AIRCRAFT OBSERVATIONS CONJUGATE TO FAST - AURORAL ARC THICKNESSES

Optical observations conjugate to the FAST satellite show good agreeme nt between the widths of auroral structures observed optically and tho se inferred from the measured electron energy flux. The implication is that these structures are imposed by processes at or above the simila r to 4000 km altitude of FAST. A variety of widths down to about 2 km were observed, but there were no examples of finer scale structures. A pre-breakup weak discrete are at the poleward edge of the diffuse aur ora showed electron produced optical structures located on either side of upward going ion beams. The optical emission in the equatorward pa rt of the diffuse aurora was caused almost exclusively by precipitatin g ions. The optical observations were made over northern Alaska betwee n Jan 31 and Feb 16, 1997, from a jet aircraft carrying an all-sky and three narrow-field TV cameras.