Forbush decrease: Difference between revisions
Corrected logical contradiction with para. 1, 2nd sentence. GCR intensity is DECREASED by solar wind from CMEs during solar max. |
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[[File:ExtremeEvent 20120304-00h 20120317-24h.jpg|thumb|right|320px|Forbush Decrease in March 2012.<ref>{{cite web | title=Extreme Space Weather Events | publisher=[[National Geophysical Data Center]] | url=http://sxi.ngdc.noaa.gov/sxi_greatest.html}}</ref>]] |
[[File:ExtremeEvent 20120304-00h 20120317-24h.jpg|thumb|right|320px|Forbush Decrease in March 2012.<ref>{{cite web | title=Extreme Space Weather Events | publisher=[[National Geophysical Data Center]] | url=http://sxi.ngdc.noaa.gov/sxi_greatest.html}}</ref>]] |
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The Forbush decrease is usually observable by [[particle detector]]s on Earth within a few days after the CME, and the decrease takes place over the course of a few hours. Over the following several days, the |
The Forbush decrease is usually observable by [[particle detector]]s on Earth within a few days after the CME, and the decrease takes place over the course of a few hours. Over the following several days, the galactic cosmic ray intensity returns to normal. Forbush decreases have also been observed by humans on ''[[Mir]]'' and the [[International Space Station]] (ISS), and by instruments onboard ''[[Pioneer 10]]'' and ''[[Pioneer 11|11]]'' and ''[[Voyager 1]]'' and ''[[Voyager 2|2]]'', even past the orbit of [[Neptune]]. |
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The magnitude of a Forbush decrease depends on three factors: |
The magnitude of a Forbush decrease depends on three factors: |
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==See also== |
==See also== |
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*[[Ionizing radiation]] |
*[[Ionizing radiation]] |
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*[[ |
*[[Cosmic ray]] |
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*[[Coronal mass ejection]] |
*[[Coronal mass ejection]] |
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Revision as of 00:52, 4 December 2018
A Forbush decrease is a rapid decrease in the observed galactic cosmic ray intensity following a coronal mass ejection (CME). It occurs due to the magnetic field of the plasma solar wind sweeping some of the galactic cosmic rays away from Earth. The term Forbush decrease was named after the American physicist Scott E. Forbush, who studied cosmic rays in the 1930s and 1940s.
Observation
The Forbush decrease is usually observable by particle detectors on Earth within a few days after the CME, and the decrease takes place over the course of a few hours. Over the following several days, the galactic cosmic ray intensity returns to normal. Forbush decreases have also been observed by humans on Mir and the International Space Station (ISS), and by instruments onboard Pioneer 10 and 11 and Voyager 1 and 2, even past the orbit of Neptune.
The magnitude of a Forbush decrease depends on three factors:
- the size of the CME
- the strength of the magnetic fields in the CME
- the proximity of the CME to the Earth
A Forbush decrease is sometimes defined as being a decrease of at least 10% of galactic cosmic rays on Earth, but ranges from about 3% to 20%. Reductions of 30% or more have been recorded aboard the ISS.
The overall rate of Forbush decreases tends to follow the 11-year sunspot cycle. It is more difficult to shield astronauts from galactic cosmic rays than from solar wind, so future astronauts might benefit most from radiation shielding during solar minima, when the suppressive effect of CMEs is less frequent.
Effects on the atmosphere
A 2009 peer reviewed article[2] found that low clouds contain less liquid water following Forbush decreases, and for the most influential events the liquid water in the oceanic atmosphere can diminish by as much as 7%. Further peer-reviewed work found no connection between Forbush decreases and cloud properties[3][4] until the connection was found in diurnal temperature range,[5] and since confirmed in satellite data.[6]
See also
External links
- Who's Afraid of a Solar Flare? from Science@NASA
- Cosmic Ray Data Applications to Space Weather Forecasting
References
- ^ "Extreme Space Weather Events". National Geophysical Data Center.
- ^ "Cosmic ray decreases affect atmospheric aerosols and clouds". Geophys. Res. Lett. 17 June 2009.
- ^ "Atmospheric data over a solar cycle: no connection between galactic cosmic rays and new particle formation".
- ^ "Sudden Cosmic Ray Decreases. No change of cloud cover" (PDF).
- ^ "Forbush decreases – clouds relation in the neutron monitor era". Astrophys. Space Sci. Trans. 31 August 2011.
- ^ Svensmark, J; Enghoff, M. B.; Shaviv, N; Svensmark, H (September 2016). "The response of clouds and aerosols to cosmic ray decreases". J. Geophys. Res. Space Phys. 121 (9): 8152–8181. Bibcode:2016JGRA..121.8152S. doi:10.1002/2016JA022689. Retrieved June 5, 2017.