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xtwang@umich.edu
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- Creator:
- Xiantong Wang
- Description:
- Bursty bulk flows (BBFs) are identified as the fast earthward-propagating flows from magnetic reconnection in Earth's magnetotail. BBFs are related to particle energization process reported by satellite observations. For the first time, we use a novel numerical model that simulates kinetic physics directly in a global model. The energization of the electrons associated with BBF is demonstrated by the model. The electron velocity distribution functions (VDFs) extracted from multiple locations associated with BBF demonstrate good agreements with the observations. The energy-dependent electron pitch angle distribution at the leading part of the BBF can be explained by the enhancement of the local magnetic field.
- Discipline:
- Science
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- Creator:
- Xiantong Wang
- Description:
- Magnetospheric sawtooth oscillations are observed during strong and steady solar wind driving conditions. The simulation results of our global MHD model with embedded kinetic physics show that when the total magnetic flux carried by constant solar wind exceeds a threshold, sawtooth-like magnetospheric oscillations are generated. Different from previous works, this result is obtained without involving time-varying ionospheric outflow in the model. The oscillation period and amplitude agree well with observations. The simulated oscillations cover a wide range of local times, although the distribution of magnitude as a function of longitude is different from observations. Our comparative simulations using ideal or Hall MHD models do not produce global time-varying features, which suggests that kinetic reconnection physics in the magnetotail is a major contributing factor to sawtooth oscillations.
- Discipline:
- Science
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- Creator:
- Xiantong Wang
- Description:
- We perform a geomagnetic event simulation using a newly developed magnetohydrodynamic with adaptively embedded particle-in-cell (MHD-AEPIC) model. We have developed effective criteria to identify reconnection sites in the magnetotail and cover them with the PIC model. The MHD-AEPIC simulation results are compared with Hall MHD and ideal MHD simulations to study the impacts of kinetic reconnection at multiple physical scales. At the global scale, the three models produce very similar SYM-H and SuperMag Electrojet (SME) indexes, which indicates that the global magnetic field configurations from the three models are very close to each other. At the mesoscale we compare the simulations with in situ Geotail observations in the tail. All three models produce reasonable agreement with the Geotail observations. The MHD-AEPIC and Hall MHD models produce tailward and earthward propagating fluxropes, while the ideal MHD simulation does not generate flux ropes in the near-earth current sheet. At the kinetic scales, the MHD-AEPIC simulation can produce a crescent shape distribution of the electron velocity space at the electron diffusion region which agrees very well with MMS observations near a tail reconnection site. These electron scale kinetic features are not available in either the Hall MHD or ideal MHD models. Overall, the MHD-AEPIC model compares well with observations at all scales, it works robustly, and the computational cost is acceptable due to the adaptive adjustment of the PIC domain.
- Keyword:
- MHD, PIC, and Magnetosphere
- Discipline:
- Science