Takeo Hirasawa

Polar patrol balloon experiment in Antarctica

Abstract Since 1984 the National Institute of Polar Research, the Institute of Space and Astronautical Science and collaborative scientists have searched for feasibility of the long-term circumpolar balloon experiment called Polar Patrol Balloon (PPB) project. This project aims at establishing a station network in the stratosphere over the Antarctic region for geophysical and astrophysical observations. Three test flights in 1987 and 1990 at Syowa Station have convinced us that PPB would come back to the launching site with a good possibility. During 1991–1993 the PPB experiments will consequently be made for scientific researches at Syowa Station. This paper reports unique advantages of this PPB experiment and briefly reviews the past PPB experiments.

Polar patrol balloon project in Japan

Abstract Since 1984, the National Institute of Polar Research and the Institute of Space and Astronautical Science have studied the feasibility of a long-term circumpolar balloon experiment, called Polar Patrol Balloon (PPB) project. This project aims at establishing a PPB system to bring scientific payloads in the stratosphere over the Antarctic region. Three test flights in 1987 and 1990 at Syowa Station convinced us that the PPB would have a good chance of coming back to the launching area, provided that we utilize the advantage of no sunset during the summer season in Antarctica. The PPB experiments were consequently made in 1990 to 1991. PPB #1 which was launched on 25 Dec 1990 reached a height of 30 km and drifted westwards. At 22:30 (UT) on 8 Jan 1991, the PPB passed 400 km north of Syowa Station; this means that the PPB accomplished a complete circumpolar flight over Antarctica. Second flight (#2) was successively launched on 5 Jan 1991. A further 3rd flight (#3) was carried out for 23–28 Sept 1991 when an Antarctic ozone hole was well developed.

A new direction finding technique for auroral VLF hiss based on the measurement of time differences of arrival at three spaced observing points

Abstract A newly developed direction finding (DF) technique for auroral hiss based on the measurement of time differences of wave arrival was carried out in 1978 at Syowa Station (geomag. lat. -70.4°), Antarctica and its two slave unmanned observing points located at about 20 km distances from Syowa. The auroral hiss signals (0.3–100 kHz) received at the two spaced points were transmitted to Syowa by a wide-band telemeter of 2 GHz. The arrival time difference of auroral hiss between Syowa and each spaced point was automatically determined by cross-correlating the waveforms of the received signals, and then the incident and azimuthal angles were measured with an accuracy of about 10°. It has been found that the new DF technique can determine localized exit regions at the ionospheric level which show rapid temporal movements. A comparison of the DF results with ground-based auroral data has shown that impulsive type auroral hiss with a wide-band frequency range has not emerged from the whole region of a bright aurora but from some localized regions of bright electron auroras at the ionospheric level, and that the arrival directions of auroral hiss change rapidly in accordance with the auroral movements.