Ion velocity distributions within the LLBL and their possible implication to multiple reconnections

Abstract

Abstract. We analyze two LLBL crossings made by the Interball-Tail satellite under a southward or variable magnetosheath magnetic field: one crossing on the flank of the magnetosphere, and another one closer to the subsolar point. Three different types of ion velocity distributions within the LLBL are observed: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counterstreaming components of magnetosheath-type, and (c) distributions with three components, one of which has nearly zero parallel velocity and two counter-streaming components. Only the (a) type fits to the single magnetic flux tube formed by reconnection between the magnetospheric and magnetosheath magnetic fields. We argue that two counterstreaming magnetosheath-like ion components observed by Interball within the LLBL cannot be explained by the reflection of the ions from the magnetic mirror deeper within the magnetosphere. Types (b) and (c) ion velocity distributions would form within spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath and from magnetospheric plasma. The shapes of ion velocity distributions and their evolution with decreasing number density in the LLBL indicate that a significant part of the LLBL is located on magnetic field lines of long spiral flux tube islands at the magnetopause, as has been proposed and found to occur in magnetopause simulations. We consider these observations as evidence for multiple reconnection Xlines between magnetosheath and magnetospheric flux tubes.

Kinetic signatures during a quasi‐continuous lobe reconnection event: Cluster Ion Spectrometer (CIS) observations

“…Although kinetic signatures related to reconnection have been repeatedly reported in the literature [e.g., Gosling et al , 1991, 1996; Fuselier , 1995; Fuselier et al , 1995, 1997; Bauer et al , 2001; Vaisberg et al , 2004], they are not present at all the MP crossings which satisfy the Walén test. For instance, Bauer et al [2001], in a statistical study, report that they observe D‐shaped distribution functions in the transmitted magnetosheath and magnetospheric populations “only for the minority of the Walén events.” Also Phan et al [2004] say that even in clear reconnection events, the transmitted magnetosheath population in the BL does not always display the characteristic D shape and suggest that one reason could be the distance from the reconnection site.…”

Simultaneous Double Star and Cluster FTEs observations on the dawnside flank of the magnetosphere

“…Moreover, the coexistence of high-latitude (lobe) and low-latitude reconnection sites has been observed (Sandholt et al, 1998;Pitout et al, 2002). Finally, simulations by Berchem et al (1995) and recent observations by Vaisberg et al (2004) suggested the possible existence of multiple Xlines forming isolated magnetic flux ropes on the dayside, as well as on the flanks of the magnetopause, for various IMF conditions. These results support the multiple reconnection lines model of Lee and Fu (1985).…”