D. S. Hall

A magnetic boundary signature within flux transfer events

Abstract We present high resolution AMPTE-UKS data for a FTE signature in the magnetosphere. When the observations are confronted with the canonical model for such events, we find that we can substantiate clearly the existence of the two field regions (draping vs twisting) predicted from the model. In addition to these regions there is a separate, distinct region close to the expected boundary between open and closed field lines which we estimate to be of order ten ion gyroradii thick. This region is distinguished by a distinctive field and particle signature. The magnetic signature has not been reported before, but the electron signature bears a close resemblance to the electron heat flow layer reported in the ISEE data by Scudder et al. [1984 in Magnetic Reconnection in Space and Laboratory Plasmas (Edited by Hones E.W., Jr.), p. 153. AGU, Washington]. Other observations we report are the occurrence of a large flow burst and, in the central region of the FTE signature, the presence of magnetic field oscillations of period ∼ 3 s.

AMPTE-UKS observations of current sheets in the solar wind

Abstract Active current sheets or diamagnetic cavities in the solar wind have been observed both by the AMPTE-UKS spacecraft on a number of occasions, and independently from ISEE by Thomsen et al /1/. Preliminary results from one of these UKS observations have been discussed recently by Schwartz et al /2/. In this paper we consider these phenomena in more detail. Results are presented for the position of five events. High resolution plasma data and plasma wave activity associated with these current sheets are examined.

Electron acceleration by lower hybrid waves on auroral field lines

Particle measurements show that electron acceleration on auroral field lines is a statistical, velocity-dependent, process. It is proposed that the process is stochastic acceleration by waves, and demonstrated that lower hybrid waves seen on auroral field lines have the right properties to account for the electron acceleration. It is further shown that the lower hybrid wave power measured on auroral field lines can be generated by the streaming ions observed at the boundary of the plasma sheet, and that this wave power is sufficient to account for the electron power observed close to the atmosphere.

Measurements of the angular distribution of precipitating electrons in a breakup aurora

Abstract Measurements of the complete pitch-angle distribution of precipitating auroral electrons in the energy range 0.5 to 25 keV in several arcs are presented. The measurements were made with a time resolution of 2s between altitudes of 400 and 700 km by electrostatic analysers carried on a sounding rocket. The angular structure and temporal development of suprathermal burst events are discussed, together with constraints on the responsible mechanism, and a possible mechanism is suggested.