TANGENTIAL DISCONTINUITIES AT HIGH HELIOGRAPHIC LATITUDES (SIMILAR-TO-80-DEGREES)

In this study, tangential discontinuities (TDs) near -80 degrees heliographic latitude have been studied. Based on our quantitative definitions, we find that the TDs may generally be divided into two clear types. There is a distinct population of TDs small (< 40 degrees) directional changes. About 19% of all high-latitude TDs are in this category. These types of TDs are found at the edges of mirror mode structures. The latter are presumed to be locally generated by ion anisotropies, based on examination of the mirror mode instability criteria. Another 50% of high latitude TDs are associated with large field directional changes (> 60 degrees). These TDs typically are found at the boundary between two streams. The discontinuities have large normals in the plane perpendicular to the background field, as might be expected for features generated by currents flowing along the field. These discontinuities usually have larger current intensities than those of the mirror-mode related TDs. The remainder of the discontinuities have angular changes which lie in between the mirror-mode-associated and the current-sheet-associated TDs.