Enhancement of oxygen in the magnetic island associated with dipolarization fronts

Abstract

A significant enhancement of O+ is observed by Cluster inside an earthward propagating magnetic island behind a dipolarization front (DF). Such enhancement, from 0.005 to 0.03 cm−3, makes the O+ flux inside the magnetic island ~20 times larger than that outside the magnetic island. In the meantime, the H+ density is nearly a constant, 0.1 cm−3, during the magnetic‐island encounter. This results in a dramatic increase of the density ratio, nOprefix+true/nHprefix+, from 0.05 to 0.3 (about 10 times as large as the average value in the plasma sheet) and a dramatic decrease of the local Alfvén speed from VA ≈ 770 km/s to VA ≈ 430 km/s inside the magnetic island. The decrease of Alfvén speed indicates an asymmetric reconnection and a slow magnetic reconnection rate near the secondary X line. Since the reconnection rates at the primary X line and secondary X line are imbalanced, the DFs and magnetic islands are pushed to propagate earthward by the outflow of the primary reconnection, as demonstrated in recent simulations.

Broadband high‐frequency waves detected at dipolarization fronts

“…In this study, we use the single‐point method to estimate the current density [ Fu et al ., ]. Since the DF normal detected by C1 is [0.89, 0.41, 0.09] in GSM coordinates, it is reasonable to assume that C1 crossed close to the central part of the DF [ Runov et al ., ; Wang et al ., ]. Figures b and c show the current density derived from the single‐spacecraft method in GSM coordinates and in the inverted spin reference (ISR2) coordinate system, respectively.…”

Energy Range of Electron Rolling Pin Distribution Behind Dipolarization Front

“…Behind the DF, it is a strong magnetic field region, termed flux pileup region (FPR; Fu et al, ; Fu, Khotyaintsev, Vaivads, André, Sergeev, et al, ; Hoshino et al, ; Khotyaintsev et al, ) or dipolarizing flux bundle (Liu et al, , ). Such region provides a favorable condition for suprathermal electron acceleration (Ashour ‐ Abdalla et al, ; Birn et al, ; Duan et al, ; Fu et al, ; Fu, Khotyaintsev, et al, ; Fu et al, ; Gabrielse et al, , ; Grigorenko et al, , ; Liu, Fu, Xu, Wang, et al, ; Liu, Fu, Xu, Cao, & Liu, ; Liu, Liu, et al, ; Liu & Fu, ; Lu et al, ; Pan et al, ; Vaivads et al, ; Wang et al, ; Wu et al, ; Xu, Fu, Liu, & Wang, ; Zhou et al, ). However, to well understand the acceleration process, the electron pitch angle distribution (PAD) is important information and should be investigated.…”

Ionospheric Cold Ions Detected by MMS Behind Dipolarization Fronts

“…Cold ions of ionospheric origin (tens of eV) are abundant in the Earth's magnetosphere (e.g., André & Cully, ; Chappell et al, ; Engwall et al, ; Fu, Tu, Cao, et al, ; Fu, Tu, Song, et al, ; Kronberg et al, ; Yau & André, ). They are commonly detected at the magnetopause (e.g., Toledo‐Redondo et al, , ) and in the magnetotail (e.g., Alm et al, ; Liu et al, ; Wang et al, , ), especially in the lobes (e.g., Nilsson et al, ). In the lobes, the cold ions slowly convect with the magnetic field toward the plasma sheet and may have a finite velocity parallel to the magnetic field.…”