Magnetotail Configuration During a Steady Convection Event as Observed by Low-Altitude and Magnetospheric Spacecraft

摘要

Motivated by ongoing discussion regarding the magnetic configuration in the near-Earth and midtail regions and its role in populating the inner magnetosphere during long-duration steady magnetospheric convection (SMC) events, we analyze a rich collection of observations during ~10 hr of strong, steady solar wind driving. Auroral boundaries and regions of stretched and dipolarized magnetic field in the plasma sheet were monitored using solar electron loss cone anisotropy observed by low-altitude spacecraft. Following a southward turning of the interplanetary magnetic field and a subsequent 3- to 4-hr period of large-scale substorm-related reconfigurations and plasma injections, the near-Earth magnetic configuration evolved into a nonstandard type, which lasted until the end of this SMC event (5 hr). During that time a dipolarized region with complicated Bz landscape persisted in the midtail, while the configuration was very stretched in the near tail. This was manifested as a highly depressed magnetic Bz component at geostationary orbit and as persistent nonadiabatic electron scattering at the periphery of the outer radiation belt. In addition, in situ observations suggest that a thin current sheet extended longitudinally toward the dawn terminator. In the return convection region near the terminator, observations of this azimuthal current sheet were sporadically interrupted/modulated by earthward convecting plasma structures, either remnants of reconnection-produced plasma bubbles or flapping waves. The hybrid magnetotail configuration (dipolar in the midtail and stretched in the near tail) observed during this long-duration SMC event poses a challenge for empirical magnetospheric modeling.