Toshimi Okada’s research while affiliated with Toyama Prefectural University and other places

Circum-Antarctic balloons were launched from Syowa Station by the 44th Japanese Antarctic Research Experiment team in January 2003. Two balloons equipped with identical instruments were flown in formation around the Antarctic continent, in an attempt to separate temporal and spatial variations of the auroral phenomena. In this paper, we report instrument design, operation and some initial results of the ELF/VLF wave experiment by PPB No. 8 and 10 balloons.

The first campaign of the Polar Patrol Balloon (PPB) experiment (1st-PPB) was carried out at Syowa Station in Antarctica during 1990–1991 and 1992–1993. Based on the results of the 1st-PPB experiment, the next campaign (2nd-PPB) was carried out in the austral summer of 2002–2003. This paper will present stratospheric conductivity results from the 2nd-PPB experiment. In that experiment, three balloons were launched for the purpose of upper atmosphere physics observation (three balloons). Payloads of these three flights were identical with each other, and were launched as close together in time as allowed by weather conditions to constitute a cluster of balloons during their flights. Such a “Balloon Cluster” is suitable to observe temporal evolution and spatial distribution of phenomena in the ionospheric regions and boundaries that the balloons traversed during their circumpolar trajectory. More than 20 days of simultaneous fair weather 3-axis electric field and stratospheric conductivity data were obtained at geomagnetic latitudes ranging from sub-auroral to the polar cap. Balloon separation varied from ∼60 to >1000 km. This paper will present stratospheric conductivity observations with emphasis on the temporal and spatial variations that were observed.

Vertical electric current density was obtained from direct electric field and conductivity measurements on two stratospheric balloon payloads during the 2nd polar patrol balloon (PPB) campaign from Syowa Station in Antarctica during January 2003. Payloads of these two flights were identical and were launched 8-h apart resulting in separation distances of a few hundred km during the time of overlapping data. The float altitude of each was a little over 30 km. The global circuit return current derived from these measurements is compared to the global lightning activity determined by the world wide lightning location (WWLLN) network. The total number of lightning events detected anywhere in the world are simply summed to form an hourly lightning flash rate for the time of the PPB data. The WWLLN and return current density data are shown to have a strong correlation, often with a strong universal time daily variation, similar to that expected for the global circuit.

SEKKI" phenomena often appear in the Japanese historical literatures as distinct red emission in the nocturnal sky. The Japanese word "SEKKI" means the red atmosphere. We compile 16 events of SEKKI for 12–19th centuries in the literatures. In order to understand the SEKKI phenomena, we compared 2 events of SEKKI on February 21, 1204, and September 17, 1770, with the characteristics of low-latitude auroras studied recently by modern scientific methods. We conclude that these historical SEKKI phenomena are probably giant low-latitude auroras.