Modeling the Out-of-Ecliptic Interplanetary Magnetic Field in the Declining Phase of Sunspot Cycle 22

Abstract

We have developed a new model of the coronal and interplanetary magnetic field. The model includes the effects of large-scale horizontal electric currents flowing in the inner corona, of the warped heliospheric current sheet, and of heliospheric volume currents in the super-Alfvenic solar wind. The model determines the interplanetary magnetic field (IMF) strength as well as its polarity from measurements of the photospheric magnetic field. A detailed comparison between the observed and calculated in-ecliptic IMF Bx in Cycles 22, confirms the fitness of the optimal set of free parameters inferred using data in Cycle 21. We can predict the latitudinal gradient of Bx in the declining phase of Cycle 22 and the temporal variation of the amplitude of the radial component of the IMF at various latitudes. The calculated IMF polarity and Bx strength agree best with the in-ecliptic observations when the photospheric field (measured with a A5250A magnetograph) is scaled up by a factor of two. Ulysses may provide the critical data to improve the model and check these inferences.