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We investigate the onset of magnetic reconnection, utilizing a fully kinetic Particle‐In‐Cell (PIC) simulation. Characteristic features of the electron phase‐space distributions immediately before reconnection onset are identified. These include signatures of pressure non‐gyrotropy in the velocity distributions, and lemon shaped distributions in the in‐plane velocity directions. Further, we explain how these features form through particle energization by the out‐of‐plane electric field. Identification of these features in the distributions can aid in analysis of data where clear signatures of ongoing reconnection are not yet present. In any environment where magnetic fields and charged particles interact, magnetic reconnection will occur if the conditions are favorable. Magnetic reconnection can be described as magnetic explosions, since it releases stored magnetic energy and converts it into heat and movement of the plasma particles. In this paper, we use numerical simulations to take a closer look at how the reconnection process initiates, a fundamental question still not fully understood. Signatures indicating reconnection onset can be identified in the electron distributionsOnset signatures persist over extended spatial and temporal scalesThe particle distributions immediately preceding onset are characterized by features of non‐gyrotropy and acceleration Signatures indicating reconnection onset can be identified in the electron distributions Onset signatures persist over extended spatial and temporal scales The particle distributions immediately preceding onset are characterized by features of non‐gyrotropy and acceleration

Using fully kinetic particle‐in‐cell modeling, we investigate how magnetic reconnection responds to a varying guide field in one of the inflow regions. We find that the reconnection rate varies significantly when the orientation of the magnetic field changes between being strictly antiparallel and having a guide field. These variations are fairly consistent with the scaling relation for asymmetric reconnection developed by Cassak and Shay (2007). However, the rate is also found to be nonlinearly modulated by changes in the ion inflow velocity. The spatio‐temporal change in the inflow velocity arises as the magnetic forces reconfigure to regions of different magnetic field strengths. The variations in the inflow magnetic field configuration allow for different gradients in the magnetic field, leading to asymmetries in the magnetic tension force. By momentum conservation, this facilitates asymmetries in the inflow velocity, which in turn affects the flux transport into the reconnection site. The outflow is found to be less laminar when the inflow varies, and various signatures of the inflow variations are identified in the outflow. Magnetic reconnection can be described as magnetic explosions, where energy stored in magnetic fields is converted into heat and movement of particles. It can happen in all environments where magnetic fields and charged particles interact, such as in the Sun, in planetary magnetospheres, and in fusion reactors on Earth. In this article, using numerical simulations, we present new insight into how magnetic reconnection behaves when the magnetic fields vary during the reconnection process. Spatio‐temporal effects in the inflow conditions causes modulations in the reconnection rate and introduces time‐dependent effectsThe asymmetrically varying guide field alters the force balance between the current sheet and inflow regionThe outflow regions show nonlaminar exhaust structures induced by the changing inflow Spatio‐temporal effects in the inflow conditions causes modulations in the reconnection rate and introduces time‐dependent effects The asymmetrically varying guide field alters the force balance between the current sheet and inflow region The outflow regions show nonlaminar exhaust structures induced by the changing inflow

We investigate how magnetic reconnection is influenced by an inflow of a dense cold ion population. We compare two 2.5D Particle‐In‐Cell simulations, one containing the cold population and one without. We find that the cold population influences the reconnection process on both global and kinetic scales, and that the dominant contribution can be explained through mass‐loading. We provide an analysis of how these multiscale changes are related through kinetic processes in the ion diffusion region, the so‐called micro‐macro coupling of mass‐loading. The inertia of the cold ion population is found to be the significant link that connects the changes on different scales. The cold and warm populations exhibit counter streaming behavior when and after the ion diffusion region reorganizes itself in response to the arrival of the cold population. This signature of the cold population should be observable by spacecraft observatories such as MMS. We investigate how magnetic reconnection is influenced by a dense inflow of cold ions. We find that the cold ions influence the reconnection process on both large and small scales, and that these are connected through the cold ion inertia. We also see cold and warm ions moving in opposite directions close to the reconnection site, which should be observable by spacecraft observatories. Cold ions in the inflow region affect reconnection on both micro‐ and macro‐scalesThe micro‐macro coupling of mass‐loading is mediated by the cold ion inertiaCold and warm ions are counter streaming close to the ion diffusion region boundary Cold ions in the inflow region affect reconnection on both micro‐ and macro‐scales The micro‐macro coupling of mass‐loading is mediated by the cold ion inertia Cold and warm ions are counter streaming close to the ion diffusion region boundary