Weak auroral emissions and particle precipitations in the dusk auroral oval

Faint auroral displays in the low-latitude region of the duskside auroral oval were examined by using 5577 A, 6300 A, and 4861 A auroral images from three monochromatic all-sky television cameras at Syowa Station, Antarctica, and simultaneous precipitating auroral particle data obtained by the U.S. Air Force/Defense Meteorological Satellite Program (USAF/DMSP) F6 satellite. In the low-latitude region of the duskside auroral oval, we found three types of auroral displays with weak optical intensity: (1) proton auroras, (2) pulsating auroras, and (3) faint discrete auroral arcs distinct only in the 6300 A emission. In usual cases, the energy input into this region is mostly carried y proton precipitations to produce proton auroras mainly at wavelengths of 4861 A and 5577 A. Pulsating features are sometimes observed in the diffuse auroral region in the dusk sector. Comparing auroral images with the nearly simultaneous data of precipitating auroral particles, we confirmed that the pulsating auroras are associated with the intensification of precipitating electron flux from the central plasma sheet. Furthermore, electrons are the main contributors to the energy input into the duskside auroral oval in this case. We also found that discrete auroras sometimes appeared in the 6300 A images, but not in images at other wavelengths. They appear in the equatorial part of the dusk auroral oval. These 6300 A discrete auroras correspond to weak precipitation spikes of low-energy electrons simultaneously measured by DMSP satellites. The flux and average energy of these electron spikes are about 108/(cm2 sr s) and 100 eV, respectively. They are intense enough to excite 6300 A emissions but not 5577 A emissions, as detected from the ground observations. copyright American Geophysical Union 1989