Observation of multiple sub‐cavities adjacent to single separatrix

Abstract

AbstractWe investigate a direct south‐north crossing of a reconnection ion diffusion region in the magnetotail. During this crossing, multiple electron density dips with a further density decrease within the cavity, called sub‐cavities, adjacent to the northern separatrix are observed. The correlation between electron density sub‐cavities and strong electric field fluctuations is obvious. Within one of the sub‐cavities, a series of very strong oscillating perpendicular electric field and patchy parallel electric field are observed. The parallel electric field is nearly unipolar and directs away from X line. In the same region, inflow electrons with energy up to 100 keV are injected into the X line. Based on the observations, we conclude that the high‐energy inflowing electrons are accelerated by the patchy parallel electric field. Namely, electrons have been effectively accelerated while they are flowing into the X line along the separatrix. The observations indicate that the electron acceleration region is widely larger than the predicted electron diffusion region in the classical Hall magnetic reconnection model.