Do the Jovian Bow Shock and Magnetopause Surfaces in the Joy et al. (2002) Model Predict Measured Boundary Normals Correctly

Joy et al. [2002] provided probabalistic descriptions of the jovian bow shock and magnetopause locations by mapping spacecraft observations to the sub-solar point along model surfaces derived from the MHD simulation of Ogino et al. [1998]. The resulting statistics are strongly affected by the surface models used in the mapping process. Here we analyze the quality of the surface models used in that mapping by comparing the normal directions of the observed boundary crossings to the normal directions predicted by the model surfaces. We have identified 116 magnetopause and 132 bow shock crossings in the Galileo data from orbits 0-34 using both the plasma wave (PWS) and magnetometer (MAG) data sets. We have determined the boundary normal directions for both these newly identified crossings as well as the previously published crossings of Galileo, Ulysses, Voyager and Pioneer. When possible, boundary normals were determined from the MAG data by the minimum variance technique of Sonnerup and Cahill [1967]. Some boundary crossings could not be analyzed because of data gaps or inadequate sampling resolution. The analyzed boundary crossings (130 magnetopause, 156 bow shock) are well distributed in local time (~03:00 19:00) and are mostly near equatorial. Initial results indicate that the shape models used by Joy et al. [2002] are reasonable. We will examine the small non-zero mean difference between the observed and model boundary surfaces to determine whether the discrepancy is statistically significant. The large variance of the observed normal directions about the mean may imply that the normal directions fluctuate because of surface waves on the boundaries or that steady state models do not apply in the presence of changing solar wind conditions. Abstract