“Magnetic Reconnection: New Results from Cluster and Double Star Measurements
Magnetic reconnection (MR) is a fundamental process in plasmas by which magnetic field topology changes and connections of plasma particles with the magnetic field are re-arranged. MR is believed to play a key role in explosive energy release events in the solar-terrestrial system, such as the solar flares, coronal mass ejections and magnetospheric substorms, as well as in transferring energy from the solar wind to the magnetosphere. It is thus an important ingredient of solar-terrestrial physics. In the past half a century, great progresses in understanding of MR process has been gained through theoretical analysis, numerical simulations, and experimental and satellite observations. Nevertheless, many fundamental questions remain to be answered. The three dimensional (3D) features of MR are one of them attracting much attention in recent years.
Though 3D reconnection theories, specially the kinematic and topological models, have been developed in plasma and fluid physics as well as mathematics, it is lack of in situ measurements to confirm if they correctly reveal the nature of the physical world. A direct observation of 3D MR geometry was never able to make until launching of ESA Cluster constellation. The Cluster mission provides the first opportunity to detect the 3D magnetic structure through 4-point measurement as the spacecraft traverse the heart of the MR region. In addition, coordinated Double Star (DS) and Cluster observations enable us to see, for the first time, the evolution of structures at small scales within the Cluster tetrahedron, and then at large scales with Cluster and DS conjunction. The comparative Cluster-DS measurements also make it possible to observe the global pattern of MR at the magnetopause. This lecture devotes to review a part of new results from Cluster and DS measurements, which help to gain better underrstanding of MR on the bases of observations.