Geophysics

Sandpile Dynamics of the Magnetosphere

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Science  21 Apr 2000:
Vol. 288, Issue 5465, pp. 401
DOI: 10.1126/science.288.5465.401c

Earth's magnetosphere, a plasma-rich region shaped by the interaction between Earth's magnetic field and the solar wind, shields the atmosphere and protects us from damage by charged particles from interplanetary space. The solar wind, a supersonic flow of charged particles from the sun, bombards the magnetosphere with particles and ionizing radiation, which generates aurorae and, during storms, creates magnetic disturbances that affect satellite communications.

Aurorae are produced when magnetospheric electrons and protons traveling along magnetic fields lines collide with oxygen and nitrogen atoms in the upper atmosphere above the poles. Lui et al. analyzed global images of aurorae gathered by satellites during January 1997 to evaluate the output of energy over the entire magnetosphere. The temporal distribution of auroral ‘blobs’ recorded during quiet and substorm times showed similar power law relations, indicating that localized relaxations in the magnetosphere occurred with avalanche, or “sandpile” dynamics. That is, regardless of solar wind intensity, aurorae dissipate energy through nonequilibrium states that have no intrinsic length scales. This global observation improves our understanding of the state of the magnetosphere and will help to improve space weather forecasts.—LR

Geophys. Res. Lett.27, 911 (2000).

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