seasonally averaged electromagnetic energy input to the atmosphere. Based on observed lower Poynting flux on the nightside this asymmetry may also exist for auroral emissions. Similar offsets may drive asymmetric energy input, and potentially aurora, on other planets.

Highlights

Terrestrial space weather involves the transfer of energy and momentum from the solar wind into geospace
A critical component of this magnetosphere–ionosphere coupling (MIC) involves large-scale field-aligned currents (FACs) which flow in patterns of upwards and downwards sheets in response to solar wind forcing[1,2] and which are related to convection plasma flows in the magnetosphere arising from coupling to the solar wind through magnetic reconnection[3]
We advance a paradigm which can explain the observed persistent asymmetry and northern preference for incoming Poynting flux at Swarm altitudes based on the known offset of the magnetic dipole moment from the centre of the Earth towards the northwest Pacific[22]. This offset generates different relative effective solar illumination of the auroral ovals in the northern and southern hemispheres arising from the rotation of the Earth

Summary

Introduction

Terrestrial space weather involves the transfer of energy and momentum from the solar wind into geospace. We show, using Swarm satellite data, a preference for electromagnetic energy input at 450 km altitude into the northern hemisphere, on both the dayside and the nightside, when averaged over season We propose that this is explained by the offset of the magnetic dipole away from Earth’s center. Asymmetries in the aurora may occur as a result of differential solar illumination[10], from potential interhemispheric differences in ionosphere–thermosphere coupling as due to the offset of the magnetic dipole from the Earth’s centre, as well as from higherorder multipole terms[11] These studies demonstrate that the auroral forms and their intensities in the two hemispheres can be asymmetric. As that study only considered northern summer months, they were unable to assess whether such asymmetry would reverse 6 months later, nor whether there was any systematic seasonably averaged interhemispheric asymmetry

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