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 a-sigma 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 (...
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EDP Sciences
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Online Access: | https://centaur.reading.ac.uk/95181/ https://centaur.reading.ac.uk/95181/8/swsc200083.pdf https://centaur.reading.ac.uk/95181/1/390_Lockwood_Paper4n_Fa.pdf |
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ftunivreading:oai:centaur.reading.ac.uk:95181 2024-09-09T19:41:03+00:00 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. 2021-02-17 text https://centaur.reading.ac.uk/95181/ https://centaur.reading.ac.uk/95181/8/swsc200083.pdf https://centaur.reading.ac.uk/95181/1/390_Lockwood_Paper4n_Fa.pdf en eng EDP Sciences https://centaur.reading.ac.uk/95181/8/swsc200083.pdf https://centaur.reading.ac.uk/95181/1/390_Lockwood_Paper4n_Fa.pdf Lockwood, M. <https://centaur.reading.ac.uk/view/creators/90001127.html> orcid:0000-0002-7397-2172 , Haines, C., Barnard, L. A. <https://centaur.reading.ac.uk/view/creators/90005020.html> orcid:0000-0001-9876-4612 , Owens, M. J. <https://centaur.reading.ac.uk/view/creators/90003236.html> orcid:0000-0003-2061-2453 , Scott, C. J. <https://centaur.reading.ac.uk/view/creators/90003900.html> orcid:0000-0001-6411-5649 , Chambodut, A. and McWilliams, K. A. (2021) 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. Journal of Space Weather and Space Climate, 11. 15. ISSN 2115-7251 doi: https://doi.org/10.1051/swsc/2020077 <https://doi.org/10.1051/swsc/2020077> cc_by_4 Article PeerReviewed 2021 ftunivreading https://doi.org/10.1051/swsc/2020077 2024-06-25T15:04:04Z We use the am, an, as and the a-sigma 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 about 76% in quiet times. For the northern hemisphere these are 15% and 38% modulations. Motion towards/away from 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 ... Article in Journal/Newspaper Geomagnetic Pole CentAUR: Central Archive at the University of Reading Journal of Space Weather and Space Climate 11 15 |
institution |
Open Polar |
collection |
CentAUR: Central Archive at the University of Reading |
op_collection_id |
ftunivreading |
language |
English |
description |
We use the am, an, as and the a-sigma 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 about 76% in quiet times. For the northern hemisphere these are 15% and 38% modulations. Motion towards/away from 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 ... |
format |
Article in Journal/Newspaper |
author |
Lockwood, Mike Haines, Carl Barnard, Luke A. Owens, Mathew J. Scott, Chris J. Chambodut, Aude McWilliams, Kathryn A. |
spellingShingle |
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 |
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://centaur.reading.ac.uk/95181/ https://centaur.reading.ac.uk/95181/8/swsc200083.pdf https://centaur.reading.ac.uk/95181/1/390_Lockwood_Paper4n_Fa.pdf |
genre |
Geomagnetic Pole |
genre_facet |
Geomagnetic Pole |
op_relation |
https://centaur.reading.ac.uk/95181/8/swsc200083.pdf https://centaur.reading.ac.uk/95181/1/390_Lockwood_Paper4n_Fa.pdf Lockwood, M. <https://centaur.reading.ac.uk/view/creators/90001127.html> orcid:0000-0002-7397-2172 , Haines, C., Barnard, L. A. <https://centaur.reading.ac.uk/view/creators/90005020.html> orcid:0000-0001-9876-4612 , Owens, M. J. <https://centaur.reading.ac.uk/view/creators/90003236.html> orcid:0000-0003-2061-2453 , Scott, C. J. <https://centaur.reading.ac.uk/view/creators/90003900.html> orcid:0000-0001-6411-5649 , Chambodut, A. and McWilliams, K. A. (2021) 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. Journal of Space Weather and Space Climate, 11. 15. ISSN 2115-7251 doi: https://doi.org/10.1051/swsc/2020077 <https://doi.org/10.1051/swsc/2020077> |
op_rights |
cc_by_4 |
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_ |
1809910528736231424 |