Plasma Conditions in the Polar Ionosphere Observed in SPW Experiments of PPS System on Board the Ohzora (EXOS-C) Satellite

The data of the stimulated plasma wave experiments (SPW) obtained from the planetary plasma sounder (PPS) aboard the Ohzora (EXOS-C) satellite have been analyzed for the initial three months. From the ionograms of SPW experiments 1) vertical profiles of the topside ionosphere, 2) irregularity of the plasma distribution and 3) identification of the modes of the naturally emitted plasma waves have been obtained. The studies on these subjects lead to the following results. (i) In the polar region ionosphere, the auroral particle precipitations generate the intense plasma waves even in the satellite level. (ii) Associated with the generations of the intense plasma waves caused by the particle precipitation, there are irregularities of the plasma distribution in the topside ionosphere which become the origin of the scattering effects on the transmitted RF pulses. (iii) Enhancement of the electron density takes place caused by the enhanced precipitation of the auroral particles in the auroral region. At the same time remarkable heat input which is indicated by increasing of the electron temperature is also confirmed. (iv) Near the auroral zone in the lower latitude side than the auroral regions, there is also the region where the heat input is taking place in milder manner than the case of the auroral regions. (v) Large energy input into the auroral zone triggers a relatively large scale disturbance propagating in the polar cap ionosphere in the form of the traveling ionospheric disturbance (TID).