Rotational Discontinuities in the Magnetopause of an Open Magnetosphere

In this paper, we analyze the fine structure of rotational discontinuities (RDs) in the magnetopause of an open magnetosphere using four-point magnetic field measurements recorded by the Magnetospheric MultiScale mission. An RD is commonly observed within the magnetopause when reconnection occurs in the magnetopause. Furthermore, an RD usually occurs closer to the magnetosheath side of the magnetopause. The magnetic structure of RD is usually much thinner than 110 km. The magnetic field rotation maxima and magnetic strength minima are within the RD. The radius of curvature of the magnetic field lines reaches a minimum in the RD (similar to 83-1,491 km). In addition, the radius of curvature of the magnetic field lines of the RD is usually much larger than the thickness of the magnetic structure of the RD, indicating that the magnetic field lines almost lie in the RD. Generally, a field-aligned current dominates in the RD.