AURORAL OBSERVATION AT SYOWA STATION, 1967-1968

Abstract

The auroral observations carried out by the 8th wintering party of the Japanese Antarctic Research Expedition, 1967-68, included 1 All-sky camera 2 Visual and photographic observations of aurora 3 Observation of auroral pulsations 4 Auroral photometry along the geomagnetic meridian 5 Observation of the auroral radio noise A description of each observation and obtained results are briefly given 1 Auroral pulsations A special photometer was designed for investigating the detailed characteristics of auroral pulsations and their relationships with geomagnetic pulsations The photometer (Fig 1) consists of a single telescope equipped with a band-pass filter (4278 A) The field of view is 5° The amplified anode current of the RCA lp21 photomultipliers is fed to three electrical band-pass filters (f_1, 001-01 Hz, f_2, 01-2 Hz, f_3, 2-30 Hz), and recorded by a slow running tape-recorder The outputs of the band-pass filters are separately registered on multi-channel pen recorders together with the signals of the geomagnetic pulsations By means of this photometric system, data of more than 300 clear night hours were recorded (Fig 3) Figs 4-8 illustlate the various types of auroral luminosity fluctuations together with the geomagnetic field fluctuations Auroral pulsations observed at Syowa Station can be classified into the following five types. A. Irregular fluctuations with large amplitudes (a few tens of KR) observed mostly at the onset of an auroral substorm (Fig 4) B Pulse-like auroral pulsations with a period of about 20-40 seconds, the amplitudes of which are sometimes greater than 10 KR Pulsations of this type are frequently observed in the early morning hours of magnetic disturbed days (Fig 5). C Long-lived auroral pulsations with a sinusoidal waveform. Their periods and amplitudes are about 10 seconds and a few KR, respectively. This type is dominant in the morning hours (Fig. 6). D. Rapid fluctuations of auroral luminosity with a period of about 2-0.5 seconds (Fig 7, A and B). E. Extremely rapid fluctuations with a frequency of about 20-30 Hz (Fig. 8, A and B) Waveform correlation between auroral and geomagnetic pulsations depends on their periods. Most auroral rapid fluctuations of period shorter than 5 seconds are not accompanied by geomagnetic fluctuations Auroral and geomagnetic pulsations of period longer than 10 seconds have similar waveforms. 2. Photometry of aurora along the geomagnetic meridian A meridian scanning photometer was designed for investigating the time and space variations of the auroral luminosity (Fig 2). A rotating mirror scans from north to south along the geomagnetic meridian. The scanning time of this photometer is 12 seconds. In the auroral zone, it is desirable to measure the auroral luminosity from 0.1 KR to a few hundreds KR (about 50-60 dB). Therefore, signals of the auroral luminosity are amplified by the high, medium and low gain amplifiers and are separately registered on a 3-channel pen-recorder. Fig. 10 illustrates an example of the chart record obtained The data shown in Figs. 11 and 12 were derived from the above records. Considering the data taken over a period of 25 days (listed in Table 2), the following relationships were thought to exist at the time of occurrence of auroral substorms. a. Auroral arcs begin to move equatorwards about an hour-20 minutes before the onset of the auroral substorm. b. The equatorward movement of auroral arcs take place generally in about 5-10 minutes. c. At the onset-time of an auroral substorm, the luminosity of auroral arcs suddenly intensified. d. Within a few minutes after the onset of the storm, the aurora spreads and blankets the sky, in which very bright arcs exist, with rapidly fluctuating luminosity. These arcs move towards the pole, in general, at a speed of about 200-300 km/s. e. At the end phase of the substorm, the aurora become active on the polar side of Syowa Station 3. Spatial and temporal variations of auroral forms Continuous photographic observations of aurora were carried out. Fig. 13 illustrates the auroral forms during an auroral substorm. Fig. 14 illustrates the space and time variations of corona at the zenith. Fig. 15 illustrates the formations and eastward movements of auroral loops.