SM51A-2543
Two types of flow reversal events observed in magnetotail

Friday, 18 December 2015
Poster Hall (Moscone South)
Iku Shinohara1,2, Tsugunobu Nagai3, Masaki Fujimoto2, Hirotsugu Kojima4 and Seiji Zenitani5, (1)JAXA, Sagamihara Kanagawa, Japan, (2)ISAS/JAXA, Kanagawa, Japan, (3)Tokyo Institute of Technology, Tokyo, Japan, (4)Kyoto University, Research Institute for Sustainable Humanosphere, Kyoto, Japan, (5)NAOJ National Astronomical Observatory of Japan, Tokyo, Japan
Abstract:
Geotail survey in magnetotail provides us with about 200 rapid flow reversal events where tailward flow (< -500 km/s) turns to earthward flow (> +300 km/s) within 10 minutes. We selected 46 definite flow reversal events from them in order to study the physics of X-lines, removing events where stationary plasma and/or tail lobe components are observed at the timing of flow reversals.

We found that flow reversal events can be classified into two types according to electron heating/acceleration and low frequency wave activity. About 2/3 of the flow reversal events look “active.” In these events, strong electron heating/acceleration and existence of ion-electron decoupling region are commonly observed. The intense wave active in the lower-hybrid frequency range is also observed even in high β region around the neutral sheet. These features are consistent with the collisionless reconnection model demonstrated by recent full kinetic numerical simulations. In contrast, other 1/3 of flow reversal events do not present any of them. No visible ion-electron decoupling is found in these "non-active" flow reversal events. This new finding indicates that the strong wave activity in the electric field would be related to the ion-electron decoupling process and that wave activity is a possible indicator for liveliness of reconnection (= evidence of fast electron flow).

The fact that the non-active flow reversals tend to be distributed at the outer fringes of the active flow reversal regions implies that they are related to the three-dimensional structure of magnetic reconnection. In this presentation, we will discuss physical meaning of the difference between active and non-active flow reversal events. It is hard to discuss further collectively the nature of the non-active flow reversals only with single spacecraft measurements. This would be a good topic to be explored using multi-spacecraft data.