11:15 AM - 11:30 AM
[PEM13-08] Comparison of Plasmapause Position with the History of Solar Wind Electric Fields
Keywords:plasmasphere, inner magnetosphere, solar wind, magnetospheric convection
The plasmapause is the boundary between the Earth's plasmasphere, which consists of low-energy plasma of ionospheric origin, and the outer region where plasma density is lower. The plasmapause plays a crucial role in controlling the generation region of waves that scatter and accelerate radiation belt electrons. However, its position varies in a complex manner due to the influence of electric fields within the magnetosphere and plasma supply from the ionosphere. As a result, predictive models based on geomagnetic indices have limited accuracy. For example, a significant discrepancy was observed during the extreme erosion of the plasmasphere caused by the September 2017 magnetic storm (Dst minimum -147 nT) (Obana et al., 2019).
In this study, instead of geomagnetic disturbance indices, we use the solar wind electric field as a proxy for the magnetospheric convection electric field and focus on its history to propose an improvement to the empirical model. We determine the plasmapause position as follows. First, we use electric field spectrum data obtained from the Plasma Wave Experiment (PWE) onboard the Arase satellite and the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) onboard the Van Allen Probes to calculate electron density. If the electron density decreases by a factor of five or more within a range of ΔL<0.1, the event is identified as a plasmapause crossing and listed. The extracted plasmapause crossing events are then sorted by Magnetic Local Time (MLT) and compared with various geomagnetic disturbance indices and solar wind electric fields.
Thus far, an analysis of 238 days of Arase PWD data from September 2017 to December 2023 has identified over 300 plasmapause crossing events. The equatorial radial distance of the plasmapause (Lpp) was compared with the solar wind electric field (Ey), SYM-H, and the Kp index. The results show that the 48-hour average of Ey exhibited the highest correlation with Lpp. Furthermore, we classified Lpp into six different MLT bins and examined the correlation between Lpp and Ey by varying the averaging time of Ey. The highest correlation (correlation coefficient of 0.8) was found between Lpp in the 22–2 MLT sector and the 45-hour averaged Ey. In other MLT sectors, although the correlation was slightly lower, optimal correlations were obtained for Lpp in 2–6 MLT with a 45-hour average Ey, in 6–10 MLT with a 9-hour average Ey, in 10–14 MLT with a 12-hour average Ey, in 14–18 MLT with a 21-hour average Ey, and in 18–22 MLT with a 27-hour average Ey. However, it is known that the nightside plasmapause responds to IMF polarity changes within approximately 30 minutes and undergoes erosion (Goldstein et al., 2003), making the 45-hour averaging time unexpectedly long. Moreover, the finding that Lpp on the nightside correlates more strongly with a longer-averaged Ey compared to Lpp on the dayside appears peculiar, necessitating further detailed investigation.
In this study, we present new results by incorporating electron density estimation data derived from hiss waves observed by the Van Allen Probes and refining the statistical processing method for Ey.
In this study, instead of geomagnetic disturbance indices, we use the solar wind electric field as a proxy for the magnetospheric convection electric field and focus on its history to propose an improvement to the empirical model. We determine the plasmapause position as follows. First, we use electric field spectrum data obtained from the Plasma Wave Experiment (PWE) onboard the Arase satellite and the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) onboard the Van Allen Probes to calculate electron density. If the electron density decreases by a factor of five or more within a range of ΔL<0.1, the event is identified as a plasmapause crossing and listed. The extracted plasmapause crossing events are then sorted by Magnetic Local Time (MLT) and compared with various geomagnetic disturbance indices and solar wind electric fields.
Thus far, an analysis of 238 days of Arase PWD data from September 2017 to December 2023 has identified over 300 plasmapause crossing events. The equatorial radial distance of the plasmapause (Lpp) was compared with the solar wind electric field (Ey), SYM-H, and the Kp index. The results show that the 48-hour average of Ey exhibited the highest correlation with Lpp. Furthermore, we classified Lpp into six different MLT bins and examined the correlation between Lpp and Ey by varying the averaging time of Ey. The highest correlation (correlation coefficient of 0.8) was found between Lpp in the 22–2 MLT sector and the 45-hour averaged Ey. In other MLT sectors, although the correlation was slightly lower, optimal correlations were obtained for Lpp in 2–6 MLT with a 45-hour average Ey, in 6–10 MLT with a 9-hour average Ey, in 10–14 MLT with a 12-hour average Ey, in 14–18 MLT with a 21-hour average Ey, and in 18–22 MLT with a 27-hour average Ey. However, it is known that the nightside plasmapause responds to IMF polarity changes within approximately 30 minutes and undergoes erosion (Goldstein et al., 2003), making the 45-hour averaging time unexpectedly long. Moreover, the finding that Lpp on the nightside correlates more strongly with a longer-averaged Ey compared to Lpp on the dayside appears peculiar, necessitating further detailed investigation.
In this study, we present new results by incorporating electron density estimation data derived from hiss waves observed by the Van Allen Probes and refining the statistical processing method for Ey.