The quasi-parallel shock wave detected by ULYSSES on day 92:109.

Abstract

On day 92:109, at about 5.4 AU and 9° south, Ulysses detected a strong quasi-parallel shock wave leading an interaction region. We describe this singular event on different temporal scales, placing emphasis on the magnetic field observations. The solar wind preceding the shock presented very unusual long-lived conditions: for about one day the interplanetary magnetic field was closely radially oriented and this was associated with a strong anisotropy in proton temperature (T_p_{//}__/T_p_perp__<1). The wave activity in the upstream and downstream regions have the largest spatial extent for any interplanetary shock wave reported before. In the foreshock region we identified 10^-2^Hz waves and continual distributions of backstream ions up to 28.5 hours (>=0.29AU) ahead of the shock. The downstream region was characterized by large amplitude, low frequency (f<=10^-3^Hz), compressive perturbations for about 34 hours. The temporal fluctuations around the shock transition do not allow us to apply the techniques based on the Rankine-Hugoniot relations to infer the shock parameters.