We present observations on 24 April 2023 by the Magnetospheric Multiscale spacecraft at the dayside, mid-latitude magnetopause, when an interplanetary magnetic cloud (MC) with sub-Alfvénic flows and northward and dawnward interplanetary magnetic field components impacted Earth’s magnetosphere. The aim is to reveal the processes of solar wind-magnetosphere interaction under sub-Alfvénic solar wind with northward magnetic field. Our analysis of electron and ion data suggests that magnetopause reconnection occurred near both polar cusps, forming boundary layers on closed magnetic field lines on both the MC and magnetospheric sides of the magnetopause. Grad-Shafranov, electron-magnetohydrodynamics, and polynomial reconstructions of magnetopause current layers show that local (equator-of-the-cusp) reconnection occurred in a sub-ion-scale magnetopause current sheet with a low magnetic shear angle (30°). Interestingly, the local reconnection was observed between the two (MC-side and magnetosphere-side) layers of closed field lines. It indicates that reconnected field lines from double cusp reconnection were interacting to induce another reconnection at the mid-latitude magnetopause. Our results suggest that magnetopause reconnection was more efficient or frequent under sub-Alfvénic solar wind with much lower beta plasma conditions than typical conditions. We will discuss the role of such efficient reconnection in the formation of low-latitude boundary layers.

We present in-depth analysis of three southward-moving meso-scale (ion- to magnetohydrodynamic-scale) flux transfer events (FTEs) and subsequent crossing of a reconnecting electron-scale current sheet (ECS), which were observed on 8 December 2015 by the Magnetospheric Multiscale spacecraft near the subsolar magnetopause under southward and duskward magnetosheath magnetic field conditions. Our aims are to understand the generation mechanism of ion-scale magnetic flux ropes (ISFRs) and to reveal causal relationship among magnetic structures of the ECS, electromagnetic energy conversion, and kinetic processes in magnetic reconnection layers. Magnetic field reconstruction methods show that a flux rope with a length of about one ion inertial length existed and was growing in the ECS, supporting the idea that ISFRs can be generated from secondary magnetic reconnection in ECS. Grad-Shafranov reconstruction applied to the three FTEs shows that the FTE flux ropes had axial orientations similar to that of the ISFR in the ECS. This suggests that these FTEs also formed through the same secondary reconnection process, rather than multiple X-line reconnection at spatially separated locations. Four-spacecraft observations of electron pitch-angle distributions and energy conversion rate suggest that the ISFR had three-dimensional magnetic topology and secondary reconnection was patchy or bursty. Previously reported positive and negative values of , with magnitudes much larger than expected for typical magnetopause reconnection, were seen in both magnetosheath and magnetospheric separatrix regions of the ISFR. Many of them coexisted with bi-directional electron beams and intense electric field fluctuations around the electron gyrofrequency, consistent with their origin in separatrix activities.