Fumio Tohyama

Small‐scale field‐aligned currents observed by the Akebono (EXOS‐D) satellite

The EXOS-D fluxgate magnetometer data obtained at 3,000-10,000 km altitude have shown that small-scale field-aligned currents always exist in large-scale region 1, region 2, cusp and polar cap current systems. Assuming that these small-scale field-aligned currents have current sheet structure, the width of current sheet is estimated to be 5-20 km at ionospheric altitude. By comparing the magnetometer data with charged particle and high frequency plasma wave data simultaneously obtained from EXOS-D, it is found that small-scale currents have one-to-one correspondence with localized electron precipitation events characterized by flux enhancement over a wide energy range from 10 eV to several keV and broadband electrostatic bursts occasionally extending above local plasma frequencies or electron cyclotron frequencies.

Field-aligned current signatures during the March 13–14, 1989, Great Magnetic Storm

Characteristics of field-aligned currents (FACs) in the evening and morning regions during the March 13–14, 1989, great magnetic storm have been determined using magnetic and electric field data obtained from the EXOS D spacecraft. This storm began with an SSC at 0128 UT on March 13, and the second SSC occurred at 0747 UT on the same day. The storm continued until March 14. The equatorward boundary of the FAC region began to move equatorward right after the first SSC in both the evening and morning sectors, but the poleward boundary did not immediately respond to the SSC. The equatorward boundary of the FAC system reached as low as below 48° invariant latitude, which corresponds to L = 2.2, and the latitudinal width of the FAC region increased greatly, particularly in the morning sector (∼33° in invariant latitude). In the evening sector the conventional current system characterized by a pair of upward region 1 and downward region 2 FACs changed into complicated patterns consisting of many pairs of upward and downward FACs with the development of the storm, particularly around 22 UT on March 13 when an intense eastward electrojet was observed as low as 50° invariant latitude on the ground. In the morning sector an additional large-scale upward FAC was observed poleward of the conventional downward region 1 and upward region 2 FAC system throughout the storm. In addition, a pair of FACs with a narrow latitudinal width (∼1.5°) was observed at the poleward boundary of the extra upward FAC.

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.