关键词: 磁重联, 磁零点, 分形面, 零点连线, 低杂波频率振荡

Abstract: Magnetic reconnection is considered to be of crucial importance not only to space science but also to magnetically confined fusion,as well as many basic processes in astrophysics and cosmology. In general, except on a closed field line, three, dimensional (3D) magnetic reconnection occurs on the separator connecting magnetic nulls and separatrices, which are determined by the eigenvectors of the magnetic field gradient matrixes of the null pair. Due to the 3D geometric property, the null can only be detected by an at least 4, point measurement so far uniquely provided by the Cluster mission. Here the authors review the recent progresses in applying the Poincare method of magnetic null identification to find out: (1) the in situ evidences of four types of nulls (A, B, As and Bs) and their fans and spines; (2) the spatial scale of the spine structure of the null being of the order of local ion inertial length scale, suggesting that the Hall effect should be important in 3D reconnection dynamics; (3) the in situ evidence for the existence of A, B, B, As null pairs and the separator lines combining the null pairs; and (4) the existence of a lower hybrid oscillation in the immediate vicinity of the A, B separator line, which provides a possible mechanism for electron heating and acceleration in the reconnection process. It is the first in situ evidence for complete 3D reconnection geometry and associated dynamics, a crucial step toward to establish an observational framework of 3D reconnection.

Key words: magnetic reconnection, null, separatrix, separator, lower, hybrid oscillation