R. P. Rijnbeek

A survey of flux transfer events recorded by the UKS spacecraft magnetometer

Abstract The UKS spacecraft operated from August 1984 through to January 1985. During that time, it made multiple crossings of the magnetopause in local time sectors extending from mid-afternoon to just behind the dawn meridian. We have surveyed the magnetometer records from these magnetopause encounters and have compiled a catalogue of flux transfer events (FTEs using criteria identical to those employed by Rijnbeek et al. (1984, J. Geophys. Res. 89, 786) in their survey of ISEE spacecraft magnetometer data. Using the catalogue, we find that FTE occurrence determined from the UKS data set is substantially less than that detected using data from the early ISEE 1 2 spacecraft orbits. The UKS data set shows a correlation between FTE occurrence and southward external magnetic field, but there are several instances of passes in which no FTEs are detected but for which the external field was unam- biguousluy southward. The passes with the largest number of events are those for which the field outside the magnetopause has a large BM component. We conclude that the lower latitude of the UKS encounters is responsible for the discrepancy with the ISEE occurrence. The most likely source region appears to be near the subsolar region.

Two-regime flux transfer events

Abstract We have examined a sizeable set of flux transfer event (FTE) signatures observed simultaneously by the ISEE 1 and ISEE 2 spacecraft when they were separated by large distances, of order a few thousand kilometres. In this paper we describe events in which simultaneous signatures were observed when the spacecraft were on opposite sides of the magnetopause. We call such events “two-regime” events. Sometimes clear events at one spacecraft are associated with weak perturbations at the other which do not satisfy the criteria used hitherto for FTEs. The data presented here are consistent with the interpretation that the perturbations are caused by a single reconnected flux tube which causes a disturbance on both sides of the magnetopause.

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.

Detection of FTEs by the AMPTE-UKS magnetometer

Abstract The AMPTE-UKS spacecraft repeatedly crossed the dayside magnetopause during its five month period of operation (August 1984 – January 1985). We have surveyed magnetometer records from these magnetopause encounters and compiled a catalogue of flux transfer events (FTEs) using the same identification criteria as Rijnbeek et al. /1/ used in their survey of ISEE data. This catalogue comprises 59 events detected on 41 orbits. Comparing occurrence statistics we find the rate of detection of FTEs by UKS is down by a factor of 2.5 on that recorded by the ISEE spacecraft in 1977 and 1978. We suggest the lower latitude of the UKS magnetopause encounters is responsible for this discrepancy.

Magnetic stresses during the solar wind barium release of 27 December 1984

Abstract We reexamine the magnetic field measurements from the Ba + ion release, made as part of the international AMPTE space programme on 27 December 1984. Observations from the Earth showed that the initial motion of the ion cloude was southward (-Z GSE ). Examination of the magnetic field structure at the two spacecraft in the vicinity of the release indicates that there was a net southward force acting during the period immediately preceeding the motion. We show that this force was adequate to accelerate the cloud in the southward direction. We propose that the momentum acquired by the core of the cloud in this process is balanced by ions on the flanks (in Y GSE ) accelerating northward with the stress being communicated through the field.