Planar magnetic structures in coronal mass ejection-driven sheath regions
Planar magnetic structures (PMSs) are periods in the solar wind during which interplanetary magnetic field vectors are nearly parallel to a single plane. One of the specific regions where PMSs have been reported are coronal mass ejection (CME)-driven sheaths. We use here an automated method to id...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2016-02-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/34/313/2016/angeo-34-313-2016.pdf |
| _version_ | 1811315363811426304 |
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| author | E. Palmerio E. K. J. Kilpua N. P. Savani N. P. Savani |
| author_facet | E. Palmerio E. K. J. Kilpua N. P. Savani N. P. Savani |
| author_sort | E. Palmerio |
| collection | DOAJ |
| description | Planar magnetic structures (PMSs) are periods in the solar wind during which
interplanetary magnetic field vectors are nearly parallel to a single plane.
One of the specific regions where PMSs have been reported are coronal mass
ejection (CME)-driven sheaths. We use here an automated method to identify
PMSs in 95 CME sheath regions observed in situ by the Wind and ACE spacecraft
between 1997 and 2015. The occurrence and location of the PMSs are related to
various shock, sheath, and CME properties. We find that PMSs are ubiquitous in
CME sheaths; 85 % of the studied sheath regions had PMSs with the mean
duration of 6 h. In about one-third of the cases the magnetic field
vectors followed a single PMS plane that covered a significant part (at least
67 %) of the sheath region. Our analysis gives strong support for two
suggested PMS formation mechanisms: the amplification and alignment of solar
wind discontinuities near the CME-driven shock and the draping of the
magnetic field lines around the CME ejecta. For example, we found that the
shock and PMS plane normals generally coincided for the events where the PMSs
occurred near the shock (68 % of the PMS plane normals near the shock were
separated by less than 20° from the shock normal), while deviations
were clearly larger when PMSs occurred close to the ejecta leading edge. In
addition, PMSs near the shock were generally associated with lower upstream
plasma beta than the cases where PMSs occurred near the leading edge of the
CME. We also demonstrate that the planar parts of the sheath contain a higher
amount of strong southward magnetic field than the non-planar parts,
suggesting that planar sheaths are more likely to drive magnetospheric
activity. |
| first_indexed | 2024-04-13T11:29:03Z |
| format | Article |
| id | doaj.art-b2a79083ef1d4da4920104938563cffd |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-04-13T11:29:03Z |
| publishDate | 2016-02-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-b2a79083ef1d4da4920104938563cffd2022-12-22T02:48:37ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762016-02-013431332210.5194/angeo-34-313-2016Planar magnetic structures in coronal mass ejection-driven sheath regionsE. Palmerio0E. K. J. Kilpua1N. P. Savani2N. P. Savani3University of Helsinki, Department of Physics, P.O. Box 64, 00014 Helsinki, FinlandUniversity of Helsinki, Department of Physics, P.O. Box 64, 00014 Helsinki, FinlandGoddard Planetary Heliophysics Institute (GPHI), University of Maryland, Baltimore County, Maryland, USANASA Goddard Space Flight Center, Greenbelt, MD 20771, USAPlanar magnetic structures (PMSs) are periods in the solar wind during which interplanetary magnetic field vectors are nearly parallel to a single plane. One of the specific regions where PMSs have been reported are coronal mass ejection (CME)-driven sheaths. We use here an automated method to identify PMSs in 95 CME sheath regions observed in situ by the Wind and ACE spacecraft between 1997 and 2015. The occurrence and location of the PMSs are related to various shock, sheath, and CME properties. We find that PMSs are ubiquitous in CME sheaths; 85 % of the studied sheath regions had PMSs with the mean duration of 6 h. In about one-third of the cases the magnetic field vectors followed a single PMS plane that covered a significant part (at least 67 %) of the sheath region. Our analysis gives strong support for two suggested PMS formation mechanisms: the amplification and alignment of solar wind discontinuities near the CME-driven shock and the draping of the magnetic field lines around the CME ejecta. For example, we found that the shock and PMS plane normals generally coincided for the events where the PMSs occurred near the shock (68 % of the PMS plane normals near the shock were separated by less than 20° from the shock normal), while deviations were clearly larger when PMSs occurred close to the ejecta leading edge. In addition, PMSs near the shock were generally associated with lower upstream plasma beta than the cases where PMSs occurred near the leading edge of the CME. We also demonstrate that the planar parts of the sheath contain a higher amount of strong southward magnetic field than the non-planar parts, suggesting that planar sheaths are more likely to drive magnetospheric activity.https://www.ann-geophys.net/34/313/2016/angeo-34-313-2016.pdf |
| spellingShingle | E. Palmerio E. K. J. Kilpua N. P. Savani N. P. Savani Planar magnetic structures in coronal mass ejection-driven sheath regions Annales Geophysicae |
| title | Planar magnetic structures in coronal mass ejection-driven sheath regions |
| title_full | Planar magnetic structures in coronal mass ejection-driven sheath regions |
| title_fullStr | Planar magnetic structures in coronal mass ejection-driven sheath regions |
| title_full_unstemmed | Planar magnetic structures in coronal mass ejection-driven sheath regions |
| title_short | Planar magnetic structures in coronal mass ejection-driven sheath regions |
| title_sort | planar magnetic structures in coronal mass ejection driven sheath regions |
| url | https://www.ann-geophys.net/34/313/2016/angeo-34-313-2016.pdf |
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