SOLAR-CYCLE VARIATIONS IN THE SIZE AND SHAPE OF THE MAGNETOPAUSE

The 10 years of the ISEE 1 and 2 mission covering much of solar cycle 21 and the beginning of solar cycle 22 allow us to study the position, shape, and motion of the magnetopause throughout the course of changing solar activity. We have determined the size and shape of the magnetopause for each observing season using the ISEE 1 and 2 magnetometer data. IMP 8 data were used to monitor the solar wind changes with the solar cycle. During the 1979-1980 season, at solar maximum the solar wind dynamic pressure was at its lowest values, and at solar minimum the solar wind pressure was at its largest values, more than double the value in the 1979-1980 season. During this solar cycle the magnetopause was about 0.5 R(E) farther when the interplanetary magnetic field (IMF) was strongly northward than when strongly southward. Both standoff distance values are found to be smaller than the value found by Fairfield [1971]. The standoff distance of the magnetopause for northward IMF is anticorrelated with the solar wind pressure as expected. However, the standoff distance for southward IMF seems relatively insensitive to solar wind dynamic pressure.