Dipole tilt effect on magnetopause reconnection and the steady‐state magnetosphere‐ionosphere system: global MHD simulation
File(s)2019JA027510.pdf (5.82 MB)
Published version
Author(s)
Eggington, JWB
Eastwood, JP
Mejnertsen, L
Desai, RT
Chittenden, JP
Type
Journal Article
Abstract
The Earth’s dipole tilt angle changes both diurnally and seasonally and introduces numerous variabilities in the coupled magnetosphere‐ionosphere system. By altering the location and intensity of magnetic reconnection, the dipole tilt influences convection on a global scale. However, due to the nonlinear nature of the system, various other effects like dipole rotation, varying IMF orientation and non‐uniform ionospheric conductance can smear tilt effects arising purely from changes in coupling with the solar wind. To elucidate the underlying tilt angle‐dependence, we perform MHD simulations of the steady‐state magnetosphere‐ionosphere system under purely southward IMF conditions for tilt angles from 0°‐90°. We identify the location of the magnetic separator in each case, and find that an increasing tilt angle shifts the 3‐D X‐line southward on the magnetopause due to changes in magnetic shear angle. The separator is highly unsteady above 50° tilt angle, characteristic of regular FTE generation on the magnetopause. The reconnection rate drops as the tilt angle becomes large, but remains continuous across the dayside such that the magnetosphere is open even for 90°. These trends map down to the ionosphere, with the polar cap contracting as the tilt angle increases, and region‐I field‐aligned current (FAC) migrating to higher latitudes with changing morphology. The tilt introduces a north‐south asymmetry in magnetospheric convection, thus driving more FAC in the northern (sunward‐facing) hemisphere for large tilt angles than in the south independent of conductance. These results highlight the strong sensitivity to onset time in the potential impact of a severe space weather event.
Date Issued
2020-07-18
Date Acceptance
2020-05-19
Citation
Journal of Geophysical Research: Space Physics, 2020, 125 (7), pp.1-17
ISSN
2169-9380
Publisher
American Geophysical Union (AGU)
Start Page
1
End Page
17
Journal / Book Title
Journal of Geophysical Research: Space Physics
Volume
125
Issue
7
Copyright Statement
©2020. The Authors.
This is an open access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
This is an open access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Sponsor
Natural Environment Research Council (NERC)
Natural Environment Research Council (NERC)
Identifier
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JA027510
Grant Number
NE/P017347/1
NE/P017142/1
Subjects
0201 Astronomical and Space Sciences
0401 Atmospheric Sciences
Publication Status
Published
Date Publish Online
2020-06-19