Localized and Intense Energy Conversion in the Diffusion Region of Asymmetric Magnetic Reconnection

Abstract

We analyze a high‐resolution simulation of magnetopause reconnection observed by the Magnetospheric Multiscale mission and explain the occurrence of strongly localized dissipation with an amplitude more than an order of magnitude larger than expected. Unlike symmetric reconnection, wherein reconnection of the ambient reversed magnetic field drives the dissipation, we find that the annihilation of the self‐generated, out‐of‐plane (Hall) magnetic field plays the dominant role. Electrons flow along the magnetosheath separatrices, converge in the diffusion region, and jet past the X‐point into the magnetosphere. The resulting accumulation of negative charge generates intense parallel electric fields that eject electrons along the magnetospheric separatrices and produce field‐aligned beams. Many of these features match Magnetospheric Multiscale observations.

Localized Oscillatory Energy Conversion in Magnetopause Reconnection

“…Swisdak et al () show by plasma simulation the development of structures they identify as standing oblique whistler waves for parameters derived from the 16 October 2015 event we have described. In their simulation the standing oscillatory structure is generated by electrons streaming along the outer reconnection separatrix that are accelerated through the magnetic null region toward the electron stagnation regions by a strong E N component.…”

“…It was further shown for the 8 December 2015 event that the peak positive J · E 0 value aligned with the appearance of a strong electron beam along the boundary-normal M direction producing the out-of-plane current of reconnection. Swisdak et al (2017) show by plasma simulation the development of structures they identify as standing oblique whistler waves for parameters derived from the 16 October 2015 event we have described. In their simulation the standing oscillatory structure is generated by electrons streaming along the outer reconnection separatrix that are accelerated through the magnetic null region toward the electron stagnation regions by a strong E N component.…”

“…As shown in this letter, strong energy conversion that is highly localized within the electron diffusion region (EDR) can occur at both the X-line and the electron stagnation region, and which region dominates depends on the guide field. Particle-in-cell simulations of one of the same events by Swisdak et al (2017) show the development of the standing oblique whistler waves and the strong energy conversion they produce near the electron stagnation region. We note that localized strong energy conversion has also been reported from simulations by Zenitani et al (2011) and Pritchett (2013).…”

High‐Frequency Wave Generation in Magnetotail Reconnection: Linear Dispersion Analysis

“…As shown in panel (e) the maximum positive energy conversion rate (measured by J · E ) occurred toward the Earthward side of the X‐line where wave activity was relatively weak, while the strongest wave emissions occurred toward its tailward side where J · E was mostly negative. The bipolar signature of J · E is commonly observed by MMS, particularly at the dayside magnetopause (Burch, Webster, et al, ; Swisdak et al, ). Panels (b) and (g) show the wave power spectral density for the AC magnetic and electric fields, respectively.…”

Energy Conversion and Electron Acceleration in the Magnetopause Reconnection Diffusion Region

“…In the stagnation region the parallel and perpendicular components of J · E′ showed bipolar signatures, but the net J · E′ remained positive. The J · E′ < 0 regions are associated with the conversion of particle energy to electromagnetic energy through a process that is not yet completely understood although observations (Burch et al () and simulations (Swisdak et al, ) provide some clues.…”