Simultaneous observation of radar aurora and visible aurora over Mizuno Station

Abstract

Simultaneous observation of radar aurora and visible aurora in a small area (15×20km) around an altitude of 100km over Mizuho Station was made during a moderate substorm occurred before the midnight of October 5,1985. The radar aurora was observed by a 50MHz Doppler radar at Syowa Station while the visible aurora was monitored by a zenith photometer (4278 A) with a view angle of about 7° at Mizuho Station, 270km south-east of Syowa. It is found that within the bright auroral arc the radar echo intensity (therefore, the ionospheric electric field) is suppressed. Strong echoes caused by the gradient-drift instability appeared between the arcs. Within the faint, diffuse-like aurora which followed the bright arcs, the radar echoes due to the two-stream plasma instability driven by the electric field exceeding 25mV/m were detected