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. The outer boundary of the Earth's own magnetic field extends into space and is shaped by the constant outflow of ionized particles from the Sun, that is, the so-called solar wind, into a bullet shape. The blunt side facing the Sun is called the dayside magnetopause where the Sun's magnetic field carried along by the solar wind interacts with the Earth's magnetic field. Under the condition of the Sun's magnetic field possessing a southward component, the interaction becomes more intense and energetic, often leading to a continuous change of topology/connectivity between the two fields. Such a process, dubbed magnetic reconnection, is also accompanied with enhanced particle motion, of which signatures can manifest in the in situ spacecraft measurements. Correspondingly such enhanced disturbances may map nearly simultaneously along the Earth's magnetic field lines onto the Earth's upper atmosphere and observed by the ground-based radars. By analyzing and correlating these observations at different but inter-connected sites, we carry out a study to characterize and relate the physical quantity of magnetic flux accumulated through the reconnection process. We also illustrate in detail the formation of one type of commonly associated magnetic field structure at the dayside magnetopause. Magnetic flux contents for flux transfer event (FTE) flux ropes are characterized in terms of the toroidal (axial) and poloidal components The total poloidal flux may correspond to the amount of flux "opened" in the corresponding polar cap region of the ionosphere Sequential magnetic reconnection between adjacent field lines can inject poloidal flux into the flux rope during its formation process