A TEST OF SOURCE-SURFACE MODEL PREDICTIONS OF HELIOSPHERIC CURRENT SHEET INCLINATION

The orientation of the heliospheric current sheet predicted from a sou rce surface model is compared with the orientation determined from min imum-variance analysis of ISEE 3 magnetic field data at 1 AU near sola r maximum. Of the 37 cases analyzed, 28 have minimum variance normals that lie orthogonal to the predicted Parker spiral direction. For thes e cases, the correlation coefficient between the predicted and measure d inclinations is 0.6. However, for the subset of 14 cases for which t ransient signatures (either interplanetary shocks or bidirectional ele ctions) are absent, the agreement in inclinations improves dramaticall y, with a correlation coefficient of 0.96. These results validate not only the use of the source surface model as a predictor but also the p reviously questioned usefulness of minimum variance analysis across co mplex sector boundaries. In addition, the results imply that interplan etary dynamics have little effect on current sheet inclination at 1 AU . The dependence of the correlation on transient occurrence suggests t hat the leading edge of a coronal mass ejection (CME), where transient signatures are detected, disrupts the heliospheric current sheet but that the sheet re-forms between the trailing legs of the CME. In this way the global structure of the heliosphere, reflected both in the sou rce surface maps and in the interplanetary sector structure, can be ma intained even when the CME occurrence rate is high.