[PEM22-P07] N2+ resonant scattering light observation in the sunlit topside ionosphere with the auroral spectrograph
Keywords:aurora, nitrogen molecular ion, up flow
The ASG consists of a fish-eye lens, slit, grism and a cooled CCD detector which covers the wavelength range of 420-730 nm with a 2.0 nm spectral resolution and field of view of 180°along the magnetic meridian. The ASG have been operating since 2000, but measuring N2+ emission 427.8 nm since 2004. The preceding study figured out that there is a high probability that the N2+ outflow occurs in geomagnetically disturbed condition (Kp > 4) [Mizuno et al., 2005]. Therefore, we analyzed the 65 events during from 2004 to 2016 which the sun does not illuminate the ground and the Kp indices were greater than 4 for more than 9 hours. Then, if a single aurora arc appears in the geomagnetically southward direction, we can regard the auroral distribution as the auroral height profile. In this case, we can roughly assume the emission height with the simultaneous 557.7 and 630.0 nm emission. The oxygen emission at 557.7 nm is considered to be caused only by precipitating electrons, and if the 427.8 nm emission is distributed higher (larger elevation angle) than 557.7 nm, this 427.8 nm emission is resonant scattering light. We found 5 events in this cases of all 65 events. The Kp indices of these events are 4-, 2+, 3+, 4-, 6-, 5, and we found that there were two cases which are during geomagnetically disturbed conditions and not disturbed ones. Around 0700 UT on December 21, 2014 (Kp=2+), the maximum 427.8 nm emission is 400 R and Dst indice is -10 nT (an hour before the 427.8 nm observation). Then, the 427.8 nm emission peak is assumed to be at 380 km if the 630.0 nm emission peak is considered to be at 250 km. While, around 0100 UT on December 21, 2015, a geomagnetic storm occurred (Dst indice is -150 nT), and N2+ emission was observed at intensity of 800 R. Then, N2+ emission peak is 340 km and the emission at intensity more than 200 R extended up to 1,000 km and more. Of all 5 events, the N2+ emission peak is in 300~400 km in 4 events, the altitudes which the intensity are less than 200 R are higher increasing the activity of geomagnetism. This result suggests that N2+ is produced in the lower F-region and then upflowing with the geomagnetic activity. This is consistent with the preceding study.