A Forbush decrease is a rapid decrease in the observed galactic cosmic ray intensity following a

coronal mass ejection A coronal mass ejection (CME) is a significant ejection of plasma mass from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accepted theoretical understandin ...

(CME). It occurs due to the

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

of the plasma

solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...

sweeping some of the galactic cosmic rays away from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. The term ''Forbush decrease'' was named after the

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, p ...

physicist Scott E. Forbush, who studied

cosmic rays Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar ...

in the 1930s and 1940s.

Observation

The Forbush decrease is usually observable by

particle detector In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify ionizing elementary particle, particles, such as t ...

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 ''

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'' and the

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(ISS), at other locations in the inner heliosphere such as the

Solar Orbiter The Solar Orbiter (SolO) is a Sun-observing probe developed by the European Space Agency (ESA) with a National Aeronautics and Space Administration (NASA) contribution. Solar Orbiter, designed to obtain detailed measurements of the inner heli ...

spacecraft, and at Mars with the

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rover's Radiation assessment detector and the

MAVEN MAVEN is a NASA spacecraft orbiting Mars to study the loss of that planet's atmospheric gases to space, providing insight into the history of the planet's climate and water. The name is an acronym for "Mars Atmosphere and Volatile Evolution" w ...

orbiter, as well as in the outer solar system by instruments onboard ''

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'' and '' 11'' and ''

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'' and '' 2'', even past the orbit of

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. 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%. The amplitude is also highly dependent on the energy of cosmic rays that is observed by the specific instrument, where lower energies typically show larger decreases. Reductions of 30% or more have been recorded aboard the ISS. The overall rate of Forbush decreases tends to follow the 11-year

sunspot Sunspots are temporary spots on the Sun's surface that are darker than the surrounding area. They are one of the most recognizable Solar phenomena and despite the fact that they are mostly visible in the solar photosphere they usually aff ...

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 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 until the connection was found in diurnal temperature range, and since confirmed in satellite data.

References

External links

Who's Afraid of a Solar Flare?
from Science@NASA
Cosmic Ray Data Applications to Space Weather Forecasting
{{DEFAULTSORT:Forbush Decrease Cosmic rays Solar phenomena

Observation

Effects on the atmosphere

See also

References

External links