IMAGING THE EFFECT OF DIPOLE TILT ON MAGNETOTAIL BOUNDARIES

Eight years of IMP 8, four years of ISEE 2, and one year of IMP 7 magnetometer data have been combined to produce an ''image'' of the average magnetic field for a YZ cross section (aberrated GSM) of the magnetotail at a downtail distance of 25 R(E). The shape of the neutral sheet and magnetopause boundaries can be observed directly from the images. A fitting function that qualitatively matches the observed boundary shape can then be chosen. This approach improves on previous fits to possibly unsuitable functional forms specified independently of the data. In addition, as a refinement of previous studies, we have corrected for varying solar wind dynamic pressure and the effects of tail flaring. We find the magnetopause is displaced above the XY plane with increasing dipole tilt. The neutral sheet is found to curve slightly more than the model of Fairfield (1980) during times of large dipole tilt and near the flanks appears to differ substantially from the neutral sheet shape given by the analytic model of Voigt [1984], the more recent neutral sheet model of Dandouras (1988) based on the Voigt model, and the semi-empirical model of Tsyganenko (1989).