17:15 〜 18:45
[PEM13-P05] Study of the variation of ring current ions in the inner magnetosphere during magnetic storms on 22 July 2009 based on the GEMSIS magnetosphere-ionosphere coupled model
キーワード：内部磁気圏、環電流、磁気圏電離圏結合、ドリフト運動論モデル、沿磁力線電流
During magnetic storms, energetic particles are injected on the nightside and westward ring current is formed in the inner magnetosphere. Understanding the dynamics of ring current particles is important for both the inner magnetosphere and ionosphere, since the ring current causes the variation of the magnetic field and transports the energy from the magnetosphere to the ionosphere through the field aligned current (FAC). The distribution of the ring current during magnetic storms depends on its transport and acceleration by the electric field and its loss [e.g., Fok et al., 2001]. Recently, we could reproduce the transport of energetic ions by the convection electric field and the formation of the ring current and plasmasphere during substorms based on the GEMSIS magnetosphere-ionosphere coupled model [Yamakawa et al., 2023]. However, this simulation was performed under simplified and static conditions for Region-1 FAC and ion injection on the nightside, which are not the case with the actual inner magnetosphere. The purpose of this study is to investigate the variation of ring current particles during magnetic storms with the input of time-varying Region-1 FAC and ion injection, which are based on the observed solar wind parameters.
In this study, we focused on a magnetic storm on 22 July 2009 and compared simulation results with previous ring current model (CRCM) [Fok et al., 2001] and spacecraft observations. On 22 July 2009, the Dst dropped nearly -80 nT at 0700 and 1000 UT [Fok et al., 2010]. We investigated the variation of the inner magnetosphere based on the magnetosphere-ionosphere coupled model between GEMSIS-RC [Amano et al., 2011] and GEMSIS-POT [Nakamizo et al., 2012]. GEMSIS-RC model solves 5-D drift-kinetic equation for ion PSD and Maxwell equations self-consistently. GEMSIS-POT is a 2-D potential solver in the ionosphere. We included the loss term of ring current ions due to charge exchange in the model. The coupled model enabled us to simulate the transport, acceleration, and loss of ring current ions and formation of the plasmasphere. The density and temperature of energetic ions at outer boundary on the nightside are based on the empirical model [Tsyganenko and Mukai, 2003] and the distribution of Region-1 FAC is given by the Weimer model [Weimer, 2001] as well as previous ring current model [Fok et al., 2010]. These empirical models suggest that the intensity of Region-1 FAC and ion injection on the nightside depend on the solar wind condition. In this study, the latitudinal distribution of the FAC between lat = 65 and 80 was fitted with a Gaussian function at each MLT grid. By fitting the FAC, we obtained the smoothed distribution of Region-1 FAC, which was used for potential calculation in GEMSIS-POT. In this presentation, we will discuss the variation of ring current ions and the magnetic field on the ground by comparing with the results of CRCM model and observations. We will also focus on the possibility of the excitation of ULF waves by ring current ions during the storm-time.
In this study, we focused on a magnetic storm on 22 July 2009 and compared simulation results with previous ring current model (CRCM) [Fok et al., 2001] and spacecraft observations. On 22 July 2009, the Dst dropped nearly -80 nT at 0700 and 1000 UT [Fok et al., 2010]. We investigated the variation of the inner magnetosphere based on the magnetosphere-ionosphere coupled model between GEMSIS-RC [Amano et al., 2011] and GEMSIS-POT [Nakamizo et al., 2012]. GEMSIS-RC model solves 5-D drift-kinetic equation for ion PSD and Maxwell equations self-consistently. GEMSIS-POT is a 2-D potential solver in the ionosphere. We included the loss term of ring current ions due to charge exchange in the model. The coupled model enabled us to simulate the transport, acceleration, and loss of ring current ions and formation of the plasmasphere. The density and temperature of energetic ions at outer boundary on the nightside are based on the empirical model [Tsyganenko and Mukai, 2003] and the distribution of Region-1 FAC is given by the Weimer model [Weimer, 2001] as well as previous ring current model [Fok et al., 2010]. These empirical models suggest that the intensity of Region-1 FAC and ion injection on the nightside depend on the solar wind condition. In this study, the latitudinal distribution of the FAC between lat = 65 and 80 was fitted with a Gaussian function at each MLT grid. By fitting the FAC, we obtained the smoothed distribution of Region-1 FAC, which was used for potential calculation in GEMSIS-POT. In this presentation, we will discuss the variation of ring current ions and the magnetic field on the ground by comparing with the results of CRCM model and observations. We will also focus on the possibility of the excitation of ULF waves by ring current ions during the storm-time.