Observation result of the top-side ionosphere with RPA aboard TAIYO

The retarding potential analyzer (RPA) which was mounted on the scientific satellite ''TAIYO'' is still working properly both in real time and stored mode observations. In connection with some reported abnormalities of the geomagnetic field, preliminary analysis was made on the ion transition height, based on the results of the stored mode observation with the RPA. The main subjects of this report are the analysis and the examination on the measured results of the longitude dependence of the O-H positive ion transition height in daytime. The observed results indicated that the transition height can be divided into two regions: the one at about 1000 km (from 30 deg E to 170 deg E); and the other at about 700 km (from 170 deg E through 360 deg E to 30 deg E). A map of the distribution of the height at which the content of positive hydrogen ions become 100% is presented. It is also indicated that the region of low transition height in daytime coincides with the region of the geomagnetic abnormality around Brazil. The relation between the abundance of positive hydrogen ions and the geomagnetic abnormality is discussed, based on other observed results. (Aoki, K.)