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, nO<mo form="prefix">+>/nH<mo form="prefix">+, 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.
- Publication:
-
Journal of Geophysical Research (Space Physics)
- Pub Date:
- January 2017
- DOI:
- 10.1002/2016JA023019
- Bibcode:
- 2017JGRA..122..185W
- Keywords:
-
- oxygen;
- magnetic island;
- dipolarization fronts;
- X line;
- magnetic reconnection;
- FOTE