A SEARCH FOR UPSTREAM PRESSURE PULSES ASSOCIATED WITH FLUX-TRANSFER EVENTS - AND AMPTE ISEE CASE-STUDY

On September 19, 1984, the Active Magnetospheric Particle Tracers Expl orers (AMPTE) United Kingdom Satellite (UKS) and Ion Release Module (I RM) and ISEE 1 and 2 spacecraft passed outbound through the dayside ma gnetopause at about the same time. The AMPTE spacecraft pair crossed f irst and were in the near-subsolar magnetosheath for more than an hour . Meanwhile the ISEE pair, about 5 R(E) to the south, observed flux tr ansfer event (FTE) signatures. We use the AMPTE UKS and IRM plasma and field observations of magnetosheath conditions directly upstream of t he subsolar magnetopause to check whether pressure pulses are responsi ble for the FTE signatures seen at ISEE. Pulses in both the ion therma l pressure and the dynamic pressure are observed in the magnetosheath early on when IRM and UKS are close to the magnetopause, but not later . These large pulses appear to be related to reconnection going on at the magnetopause nearby. AMPTE magnetosheath data far from the magneto pause do not show a pressure pulse correlation with FTEs at ISEE. More over, the magnetic pressure and tension effects seen in the ISEE FTEs are much larger than any pressure effects seen in the magnetosheath. A superposed epoch analysis based on small-amplitude peaks in the AMPTE magnetosheath total static pressure (nkT + B2/2mu(o)) hint at some bo undary effects, <5 nT peak-to-peak variations in the ISEE 1 and 2 B(N) signature starting about 1 min after the pressure peak epoch. However , these variations are much smaller than the standard deviations of th e B(N) field component. Thus the evidence from this case study suggest s that upstream magnetosheath pressure pulses do not give rise to FTEs , but may produce very small amplitude signatures in the magnetic fiel d at the magnetopause.