ECE PhD Thesis Defense: Wei Zhang

ECE PhD Thesis Defense: Wei Zhang

Title: Evolution of Magnetopause Reconnection and Surface Waves in the Solar Wind-Magnetosphere-Ionosphere Coupling System

Presenter: Wei Zhang

Advisor: Professor Toshi Nishimura

Chair: Professor Anna Swan

Committee: Professor Toshi Nishimura, Professor Jushua Semeter, Professor Min-Chang Lee, Dr. Yuxi Chen

Google Scholar Link: https://scholar.google.com/citations?hl=zh-CN&authuser=1&user=wNSlU-IAAAAJ

Abstract: An important problem in geospace physics is how dayside solar wind energy is transferred into the magnetosphere–ionosphere (M–I) system through multiple coupling pathways, including magnetopause magnetic reconnection and ultralow-frequency (ULF) wave activity. This dissertation examines (i) the evolution of the magnetopause X-line extent and dayside convection during an interplanetary magnetic field (IMF) southward turning; (ii) the kinetic processes underlying the magnetopause reconnection; and (iii) the structure and propagation of the Pc5 event. To analyze magnetopause reconnection, we combine SuperDARN line-of-sight velocities with high-resolution two-dimensional convection maps reconstructed using the spherical elementary current systems (SECS) method, and interpret the observations using global simulations. For a southward-turning event with sustained negative IMF By, the enhanced poleward flows near the open–closed boundary (OCB) develop about 20 minuetes after the IMF southward turning and expand predominantly duskward. Contrary to the common assumption that poleward ionospheric flows directly represent reconnection outflows at the magnetopause X-line, both ideal magnetohydrodynamic (MHD) and MHD with adaptively embedded particle-in-cell physics (MHD-AEPIC) indicate that the observed ionospheric evolution is more closely lin ked to off-equatorial magnetopause flows, which are driven primarily by J×B forces (dominated by magnetic tension) near the X-line, and are further shaped by upstream magnetosheath flow patterns. The inferred X-line spreading is consistent with the Alfvén wave speed along the guide field in the magnetosheath flow frame. MHD-AEPIC further shows that kinetic processes produce a highly dynamic magnetopause with multiple X-lines and transient flux ropes, yielding ionospheric flow widths, magnitudes, and evolution that are more consistent with observations than ideal MHD, which tends to produce overly narrow and fast channels. For ULF coupling, we analyze two dawnside Pc5 events using space-ground conjunctions (THEMIS, all-sky imagers, ground magnetometers, and DMSP/SSUSI). The results indicate slow or drift mirror mode waves coupled to standing Alfvén waves in the magnetosphere. The ionosphere exhibits multiple dawnside current vortices with quasi-periodic auroral arcs, supporting magnetopause surface waves, likely driven by Kelvin–Helmholtz instability, as the primary driver of the pronounced dawn–dusk asymmetry. Collectively, these findings establish quantitative, multi-diagnostic constraints linking ionospheric flow and current morphology to magnetopause reconnection geometry, kinetic structuring, and surface wave dynamics, advancing the interpretation of dayside M–I coupling as a system.