[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-11] A New Index for Estimating the Plasmapause Position in the Night Side Magnetosphere

*Yuki Obana¹, Yusuke Ebihara², Atsuki Shinbori³, Fuminori Tsuchiya⁴, Atsushi Kumamoto⁵, Yoshiya Kasahara⁶, Ayako Matsuoka⁷, Mariko Teramoto⁹, Tomoaki Hori³, Yoshizumi Miyoshi³, Iku Shinohara⁸ (1.International Research Center for Space and Planetary Environmental Science, Kyushu University, 2.Research Institute for Sustainable Humanosphere, Kyoto University, 3.Institute for Space-Earth Environmental Research, The University of Nagoya, 4.Planetary Plasma and Atmospheric Research Center, Tohoku University , 5.Graduate School of Science, Tohoku University, 6.Emerging Media Initiative, Kanazawa University, 7.Data Analysis Center for Geomagnetism and Space Magnetism, Kyoto University, 8.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 9.Faculty of Engineering, Kyushu Institute of Technology)

Keywords:inner-magnetosphere, plasmasphere, magnetospheric convection, magnetosphere-ionosphere coupling

We have statistically investigated the location of the plasmapause using data from the High Frequency Analyzer (HFA) of the Plasma Wave Experiment (PWE) onboard the Arase spacecraft.
The HFA is a subsystem of the PWE onboard the Arase spacecraft. The electric field spectrogram provided by the HFA covers the frequency range from 10 kHz to 10 MHz. Such a wide frequency coverage allows continuous observation of the plasma waves, which provide information about the electron density around the satellite, from the tenuous magnetosphere to the dense topside ionosphere. This makes it possible to detect the plasmapause even if the plasmasphere is deeply eroded. Our event list includes many deep erosion events compared to the list in other study using other satellite data.
So far, we have obtained the following results. We have included the 33 plasmapause crossing events observed by the Arase satellite in the nightside (MLT=18~6) magnetosphere. The plasmapause locations (Lpp) were compared with the three geomagnetic indicators, the mean of Ey, the SYM-H minimum, and the Kp maximum. The Ey is the dawn-to-dusk component of the solar wind-driven electric field (E= u × B, where u is the flow velocity and B is the magnetic field vector). The SYM-H minimum of the previous 24 h and the Kp maximum of the previous 36-2 h showed a high correlation with Lpp when we used all 33 events. However, they did not show a good correlation with Lpp when only 13 events with Lpp<3 were used. On the other hand, the average values of Ey during the previous 72 or 86 hours showed a good correlation in both comparisons using all 33 events and using only 13 events with Lpp < 3. These results suggest that the Ey history is important for the plasmapause to be pushed into the deep inner magnetosphere.
Our results suggest a new empirical model for predicting plasmapause positions that is valid even when the plasmapause is located in the deep inner magnetosphere.