Near-Earth Magnetotail Reconnection Powers Space Storms.

Abstract

Space storms1 are the dominant contributor to space weather. During storms, rearrangement of the solar wind and Earth’s magnetic field lines at the dayside enhances global plasma circulation in the magnetosphere2,3. As this circulation proceeds, energy is dissipated into heat in the ionosphere and near-Earth space. As Earth’s dayside magnetic flux is eroded during this process, magnetotail reconnection must occur to replenish it. However, whether dissipation is powered by magnetotail (nightside) reconnection, as in storms’ weaker but more commonplace relatives, substorms4,5, or by enhanced global plasma circulation driven by dayside reconnection is unknown. Here we show that magnetotail reconnection near geosynchronous orbit powered an intense storm. Near-Earth reconnection at geocentric distances of ~6.6–10 Earth radii—probably driven by the enhanced solar wind dynamic pressure and southward magnetic field—is observed from multi-satellite data. In this region, magnetic reconnection was expected to be suppressed by Earth’s strong dipole field. Revealing the physical processes that power storms and the solar wind conditions responsible for them opens a new window into our understanding of space storms. It encourages future exploration of the storm-time equatorial near-Earth magnetotail to refine storm driver models and accelerate progress towards space weather prediction. Magnetic reconnection in the near-Earth magnetotail is observed to power a space storm, although suppression of magnetic reconnection caused by the Earth’s magnetic dipole was expected close to Earth.