Quantitative Analysis of Electron Acceleration in Coalescing Magnetic Flux Ropes at Earth’s Magnetopause

Coalescence of magnetic flux ropes (MFRs) is suggested as a crucial mechanism for electron acceleration in various astrophysical plasma systems. However, how electrons are being accelerated via MFR coalescence is not fully understood. In this paper, we quantitatively analyze electron acceleration during the coalescence of three MFRs at Earth’s magnetopause using in-situ Magnetospheric Multiscale (MMS) observations. We find that suprathermal electrons are enhanced in the coalescing MFRs than those in the ambient magnetosheath and non-coalescing MFRs. Both first-order Fermi and E acceleration were responsible for this electron acceleration, while the overall effect of betatron mechanism decelerated the electrons. The most intense Fermi acceleration was observed in the trailing part of the middle MFR, while E acceleration occurred primarily at the reconnection sites between the coalescing MFRs. For non-coalescing MFRs, the dominant acceleration mechanism is the E acceleration. Our results further consolidate the important role of MFR coalescence in electron acceleration in space plasma.