Properties of Extremely Asymmetric Magnetic Reconnection

The behavior of extremely asymmetric magnetic reconnections is numerically investigated. The asymmetry is defined as the ratio k of the magnetic fields on both sides of the isothermal initial current sheet. This work is an extension of our previous research for 1 < k ≤ 2 to further asymmetry 2 < k ≤ 20. In our previous work, Nitta et al., we clarified that even for a slight asymmetry k ≤ 2, the reconnection structure drastically changes from symmetric standard models like the Petschek model. The properties of the asymmetric system are a (1) two-layered non-uniform reconnection jet, (2) contact discontinuity (CD) in the lower beta side (LBS) plasmoid between the plasmas coming from both sides of the current sheet, and (3) forward fast shock (FFS) in front of the higher beta side (HBS) plasmoid. We aim to clarify, in this paper, how these properties change and whether new aspects appear for further asymmetric cases. We have confirmed that, even under strongly asymmetric circumstances, the CD in the LBS plasmoid and the two-layered jet structure hold; however, the FFS disappears for extremely asymmetric cases. The fraction of the HBS plasma component increases in the reconnection outflow as k increases. The reconnection rate decreases as a power-law function of k.