The 1986FEB Solar Activity - a Comparison of Giotto VEGA-1 and IMP-8 Soalr Wind Measurements with Magnetohydrodynamic Simulations

Abstract

Large disturbances in the interplanetary medium were observed by several spacecraft during a period of enhanced solar activity in early February 1986. The locations of six solar flares and the spacecraft considered here encompassed more than 100° of heliolongitude. These flares during the minimum of cycle 21 set the stage for an extensive multi-spacecraft comparison performed with a two-dimensional, magnetohydrodynamic (MHD) numerical experiment. The plasma instruments on the European Space Agency (ESA)'s GIOTTO spacecraft, on its way to encounter Comet Halley in March 1986, made measurements of the solar wind for up to 8 hours per day during February. We compare solar wind measurements from the Johnstone Plasma Analyzer (JPA) experiment on GIOTTO with the MHD simulation of the interplanetary medium throughout these events. Using plasma data obtained by the IMP-8 satellite in addition, it appears that an extended period of high solar wind speed is required as well as the simulated flares to represent the interplanetary medium in this case. We also compare the plasma and magnetometer data from VEGA-1 with the MHD simulation. This comparison tends to support an interpretation that the major solar wind changes at both GIOTTO and VEGA-1 on 8 February, 1986 were due to a shock from a W05° solar flare on 6 February, 1986 (06:25 UT). The numerical experiment is considered, qualitatively, to resemble the observations at the former spacecraft, but it has less success at the latter one.