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
International audience 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....
Published in: | Journal of Space Weather and Space Climate |
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ftinsu:oai:HAL:insu-03707763v1 2023-06-18T03:40:41+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. Ecole et Observatoire des Sciences de la Terre (EOST) Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS) 2021 https://hal-insu.archives-ouvertes.fr/insu-03707763 https://hal-insu.archives-ouvertes.fr/insu-03707763/document https://hal-insu.archives-ouvertes.fr/insu-03707763/file/swsc200083.pdf https://doi.org/10.1051/swsc/2020077 en eng HAL CCSD info:eu-repo/semantics/altIdentifier/arxiv/2012.13324 info:eu-repo/semantics/altIdentifier/doi/10.1051/swsc/2020077 insu-03707763 https://hal-insu.archives-ouvertes.fr/insu-03707763 https://hal-insu.archives-ouvertes.fr/insu-03707763/document https://hal-insu.archives-ouvertes.fr/insu-03707763/file/swsc200083.pdf ARXIV: 2012.13324 BIBCODE: 2021JSWSC.11.15L doi:10.1051/swsc/2020077 http://creativecommons.org/licenses/by/ info:eu-repo/semantics/OpenAccess Journal of Space Weather and Space Climate https://hal-insu.archives-ouvertes.fr/insu-03707763 Journal of Space Weather and Space Climate, 2021, 11, ⟨10.1051/swsc/2020077⟩ magnetosphere geomagnetic activity Universal Time variations polar cap motions dipole tilt effects Physics - Space Physics Astrophysics - Earth and Planetary Astrophysics Physics - Geophysics [SDU]Sciences of the Universe [physics] info:eu-repo/semantics/article Journal articles 2021 ftinsu https://doi.org/10.1051/swsc/2020077 2023-06-05T20:26:36Z International audience 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 ... Article in Journal/Newspaper Geomagnetic Pole Institut national des sciences de l'Univers: HAL-INSU Journal of Space Weather and Space Climate 11 15 |
institution |
Open Polar |
collection |
Institut national des sciences de l'Univers: HAL-INSU |
op_collection_id |
ftinsu |
language |
English |
topic |
magnetosphere geomagnetic activity Universal Time variations polar cap motions dipole tilt effects Physics - Space Physics Astrophysics - Earth and Planetary Astrophysics Physics - Geophysics [SDU]Sciences of the Universe [physics] |
spellingShingle |
magnetosphere geomagnetic activity Universal Time variations polar cap motions dipole tilt effects Physics - Space Physics Astrophysics - Earth and Planetary Astrophysics Physics - Geophysics [SDU]Sciences of the Universe [physics] 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 Physics - Space Physics Astrophysics - Earth and Planetary Astrophysics Physics - Geophysics [SDU]Sciences of the Universe [physics] |
description |
International audience 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 ... |
author2 |
Ecole et Observatoire des Sciences de la Terre (EOST) Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS) |
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 |
HAL CCSD |
publishDate |
2021 |
url |
https://hal-insu.archives-ouvertes.fr/insu-03707763 https://hal-insu.archives-ouvertes.fr/insu-03707763/document https://hal-insu.archives-ouvertes.fr/insu-03707763/file/swsc200083.pdf https://doi.org/10.1051/swsc/2020077 |
genre |
Geomagnetic Pole |
genre_facet |
Geomagnetic Pole |
op_source |
Journal of Space Weather and Space Climate https://hal-insu.archives-ouvertes.fr/insu-03707763 Journal of Space Weather and Space Climate, 2021, 11, ⟨10.1051/swsc/2020077⟩ |
op_relation |
info:eu-repo/semantics/altIdentifier/arxiv/2012.13324 info:eu-repo/semantics/altIdentifier/doi/10.1051/swsc/2020077 insu-03707763 https://hal-insu.archives-ouvertes.fr/insu-03707763 https://hal-insu.archives-ouvertes.fr/insu-03707763/document https://hal-insu.archives-ouvertes.fr/insu-03707763/file/swsc200083.pdf ARXIV: 2012.13324 BIBCODE: 2021JSWSC.11.15L doi:10.1051/swsc/2020077 |
op_rights |
http://creativecommons.org/licenses/by/ info:eu-repo/semantics/OpenAccess |
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_ |
1769005936607756288 |