Magnetic Reconnection in the Magnetotail: Review of the Japanese Contribution with the Spacecraft Geotail

Abstract

This paper reviews the Japanese contribution to our current understanding of magnetic reconnection with the spacecraft Geotail. Past spacecraft observations have examined mainly the MHD characteristics of magnetic reconnection in the Earth's magnetotail, whereas Geotail has revealed various characteristics of magnetic reconnection at the kinetic level as well as the MHD level. At the MHD level, the role of magnetic reconnection in substorm physics is studied. It is firmly established that magnetic reconnection for substorm onsets takes place in the spatially limited region in the premidnight magnetotail at radial distances of 20–30 RE. Geotail observations provide strong evidence that reconnection observations in the magnetotail precede common substorm indicators on the ground. At the kinetic level, ion dynamics in magnetic reconnection is examined, and Hall physics (ion- electron decoupling) is confirmed first in the vicinity of the magnetic reconnection site.