Velocity distribution on ice sheet in Prince Olav Coast, East Antarctica

A refraction experiment with a 100-kg charge was carried out in the ice sheet in the Prince Olav Coast, East Antarctica by the 21st Japanese Antarctic Research Expedition (JARE-21) in 1980. Prominent Rayleigh waves were clearly recorded in a distance range of 2 to 8 km from the explosion point. The maximum period of Rayleigh waves was 0.7 s with a phase velocity of 1.8 km/s. A phase velocity of surface waves is considered to be most sensitive to the P- and S-wave velocity structures of ice layers to a depth of one-fourth of the wave length. Since the longest wave length of Rayleigh waves in the present experiment is estimated to be 1300m for the maximum period of 0.7s (1.8 km/s in phase velocity), P- and S-wave velocity structures of ice layers to a depth of 300 to 400 m may be inferred from the dispersion curves. Assuming velocity structures of ice sheet in the Mizuho Plateau based on the previous works of JARE, theoretical dispersion curves were calculated for three different velocity structures and they were compared with the observed ones. For example, the calculated phase velocities at the period of 0.4s were 1.85 km/s for the highest velocity model, 1.7 km/s for the middle and 1.6 km/s for the lowest one, and the observed phase velocity at the period of 0.4s was 1.75 km/s. The velocity structure of P- and S-waves in the upper part of ice sheet estimated from observed dispersion curves of Rayleigh waves is three percents higher than those of the averaged one in the Mizuho Plateau. The P- and S-wave velocities from 100 to 1000 m in depth range from 3.7 to 4.0 km/s, and from 1.8 to 2.0 km/s

Space-time Variation of Aurora and Geomagnetic Disturbances : Auroral Observations at Syowa Station in Antarctica (AERONOMY)

The program of auroral observations carried out by the 8th wintering party of the Japanese Antarctic Research Expedition, 1967-1968, consisted of 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. Description of each observation and results obtained are briefly summarized in the following. 1. Space-time variations of aurora and geomagnetic disturbances A meridian scanning photometer was designed for investigating the time and space variations of auroral luminosity. The meridian time-sequence of auroral luminosity (4278Å) was derived from the data obtained by this photometer. Based on this meridian time-sequence of aurora, the space and time variations of aurora during the auroral substorms and the magnetic field variations associated with the auroral displays are investigated in detail. 2. Auroral pulsations A special photometer was designed for investigating the detailed characteristics of auroral pulsations and their relationships with geomagnetic pulsations. Auroral pulsations observed at Syowa Station can be classified into the following five types : A. Irregular fluctuations with large amplitudes observed mostly at the onset of an auroral substorm. B. Pulse-like auroral pulsations with a period of about 20-40 seconds. C. Long-lived auroral pulsations with a sinusoidal waveform. Their period and amplitude are about 10 seconds and a few KR, respectively. D. Rapid fluctuations of auroral luminosity with a period of about 0.5-2.0 seconds. E. Extremely rapid fluctuations with a frequency of about 20-30 Hz. Characteristics of each auroral pulsation are investigated and summarized