PRESSURE ENHANCEMENT ASSOCIATED WITH MERIDIONAL FLOW IN HIGH-SPEED SOLAR-WIND - POSSIBLE EVIDENCE FOR AN INTERPLANETARY MAGNETIC-FLUX ROPE

A sizable total-pressure (magnetic pressure plus kinetic pressure) enh ancement was found within the high-speed wind stream observed by Helio s 2 in 1976 near 0.3 AU. The proton density and temperature and the ma gnetic magnitude simultaneously increased for about 6 h. This pressure rise was associated with a comparatively large southward flow velocit y component (with V-= approximate to -100 km . s(-1)) and magnetic-fie ld rotation. The pressure enhancement was associated with unusual feat ures in the electron distribution function. It shows a wide angular di stribution of electron counting rates in the low-energy (57.8 eV) chan nel, while previous to the enhancement it exhibits a wide angular dist ribution of electron count rate in the high-energy (112, 221 and 309 e V) channels, perhaps indicating the mirroring of electrons in the conv erging field lines of the background magnetic held. These fluid and ki netic phenomena may be explained as resulting from an interplanetary m agnetic flux rope which is not fully convected by the flow but moves a gainst the background wind towards the Sun.