The Relationship of the Large-Scale Solar Field to the Interplanetary Magnetic Field: What Will Ulysses Find?
STANFORD UNIV CA CENTER FOR SPACE SCIENCE AND ASTROPHYSICS
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Photospheric magnetic fields together with a potential field model can be used to calculate the configuration of the interplanetary magnetic field IMF. The IMF is organized into large regions of opposite polarity separated by a neutral sheet NS. Small quadripolar warps in a roughly equatorial NS produce the four-sector structure commonly observed in the IMF at Earth near solar minimum. Soon after minimum the latitudinal extent of the NS increases substantially. Near maximum the structure is more complex, occasionally including multiple neutral sheets. The IMF structure simplifies and becomes very stable during the declining phase. Large-scale structures persist for up to two years during the entire cycle. From 1978 through 1983 the NS extended to at least 50 deg.. Like coronal holes, the computed coronal field shows evidence of decreased differential rotation. Patterns in the inferred IMF polarity from solar cycle 16 - 21 are very similar. This suggests that structures observed by Ulysses during the coming cycle will be similar to those in the past. Reprints .