Characterization of magnetic flux contents for two flux transfer events from both in situ and ionospheric observations

Flux transfer events (FTEs) are a type of magnetospheric phenomena that exhibit distinctive observational signatures from the in situ spacecraft measurements. They are generally believed to possess a magnetic field configuration of a magnetic flux rope and formed through magnetic reconnection at the dayside magnetopause, sometimes accompanied with enhanced plasma convection in the ionosphere. We examine two FTE intervals under the condition of southward interplanetary magnetic field (IMF) with a dawn-dusk component. We apply the Grad-Shafranov (GS) reconstruction method to the in situ measurements by the Magnetospheric Multiscale (MMS) spacecraft to derive the magnetic flux contents associated with the FTE flux ropes. In particular, given a cylindrical magnetic flux rope configuration derived from the GS reconstruction, the magnetic flux content can be characterized by both the toroidal (axial) and poloidal fluxes. We then estimate the amount of magnetic flux (i.e., the reconnection flux) encompassed by the area "opened" in the ionosphere, based on the ground-based Super Dual Auroral Radar Network (SuperDARN) observations. We find that for event 1, the FTE flux rope is oriented in the approximate dawn-dusk direction, and the amount of its total poloidal magnetic flux falls within the range of the corresponding reconnection flux. For event 2, the FTE flux rope is oriented in the north-south direction. Both the FTE flux and the reconnection flux have greater uncertainty. We provide a detailed description about a formation scenario of sequential magnetic reconnection between adjacent field lines based on the FTE flux rope configurations from our results.