This paper presents a dynamic plasmapause location model established based on 5 years of Time History of Events and Macroscale Interactions during Substorms (THEMIS) measurements from 2009 to 2013. In total, 5878 plasmapause crossing events are identified, sufficiently covering all 24 magnetic local time (MLT) sectors. Based on this plasmapause crossing database, we investigate the correlations between plasmapause locations with solar wind parameters and geomagnetic indices. Input parameters for the best fits are obtained for different MLT sectors, and finally, we choose five input parameters to build a plasmapause location model, including 5 min‐averaged SYM‐H, AL, and AU indices as well as hourly‐averaged AE and Kp indices. two out‐of‐sample comparisons on the evolution of the plasmapause is shown during two magnetic storms, demonstrating good agreement between model results and observations. Two major advantages are achieved by this model. First, this model provides plasmapause locations at 24 MLT sectors, still providing good consistency with observations. Second, this model is able to reproduce dynamic variations of the plasmapause on timescales as short as 5 min.

Spacecraft observations often reveal the presence of marginally stable chorus and electron cyclotron harmonic (ECH) waves across a spatial scale about several Earth radii (R E ), which is much larger than the spatial scale of the localized injections that are thought to generate them. Given the importance of these waves for electron acceleration, scattering, and loss to the atmosphere, here we investigate how such broad, periodic wave excitation might occur. We show that it can be attributed to modulation of hot (resonant) electron distributions by ultralow frequency (ULF) waves, which transport electrons radially inward/outward by as much as ∼1.5 R E . Unstable electrons (and chorus waves generated by them) from higher L-shells (presumably from the azimuthally extended flow-braking region) are thus brought to lower L-shells. Half a ULF cycle later, outward electron transport increases the loss cone anisotropy (the perpendicular velocity gradient near the loss cone), resulting in periodic generation of ECH waves with intensities that are anticorrelated with chorus wave intensity. Such wave generation and intermittent electron precipitation (modulated on the spatial/temporal scale of a ULF wavelength/wave period) across large spatial scales could explain the pulsating aurora.

The effect of the plasmapause on equatorially radially propagating fast magnetosonic (MS) waves in the Earth's dipole magnetic field is studied by using finite difference time domain method. We run 1‐D simulation for three different density profiles: (1) no plasmapause, (2) with a plasmapause, and (3) with a plasmapause accompanied with fine‐scale density irregularity. We find that (1) without plasmapause the radially inward propagating MS wave can reach ionosphere and continuously propagate to lower altitude if no damping mechanism is considered. The wave properties follow the cold plasma dispersion relation locally along its trajectory. (2) For simulation with a plasmapause with a scale length of 0.006 RE compared to wavelength, only a small fraction of the MS wave power is reflected by the plasmapause. WKB approximation is generally valid for such plasmapause. (3) The multiple fine‐scale density irregularities near the outer edge of plasmapause can effectively block the MS wave propagation, resulting in a terminating boundary for MS waves near the plasmapause.

In this paper, we perform a 1‐D particle‐in‐cell (PIC) simulation model consisting of three species, cold electrons, cold ions, and energetic ion ring, to investigate spectral structures of magnetosonic waves excited by ring distribution protons in the Earth's magnetosphere, and dynamics of charged particles during the excitation of magnetosonic waves. As the wave normal angle decreases, the spectral range of excited magnetosonic waves becomes broader with upper frequency limit extending beyond the lower hybrid resonant frequency, and the discrete spectra tends to merge into a continuous one. This dependence on wave normal angle is consistent with the linear theory. The effects of magnetosonic waves on the background cold plasma populations also vary with wave normal angle. For exactly perpendicular magnetosonic waves (parallel wave number k|| = 0), there is no energization in the parallel direction for both background cold protons and electrons due to the negligible fluctuating electric field component in the parallel direction. In contrast, the perpendicular energization of background plasmas is rather significant, where cold protons follow unmagnetized motion while cold electrons follow drift motion due to wave electric fields. For magnetosonic waves with a finite k||, there exists a nonnegligible parallel fluctuating electric field, leading to a significant and rapid energization in the parallel direction for cold electrons. These cold electrons can also be efficiently energized in the perpendicular direction due to the interaction with the magnetosonic wave fields in the perpendicular direction. However, cold protons can be only heated in the perpendicular direction, which is likely caused by the higher‐order resonances with magnetosonic waves. The potential impacts of magnetosonic waves on the energization of the background cold plasmas in the Earth's inner magnetosphere are also discussed in this paper.