The polar wind or plasma fountain is a permanent outflow of plasma from the polar regions of Earth's magnetosphere, caused by the interaction between the

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...

and the Earth's atmosphere. The solar wind ionizes gas molecules in the upper atmosphere to such high energy that some of them reach escape velocity and pour into space. A considerable percentage of these ions remain bound inside Earth's magnetic field, where they form part of the radiation belts. The term was coined in 1968 in a pair of articles by Banks and Holzer and by

Ian Axford Sir William Ian Axford (2 January 1933 – 13 March 2010) was a New Zealand space scientist who was director of Germany's Max Planck Institute for Aeronomy from 1974 to 1990. Axford's research was focused on the interaction of the sun with the ...

. Since the process by which the ionospheric plasma flows away from the Earth along magnetic field lines is similar to the flow of solar plasma away from the sun's corona (the

), Axford suggested the term "polar wind." The idea for the polar wind originated with the desire to solve the paradox of the terrestrial

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

budget. This paradox consists of the fact that helium in the Earth's atmosphere seems to be produced (via radioactive decay of

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

and

thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...

) faster than it is lost by escaping from the upper atmosphere. The realization that some helium could be ionized, and therefore escape the earth along open magnetic field lines near the magnetic poles (the 'polar wind'), is one possible solution to the paradox. Further research came from the Retarding Ion Mass Spectrometer instrument on the Dynamics Explorer

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...

, in the 1980s. Recently, the SCIFER sounding rocket was launched into the plasma heating region of the fountain.

References

{{Magnetospherics Atmosphere Terrestrial plasmas Space plasmas