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 magn etometer data have been combined to produce an ''image'' of the averag e magnetic field for a YZ cross section (aberrated GSM) of the magneto tail 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 s hape can then be chosen. This approach improves on previous fits to po ssibly 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 flarin g. We find the magnetopause is displaced above the XY plane with incre asing dipole tilt. The neutral sheet is found to curve slightly more t han the model of Fairfield (1980) during times of large dipole tilt an d near the flanks appears to differ substantially from the neutral she et 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).