ISEE observations of the plasma sheet boundary, plasma sheet, and neutral sheet: 1. Electric field, magnetic field, plasma, and ion composition
Authors: Cattell C. A. , Mozer F. S. , Hones E. W. , Anderson R. R. , Sharp R. D. 
Published: February 2008

The first simultaneous study of dc and ac electric and magnetic fields, E × B velocity, plasma flows, β, total energy density, energetic particles, and ion composition from the ISEE satellites and ground and interplanetary magnetic fields has been made to determine (1) the relationship of the previously observed electric fields at the plasma sheet boundary and at the neutral sheet to plasma parameters, and (2) whether the phenomena occurring during quiet and active times were consistent with the formation of a near‐earth neutral line during substorms or with the boundary layer model. The following observations during the two substorms studied are in agreement with predictions of the neutral‐line model: (1) the buildup of energy stored in the tail magnetic field for 1–2 hours prior to onset, followed by its rapid decrease after onset, (2) the enhanced convection of magnetic field lines and plasma into the neutral sheet from above and below as indicated by the E × B velocity, (3) tailward convection of field lines and plasma (Ey (dawnward and duskward) and Bz (northward and southward) anticorrelated in sign) at onset, followed by thinning of the plasma sheet, and then convection earthward (Ey and Bz correlated in sign) during recovery of the plasma sheet, (4) repeated encounters with the neutral sheet during the times of the large electric fields and fast plasma flows, indicating that both existed throughout the plasma sheet and not just at the boundary and that the substorm‐associated phenomena were initiated within the plasma sheet; and (5) heating of electrons in association with fast tailward flow and southward Bz. In addition, there was a ramplike enhancement in the dawn‐dusk electric field of ∼10–20 mV/m lasting for the ∼20–40 min duration of the substorms at the satellite and maximizing near the beginning of the recovery phase. Comparison of the associated potential drop to previously reported values for the polar cap potential implies that the field was primarily inductive and large enough to account for the relativistic electrons observed in association with substorms if it extended across ∼10 RE in the dawn‐dusk direction. The wave data (paper 2) showed the existence of whistler mode turbulence within and near the neutral sheet during these substorms which could scatter electrons to destabilize the tearing mode. Evidence for the possible occurrence of localized reconnection near ∼20 RE during nonsubstorm times was also found. Contrary to the assertions of the plasma sheet boundary layer model, we find a gradation from periods when there was a definite boundary with rapid field‐aligned flow and a quiescent central plasma sheet to cases (during magnetically active intervals) when the entire plasma sheet was rapidly moving with a large E×B component of the flow. These observations are consistent with the satellite being located at varying distances from the neutral line and diffusion region where reconnection and plasma acceleration were occurring. Although the z component (into or out of the ecliptic plane) of E × B convection was generally toward the neutral sheet, there were examples when it was consistent with the inferred motion of the plasma sheet past the satellite. A synthesis of previous reports on large electric fields at the plasma sheet boundary and variable fields at the neutral sheet including the associated plasma flows is also described.