Corotating interaction regions at high latitudes - Report of Working Group3

Ulysses observed a stable strong CIR from early 1992 through 1994 during it s first journey into the southern hemisphere. After the rapid latitude scan in early 1995, Ulysses observed a weaker CIR from early 1996 to mid-1997 i n the northern hemisphere as it traveled back to the ecliptic at the orbit of Jupiter. These two CIRs are the observational basis of the investigation into the latitudinal structure of CIRs. The first CIR was caused by an ext ension of the northern coronal hole into the southern hemisphere during dec lining solar activity, whereas the second CIR near solar minimum activity w as caused by small warps in the streamer belt. The latitudinal structure is described through the presentation of three 26-day periods during the sout hern CIR. The first at similar to 24 degrees S shows the full plasma intera ction region including fast and slow wind streams, the compressed shocked f lows with embedded stream interface and heliospheric current sheet (HCS), a nd the forward and reverse shocks with associated accelerated ions and elec trons. The second at 40 degrees S exhibits only the reverse shock, accelera ted particles, and the 26-day modulation of cosmic rays. The third at 60 de grees S shows only the accelerated particles and modulated cosmic rays. The possible mechanisms for the access of the accelerated particles and the CI R-modulated cosmic rays to high latitudes above the plasma interaction regi on are presented. They include direct magnetic field connection across lati tude due to stochastic field line weaving or to systematic weaving caused b y solar differential rotation combined with non-radial expansion of the fas t wind. Another possible mechanism is particle diffusion across the average magnetic field, which includes stochastic field line weaving. A constraint on connection to a distant portion of the CIR is energy loss in the solar wind, which is substantial for the relatively slow-moving accelerated ions. Finally, the weaker northern CIR is compared with the southern CIR. It is weak because the inclination of the streamer belt and HCS decreased as Ulys ses traveled to lower latitudes so that the spacecraft remained at about th e maximum latitudinal extent of the HCS.