{{Short description|Region of Earth's magnetosphere consisting of cool plasma}} thumb
The '''plasmasphere''', or '''inner magnetosphere''', is a region of the Earth's magnetosphere consisting of low-energy (cool) plasma. It is located above the ionosphere. The outer boundary of the plasmasphere is known as the '''plasmapause''', which is defined by an order of magnitude drop in plasma density. In 1963 American scientist Don Carpenter and Soviet astronomer {{ILL|Konstantin Gringauz|ru|Грингауз, Константин Иосифович}} proved the plasmasphere and plasmapause's existence from the analysis of very low frequency (VLF) whistler wave data. Traditionally, the plasmasphere has been regarded as a well behaved cold plasma with particle motion dominated entirely by the geomagnetic field and, hence, co-rotating with the Earth.
==History== The discovery of the plasmasphere grew out of the scientific study of whistlers, natural phenomena caused by very low frequency (VLF) radio waves. Whistlers were first heard by radio operators in the 1890s.<ref name="gallagher">{{cite web |last1=Gallagher |first1=D. L. |title=Discovering the Plasmasphere |url=https://plasmasphere.nasa.gov/discovery.html |website=Space Plasma Physics |publisher=NASA Marshall Space Flight Center |access-date=1 December 2020 |location=Huntsville, AL |date=27 May 2015}}</ref> British scientist Llewelyn Robert Owen Storey had shown lightning generated whistlers in his 1953 PhD dissertation.<ref name="gallagher"/><ref name="ethw">{{cite web |title=Owen Storey |url=https://ethw.org/Owen_Storey |publisher=Engineering and Technology History Wiki |access-date=1 December 2020 |date=29 January 2019}}</ref> Around the same time, Storey had posited the existence of whistlers meant plasma was present in Earth's atmosphere, and that it moved radio waves in the same direction as Earth's magnetic field lines.<ref name="gallagher"/><ref name="ethw"/> From this he deduced but was unable to conclusively prove the existence of the plasmasphere.<ref name="ethw"/> In 1963 American scientist Don Carpenter and Soviet astronomer Konstantin Gringauz—independently of each other, and the latter using data from the ''Luna 2'' spacecraft—experimentally proved the plasmasphere and plasmapause's existence, building on Storey's thinking.<ref name="gallagher"/>
In 1965 Storey and French scientist M. P. Aubry worked on FR-1, a French scientific satellite equipped with instruments for measuring VLF frequencies and the local electron density of plasma. Aubry and Storey's studies of FR-1 VLF and electron density data further corroborated their theoretical models: VLF waves in the ionosphere occasionally passed through a thin layer of plasma into the magnetosphere, normal to the direction of Earth's magnetic field.<ref name="aubry">{{cite journal |last1=Aubry |first1=M. P. |title=Some results of the FR-1 satellite experiment on the VLF wave field in the zone close to the transmitter |journal=Journal of Atmospheric and Terrestrial Physics |date=1968 |volume=30 |issue=6 |pages=1161–1182 |doi=10.1016/S0021-9169(68)80005-4|bibcode=1968JATP...30.1161A }}</ref>{{rp|1181}}<ref name="storey">{{cite journal |last1=Storey |first1=Llewelyn Robert Owen |title=Preliminary results on VLF propagation in the lower magnetosphere obtained by the FR 1 satellite |journal=Space Research |date=1967 |issue=7 |pages=588–603 |publisher=North Holland Publishing Co. |location=Amsterdam}}</ref> Throughout the 1970s, Storey continued studying VLF waves using data gathered by FR-1.<ref name="ethw"/> Data received from the VLF receiver on OV3-3, launched 4 August 1966, determined the location of the plasmapause.<ref name=geo>{{cite journal|url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JA077i010p01802|journal=Journal of Geophysical Research|title=Observations of SAR arcs from OV1-10|author1=S. R. LaValle|author2=D. D. Elliott|date=1 April 1972|volume=77|issue=10|pages=1802–1809|doi=10.1029/JA077i010p01802|bibcode=1972JGR....77.1802L|url-access=subscription}}</ref>
In 2014 satellite observations from the THEMIS mission have shown that density irregularities such as plumes or biteouts may form.<ref name="THEMIS">{{cite web |url=https://www.nasa.gov/content/goddard/themis-discovers-new-process-that-protects-earth-from-space-weather|title=NASA's THEMIS Discovers New Process that Protects Earth from Space Weather |author=Karen C. Fox |date=March 6, 2014 |website=www.nasa.gov |publisher=NASA |access-date=April 11, 2017 }}</ref><ref>{{cite journal |author1=B. M. Walsh |author2=J. C. Foster |author3=P. J. Erickson |title=Simultaneous Ground- and Space-Based Observations of the Plasmaspheric Plume and Reconnection |date=7 March 2014 |volume=343 |journal=Science |issue=6175 |pages=1122–5 |doi=10.1126/science.1247212 |pmid=24604196 |bibcode=2014Sci...343.1122W |s2cid=206553014 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150007962.pdf|hdl=2060/20150007962 |hdl-access=free }}</ref> It has also been shown that the plasmasphere does not always co-rotate with the Earth. The plasma of the magnetosphere has many different levels of temperature and concentration. The coldest magnetospheric plasma is most often found in the plasmasphere. However, plasma from the plasmasphere can be detected throughout the magnetosphere because it gets blown around by the Earth's electric and magnetic fields. Data gathered by the twin Van Allen Probes show that the plasmasphere also limits highly-energetic ultrarelativistic electrons from cosmic and solar origin from reaching low earth orbits and the surface of the planet.<ref>{{cite web| url = https://www.latimes.com/science/sciencenow/la-sci-sn-star-trek-invisible-shield-electron-van-allen-radiation-belts-20141126-story.html| title = Star Trek-like invisible shield protects Earth from 'killer electrons' - Los Angeles Times| website = Los Angeles Times| date = 27 November 2014}} </ref><ref>{{cite web | url=http://newsoffice.mit.edu/2014/plasma-shield-against-harmful-radiation-1126 | title=Plasma shield | date=26 November 2014 }}</ref>
<gallery> File:Earth_plasmasphere.jpg|A view from the IMAGE satellite showing Earth's plasmasphere using its Extreme Ultraviolet (EUV) imager instrument. File:Radiation Belts & Plasmapause.ogv|Visualization of the radiation belts with confined charged particles (blue & yellow) and plasmapause boundary (blue-green surface). </gallery>
==See also== {{Portal|Space}} *Magnetosphere chronology
==References== {{Reflist}}
==Further reading== * Carpenter, D. L., Whistler evidence of a 'knee' in the magnetospheric ionization density profile, J. Geophys. Res., 68, 1675–1682, 1963. * Nishida, A., Formation of plasmapause, or magnetospheric plasma knee, by combined action of magnetospheric convections and plasma escape from the tail, J. Geophys. Res., 71, 5669, 1966. * Sandel, B. R., et al., Extreme ultraviolet imager observations of the structure and dynamics of the plasmasphere, Space Sci. Rev., 109, 25, 2003.
==External links== * [https://web.archive.org/web/20160828213813/http://plasmasphere.nasa.gov/ NASA web site] * [https://archive.today/20121215023346/http://www.windows.ucar.edu/cgi-bin/tour_def/glossary/plasmasphere.html University of Michigan description] * [https://web.archive.org/web/20070109034431/http://www.cs.uah.edu/visgig/research/research.html University of Alabama in Huntsville research] * [http://pluto.space.swri.edu/IMAGE/glossary/plasmasphere.html Southwest Research Institute description] * [http://euv.lpl.arizona.edu/euv/index.html IMAGE Extreme Ultraviolet Imager] * [http://pluto.space.swri.edu/image/plasmasphere_images.html EUV Images of the plasmasphere]
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Category:Terrestrial plasmas Category:Space plasmas Category:Atmosphere Category:Geomagnetism Category:Articles containing video clips