Forbush decrease 2895407 161441836 2007-10-01T01:41:25Z 219.90.221.229 [[WP:UNDO|Undid]] revision 161130004 by [[Special:Contributions/81.110.123.73|81.110.123.73]] ([[User talk:81.110.123.73|talk]]) 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 (physics)|plasma]] [[solar wind]] sweeping some of the galactic cosmic rays away from Earth. ==Observation== 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 solar cosmic ray intensity returns to normal. Forbush decreases have also been observed by humans on [[Mir]] and the [[International Space Station]], and by instruments onboard [[Pioneer 10]] and [[Pioneer 11|11]] and [[Voyager 1]] and [[Voyager 2|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. Because it is more difficult to shield astronauts from galactic cosmic rays than from solar wind, it is hypothesized that future astronauts might benefit most from radiation shielding during [[solar maximum|solar maxima]], when CMEs are most prevalent. ==History== The term ''Forbush decrease'' was named after the American physicist [[Scott E. Forbush]], who studied cosmic rays in the 1930s and 1940s. ==See also== *[[Ionizing radiation]] *[[Solar cosmic ray]] *[[Coronal mass ejection]] ==External links== *[http://science.slashdot.org/article.pl?sid=05/10/12/236219 Slashdot article on the Forbush decrease] *[http://science.nasa.gov/headlines/y2005/07oct_afraid.htm Who's Afraid of a Solar Flare?] from Science@NASA *[http://www.ips.gov.au/Geophysical/1/4 Cosmic Ray Data Applications to Space Weather Forecasting] [[Category: Cosmic rays]] [[Category: Solar phenomena]] [[de:Forbush-Ereignis]]