Study on the characteristics of geospace based on global simulation

Abstract

In recent decades, space weather forecasting has become increasingly important since the significant impact of the geospace environment on human activities. To enhance the precision of space weather forecasting, a comprehensive and thorough investigation of magnetosphere-ionosphere (M-I) coupling is necessary. Numerical simulations offer a valuable tool for studying the M-I coupling, which can be validated through observations and statistical models. However, physics-based long-run global simulations have been infrequent in previous studies. Therefore, an ideal and two long-run simulations using novel two-way coupled global models are conducted in four parts. In the first part, I focus on geomagnetic substorms. Large-scale electromagnetic energy transport during a geomagnetic substorm is in the form of Alfvén waves, which is key to M-I coupling and has not been investigated quantitatively in physics-based models for space weather forecasting. Therefore, I use Grid Agnostic MHD for Research Applications (GAMERA)-Ring Current Model (RCM) (GR) to investigate the evolution of Alfvénic Poynting flux during an idealized substorm-steady magnetospheric convection (SMC). In the second part, I study the statistical features of M-I coupling including field-aligned current, polar cap potential, ionospheric Joule heating, and the downward Alfvénic Poynting flux, binned by the interplanetary magnetic field (IMF) clock angles and geomagnetic Kp indices using another novel two-way M-I model, GAMERA - Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) (GT) over an entire Carrington Rotation (March 20- April 16, 2008) event, which are compared with observations and empirical models. Unlike previous simulations that were only aimed at ideal conditions or short-term events, this is the first long-run global simulation of the new coupled model. In the third part, I conducted the same long-run simulation using GR and performed the same statistical and comparative analysis to test the coupling characteristics and applicability of the new model. These simulations establish an extensive database and significantly enhance the value of physics-based simulations in space weather forecasting research. Finally, I combine the ideal simulation and the entire Carrington Rotation using GR to study plasmaspheric plumes, which is an important aspect of the coupled response of the entire inner magnetosphere and ionosphere. These plumes impact ionospheric disturbances, magnetic variations, particle precipitation and other space weather processes. Based on these new simulations and synoptic analyses, several key findings have been discovered. Firstly, during the substorm expansion phase, the Alfvénic Poynting flux is enhanced by approximately 200%, and the dawn-dusk asymmetry of the Alfvénic oval is diminished. Secondly, the simulated M-I coupling parameters by GT and GR are mostly consistent with empirical models and observations, with GT and GR showing more reasonable Joule heating than the Weimer model, suggesting the importance of the physics-based model in long-term space weather research and forecast. Moreover, with drift-kinetic ring current model coupled, geospace simulations reproduce plasmaspheric plumes during periods of southward IMF, which can persist as long as the Kp index remains elevated, and higher solar wind velocities can facilitate their development. Overall, these comprehensive analyses contribute to a much-advanced understanding of M-I coupling for future physics-based space weather forecasting and model development.