Editing Earth's magnetic field (section)

=== Short-term variations ===
[[File:Magnetic Storm Oct 2003.jpg|thumb|'''Background''': a set of traces from magnetic observatories showing a [[magnetic storm]] in 2000.<br /> '''Globe''': map showing locations of observatories and contour lines giving horizontal magnetic intensity in [[Micro-|μ]] [[Tesla (unit)|T]].]]

The geomagnetic field changes on time scales from milliseconds to millions of years. Shorter time scales mostly arise from currents in the ionosphere ([[ionospheric dynamo region]]) and magnetosphere, and some changes can be traced to geomagnetic storms or daily variations in currents. Changes over time scales of a year or more mostly reflect changes in the [[Earth's interior]], particularly the iron-rich [[structure of the Earth|core]].<ref name="MMMch2" />

Frequently, the Earth's magnetosphere is hit by [[solar flare]]s causing geomagnetic storms, provoking displays of aurorae. The short-term instability of the magnetic field is measured with the [[K-index]].<ref>{{cite web |url=http://www.swpc.noaa.gov/info/Kindex.html |title=The K-index |publisher=Space Weather Prediction Center |access-date=20 October 2013 |url-status=dead |archive-url=https://web.archive.org/web/20131022183358/http://www.swpc.noaa.gov/info/Kindex.html |archive-date=22 October 2013 }}</ref>

Data from [[THEMIS]] show that the magnetic field, which interacts with the solar wind, is reduced when the magnetic orientation is aligned between Sun and Earth – opposite to the previous hypothesis. During forthcoming solar storms, this could result in [[Power outage|blackouts]] and disruptions in [[artificial satellite]]s.<ref>{{cite web |first=Bill |last=Steigerwald |url=http://www.nasa.gov/mission_pages/themis/news/themis_leaky_shield.html |title=Sun Often "Tears Out A Wall" In Earth's Solar Storm Shield |work=THEMIS: Understanding space weather |publisher=NASA |date=16 December 2008 |access-date=20 August 2011 |archive-date=16 March 2010 |archive-url=https://web.archive.org/web/20100316055408/http://www.nasa.gov/mission_pages/themis/news/themis_leaky_shield.html |url-status=dead }}</ref>