Quantitative Analysis of Electron Acceleration in Coalescing Magnetic
Flux Ropes at Earth's Magnetopause
Abstract
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.