A review of discontinuities and Alfven waves in interplanetary space: Ulysses results

The Ulysses mission is the first to explore our heliosphere at all latitude s up to +/- 80 degrees and therefore is an ideal mission to study potential gradients in heliolatitude land radial distance) of discontinuity occurren ce rates and types. Directional discontinuities (DDs) are shown to be depen dent on the type of solar wind streams that they are embedded in. The occur rence rate of DDs is 5-10 times higher in high-speed streams than in slow s treams. The explanation is that nonlinear Alfven waves dominate the high-sp eed streams and rotational discontinuities are the phase-steepened edges of the Alfven waves. Dissipation at these phase-steepened Alfven waves have b een sought but not found. An e(-(R-1)/5) decrease in discontinuity rate wit h increasing radial distance (R in units of AU) is partially an artifact of the selection criteria (discontinuity thickening), but dissipation at a re latively slow rate cannot be ruled out at this time. There is no obvious la titudinal gradients in discontinuity types or occurrence rates. Somewhat su rprisingly, tangential discontinuities are detected at high latitudes. Thes e have been associated with the edges of local small-scale magnetic decreas es. A pair of slow shocks were detected at 5.3 AU. The speeds are similar t o fast mode shock speeds. When Alfven waves in highspeed streams impinge up on the Earth's magnetosphere, near-continuous substorms (called HILDCAAs) o ccur, leading to the pumping of an extraordinary amount of energy into the nightside ionosphere. Current discontinuity and Alfven wave research proble ms are discussed.