Investigation of Ion-slippage Process in the near-Earth plasma sheet

Abstract:

Substorm onsets in the magnetosphere are characterized by the commencement of the reconfiguration of the magnetic field from highly stretched to dipole-like. However, the triggering mechanisms remain highly controversial, although it is accepted that certain non-ideal MHD process that violates the frozen-in flux condition must occur the near-Earth plasma sheet. Without specifying the microphysics, we assume that such violation will lead ions to slip with respect to the magnetic field line while electrons remain magnetized. Such a process will give rise to a bubble with reduced flux-tube entropy earthward of a blob that exhibits increased-flux tube entropy. We use the inertialized Rice Convection Model (RCM-I) to simulate the whole process and compare with observations. In RCM-I model, we imposed the bubble-blob pair artificially by introducing a disturbance in entropy in the near-Earth plasma sheet. The bubble-blob center was located near ~14Re and the flux-tube entropy was increased or decreased by a total of 75% during a period of ~30s. Simulated results show rapid thinning between the bubble and blob, similar to the so-called explosive growth phase in previous studies. Analysis further shows that the system may evolve towards tearing instability. At the same time, a thin auroral arc appeared in the ionosphere with strong westward current, strong eastward drift and upward field-aligned current. Multi-satellite observations provide some evidence for the simulated ionospheric manifestations.