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In the space plasma environments, there are a variety of electromagnetic structures, including current sheets, magnetic holes and flux ropes, for which scales range from fluid down to ion or even electron kinetic scales. Our understanding of these structures, especially their electromagnetic field profiles and particle distributions, has been greatly improved due to the recent improvement in spacecraft technologies and enhancement in the observational database. To fully achieve the three-dimensional configurations of these structures, it is insufficient to use only the observations but also the theoretical models and numerical simulations. This paper briefly reviews the general framework of constructing theoretical models over these structures, which are self-consistent equilibrium solutions of Vlasov-Maxwell equations. In this framework, to ensure the satisfaction of the equilibrium Vlasov equation, particle distribution is expressed as a function of the particle invariant's motion. The moments of the particle distributions are then substituted into the Maxwell equations to solve the profiles of electromagnetic fields, which are further used to determine the particle phase space densities that can be compared directly to spacecraft observations. In recent years, this framework has been widely applied in the modeling and reconstruction of electromagnetic structures, demonstrating the ubiquitous presence of kinetic equilibrium structures in space plasmas. Moreover, the self-consistent models can be used as initial conditions of kinetic simulations. Finally, we discuss the open questions and future directions in studying kinetic structures in space plasmas.

High-resolution global magnetohydrodynamics (MHD) simulations include both meso- and global-scale processes occurring at the magnetopause, which interact to determine the time-dependent orientation of the day-side x-line (DXL). This study demonstrates that the global orientation of the DXL in GAMERA global MHD simulations varies on a time scale of minutes during steady southward interplanetary magnetic field conditions. This behavior manifests in observational data when reconnection outflows indicate that the direction to the x-line is opposite to the prediction from a steady-state model of the reconnection location. Because steady-state models of the DXL do not capture dynamics that are independent of solar wind variations, particularly surface waves and flux transfer events, they represent a time-averaged state of the system.

Sheath regions of interplanetary coronal mass ejections (ICMEs) are formed when the upstream solar wind is deflected and compressed due to the propagation and expansion of the ICME. Small-scale flux ropes found in the solar wind can thus be swept into ICME-driven sheath regions. They may also be generated locally within the sheaths through a range of processes. This work applies wavelet analysis to obtain the normalized reduced magnetic helicity, normalized cross helicity, and normalized residual energy, and uses them to identify small-scale flux ropes and Alfvén waves in 55 ICME-driven sheath regions observed by the Wind spacecraft in the near-Earth solar wind. Their occurrence is investigated separately for three different frequency ranges between 10–2 − 10–4 Hz. We find that small scale flux ropes are more common in ICME sheaths than in the upstream wind, implying that they are at least to some extent actively generated in the sheath and not just compressed from the upstream wind. Alfvén waves occur more evenly in the upstream wind and in the sheath. This study also reveals that while the highest frequency (smallest scale) flux ropes occur relatively evenly across the sheath, the lower frequency (largest scale) flux ropes peak near the ICME leading edge. This suggests that they could have different physical origins, and that processes near the ICME leading edge are important for generating the larger scale population.

We investigate here the magnetic properties of a large-scale magnetic flux rope related to a coronal mass ejection (CME) that erupted from the Sun on September 12, 2014 and produced a well-defined flux rope in interplanetary space on September 14–15, 2014. We apply a fully data-driven and time-dependent magnetofrictional method (TMFM) using Solar Dynamics Observatory (SDO) magnetograms as the lower boundary condition. The simulation self-consistently produces a coherent flux rope and its ejection from the simulation domain. This paper describes the identification of the flux rope from the simulation data and defining its key parameters (e.g., twist and magnetic flux). We define the axial magnetic flux of the flux rope and the magnetic field time series from at the apex and at different distances from the apex of the flux rope. Our analysis shows that TMFM yields axial magnetic flux values that are in agreement with several observational proxies. The extracted magnetic field time series do not match well with in-situ components in direct comparison presumably due to interplanetary evolution and northward propagation of the CME. The study emphasizes also that magnetic field time-series are strongly dependent on how the flux rope is intercepted which presents a challenge for space weather forecasting.