Cluster observation of continuous reconnection at dayside magnetopause in the vicinity of cusp

Abstract

Abstract. In this paper, we present a case study of continuous reconnection at the dayside magnetopause observed by the Cluster spacecraft. On 1 April 2003, the four Cluster spacecraft experienced multiple encounters with the Earth's dayside magnetopause under a fairly stable southwestward interplanetary magnetic field (IMF). Accelerated plasma flows, whose magnitude and direction are consistent with the predictions of the reconnection theory (the Walén relation), were observed at and around the magnetopause current layer for a prolonged interval of ∼3 h at two types of magnetopause crossings, one with small magnetic shears and the other one with large magnetic shears. Reversals in the Y component of ion bulk flow between the magnetosheath and magnetopause current layer and acceleration of magnetosheath electrons were also observed. Kinetic signatures using electron and ion velocity distributions corroborate the interpretation of continuous magnetic reconnection. This event provides strong in-situ evidence that magnetic reconnection at the dayside magnetopause can be continuous for many hours. However, the reconnection process appeared to be very dynamic rather than steady, despite the steady nature of the IMF. Detailed analysis using multi-spacecraft magnetic field and plasma measurements shows that the dynamics and structure of the magnetopause current layer/boundary can be very complex. For example, highly variable magnetic and electric fields were observed in the magnetopause current layer. Minimum variance analysis shows that the magnetopause normal deviates from the model normal. Surface waves resulting from the reconnection process may be involved in the oscillation of the magnetopause.

Recent in‐situ observations of magnetic reconnection in near‐Earth space

“…Retinò et al [2005] presented a case with accelerated flows meeting the Walén relation [e.g., Sonnerup et al, 1995] in 50 crossings occurring over a 4-hour period. Similar results were reported by Zheng et al [2005] and Nykyri et al [2006]. There is also new evidence regarding transient magnetopause reconnection in the form of socalled flux-transfer events (FTEs).…”

Collisionless magnetic reconnection in an asymmetric current sheet

“…In many of these studies, however, the solar wind conditions were not steady, so it is not clear whether the reconnection would still be intermittent even under steady boundary conditions. Recently, a number of remote sensing techniques [e.g., Pinnock et al , 2003; Frey et al , 2003] have provided indirect evidence for continuous reconnection lasting many hours, and multispacecraft in situ observations of reconnection jets at the magnetopause [ Phan et al , 2004; Zheng et al , 2005] have documented intervals of continuous reconnection lasting more than two hours under conditions of steady interplanetary magnetic field (IMF).…”

Simultaneous tracking of reconnected flux tubes: Cluster and conjugate SuperDARN observations on 1 April 2004

“…Recently, Cluster (Escoubet et al, 1997) observations of FTEs (e.g. Owen et al, 2001;Fear et al, 2005;Zheng et al, 2005;Hasegawa et al, 2006) have been combined with a variety of groundbased instruments (e.g. Lockwood et al, 2001;Wild et al, 2001Wild et al, , 2003Wild et al, , 2007Marchaudon et al, 2004), and with other spacecraft located at the magnetopause (Dunlop et al, 2005).…”