Electromagnetic Energy Conversion at Reconnection Fronts

TLDR

Earth’s magnetotail stores magnetic energy from the solar wind, which is converted back into particle energy to power auroras, heat the magnetospheric plasma, and energize the Van Allen belts. The study seeks to determine where and how this electromagnetic energy conversion takes place. Eight‑spacecraft observations show that the conversion occurs in fronts of recently reconnected magnetic flux at 1–10 electron inertial lengths, where intense current sheets convert 10–100 GW per Earth radius and several × 10^15 J, matching global magnetotail flux reduction.

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 10(15) joules of magnetic energy, consistent with global magnetotail flux reduction.