Multiple Flux Rope Dynamics: MMS Observations and Reconstruction Results

Abstract

Abstract A series of six ion-scale magnetic flux ropes (FR1–6) and a thin current sheet, encountered by Magnetospheric Multiscale spacecraft in the magnetosheath side of the dayside magnetopause boundary layer, are studied for multiple flux rope dynamics in terms of energy conversion and two-dimensional geometry structure. The thin current sheet is identified in between FR1 and FR2. The energy exchange between electromagnetic fields and plasmas is dynamic in FR1–5 and also surrounding the flux ropes, while a low-energy conversion rate is seen in FR6. Different energy conversions exist in the flux ropes: energy dynamo is predominant in FR1 and FR5, while energy dissipation is dominated in FR2–4. Both the energy dynamo and dissipation primarily result from j ∥ E ∥. Strong dissipation, surrounded by an energy dynamo, happens at the thin current sheet and is accompanied by ion agyrotropic behavior. From the reconstructed magnetic field maps, the estimated aspect ratios of the six flux ropes are 0.78, 0.16, 0.66, 0.11, 0.40, and 0.46 in order, and the thickness of the thin current sheet is ∼63 km (∼1.8 ion inertial length). Evidently, the magnetic field map shows that FR4 is a coalescing flux rope where a pronounced dissipation is present. The overall finding agrees with the previous simulation studies of multiple island coalescence.