Dartmouth Events

Abstract: Magnetic reconnection in Earth’s magnetotail requires the current sheet (CS) to thin down to ion thermal gyroradius scales or smaller to enable ion demagnetization and dissipation. However, conventional isotropic plasma models fail to reproduce such thin sheets at distances where X-lines are typically observed. Recent particle-in-cell (PIC) simulations have revealed a class of equilibria—overstretched thin current sheets (OTCSs)—formed in weakly anisotropic ion plasmas, where the current density contours extend well beyond the magnetic field lines. These structures remain stable despite their extreme aspect ratios and exhibit force balances significantly modified by weak ion anisotropy and agyrotropy, which contribute comparably to the pressure gradient. 2-D PIC simulations of OTCSs help explain the observed locations of X-lines in Earth's magnetotail. These simulations reproduce the onset of reconnection within realistic tail equilibria under conditions of weak external driving. The transition to magnetic topology change—the hallmark of reconnection—is consistently preceded by divergent plasma flows in both electron and ion populations, indicating that ion tearing initiates reconnection.

In this talk, we also discuss ongoing efforts to incorporate ion scale thin current sheets into global MHD models. These developments aim to include key kinetic physics into global models that will enable more realistic reconnection x-line formation.

Hosted by Professor Yi-Hsin Liu

Join Zoom Meeting
https://dartmouth.zoom.us/j/92751420885?pwd=QnIwN0RiSGkzMUtjQVZxRlZLMkcwQT09

Meeting ID: 927 5142 0885
Email Physics.Department@department.edu for passcode