Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect
We use the am, an, as and the aσ geomagnetic indices to the explore a previously overlooked factor in magnetospheric electrodynamics, namely the inductive effect of diurnal motions of the Earth’s magnetic poles toward and away from the Sun caused by Earth’s rotation. Because the offset of the (eccen...
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Online Access: | https://doi.org/10.1051/swsc/2020077 https://doaj.org/article/e5743068a73b4324b02c5b3d1be01ae7 |
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ftdoajarticles:oai:doaj.org/article:e5743068a73b4324b02c5b3d1be01ae7 2023-05-15T16:19:39+02:00 Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect Lockwood Mike Haines Carl Barnard Luke A. Owens Mathew J. Scott Chris J. Chambodut Aude McWilliams Kathryn A. 2021-01-01T00:00:00Z https://doi.org/10.1051/swsc/2020077 https://doaj.org/article/e5743068a73b4324b02c5b3d1be01ae7 EN eng EDP Sciences https://www.swsc-journal.org/articles/swsc/full_html/2021/01/swsc200083/swsc200083.html https://doaj.org/toc/2115-7251 2115-7251 doi:10.1051/swsc/2020077 https://doaj.org/article/e5743068a73b4324b02c5b3d1be01ae7 Journal of Space Weather and Space Climate, Vol 11, p 15 (2021) magnetosphere geomagnetic activity universal time variations polar cap motions dipole tilt effects Meteorology. Climatology QC851-999 article 2021 ftdoajarticles https://doi.org/10.1051/swsc/2020077 2022-12-31T13:46:49Z We use the am, an, as and the aσ geomagnetic indices to the explore a previously overlooked factor in magnetospheric electrodynamics, namely the inductive effect of diurnal motions of the Earth’s magnetic poles toward and away from the Sun caused by Earth’s rotation. Because the offset of the (eccentric dipole) geomagnetic pole from the rotational axis is roughly twice as large in the southern hemisphere compared to the northern, the effects there are predicted to be roughly twice the amplitude of those in the northern hemisphere. Hemispheric differences have previously been discussed in terms of polar ionospheric conductivities generated by solar photoionization, effects which we allow for by looking at the dipole tilt effect on the time-of-year variations of the indices. The electric field induced in a geocentric frame is shown to also be a significant factor and gives a modulation of the voltage applied by the solar wind flow in the southern hemisphere that is typically a ±30% diurnal modulation for disturbed intervals rising to ±76% in quiet times. For the northern hemisphere these are 15% and 38% modulations. Motion away from/towards the Sun reduces/enhances the directly-driven ionospheric voltages and reduces/enhances the magnetic energy stored in the tail and we estimate that approximately 10% of the effect appears in directly driven ionospheric voltages and 90% in changes of the rate of energy storage or release in the near-Earth tail. The hemispheric asymmetry in the geomagnetic pole offsets from the rotational axis is shown to be the dominant factor in driving Universal Time (UT) variations and hemispheric differences in geomagnetic activity. Combined with the effect of solar wind dynamic pressure and dipole tilt on the pressure balance in the near-Earth tail, the effect provides an excellent explanation of how the observed Russell-McPherron pattern with time-of-year F and UT in the driving power input into the magnetosphere is converted into the equinoctial F-UT pattern in average geomagnetic activity ... Article in Journal/Newspaper Geomagnetic Pole Directory of Open Access Journals: DOAJ Articles Journal of Space Weather and Space Climate 11 15 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
magnetosphere geomagnetic activity universal time variations polar cap motions dipole tilt effects Meteorology. Climatology QC851-999 |
spellingShingle |
magnetosphere geomagnetic activity universal time variations polar cap motions dipole tilt effects Meteorology. Climatology QC851-999 Lockwood Mike Haines Carl Barnard Luke A. Owens Mathew J. Scott Chris J. Chambodut Aude McWilliams Kathryn A. Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect |
topic_facet |
magnetosphere geomagnetic activity universal time variations polar cap motions dipole tilt effects Meteorology. Climatology QC851-999 |
description |
We use the am, an, as and the aσ geomagnetic indices to the explore a previously overlooked factor in magnetospheric electrodynamics, namely the inductive effect of diurnal motions of the Earth’s magnetic poles toward and away from the Sun caused by Earth’s rotation. Because the offset of the (eccentric dipole) geomagnetic pole from the rotational axis is roughly twice as large in the southern hemisphere compared to the northern, the effects there are predicted to be roughly twice the amplitude of those in the northern hemisphere. Hemispheric differences have previously been discussed in terms of polar ionospheric conductivities generated by solar photoionization, effects which we allow for by looking at the dipole tilt effect on the time-of-year variations of the indices. The electric field induced in a geocentric frame is shown to also be a significant factor and gives a modulation of the voltage applied by the solar wind flow in the southern hemisphere that is typically a ±30% diurnal modulation for disturbed intervals rising to ±76% in quiet times. For the northern hemisphere these are 15% and 38% modulations. Motion away from/towards the Sun reduces/enhances the directly-driven ionospheric voltages and reduces/enhances the magnetic energy stored in the tail and we estimate that approximately 10% of the effect appears in directly driven ionospheric voltages and 90% in changes of the rate of energy storage or release in the near-Earth tail. The hemispheric asymmetry in the geomagnetic pole offsets from the rotational axis is shown to be the dominant factor in driving Universal Time (UT) variations and hemispheric differences in geomagnetic activity. Combined with the effect of solar wind dynamic pressure and dipole tilt on the pressure balance in the near-Earth tail, the effect provides an excellent explanation of how the observed Russell-McPherron pattern with time-of-year F and UT in the driving power input into the magnetosphere is converted into the equinoctial F-UT pattern in average geomagnetic activity ... |
format |
Article in Journal/Newspaper |
author |
Lockwood Mike Haines Carl Barnard Luke A. Owens Mathew J. Scott Chris J. Chambodut Aude McWilliams Kathryn A. |
author_facet |
Lockwood Mike Haines Carl Barnard Luke A. Owens Mathew J. Scott Chris J. Chambodut Aude McWilliams Kathryn A. |
author_sort |
Lockwood Mike |
title |
Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect |
title_short |
Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect |
title_full |
Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect |
title_fullStr |
Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect |
title_full_unstemmed |
Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect |
title_sort |
semi-annual, annual and universal time variations in the magnetosphere and in geomagnetic activity: 4. polar cap motions and origins of the universal time effect |
publisher |
EDP Sciences |
publishDate |
2021 |
url |
https://doi.org/10.1051/swsc/2020077 https://doaj.org/article/e5743068a73b4324b02c5b3d1be01ae7 |
genre |
Geomagnetic Pole |
genre_facet |
Geomagnetic Pole |
op_source |
Journal of Space Weather and Space Climate, Vol 11, p 15 (2021) |
op_relation |
https://www.swsc-journal.org/articles/swsc/full_html/2021/01/swsc200083/swsc200083.html https://doaj.org/toc/2115-7251 2115-7251 doi:10.1051/swsc/2020077 https://doaj.org/article/e5743068a73b4324b02c5b3d1be01ae7 |
op_doi |
https://doi.org/10.1051/swsc/2020077 |
container_title |
Journal of Space Weather and Space Climate |
container_volume |
11 |
container_start_page |
15 |
_version_ |
1766006056870215680 |