Abstract
We report local secondary magnetic reconnection at Earth’s flank magnetopause by using the Magnetospheric Multiscale observations. This reconnection is found at the magnetopause boundary with a large magnetic shear between closed magnetospheric field lines and the open field lines generated by the primary magnetopause reconnection at large scales. Evidence of this secondary reconnection are presented, which include a secondary ion jet and the encounter of the electron diffusion region. Thus the observed secondary reconnection indicates a cross-scale process from a global scale to an electron scale. As the aurora brightening is also observed at the morning ionosphere, the present secondary reconnection suggests a new pathway for the entry of the solar wind into geospace, providing an important modification to the classic Dungey cycle.
Highlights
The Earth’s global magnetospheric plasma circulation, which is driven by the interaction between the magnetized solar wind and the magnetosphere, is known as the Dungey cycle (Dungey, 1961)
We have presented newly revealed secondary magnetic reconnection at Earth’s flank magnetopause from Magnetospheric Multiscale (MMS) observations
The observed secondary ion jet agrees well with predictions of magnetic reconnection with a flow shear, and the electron signatures indicate the encounter of the electron diffusion region
Summary
The Earth’s global magnetospheric plasma circulation, which is driven by the interaction between the magnetized solar wind and the magnetosphere, is known as the Dungey cycle (Dungey, 1961). When the interplanetary magnetic field (IMF) is southward, this cycle begins at the dayside magnetopause where magnetic reconnection opens previously closed magnetospheric magnetic lines. We use observations from the Magnetospheric Multiscale (MMS) mission (Burch et al, 2016) to present local secondary magnetic reconnection at the flank magnetopause, which is identified by a secondary ion jet and the encounter of the electron diffusion region. This newly discovered secondary reconnection re-closes the open magnetic field lines previously generated by magnetopause reconnection, providing a new pathway for the entry of the solar wind into the magnetosphere
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