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#ALIH [[Medan magnet Bumi]]
[[Image:Geodynamo Between Reversals.gif|thumb|Simulasi komputer mengenai medan magnetik bumi<ref name=selfconsistent>{{cite journal|last=Glatzmaier|first=Gary A.|coauthors=Roberts, Paul H.|title=A three-dimensional self-consistent computer simulation of a geomagnetic field reversal|journal=Nature|year=1995|volume=377|issue=6546|pages=203–209|doi=10.1038/377203a0|bibcode = 1995Natur.377..203G|ref=harv }}</ref><ref name=Glatzmaier>{{cite web |url=http://es.ucsc.edu/~glatz/geodynamo.html |title=The Geodynamo |last=Glatzmaier |first=Gary |publisher=University of California Santa Cruz |accessdate=20 October 2013}}</ref>]]
'''Medan magnetik bumi''', disebut juga '''medan geomagnetik''', adana [[medan magnetik]] yang menjangkau dari bagian dalam [[bumi]] hingga ke batas di mana medan magnet bertemu [[angin matahari]]. Besarnya medan magnet bumi bervariasi antara 25 hingga 65 [[Tesla (satuan)|mikrotesla]] (0.25 hingga 0.65 [[Gauss (satuan)|gauss]]). Kutub-kutub medan magnetik bumi diperkirakan miring sepuluh derajat terhadap aksis bumi, dan terus bergerak sepanjang waktu akibat pergerakan besi paduan cair di dalam inti luar bumi. Kutub magnet bumi bergerak begitu lambat sehingga [[kompas]] masih dapat berfungsi dengan baik sejak digunakan pertama kali (abad ke 11 masehi). Namun setiap beberapa ratus ribu tahun sekali, [[pembalikan geomagnetik|kutub magnetik bumi berbalik]] antara utara dan selatan. Pembalikan ini terekam di dalam pola bebatuan purbakala bumi yang mengandung unsur yang bersifat [[ferromagnetik]]. Pergerakan [[lempeng tektonik|lempeng benua]] juga dipengaruhi oleh medan magnetik.
Lapisan di atas [[ionosfer]] disebut juga dengan [[magnetosfer]], yaitu lapisan di mana medan magnetik bumi melindungi bumi dari [[radiasi kosmik]] yang dapat mengionisasi setiap partikel di atmosfer dan membuatnya terlepas dari medan gravitasi. Tanpa magnetosfer, atmosfer bumi termasuk [[lapisan ozon]] akan hilang dan menjadikan kehidupan di bumi tidak dapat berkembang sekompleks sekarang.
==Peran medan magnetik bumi==
Medan magnetik bumi memantulkan sebagian besar angin matahari, yaitu arus partikel bermuatan dari matahari yang mampu mengionisasi lapisan atmosfer bumi.<ref>{{cite journal |title=Solar wind hammers the ozone layer |first=Quirin |last=Shlermeler |date=3 March 2005 |doi=10.1038/news050228-12 |journal=News@nature |url=http://www.nature.com/news/2005/050228/full/news050228-12.html}}</ref> Gas-gas yang terkena angin matahari dapat terperangkap dalam gelembung medan magnet yang dapat terbawa arus angin matahari, sebuah proses yang mungkin pernah terjadi di [[planet Mars]].<ref>{{cite news |title=Solar wind ripping chunks off Mars |url=http://www.cosmosmagazine.com/news/2369/solar-wind-ripping-chunks-mars |work=Cosmos Online |date=25 November 2008 |accessdate=21 October 2013}}</ref><ref>{{harvnb|Luhmann|Johnson|Zhang|1992}}</ref><ref>[http://scign.jpl.nasa.gov/learn/plate1.htm Structure of the Earth]. Scign.jpl.nasa.gov. Diakses 2012-01-27.</ref>
Studi mengenai medan magnetik bumi di masa lalu disebut dengan [[Paleomagnetisme]].<ref name="McElhinny2000">{{cite book |last1=McElhinny |first1=Michael W. |last2=McFadden |first2=Phillip L. |title=Paleomagnetism: Continents and Oceans |publisher=Academic Press |year=2000 |isbn=0-12-483355-1 |ref=harv}}</ref> Polaritas dari medan magnetik bumi terekam dalam bebatuan, dan pembalikan medan magnetik bumi terkema di dalam garis-garis yang terbentuk ketika pembentukan bebatuan terjadi. Paleomagnetisme juga dapat menjadi sarana perekaman [[geokronologi]] batuan dan sedimen.<ref>{{cite book |last1=Opdyke |first1=Neil D. |last2=Channell |first2=James E. T. |title=Magnetic Stratigraphy |publisher=Academic Press |year=1996 |isbn=978-0-12-527470-8 |ref=harv}}</ref> Medan mangetik bumi juga menyebabkan bebatuan yang mengandung [[bijih tambang]] dari unsur ferromagnetik lebih mudah dicari karena menyebabkan [[anomali magnetik]] bumi.<ref>{{cite book |last1=Mussett |first1=Alan E. |last2=Khan |first2=M. Aftab |title=Looking into the Earth: An introduction to Geological Geophysics |year=2000 |publisher=Cambridge University Press |isbn=0-521-78085-3 |ref=harv}}</ref>
Manusia telah menggunakan [[kompas]] yang bergantung pada medan magnetik bumi untuk menentukan arah, sejak abad ke 11 masehi.<ref>{{cite book |last=Temple |first=Robert |title=The Genius of China |publisher=Andre Deutsch |year=2006 |isbn=0-671-62028-2 |ref=harv}}</ref> Hewan juga diketahui memanfaatkan medan magnetik bumi sebagai sarana untuk bermigrasi.<ref>http://www.antaranews.com/berita/417786/ikan-salem-punya-sistem-gps-untuk-bermigrasi</ref> Variasi medan magnetik bumi diketahui berhubungan dengan variasi curah hujan di negara tropis.<ref>{{cite news |url=http://planetearth.nerc.ac.uk/news/story.aspx?id=296 |title=Link found between tropical rainfall and Earth's magnetic field |work=Planet Earth Online |date=20 January 2009 |publisher=National Environment Research Council |accessdate=19 April 2012}}</ref>
== Referensi ==
{{reflist}}
== Bahan bacaan terkait ==
{{Refbegin}}
* {{cite book|last=Campbell|first=Wallace H.|title=Introduction to geomagnetic fields|year=2003|publisher=[[Cambridge University Press]]|location=New York|isbn=978-0-521-52953-2|edition=2nd|ref=harv}}
* {{cite book|first1=Neil F. |last1=Comins |year=2008 |title=Discovering the Essential Universe |publisher=[[W. H. Freeman]] |edition=Fourth |isbn=978-1-4292-1797-2|ref=harv}}
* {{cite journal |doi=10.1073/pnas.93.2.646 |last1=Herndon |first1=J. M. |title=Substructure of the inner core of the Earth |journal=[[PNAS]] |volume=93 |issue=2 |pages=646–648 |date=1996-01-23 |pmid=11607625 |pmc=40105|bibcode = 1996PNAS...93..646H |ref=harv }}
* {{cite journal |last1=Hollenbach |first1=D. F. |title=Deep-Earth reactor: Nuclear fission, helium, and the geomagnetic field |journal=[[PNAS]] |volume=98 |issue=20 |date=2001-09-25 |doi=10.1073/pnas.201393998 |pmid=11562483 |pmc=58687|bibcode = 2001PNAS...9811085H |last2=Herndon |first2=J. M. |pages=11085–90 |ref=harv }}
* {{cite journal |first1=Jeffrey J. |last1=Love |title=Magnetic monitoring of Earth and space |url=http://geomag.usgs.gov/downloads/publications/pt_love0208.pdf |journal=[[Physics Today]] |volume=61 |issue=2 |pages=31–37 |year=2008 |doi=10.1063/1.2883907|bibcode = 2008PhT....61b..31H |ref=harv}}
* {{cite journal |last1=Luhmann |first1=J. G. |last2=Johnson |first2=R. E. |last3=Zhang |first3=M. H. G. |title=Evolutionary impact of sputtering of the Martian atmosphere by O<sup>+</sup> pickup ions |journal=[[Geophysical Research Letters]] |volume=19 | issue=21 |pages=2151–2154 |year=1992|ref=harv|bibcode = 1992GeoRL..19.2151L |doi = 10.1029/92GL02485 }}
* {{cite book|first=Ronald T. |last=Merrill |year=2010 |title=Our Magnetic Earth: The Science of Geomagnetism|publisher=[[University of Chicago Press]]|isbn=0-226-52050-1|ref=harv}}
* {{cite book|last=Merrill|first= Ronald T.|last2=McElhinny|first2=Michael W.|last3=McFadden|first3=Phillip L.|title=The magnetic field of the earth: paleomagnetism, the core, and the deep mantle|publisher=[[Academic Press]]|year=1996|isbn=978-0-12-491246-5|ref=harv}}
* {{cite web |url=http://www.newton.dep.anl.gov/askasci/gen99/gen99256.htm |title=Temperature of the Earth's core |work=NEWTON Ask a Scientist |year=1999 |accessdate=September 2011|ref=harv}}
* {{cite book |last=Tauxe |first=Lisa |title=Paleomagnetic Principles and Practice |publisher=[[Kluwer]] |year=1998 |isbn=0-7923-5258-0 |ref=harv}}
* {{cite journal |first1=J. N. |last1=Towle |title=The Anomalous Geomagnetic Variation Field and Geoelectric Structure Associated with the Mesa Butte Fault System, Arizona |journal=Geological Society of America Bulletin |volume=9 |pages=221–225 |year=1984 |doi=10.1130/0016-7606(1984)95<221:TAGVFA>2.0.CO;2|ref=harv |issue=2|bibcode = 1984GSAB...95..221T }}
* {{cite journal |first1=James R. |last1=Wait |author1-link=James R. Wait |year=1954 |title=On the relation between telluric currents and the earth's magnetic field |journal=Geophysics |volume=19 |pages=281–289 |doi=10.1190/1.1437994|bibcode = 1954Geop...19..281W |ref=harv |issue=2}}
* {{cite book |first1=Martin |last1=Walt |author1-link=Martin Walt |year=1994 |title=Introduction to Geomagnetically Trapped Radiation |publisher=[[Cambridge University Press]] |isbn=978-0-521-61611-9|ref=harv}}
{{Refend}}
==Pranala luar==
* ''[http://www.agu.org/sections/geomag/background.html Geomagnetism & Paleomagnetism background material]''. American Geophysical Union Geomagnetism and Paleomagnetism Section.
* ''[http://geomag.usgs.gov National Geomagnetism Program]''. [[United States Geological Survey]], March 8, 2011.
* ''[http://www.geomag.bgs.ac.uk BGS Geomagnetism]''. Information on monitoring and modeling the geomagnetic field. British Geological Survey, August 2005.
* William J. Broad, ''[http://www.nytimes.com/2004/07/13/science/13magn.html?ex=1247457600&en=e8f37e14d213ba16&ei=5090&partner=rssuserland Will Compasses Point South?]''. [[New York Times]], July 13, 2004.
* John Roach, ''[http://news.nationalgeographic.com/news/2004/09/0927_040927_field_flip.html Why Does Earth's Magnetic Field Flip?]''. National Geographic, September 27, 2004.
* ''[http://www.pbs.org/wgbh/nova/magnetic/ Magnetic Storm]''. [[Public Broadcasting Service|PBS]] [[Nova (TV series)|NOVA]], 2003. (''ed''. about pole reversals)
* ''[http://www.psc.edu/science/Glatzmaier/glatzmaier.html When North Goes South]''. Projects in Scientific Computing, 1996.
* ''[http://www.phy6.org/earthmag/demagint.htm The Great Magnet, the Earth]'', History of the discovery of Earth's magnetic field by David P. Stern.
* ''[http://www-spof.gsfc.nasa.gov/Education/wmap.html Exploration of the Earth's Magnetosphere]'', Educational web site by David P. Stern and Mauricio Peredo
* ''[http://blackandwhiteprogram.com/interview/dr-dan-lathrop-the-study-of-the-earths-magnetic-field Dr. Dan Lathrop: The study of the Earth's magnetic field]''. Interview with Dr. Dan Lathrop, Geophysicist at the University of Maryland, about his experiments with the Earth's core and magnetic field. 7 - 3 - 2008
* [http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html International Geomagnetic Reference Field 2011]
* [http://www.vukcevic.talktalk.net/Global%20Mag%20Anomaly.gif Global evolution/anomaly of the Earth's magnetic field] Sweeps are in 10 degree steps at 10 years intervals. Based on data from: The Institute of Geophysics, [http://www.ethz.ch/index_EN ETH Zurich]
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