Solitary potential structures associated with ion and electron beams near 1 R-E altitude

Small-scale solitary electric potential structures are commonly observed on auroral field lines with the Polar Electric Field Instrument (EFI). This s tudy focuses on observations of solitary structures in the southern hemisph ere auroral zone at altitudes between 5500 and 7500 km. Some of the potenti al structures are similar to those observed previously by the S3-3 and Viki ng satellites and are inferred to be negative potential pulses traveling up ward along the auroral magnetic field lines, associated with upgoing ion be ams and upward currents The velocities of these "ion" solitary potentia; st ructures are estimated, using spaced EFI measurements, to be distributed wi thin solitary potential structures are estimated, using spaced EFI measurem ents, to be distributed within the range of similar to 75 - 300 km s(-1) In addition to these structures, a different type of solitary potential struc ture with opposite polarity has been observed with faster propagation veloc ities. These faster structures (termed "electron" solitary potential struct ures) are distinguishable from the slower, ion solitary structures in that their distinctive bipolar electric field signature, common to both types of solitary structure, is reversed. The ultimate distinction for the electron solitary potential structures is that they are observed on auroral field l ines in conjunction with magnetically field-aligned upflowing electron beam s. The electron solitary potential structures propagate up the field line i n the same direction as the electron beam. An example is shown of the polar ity reversal from ion to electron solitary potential structures coincident with a simultaneous shift from upgoing ion beams to upgoing electron beams.