The heliospheric magnetic field at solar maximum: Ulysses observations

At solar maximum, the large-scale structure of the heliospheric magnetic fi eld (HMF) reflects the complexity of the Sun's coronal magnetic fields. The corona is characterised by mostly closed magnetic structures and short-liv ed, small coronal holes. The axis of the Sun's dipole field is close to the solar equator; there are also important contributions from the higher orde r terms. This complex and variable coronal magnetic configuration leads to a much increased variability in the HMF on all time scales, at all latitude s. The transition from solar minimum to solar maximum conditions, as reflec ted in the HMF, is described, as observed by Ulysses during its passage to high southern heliolatitudes. The magnetic signatures associated with the i nteraction regions generated by short-lived fast solar wind streams are pre sented, together with the highly disordered period in mid-1999 when there w as a considerable reorganisation in coronal structures. The magnetic sector structure at high heliolatitudes shows, from mid-1999, a recognisable two- sector structure, corresponding to a highly inclined Heliospheric Current S heet. A preliminary investigation of the radial component of the magnetic f ield indicates that it remains, on average, constant as a function of helio latitude. Intervals of highly Alfvenic fluctuations in the rarefaction regi ons trailing the interaction regions have been, even if intermittently, ide ntified even close to solar maximum.