STRUCTURES IN THE POLAR SOLAR-WIND - PLASMA AND FIELD OBSERVATIONS FROM ULYSSES

Ulysses has frequently observed solar wind structures lasting from sev eral hours to several days since it passed into the region of solar wi nd emanating from the southern polar coronal hole at similar to 36 deg rees S. In addition to previously reported Alfven waves and coronal ma ss ejections, two other sorts of structures are routinely evident. Thi s paper provides the first report of these structures in the high-lati tude solar wind: (1) small-scale compressional structures and (2) pres sure balance structures. The compressional structures are driven by fa ster solar wind overtaking slower solar wind ahead of it and exhibit t he plasma and field properties expected for compressions. Unlike large -scale stream interaction regions observed in and near the ecliptic pl ane, these structures are much smaller scale and are nonrecurring from one rotation to the next. These smaller-scale compressional structure s appear to arise preferentially from a limited (similar to 120 degree s of heliolongitude) region in the southern polar coronal hole. The pr essure balance structures, on the other hand, are indicated by roughly equal increases in the plasma pressure and decreases in the magnetic field pressure, These structures, which are several degrees across, ar e more dense and have higher plasma pressures and betas than the surro unding solar wind. These pressure balance structures may be the interp lanetary manifestations of ''polar plumes.''