JapaneseMagnetosphere
Outline
Aiming at understanding the dynamics of the inner magnetosphere during the geospace storms, the GEMSIS-Magnetosphere working team has addressed the development of new physics-based models for the global dynamics of the ring current (GEMSIS-RC model) and radiation belt (GEMSIS-RB model). We are also developing a high-resolution global MHD simulation code, which enables us to study MHD turbulence in the solar wind-magnetosphere interaction. Integrated data analysis studies on such as topics as supply mechanisms of ring current ions and relativistic electron accelerations are also conducted using various types of geospace observations from space and from the ground. Some results are applied to studying the forecasting of radiation belt variation. Other ongoing research includes concept design for an integrated data analysis tool and a related database for effective research with various types of data, including those obtained from satellite observations, ground-based observations, and numerical simulations/models.
Contents
Simulation Studies
- Development of a GEMSIS Ring Current Model
- Development of a GEMSIS Radiation Belt Model
- Development of a High-Resolution Global MHD Simulation Model of the Earth’s Magnetosphere
Data Analysis and Applications
- Study of the Supply Process of the Ring Current
- Study of the Dynamics of Radiation Belts and Relativistic Electron Acceleration
- Development of a Space Radiation Forecast Algorithm
Development of Tools for Integrated Analyses of Spacecraft and Ground-Based Observation Data and Simulation Results
Development of a GEMSIS Ring Current Model
We are developing a new self-consistent numerical simulation code solving the five-dimensional Vlasov equation for the ring-current ions in the inner-magnetosphere coupled with Maxwell equations. Our approach is unique in that it includes MHD modes. So far, we have obtained the following results:
- A closed set of equations (five-dimensional Vlasov equation and Maxwell equations) is derived that couples the plasma dynamics and the electromagnetic field in a self-consistent manner.
- The propagation of MHD waves (fast magnetosonic, Alfven) in the inner-magnetosphere, and the modification of drift paths due to self-consistent coupling are successfully reproduced by our numerical simulations. These phenomena have not been accounted for by the current inner-magnetosphere models.
Development of a GEMSIS Radiation Belt Model
Magnetic storms can considerably change magnetic configuration in the magnetosphere. When the magnetic storm occurs, the radiation belts, which consist of high-energy relativistic electrons, are strongly affected. To understand the radiation belt’s behavior and dynamics, we have developed the GEMSIS-RB code that calculates charged particle trajectories in the magnetosphere. By using this code, we are studying the dynamics of radiation belts during the magnetic storms.
Our main achievements include the following:
- We succeeded in simulating the loss of relativistic electrons from the magnetosphere through the magnetopause boundary.
- We found that the outer radiation belt forms a two-band structure after the loss of relativistic electrons from the magnetosphere.
Development of a High-Resolution Global MHD Simulation Model of the Earth’s Magnetosphere
We have developed a high-resolution, global MHD simulation model of the Earth’s magnetosphere which is able to capture eddy and magnetic field turbulence. Our goal is to understand the transport and acceleration of plasma interacting with the turbulent fields and its impact on the geospace environment. With this model, we have successfully reproduced growth of the Kelvin-Helmholtz instability at the magnetopause, which is considered to be a leading factor in the turbulent transport of the solar wind into the magnetosphere.
Study of the Supply Process of the Ring Current
It is known by observation that the terrestrial oxygen ions (O+ ions), which originated from Earth’s atmosphere, contribute significantly to the ring current during large geospace storms, while the quiet ring current mainly consists of protons whose origin is solar wind. In order to understand the mechanisms of this drastic change in the ring current composition, we have conducted detailed analysis of the distribution function and the field data obtained from in-situ observations of geospace plasma. Main results include the relationship between the O+ supply to the ring current and variation in solar wind dynamic pressure as well as the spatial distribution of O+ inflow/outflows in the inner magnetosphere and effects of some specific solar wind structure to the ring current variation. We also started to study the relationship between the plasma sheet conditions and ring current development utilizing simultaneous observations from multiple spacecrafts.
Outputs from the data analysis studies will also be used as boundary conditions of the GEMSIS-RC model.
Study of the Dynamics of Radiation Belts and Relativistic Electron Acceleration
We have studied the solar wind - radiation belt coupling using a large database of the satellite and ground-based observations with numerical simulations. We found that flux enhancements of the outer belt largely depend on the structure of solar wind, such as CMEs and CIRs. Moreover, we revealed that non-adiabatic acceleration through wave-particle interactions is essential to produce the large flux enhancement of the outer belt associated with the fast coronal hole streams. On the other hand, we have confirmed for the first time that EMIC waves produced by the plasma instability of ring current ions cause the significant pitch angle scattering of relativistic electrons of the outer belt using both satellite and ground based observations as well as theoretical calculations.
These results can apply to the development of physical modules in the GEMSIS-RB model.
Development of a Space Radiation Forecast Algorithm
Based on the study of solar wind - radiation belt coupling, we have successfully developed the algorithm for forecasting the relativistic electron enhancement at GEO. The algorithm has been applied to the forecasting system in which the daily percentage of relativistic electron flux enhancements for the next 5 days has been uploaded to the website. These scientific results and the developed forecasting system were reported in science journals and international conferences, and introduced in the Asia-Pacific Regional Space Agency Forum (APRSAF), newspapers, and science magazines.
Construction of Databases and Development of Integrated Data Analysis Tools
We are constructing databases of observation data from various kinds of ground-based and spacecraft-borne instruments. To efficiently analyze these data, we are creating quick-look plots and developing integrated data analysis tools. We intend that the tools be very functional and user-friendly.
In this term, we have constructed a database of spacecraft data. We have also created a web tool for efficiently browsing geomagnetic field data obtained from ground-based magnetometers installed by STEL of Nagoya University and Space Environment Research Center of Kyushu University.
For future spacecraft missions, we are developing tools for integrated analyses of spacecraft and ground-based observation data and simulation results; for this purpose, we are unifying a format for ground-based data.