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) enhancement was found within the high-speed wind stream observed by Helios 2 in 1976 near 0.3 AU. The proton density and temperature and the magnetic magnitude simultaneously increased for about 6 h. This pressure rise was associated with a comparatively large southward flow velocity component (with Vz )100 km · s ) and magnetic-field rotation. The pressure enhancement was associated with unusual features in the electron distribution function. It shows a wide angular distribution of electron counting rates in the low-energy (57.8 eV) channel, while previous to the enhancement it exhibits a wide angular distribution of electron count rate in the high-energy (112, 221 and 309 eV) channels, perhaps indicating the mirroring of electrons in the converging field lines of the background magnetic field. These fluid and kinetic phenomena may be explained as resulting from an interplanetary magnetic flux rope which is not fully convected by the flow but moves against the background wind towards the Sun.