Abstract
The electron number density across the plasmapause was accurately measured using an RF sounder on board the Jikiken satellite, which was launched from Kagoshima Space Center in Japan on September 16, 1978, into an orbit with the initial apogee of 30, 051km and the perigee of 227km. The electron number density was determined by observing plasma resonances such as the electron plasma resonance (FP), the electron cyclotron resonance (nFH) and the upper hybrid resonance (FUHR), which were not affected by the turbulences surrounding the satellite. The electron number density outside of the plasmapause showed values greater by one order of magnitude than the previous observations using particle detectors. Outside the plasmapause in the dayside region, there is a good agreement with an L-4 relationship in the electron number density profile, as is consistent with a large inflation of the plasma due to a supply from the ionosphere. The location of the plasmapause has been examined as a function of the geomagnetic activity including the dead calm state. Two types of irregularities were found in the electron number density profiles crossing the plasmapause: i) a large scale irregularity with the characteristic scale in L values of 0.1-0.5 (600-3000km) in the plasmasphere and ii) an irregularity with smaller scale sizes near the plasmapause.
