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

Characteristics of the reconnection region are examined based on Magnetospheric Multiscale (MMS) observation of a plasma sheet boundary layer crossing on July 12, 2018 when both high-energy (>few keV) electrons as well as ions flowing parallel to the magnetic field showed distinct energy dispersion. Remote sensing techniques are applied to estimate location of reconnection region and injection time of these particles. The reconnection region is estimated to be located at X = (-23 +/- 1.9) R-E from electrons, comparable to that from ions, X = (-24.5 +/- 0.7) R-E by taking into account the time of flight effect as well as the effect of separatrix motion relative to the plasma. The electron injection times precede that of ions by similar to 6 s. We found that the time dispersed energetic electron beams away from X-line are accompanied by short-lived high-frequency parallel-electric field disturbances around plasma frequency. These wave packets are the first observable remote feature of reconnection. Using multi-point measurements of high energy ions, electrons, magnetic field, and parallel-electric field disturbances, reconnection electric field is estimated as 1.6-2.5 mV/m initially and decrease to similar to 0.8 mV/m within similar to 20 s. This study shows that the remote sensing scheme is an alternative method to infer the temporal/spatial changes of the magnetotail reconnection.