Observations of a Kinetic‐Scale Magnetic Hole in a Reconnection Diffusion Region

Abstract

Magnetic holes have been widely observed in various space plasma systems. The origin of magnetic holes and their influence to background plasma are under debate. In this paper, we show a kinetic‐scale electron vortex magnetic hole in a nonideal region of an active X line, which was observed by the Magnetospheric Multiscale mission at the dayside magnetopause. Intense current and nonideal electric field in the electron frame were observed within the magnetic hole, which led to a strong energy dissipation. Thus, the electron vortex magnetic hole probably provided an additional energy dissipation channel besides the electron diffusion region adjacent to the hole. We suggest that magnetic reconnection provided favorable conditions for the formation of this kinetic‐scale magnetic hole and is an important source of magnetic holes in space plasma.

Three‐Dimensional Electron‐Scale Magnetic Reconnection in Earth's Magnetosphere

“…This nonideal electric field was primarily parallel to the ambient magnetic field, thus the energy dissipation was through the current and electric field in the field-aligned direction rather than the perpendicular direction. These were the classic features of the EDR (Burch et al, 2016b;Torbert et al, 2018;Zhong et al, 2019Zhong et al, , 2020Zhou et al, 2019;Zenitani et al, 2011), consistent with the MMS trajectory shown in Figures 2b and 2c. Electrons were heated significantly in the field-aligned direction, from 50 eV in the ambient plasma to 150 eV around this EDR (Figure 4g), meanwhile, MMS observed large-amplitude high-frequency parallel electric field fluctuations (Figure 4h), which suggests the strong correlation between electron heating and the large-amplitude parallel electric fields.…”

“…An intense out‐of‐plane electron jet V eM with a peak speed of ∼1,200 km/s was observed at the center of this current sheet, while V eN (Figure 3h) exhibits a small negative peak of ∼ −400 km/s. The correlated sign change of V eL and B N implies that MMS crossed an active X‐line (Øieroset et al., 2001; Oka et al., 2016; Torbert et al., 2018; Zhong et al., 2018, 2019). This was an asymmetric reconnection since the plasma density changes from 6 to 16 cm −3 across this current sheet.…”

Statistical properties of kinetic-scale magnetic holes in terrestrial space

“…The coupling of KSMHs with whistler mode waves, including wave formation, dispersion, and growth rates, was also studied by Huang SY et al (2018, 2019). Zhong ZH et al (2019) reported a KSMH event associated with strong energy dissipation near the active X line at the dayside magnetopause. They suggested that the KSMH probably provided an additional channel for energy dissipation besides that of the electron diffusion region.…”

Whistler and Broadband Electrostatic Waves in the Multiple X‐Line Reconnection at the Magnetopause

“…Figure 2a illustrates the MMS trajectory within the magnetopause reconnection exhaust inferred from the spacecraft observations. We focus on the region between the first two MFRs (Figure 2) where a secondary reconnecting current sheet is detected (Zhong et al, 2019). This secondary magnetic reconnection is responsible for the formation of 1e).…”