Wind observations of the influence of the Sun's magnetic field on the interplanetary medium at 1 AU
T. R. Sanderson, R. P. Lin, D. E. Larson, M. P. McCarthy, G. K. Parks, J. M. Bosqued, B. Lormant, K. W. Ogilvie, R. P. Lepping, A. Szabo, A. J. Lazarus, J. T. Steinberg, and J. T. Hoeksema
Space Science Department of the European Space Agency, European space Research and Technology Centre, Noordwijk, Netherlands
We combine data from several instruments on the Wind spacecraft with ground-based observations of the position of the heliospheric current sheet for the first 2.5 years of the mission, which covers the period from the end of solar cycle 22, through solar minimum, and into the start of cycle 23. We use data from the three-dimensional (3-D) plasma instrument (3DP), magnetometer (MFI), and Solar Wind Experiment (SWE). We examine the energetic ion and electron increases associated with corotating interaction regions (CIR) and relate them to the position and shape of the current sheet. The characteristics of the energetic particle increases associated with the observed CIRs change several times during the mission. We identify these periods and find that we can relate these particle signatures of the CIRs to the plasma conditions which themselves depend upon the changing tilt and warp of the current sheet. We examine the additional increases associated with magnetic clouds and impulsive solar flares that were observed at irregular intervals during the mission. We show how the Sun's magnetic field influences the interplanetary medium at 1 AU, as variations in the shape and inclination of the source surface current sheet propagate out to 1 AU. We identify the three major sources of these variations, (1) the long-term, slowly varying tilt of the current sheet with a timescale of the solar cycle, (2) the medium-term small but significant annual movement of the position of the Earth relative to the current sheet due to the inclination of the plane of the ecliptic with respect to the heliographic equator, and (3) the short-term warps and bulges which come and go due to the appearance of active regions, lasting only a few solar rotations.
J. Geophys. Res., 103, 17,235-17,247, 1998