Predicting the heliospheric magnetic field using the current sheet-source surface model

Abstract

We have developed a current sheet-source surface (CSSS) model for quantitatively predicting the coronal and interplanetary magnetic field (IMF) from measurements of the photospheric magnetic field /1/. In-ecliptic OMNI data from Solar Cycle 21 were used to infer a set of model parameters that reproduce the observed IMF radial component ( B x ) better than earlier models. Here we extend the model calculation to Cycle 22 and compare the results with both ecliptic and high latitude observations. Comparison with the in-ecliptic data shows that the same set of model parameters can be used in Solar Cycle 22. Furthermore, the predicted maximum latitude of the heliospheric current sheet (HCS) is consistent with Ulysses' observation of the disappearance of the IMF sector pattern near 30°S between April and June, 1993. The computed B x along Ulysses' trajectory shows a similar trend to the observed total field amplitude at lower latitude. A more detailed comparison between the model prediction and Ulysses observations should allow a determination of an optimal model parameter set. The computed heliomagnetic latitude variation of B x suggests a dipole-like configuration of the large-scale coronal and heliospheric magnetic field. This may be used to understand the the 3-D structure of the solar wind speed in the declining phase of the solar cycle.