Editing Aurora (section)

=== Magnetosphere ===
[[File:Structure of the magnetosphere LanguageSwitch.svg|lang=en|thumb|upright=1.4|Schematic of Earth's [[magnetosphere]]]]

Earth's [[magnetosphere]] is shaped by the impact of the solar wind on Earth's magnetic field. This forms an obstacle to the flow, diverting it, at an average distance of about 70,000&nbsp;km (11 Earth radii or R<sub>e</sub>),<ref>{{cite journal|last1=Shue|first1=J.-H|first2=J. K.|last2=Chao|first3=H. C.|last3=Fu|first4=C. T.|last4=Russell|first5=P.|last5=Song|first6=K. K.|last6=Khurana|first7=H. J.|last7=Singer|title=A new functional form to study the solar wind control of the magnetopause size and shape|journal=J. Geophys. Res.|date=May 1997|volume=102|issue=A5|pages=9497–9511|doi=10.1029/97JA00196|bibcode=1997JGR...102.9497S }}</ref> producing a [[bow shock]] 12,000&nbsp;km to 15,000&nbsp;km (1.9 to 2.4 R<sub>e</sub>) further upstream. The width of the magnetosphere abreast of Earth is typically 190,000&nbsp;km (30 R<sub>e</sub>), and on the night side, a long "magnetotail" of stretched field lines extends to great distances (> 200 R<sub>e</sub>).

The high-latitude magnetosphere is filled with plasma as the solar wind passes Earth. The flow of plasma into the magnetosphere increases with additional turbulence, density, and speed in the solar wind. This flow is favoured by a southward component of the IMF, which can then directly connect to the high latitude geomagnetic field lines.<ref>{{cite journal|last1=Lyons|first1=L. R.|first2=H.-J.|last2=Kim|first3=X.|last3=Xing|first4=S.|last4=Zou|first5=D.-Y.|last5=Lee|first6=C.|last6=Heinselman|first7=M. J.|last7=Nicolls|first8=V.|last8=Angelopoulos|first9=D.|last9=Larson|first10=J.|last10=McFadden|first11=A.|last11=Runov|first12=K.-H.|last12=Fornacon|title=Evidence that solar wind fluctuations substantially affect global convection and substorm occurrence|journal=J. Geophys. Res.|year=2009|volume=114|issue=A11306|pages=1–14|doi=10.1029/2009JA014281|bibcode=2009JGRA..11411306L|doi-access=free }}</ref> The flow pattern of magnetospheric plasma is mainly from the magnetotail toward Earth, around Earth and back into the solar wind through the [[magnetopause]] on the day-side. In addition to moving perpendicular to Earth's magnetic field, some magnetospheric plasma travels down along Earth's magnetic field lines, gains additional energy and loses it to the atmosphere in the auroral zones. The cusps of the magnetosphere, separating geomagnetic field lines that close through Earth from those that close remotely allow a small amount of solar wind to directly reach the top of the atmosphere, producing an auroral glow.

On 26 February 2008, [[THEMIS]] probes were able to determine, for the first time, the triggering event for the onset of [[magnetospheric substorm]]s.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/themis/auroras/themis_power.html|title=NASA – THEMIS Satellites Discover What Triggers Eruptions of the Northern Lights|publisher=Nasa.gov|access-date=26 July 2011| archive-url= https://web.archive.org/web/20110629043044/http://www.nasa.gov/mission_pages/themis/auroras/themis_power.html| archive-date= 29 June 2011| url-status=live}}</ref> Two of the five probes, positioned approximately one-third the distance to the Moon, measured events suggesting a [[magnetic reconnection]] event 96 seconds prior to auroral intensification.<ref>{{cite journal|doi=10.1126/science.1160495|title=Tail Reconnection Triggering Substorm Onset|year=2008|last1=Angelopoulos|first1=V.|last2=McFadden|first2=J. P.|last3=Larson|first3=D.|last4=Carlson|first4=C. W.|last5=Mende|first5=S. B.|last6=Frey|first6=H.|last7=Phan|first7=T.|last8=Sibeck|first8=D. G.|last9=Glassmeier|first9=K.-H.|journal=Science|volume=321|issue=5891|pages=931–5|pmid=18653845|bibcode=2008Sci...321..931A|last10=Auster|first10=U.|last11=Donovan|first11=E.|last12=Mann|first12=I. R.|last13=Rae|first13=I. J.|last14=Russell|first14=C. T.|last15=Runov|first15=A.|last16=Zhou|first16=X.-Z.|last17=Kepko|first17=L.|s2cid=206514133 |doi-access=free}}</ref>

[[Geomagnetic storm]]s that ignite auroras may occur more often during the months around the [[equinox]]es. It is not well understood, but geomagnetic storms may vary with Earth's seasons. Two factors to consider are the tilt of both the solar and Earth's axis to the ecliptic plane. As Earth orbits throughout the year, it experiences an interplanetary magnetic field (IMF) from different latitudes of the Sun, which is tilted at 8 degrees. Similarly, the 23-degree tilt of Earth's axis about which the geomagnetic pole rotates with a diurnal variation changes the daily average angle that the geomagnetic field presents to the incident IMF throughout the year. These factors combined can lead to minor cyclical changes in the detailed way that the IMF links to the magnetosphere. In turn, this affects which energy from the solar wind can reach Earth's inner magnetosphere and thereby enhance auroras. Recent evidence in 2021 has shown that individual separate substorms may in fact be correlated networked communities.<ref>{{cite journal|title=Network community structure of substorms using SuperMAG magnetometers, L. Orr, S. C. Chapman, J. W. Gjerloev & W. Guo|issue=1|page=1842|journal=Nature Communications|date=23 March 2021|volume=12|doi=10.1038/s41467-021-22112-4|last1=Orr|first1=L.|last2=Chapman|first2=S. C.|last3=Gjerloev|first3=J. W.|last4=Guo|first4=W.|pmid=33758181|pmc=7988152 }}</ref>