MMS Observations of Reconnection Separatrix Region in the Magnetotail at Different Distances From the Active Neutral X‐Line

Abstract

The region surrounding the reconnection separatrix consists of many particle and wave transient features (electron, cold and hot ion beams, Hall E&B fields, kinetic Alfvén, LH, etc. waves) whose pattern and parameters may vary depending on the distance from active neutral line. We study nine quick MMS entries into the plasma sheet boundary layer (PSBL) from the tail lobe to address the meso‐scale pattern and other characteristics of phenomena for active separatrix crossings as deduced from particle observations. The outermost thin layer (a fraction of ion inertial scale, di) of low‐density plasma consists of accelerated electron beams and lobe cold ions and displays density depletions (EBL region). It is followed by hot proton beam (PBL region) in which the plasma density grows from lobe‐like towards plasma sheet‐like values; the beam energy‐dispersion is used to estimate the distance from the active neutral line. Thin (usually ≤ di) region containing intense Hall‐like Ez perturbations (HR) usually overlaps with EBL and PBL regions. It often includes correlated B perturbations suggesting the Alfvén wave‐related transport from the reconnection source; the estimated Alfvénic ratio δE/(VA δB) varied between 0.3 and 1.3 in studied examples. The HR is associated with profound plasma property changes, including the heating of cold ion beams in its innermost part, it hosts intense structured field‐aligned currents and intense E‐field fluctuations. Surprisingly, most of abovementioned findings are valid for crossings observed at large distances from the reconnection region (exceeding a few tens Re or >100 di) except for longer time‐scales and larger spatial scales of the pattern.

A Statistical Study on Wide‐Amplitude Kinetic Alfvénic Pulse at 8–12RE in the Magnetotail by THEMIS Spacecraft From 2008 to 2010

“…Case on 24 March 2009 shows the direct evidence of the access of the reconnection-generated KAW pulse to the substorm triggering region. According to Sergeev et al (2021), the distance of the KAW pulses from X-line could be few tens R E . As we have known that the location of the near-Earth X-line is around X of −20 R E (L. Q.…”

“…Recently, using MMS satellite observation, Sergeev et al. (2021) investigate the E z ‐ B y pulse at the PSBL accompanied with the DIS/DES. They found that the Hall‐type E‐B pulses are Alfvénic like, with (∆ E z /∆ B y )/ V A ratio of 0.3–1.3.…”

“…The dispersed ion/electron structure (DIS/DES) at the PSBL/lobe (e.g., Onsager et al, 1990;Varsani et al, 2017;Wellenzohn et al, 2021) are the wellknown reconnection signatures (time of flight effect) from the X-line along the separatrix region. Recently, using MMS satellite observation, Sergeev et al (2021) investigate the E z -B y pulse at the PSBL accompanied with the DIS/DES. They found that the Hall-type E-B pulses are Alfvénic like, with (∆E z /∆B y )/V A ratio of 0.3-1.3.…”

Remote Sensing of Magnetic Reconnection in the Magnetotail Using In Situ Multipoint Observations at the Plasma Sheet Boundary Layer

“…While this study, concentrate mainly on the quick disturbances associated with electron beam dynamics around electron boundary layer (EBL), remote reconnection signatures deduced from ions and associated Hall‐type field disturbance are shown by Sergeev et al. (2020) based on nine MMS PSBL crossing events including the one discussed in this study.…”

“…Signatures associated with the arrival of the different disturbances from the remote reconnection site are examined to obtain characteristics of the reconnection site including location, timing, and reconnection rate. While this study, concentrate mainly on the quick disturbances associated with electron beam dynamics around electron boundary layer (EBL), remote reconnection signatures deduced from ions and associated Hall-type field disturbance are shown by Sergeev et al (2020) based on nine MMS PSBL crossing events including the one discussed in this study.…”