Electron-scale energy transfer due to lower hybrid waves during asymmetric reconnection

TL;DR

This study uses MMS data to analyze how lower hybrid drift waves facilitate electron-scale energy transfer during asymmetric magnetopause reconnection, revealing localized, fluctuating energy exchange that results in net electron heating.

Contribution

It provides the first detailed observational evidence of electron-scale energy transfer mediated by lower hybrid waves during asymmetric reconnection.

Findings

Energy transfer is localized within the plasma mixing layer.

Energy exchange between waves and electrons is highly fluctuating.

Net energy transfer from waves to electrons leads to electron heating.

Abstract

We use Magnetospheric Multiscale (MMS) mission data to investigate electron-scale energy transfer due to lower hybrid drift waves during magnetopause reconnection. We analyze waves observed in an electron-scale plasma mixing layer at the edge of the magnetospheric outflow. Using high-resolution 7.5 ms electron moments, we obtain an electron current density with a Nyquist frequency of ~66 Hz, sufficient to resolve most of the lower hybrid drift wave power observed in the event. We then employ wavelet analysis to evaluate dJ.dE, which accounts for the phase differences between the fluctuating quantities. The analysis shows that the energy exchange is localized within the plasma mixing layer, and it is highly fluctuating, with energy bouncing between waves and electrons throughout the analyzed time and frequency range. However, the cumulative sum over time indicates a net energy transfer from the waves to electrons. We observe an anomalous electron flow toward the magnetosphere, consistent with diffusion and electron mixing. These results indicate that waves and electrons interact dynamically to dissipate the excess internal energy accumulated by sharp density gradients. We conclude that the electron temperature profile within the plasma mixing layer is produced by a combination of electron diffusion across the layer, as well as heating by large-scale parallel potential and lower hybrid drift waves.