A study of the changes of the near‐Earth plasma sheet and lobe driven by multiple substorms: Comparison with a full particle simulation of reconnection

Abstract

[1] Comparisons of multispacecraft observations and full-particle simulations are used to understand magnetotail changes during substorms and the related cross-tail current disruptions/reductions. We first show that the electric field accompanying current disruptions can be measured in the tail lobe from the drift velocity of oxygen beams. A stormy period is studied here with a fleet of spacecraft including the four Cluster spacecraft and the Double Star spacecraft TC-1 in the tail, ACE and Geotail respectively in the solar wind and magnetosheath, and five LANL geostationary satellites, thus allowing the determination of the direction of propagation of the substorm disturbances. Each substorm here corresponds to an energy-loading period followed by a dipolarization of the magnetic field seen from 11 to 18 R E . Plasma sheet thinning inside 12 R E occurs during energy loading and is enhanced at the onset of strong dissipations of magnetic energy, which precede by several minutes particle injections at 6.6 R E . Dipolarizations coincide with an increase of the lobe electric field, up to several mV/m. This study shows that the onset of the magnetic energy conversion occurs at about $10-11 R E and that once initiated, the perturbation propagates both toward the Earth and toward the distant tail. Comparisons of the measurements with recently published 2D full particle simulations of the reconnection process by Oka et al. (2008) indicate a good agreement between data and simulated magnetic lobe signatures. This suggests that the lobe magnetic changes are the signature of a tailward retreating neutral line, with its associated current disruption/reduction. Citation: Sauvaud, J. -A., et al. (2012), A study of the changes of the near-Earth plasma sheet and lobe driven by multiple substorms: Comparison with a full particle simulation of reconnection,

The pulsed nature of the nightside contribution to polar cap convection: repetitive substorm activity under steady interplanetary driving

“…It is likely that such smaller scale dipolarizations (compared to substorm onset events) also give rise to enhanced E-fields in the tail lobe, such as observed by Sauvaud et al (2012) at substorm onsets. The role of Earthward-propagating dipolarisation front flow bursts within X = −20 to −10 R E as a basic element (substructure) in the substorm process in the magnetotail is emphasized by Lyons et al (2012).…”

Investigations of the auroral luminosity distribution and the dynamics of discrete auroral forms in a historical retrospective

“…Simultaneous observations of the Double Star, Cluster, Geotail and five geostationary LANL satellites revealed according to Sauvaud et al (2012) that the dynamics of changes in the plasma sheet and of the geomagnetic field in the magnetospheric tail repeats every 2-4 h. The analysis of these results allowed determining the approximate location in the tail where the dipolarisations are initiated and the propagation direction of the disturbances. Each substorm complies with an energy-loading period, which is then followed by a dipolarisation at geocentric distances between 11 and 18 R E .…”

“…They precede the plasma particle injections at the geostationary orbit of 6.6 R E . Sauvaud et al (2012) showed that the onset of the magnetic energy conversion occurs at a tailward distance of 10-11 R E and propagates then both toward the Earth and toward the distant magnetospheric tail. According to Pudovkin et al (1991), the creation phase is dominated by an enhancement of the dawn-dusk electric field, magnetic field stretching, and plasma sheet thinning.…”

Circulation of Heavy Ions and Their Dynamical Effects in the Magnetosphere: Recent Observations and Models

“…During transport into the lobes, electric field modulations may also affect the O + trajectories. Such modulations may consist of Alfvèn waves propagating in the lobes , convection pulses propagating at low velocity in the lobes and possibly triggered by IMF B z turnings (Maggiolo et al 2006) or by dipolarization fronts associated with substorms (Sauvaud et al 2012).…”