Research Article

Electromagnetic Energy Conversion at Reconnection Fronts

Science  27 Sep 2013:
Vol. 341, Issue 6153, pp. 1478-1482
DOI: 10.1126/science.1236992

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Observing Earth's Magnetotail

Magnetic reconnection is a process that converts magnetic energy to kinetic energy, thermal energy, and particle acceleration. The process operates in Earth's magnetotail, the narrow and elongated region of the magnetosphere that extends away from the Sun, and is believed to power Earth's auroras and other space physics phenomena. Angelopoulos et al. (p. 1478) present an observational study of energy conversion in the magnetotail and the associated transport of magnetic flux during a geomagnetic substorm.

Abstract

Earth’s magnetotail contains magnetic energy derived from the kinetic energy of the solar wind. Conversion of that energy back to particle energy ultimately powers Earth’s auroras, heats the magnetospheric plasma, and energizes the Van Allen radiation belts. Where and how such electromagnetic energy conversion occurs has been unclear. Using a conjunction between eight spacecraft, we show that this conversion takes place within fronts of recently reconnected magnetic flux, predominantly at 1- to 10-electron inertial length scale, intense electrical current sheets (tens to hundreds of nanoamperes per square meter). Launched continually during intervals of geomagnetic activity, these reconnection outflow flux fronts convert ~10 to 100 gigawatts per square Earth radius of power, consistent with local magnetic flux transport, and a few times 1015 joules of magnetic energy, consistent with global magnetotail flux reduction.

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