Acceleration and modulation of energetic particles in the 3-D heliosphere by corotating interaction regions

• Published in: Advances in space research 1997-01, Vol.19 (6), p.859-868
• Main Authors: Simnett, G.M., Roelef, E.C.
• Format: Article
• Language: English
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/S0273-1177(97)00293-7

The passage of the Ulysses spacecraft over the poles of the Sun in 1994/1996 has given us a unique insight into the physics of the third dimension of the heliosphere. During the 30-month transit from Jupiter to the south polar pass, the low-latitude heliosphere was dominated by a high speed solar wind stream which produced a corotating interaction region. Below heliolatitudes of 30–40°S this was sampled by Ulysses every 26 days, and forward and reverse shocks were often detected. These were found to accelerate energetic charged particles up to around 4 MeV/nucleon. At higher latitudes the corotating interaction region was no longer sampled directly, but the effects of remote energetic particle acceleration — at perhaps 10–15 AU — on high latitude magnetic field lines were noticed in ∼50 keV electrons up to the south polar pass. This effect was not so noticeable in the northern hemisphere, although once Ulysses returned to mid-latitudes after the polar pass, recurrent electron increases were seen once more. When corrections for the spacecraft radial distance and changes in Right Ascension were made, the electron increases appeared so regularly that they could be used as a clock. Ulysses has seen the effects of acceleration of interstellar pick-up helium ions from solar wind energies up to several MeV/nucleon. The corotating interaction region has been shown to modulate the anomalous cosmic rays at energies of a few MeV/nucleon.