SPATIALLY QUASI-PERIODIC PLASMA AND ELECTROMAGNETIC SIGNATURES IN THEPOLEWARD BOUNDARY OF THE AURORAL OVAL - OBSERVATIONS ON THE MORNINGSIDE

We present observational characteristics of the spatially quasiperiodi c signatures of plasma and electric and magnetic fields observed in th e poleward boundary of the morningside auroral oval by two polar-orbit ing satellites: Akebono and DMSP F9, The two satellites observed the p roton discrete signatures at different altitudes (similar to 5000 km ( Akebono) and similar to 800 km (DMSP F9)) during nearly the same inter vals. The data indicate that the ion (proton) signatures repetitively appeared and had a good correlation with occurrence of spiky electrons associated with upward components of small-scale field-aligned curren ts and variations of electric fields. We conclude that the repetitive (quasiperiodic) proton signatures had spatially energy-dispersed signa tures, which were not due to transient effect, on the basis of a compa rison of the simultaneous observations at the different altitudes. Cha racteristic energy of each dispersed trace decreased with decreasing l atitude, and the energy-dispersed signatures frequently overlapped eac h other. A global plasma convection reversal often occurred during the quasiperiodic proton signatures, Sequential observations show that th e region with these proton signatures was latitudinally wide and exten ded significantly to higher latitudes under northward interplanetary m agnetic field conditions. It is plausible that instabilities in the ta il-flank boundary of the magnetosphere, represented by the Kelvin-Helm holtz instability, are driven by the interaction between the solar win d and the central plasma sheet and then could produce the precipitatin g ions and the electrons accompanied by the variations of the electric and magnetic fields.