Observational aspects of IMF draping-related magnetosheath accelerations for northward IMF
Acceleration of magnetosheath plasma resulting from the draping of the interplanetary magnetic field (IMF) around the magnetosphere can give rise to flow speeds that exceed that of the solar wind (<i>V</i><sub>SW</sub>) by up to ~60%. Three case event studies out of 34 ide...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-10-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/31/1779/2013/angeo-31-1779-2013.pdf |
| Summary: | Acceleration of magnetosheath plasma resulting from the draping of the
interplanetary magnetic field (IMF) around the magnetosphere can give rise to
flow speeds that exceed that of the solar wind (<i>V</i><sub>SW</sub>) by up to
~60%. Three case event studies out of 34 identified events are
described. We then present a statistical study of draping-related
accelerations in the magnetosheath. Further, we compare the results with the
recent theory of Erkaev et al. (2011, 2012). We present a methodology
to help distinguish draping-related accelerations from those caused by
magnetic reconnection. To rule out magnetopause reconnection at low
latitudes, we focus mainly on the positive <i>B</i><sub>z</sub> phase during the passage of
interplanetary coronal mass ejections (ICMEs), as tabulated in
Richardson and Cane (2010) for 1997–2009, and adding other events from 2010.
To avoid effects of high-latitude reconnection poleward of the cusp, we also
consider spacecraft observations made at low magnetic latitudes. We study the
effect of upstream Alfvén Mach number (<i>M</i><sub>A</sub>) and magnetic local time
(MLT) on the speed ratio <i>V/V</i><sub>SW</sub>. The comparison with theory is good.
Namely, (i) flow speed ratios above unity occur behind the dawn–dusk
terminator, (ii) those below unity occur on the dayside magnetosheath, and
(iii) there is a good general agreement in the dependence of the <i>V</i> ratio on
<i>M</i><sub>A</sub>. |
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| ISSN: | 0992-7689 1432-0576 |