Energy Conversion by a Twisted Magnetic Structure at Magnetopause Boundary Layer: MMS Observations

Abstract

The Earth's magnetopause is an ion‐scale boundary that separates the magnetosphere from the shocked solar wind. At such boundary, energy‐conversion processes frequently occur. Previous studies suggested that such energy conversions are related to the magnetic reconnection process. Here, we report a new mechanism that the coaction between the twisted magnetic structure and lower‐hybrid waves can also drive energy conversion (J⋅ E, J is current density and E is electric field) at the magnetopause boundary layer, by using high‐resolution measurements of the four Magnetospheric Multiscale spacecraft. We find that such energy conversion is efficient (with magnitude up to 20 nW/m3) and is attributed to an intense current filament (j ≈ 3,800 nA/m2) and a fluctuating electric field driven by lower‐hybrid waves. With the help of the First‐Order Taylor Expansion method, we find that the intense current filament is driven by a twisted magnetic structure at electron scale. Our study improves the understanding of energy‐conversion processes at the Earth's magnetopause.

Small-scale Field-aligned Currents in the Magnetopause Boundary Layer

“…Recently, Du et al (2023) have used a reconstruction method named as FOTE at the magnetopause to reveal that strong current filaments are driven by the twist of the local magnetic field. In our two events (Figures 2 and 3), it can be observed that they are also associated with strong current filaments in their vicinity; similar characteristics are prevalent in the events we tallied.…”

“…Strong currents generally correspond to strong magnetic field variations, and twist magnetic is a type of strong magnetic field variation, but it is necessary to check whether it corresponds to a twisted magnetic structure using the FOTE method (Fu et al 2015). The findings of Du et al (2023) have provided some new ideas and insights for us to explore the formation of SFACs. We will conduct further analysis on our events in the future.…”