Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm23b..06o&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM23B-06
Physics
2700 Magnetospheric Physics (6939), 2704 Auroral Phenomena (2407), 2716 Energetic Particles: Precipitating, 2730 Magnetosphere: Inner, 2764 Plasma Sheet
Scientific paper
In order to investigate the characteristics of fine-scale black aurora, observations with the multi-spectral auroral camera (MAC) on board the REIMEI satellite, which has a polar orbit in the noon-midnight meridian at an altitude of ~640 km, are being carried out. The energy and pitch angle distribution of auroral particles are simultaneously observed by the electron spectral analyzer (ESA) and the ion spectral analyzer (ISA) instruments also on board the REIMEI satellite. In the nightside auroral region, MAC can take monochromatic images at three wavelengths of N2+ 1NG band (427.8 nm), OI (557.7 nm), and N2 1PG band (670 nm), with high time (max. 120 msec) and spatial (max. 1 km) resolutions. Since the REIMEI satellite has an 3-axis stabilized attitude control system, we can point the FOV of MAC to a footprint of magnetic field line threading the satellite to realize simultaneous auroral particle and emission observations. In this study, we examined fine-scale black aurora events, whose thicknesses were less than 10km, seen in rather uniform diffuse aurora occurred in the inner plasma sheet region. It is found that the appearance of black aurora clearly corresponded to the region where the electron pitch angle distribution temporally showed the double loss cone, while the surrounding diffuse aurora corresponded to the region where the electron pitch angle showed the single loss cone. Thus, it is suggested that the black aurora is produced by the lack of precipitating electrons with the double loss cone type pitch angle distribution, probably caused by the suppression of pitch angle scattering process. It is also found that the energy dispersed precipitating electrons were observed in association with black aurora events. This fact suggests that the black aurora event may be relevant to pulsating aurora event since it is known that there is a good correlation between the existence of pulsating aurora and that of temporally precipitating energy dispersed electrons.
Asamura Kazushi
Ebihara Yasuhiro
Hirahara Masafumi
Ino Tsunehiro
Kasaba Yasumasa
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