11:15 AM - 11:30 AM
[PEM11-08] A drift-kinetic simulation study of excitation of ULF waves based on the observations of the field-aligned current and the ring current ions
Keywords:ULF waves, ring current, kinetic theory, global model
Ultra-low frequency (ULF) waves have attracted attention for a long time because they are associated with wave-particle interaction in the magnetosphere. A lot of theoretical and observational studies showed that energetic ions excite the poloidal mode waves through drift/drift-bounce instability (Southwood et al., 1969; Takahashi et al., 1990, 2017; Dai et al., 2013; Yamamoto et al., 2018, 2019) and the compressional mode waves through drift-mirror/drift-compressional instability (Hasegawa, 1969; Lanzerotti et al., 1969; Soto-Chavez et al., 2019; Mager et al., 2013; Rubtsov et al., 2017; Takahashi et al., 2022), while the waves excited by ions can cause radial transport of the relativistic electrons through a random scattering of electron drift motion (Ukhorskiy et al., 2009).
The condition for these plasma instabilities depends on the plasma environment in the magnetosphere. From the observation of a single satellite, however, the scenario of the wave excitation is not fully understood because the evaluation of the wave growth rate (e.g., Southwood et al., 1969; Mager et al., 2013) requires global distribution of energetic ions. To obtain the global distribution of the ions and understand the excitation mechanism, Yamakawa et al. (2019, 2020a,b) used a drift-kinetic (GEMSIS-RC) model developed by Amano et al. (2011) and conducted numerical simulations of the ring current with assumptions of the initial velocity distribution of the injected ions and the ionospheric pattern of the Region-1 field-aligned current.
The purpose of this study is to examine the ULF wave excitation by a numerical simulation based on the observations of the field-aligned current and the injected ions. We simulate the proton injection and the poloidal Pc 4 waves detected by RBSP-A and B on October 29, 2013. As for the initial velocity distribution of protons and the Region-1 current, we use the LANL geosynchronous satellite data and the AMPERE/Iridium satellite data, respectively. The GEMSIS-POT model (Nakamizo et al., 2012) was used to obtain the ionospheric potential and the magnetospheric convection pattern. We use the IRI-2016 model (Bilitza et al., 2017) to calculate the ionospheric conductivity.
For the robust calculation of the ionospheric potential, the latitudinal and longitudinal distributions of the observed field-aligned current should be smoothed out. In this study, the latitudinal distribution of the current between lat = 65° and lat = 80° was fitted with a Gaussian function at each MLT grid of the AMPERE data to extract the Region-1 current. From the fitted data, the central position of the Region-1 current was defined as the point where the current intensity becomes its maximum. Next, the parallel and normal directions of the Region-1 current sheet were determined from the 2-D distribution of the current around the central position. The width and thickness of the current sheet are obtained from the Gaussian fitting in the parallel and normal direcitons, respectively. From these fitting parameters, we obtained the smoothed distribution of the Region-1 current for the potential calculation. In the presentation, we will discuss the applicability of the observational data to the GEMSIS-RC/POT model and ULF wave excitation with a simulation setting based on the observational data.
The condition for these plasma instabilities depends on the plasma environment in the magnetosphere. From the observation of a single satellite, however, the scenario of the wave excitation is not fully understood because the evaluation of the wave growth rate (e.g., Southwood et al., 1969; Mager et al., 2013) requires global distribution of energetic ions. To obtain the global distribution of the ions and understand the excitation mechanism, Yamakawa et al. (2019, 2020a,b) used a drift-kinetic (GEMSIS-RC) model developed by Amano et al. (2011) and conducted numerical simulations of the ring current with assumptions of the initial velocity distribution of the injected ions and the ionospheric pattern of the Region-1 field-aligned current.
The purpose of this study is to examine the ULF wave excitation by a numerical simulation based on the observations of the field-aligned current and the injected ions. We simulate the proton injection and the poloidal Pc 4 waves detected by RBSP-A and B on October 29, 2013. As for the initial velocity distribution of protons and the Region-1 current, we use the LANL geosynchronous satellite data and the AMPERE/Iridium satellite data, respectively. The GEMSIS-POT model (Nakamizo et al., 2012) was used to obtain the ionospheric potential and the magnetospheric convection pattern. We use the IRI-2016 model (Bilitza et al., 2017) to calculate the ionospheric conductivity.
For the robust calculation of the ionospheric potential, the latitudinal and longitudinal distributions of the observed field-aligned current should be smoothed out. In this study, the latitudinal distribution of the current between lat = 65° and lat = 80° was fitted with a Gaussian function at each MLT grid of the AMPERE data to extract the Region-1 current. From the fitted data, the central position of the Region-1 current was defined as the point where the current intensity becomes its maximum. Next, the parallel and normal directions of the Region-1 current sheet were determined from the 2-D distribution of the current around the central position. The width and thickness of the current sheet are obtained from the Gaussian fitting in the parallel and normal direcitons, respectively. From these fitting parameters, we obtained the smoothed distribution of the Region-1 current for the potential calculation. In the presentation, we will discuss the applicability of the observational data to the GEMSIS-RC/POT model and ULF wave excitation with a simulation setting based on the observational data.