Magnetic reconnection is a fundamental process that plays an important role in the transfer of the solar wind mass, momentum, and energy into Earth's magnetosphere. Fundamental issues on the micro- and mesoscale characteristics of reconnection in the magnetopause boundary layer are not adequately understood. This project will use a 3-D global hybrid plasma model to investigate magnetic reconnection at the magnetopause. The hybrid code treats electrons as a fluid, but includes full particle kinetics of ions. The code and is capable of resolving the plasma physics in a broad range from ion gyro-period to the dayside convection time scale, and from the ion Larmor radius to the global scale lengths. The primary tasks of this project are: (1) determination of the 3-D structure of magnetic reconnection at the dayside magnetopause, (2) determination of the magnetic field and plasma properties and evolution of flux transfer events (FTEs) in the magnetopause reconnection, (3) investigation of the corresponding ion dynamics and velocity distributions in reconnection events at various locations, and (4) investigation of the differences between reconnection that occurs when the magnetic fields are primarily anti-parallel and reconnection that occurs when there is a strong guide field (also know as component reconnection).
The study will contribute to our understanding of 3-D, multi-scale physics of magnetic reconnection in the global magnetosphere and will improve our knowledge of the dynamical and structural properties of geospace. The 3-D hybrid modeling efforts will also have broader applications in other topics of magnetospheric, astrophysical, and laboratory plasma physics. The study will include a graduate student and it will also contribute to the National Science Foundation's goal of developing and maintaining cutting edge national computing and information infrastructure for research and education
Magnetic reconnection at the magnetopause is believed to be a fundamental physical process that leads to the transfer of the solar wind mass, momentum, and energy into the Earth's magnetosphere. The project has conducted systematic study of magnetic reconnection at dayside magnetopause by understanding the multi-scale spatial structures and time evolutions of reconnection based on a 3-D global hybrid simulation. In contrast to the existing MHD model that treats charged particles as a fluid, the hybrid code includes fully kinetics of ions, and is capable of solving physics in a broad range from ion gyro-period to the dayside convection time scale, and from the ion Larmor radius to the global scale lengths. The magnetic configuration and evolution of Flux Transfer Events (FTE) has been investigated under a purely southward IMF. Multiple X lines are formed during the magnetopause reconnection, which lead to both FTEs and quasi-steady type reconnection under a steady solar wind condition. A plasma temperature rise is seen at the center of an FTE, compared to that of the upstream plasma in the magnetosheath. The temperature enhancement is mainly in the direction parallel to the magnetic field due to the mixing of ion beams. The ion density is enhanced within FTE flux ropes due to the trapped particles, leading to a filamentary global density. A quadrupole magnetic field signature associated with the Hall effects is found to be present around FTEs. A combination of patchy reconnection and multiple X-line reconnection leads to the formation of reconnected field lines from the magnetosphere to IMF, as well as the closed field lines from the magnetosphere to the magnetosphere in the magnetopause boundary layer. The resulting bipolar signature of local normal magnetic field of FTEs is consistent with satellite observations. The spatial energy spectrum of cusp precipitating ions shows a dispersive feature consistent with satellite observations, with higher energy particles at lower latitudes and lower energy particles at higher latitudes. A component reconnection at the dayside magnetopause is also studied under a southward IMF with a finite By component. Dispersive feature is also shown in spatial spectra for precipitating ions in the cusp. When IMF clock angle is larger than 180 degree, the heaviest precipitation shifts to the dawn side. The generation of low frequency waves by the reconnection under a finite guide field has been investigated by the 3D hybrid simulation model. In the case with an infinite X-line, two quasi-steady rotational discontinuities are formed behind a plasma bulge. The plasmas are accelerated across the rotational discontinuities. There are perturbation structures in the transition region between the leading bulge and the steady discontinuities. The transverse perturbations lead to the presence of short-wavelength field-aligned structures with finite parallel electric field. In a finite X-line case, kinetic Alfv´en waves with kri ∼ 1 are found in the reconnection layer. The 3-D global hybrid simulation is the only way so far to investigate self-consistently the ion dynamics, including heating/acceleration, in global scale. Our study can provide new insights on the multi-dimensional, multi-scale spatial structures and multi-scale temporal evolutions of the magnetopause boundary layer associated with the reconnection.
