Motion of the footpoints of heliospheric magnetic field lines at the Sun: Implications for recurrent energetic particle events at high heliographic latitudes

Abstract

The interplay between the differential rotation of the footpoints of heliospheric magnetic field lines in the photosphere and the subsequent nonradial expansion of these same field lines with the solar wind from rigidly rotating coronal holes can result in extensive excursions of heliospheric magnetic field lines with heliographic latitude. Thus magnetic field lines at high latitudes can be connected directly to corotating interactions regions (CIRs) in the solar wind at low latitudes at larger heliocentric distances. A model is presented which illustrates that this effect can account for the observations from the Ulysses spacecraft that recurrent energetic particle events, which appear to originate in low-latitude CIRs, occur at the highest latitudes observed. The model also has implications for the observation that the heliospheric magnetic field appears to have a tighter than expected spiral angle at high latitudes over the south solar pole and for the modulation of galactic cosmic rays.