We investigate slow magneto-acoustic waves that are naturally excited by turbulent convection and investigate their role in the energy balance of a plage region using three dimensional (3D) radiation-MHD simulations. To study slow magneto-acoustic waves traveling along the magnetic field lines, we track 25 magnetic field lines both in space and time inside a strong magnetic element. We calculate velocity component parallel to the background field and compute the temporal power spectra at various heights above the mean solar surface. Additionally, horizontally averaged power spectra for both longitudinal (parallel to the background magnetic field) and vertical (i.e. the component perpendicular to the surface) components of velocity are calculated using time-series at fixed locations. We also degrade our simulation data to compare our results with observations. The velocity power spectra, averaged horizontally over the whole domain, show that low frequency waves may reach into the chromosphere possibly along the inclined magnetic field lines. In addition, the power spectra at high frequencies follow a power law with an exponent close to -5/3, suggestive of turbulent excitation. The horizontally averaged power spectra of vertical component of velocity at various effective resolutions show that the observed acoustic wave energy fluxes are underestimated, by a factor of three even if determined from observations carried out at a high spatial resolution of 100 km. Since the waves propagate along the non-vertical field lines, measuring the velocity component along the line-of-sight, rather than along the field contributes significantly to this underestimate. Moreover, this underestimation of energy flux indirectly indicates the importance of high-frequency waves that have a smaller spatial coherence and are thus more influenced by spatial averaging effect compared to low-frequency waves. Our results show that, in contrast to claims made in the literature, longitudinal waves within magnetic elements carry sufficient energy to heat the chromosphere.

Small-scale coherent vortical motions are ubiquitous in the photosphere. The complex dynamics between vortical flows and magnetic elements are linked to many solar events, e.g. jets and wave generation. One important magnetic structure expected to be driven by atmospheric rotational motions is the twisted magnetic flux tube. In this work, the twisted magnetic flux is defined as a new typology of a solar vortex. We applied forefront methodologies to detect the kinetic and magnetic vortices tubes in realistic magnetoconvection simulations. Both types of vortices are found in the intergranular downflow; magnetic vortices appear mostly in flow shear areas where plasma beta greater than one, whereas the kinetic vortices were detected in low plasma-beta regions. The solar vortices tend to concentrate the magnetic field locally, presenting similar dynamics at different solar atmosphere levels. Based on their plasma magnetic and kinetic energy ratio, we find two distinct magnetic vortex types with different geometries for the magnetic field lines. The kinetic vortices show upward jets and tend to encompass high magnetic fluxes; thereby, their dynamics is mainly dominated by magnetic forces. Due to the high magnetic tension, the vortical motion can only perturb the magnetic lines, and therefore the kinetic vortices are incapable of twisting the magnetic flux tube. We find that the magnetic vortices are created regardless of the existence of vortical motions.

The recent rediscovery of magnetic switchbacks by Parker Solar Probe has led to a strong interest about their origin and nature. In-situ measurements and analysis suggest a lower coronal origin and an Alfvénic nature. Through magnetohydrodynamic (MHD) numerical simulations, we test whether this scenario of switchback origins is plausible. We find that, in contrast to a relatively stable propagation of switchbacks in a uniform medium without gravity, the presence of a gravitationally stratified medium significantly impacts the stability of highly kinked switchbacks. We suggest that switchbacks generated in the deep corona are unlikely to survive out into the solar wind.

It is well accepted that resonant absorption plays an important role in the dynamics of collective modes in solar waveguides. Taking the much-studied kink modes in coronal loops as an example, we perform an examination on resonant absorption from the energetics perspective, the aim being to shed more light on the interplay between the compressional and magnetic energies. We start with a well-established energy conservation law governing arbitrary time-dependent Eulerian perturbations in linear, ideal, finite-beta, gravity-free MHD, where a source term is involved when the equilibrium magnetic field is non-potential. We then specialize to resonantly damped kink modes in a canonical equilibrium configuration, in which coronal loops are seen as straight cylinders and the inhomogeneity is restricted to a transition layer bordering the cylinder. With three-dimensional time-dependent simulations and subsequent eigen-mode computations, we first demonstrate that this source term tends to be non-negligible even when the equilibrium magnetic field deviates only slightly from a potential one. Furthermore, in the inhomogeneous layer, the wave energies tend to be dominated by the magnetic and compressional ones. However, when re-evaluated with the Lagrangian perturbations, the compressional energy becomes negligible unless in the resonant layer. This switch from the Eulerian to the Lagrangian perspective also helps reconcile two apparently competing interpretations for the source term, converging to the notion that the interaction between the equilibrium and the perturbations results effectively in the exchange between the magnetic and compressional energies. Our results are discussed in the context of future spectroscopic measurements capable of resolving the fine-scales resulting from resonant absorption.

Within the last decade, solar physics has moved into a golden era of discovery. A diverse assortment of ground- and space-based facilities, coupled with modern modelling efforts, has helped make rapid progress in the detection, identification, characterisation and understanding of dynamic motions spanning the photosphere through to the corona. Here I will discuss recent wave phenomena detected and benchmarked using an assortment of instruments at the Dunn Solar Telescope in New Mexico, USA. In particular, I will reveal wave activity captured by the Fabry-Pérot IBIS instrument, in addition to the high-cadence ROSA imaging suite. I will highlight the challenges presented when examining these features across a range of atmospheric heights, structural sizes, and ionisation states, before looking towards the future with upcoming next-generation hardware and facilities.  

A generalised model for MHD wave propagation in solar structures is, as of yet, not available. Realistic theoretical models of different possible equilibria are required to better explain the ever increasing number of detailed observations thanks to modern high resolution instruments. This allows magnetoseismology to be conducted and provides more accurate information about local plasma properties. In this work, an innovative numerical approach using classical techniques allows the dispersion diagram and eigenfunctions to be obtained for any arbitrarily-symmetric inhomogeneous equilibrium. The analytic dispersion relation is not required, therefore advancing previous studies which are restricted to analytical investigations. This proposed technique implements the shooting method to match necessary boundary conditions on continuity of displacement and total pressure of the waveguide.  As is the case with any new algorithm, the approach is tested against well-known analytical results for MHD waves in uniform slab. This work is then extended by investigating the behaviour of the dispersion diagrams and wave mode eigenfunctions when the equilibrium plasma density is inhomogeneous and modelled in the form of Gaussian and trigonometric spatial profiles. A further extension investigates the effect that a non-uniform background flow has on the properties of the wave modes. The resulting eigenfunctions of perturbed total pressure and displacement in an inhomogeneous plasma are compared with the uniform model and the physical differences are discussed which have implications for observers.

Using 3D MHD simulations, we study the heating effects and the synthetic emissions of transverse oscillation in coronal loops with the presence of radiative cooling. The coronal loop is driven at the footpoint by transverse oscillations, and subsequently the induced Kelvin–Helmholtz instability deforms the loop cross section and generates small-scale structures. Wave energy is transferred to smaller scales where it is dissipated. We find that the heating effects by transverse oscillations are promising balancing the radiative loss. We then transform the simulated straight loop to a semi-torus loop and forward-model the spectrometer and imaging emissions, mimicking the observations of Hinode/EIS and SDO/AIA. We find that the oscillation amplitudes of intensity are different at different slit positions, but the oscillation amplitudes from different spectral lines or channels are almost the same. We also find that the observed Doppler velocities are one order of magnitude smaller than real oscillation velocities in our model due to large column depth. These results are helpful for further understanding the heating effects of transverse oscillations in coronal loops and their observational signatures.

Using the three-dimensional Versatile Electron Radiation Belt (VERB-3D) code, we perform simulations to investigate the dynamic evolution of relativistic electrons in the Earth’s outer radiation belt. In our simulations, we use data from the Geostationary Operational Environmental Satellites to set up the outer boundary condition, which is the only data input for simulations. The magnetopause shadowing effect is included by using last closed drift shell, and it is shown to significantly contribute to the dropouts of relativistic electrons at high L*. We validate our simulation results against measurements from Van Allen Probes. In long-term simulations, we test how the latitudinal dependence of chorus waves can affect the dynamics of the radiation belt electrons. Results show that the variability of chorus waves at high latitudes is critical for modeling of megaelectron volt (MeV) electrons. We show that, depending on the latitudinal distribution of chorus waves under different geomagnetic conditions, they cannot only produce a net acceleration but also a net loss of MeV electrons. Decrease in high‐latitude chorus waves can tip the balance between acceleration and loss toward acceleration, or alternatively, the increase in high‐latitude waves can result in a net loss of MeV electrons. Variations in high‐latitude chorus may account for some of the variability of MeV electrons. We also calculated lifetime using the diffusion coefficients including the effect of high-latitude chorus waves.We also perform simulations for the COSPAR International Space Weather Action Team Challenge for the year 2017.  We ‘fly’ a virtual satellite through our simulation results and compare the simulated differential electron fluxes at 0.9 MeV and 57.27 degrees local pitch-angle with the fluxes measured by the Van Allen Probes. In general, our simulation results show good agreement with observations. We calculated several different matrices to validate our simulation results against satellite observations. 

We show that sub-relativistic/relativistic electron microbursts form the high‐energy tail of pulsating aurora (PsA). Whistler‐mode chorus waves that propagate along
the magnetic field lines at high latitudes cause precipitation bursts of electrons with a wide energy range from a few keV to MeV. The rising tone elements of chorus waves cause individual microbursts of subrelativistic/relativistic electrons and the internal modulation of PsA. The chorus bursts for a few seconds cause the microburst trains of subrelativistic/relativistic electrons and the main pulsations of PsA. Our simulation studies demonstrate that both PsA and relativistic electron microbursts originate simultaneously from pitch angle scattering by chorus wave‐particle interactions along the field line.

The two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 hours. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies were close to but did not exactly match the repetition frequency of QP emissions for most of the time, suggesting that those coherent QP emissions probably originated from a common source, which then propagated over a broad area in the magnetosphere. The QP emissions were amplified by local anisotropic electron distributions, and their large-scale amplitudes were modulated by the plasma density. A novel observation of this event is that chorus waves at frequencies above QP emissions exhibit a strong correlation with QP emissions. Those chorus waves intensified when the QP emissions reach their peak frequency. This indicates that embryonic QP emissions may be critical for its own intensification as well as chorus waves under certain circumstances. The low-earth-orbit POES satellite observed enhanced energetic electron precipitation in conjunction with the Van Allen Probes, providing direct evidence that QP emissions precipitate energetic electrons into the atmosphere. This scenario is quantitatively confirmed by our quasilinear diffusion simulation results.

Loss mechanisms act independently or in unison to drive rapid loss of electrons in the radiation belts. Electrons may be lost by precipitation into the Earth’s atmosphere, or through the magnetopause into interplanetary space. Whilst this magnetopause shadowing is well understood to produce dropouts in electron flux, it is less clear if shadowing continues to remove particles in tandem with electron acceleration processes, limiting the overall flux increase. We investigate the contribution of shadowing to overall radiation belt fluxes throughout a geomagnetic storm. We use new, multi-spacecraft phase space density calculations to decipher electron dynamics during each storm phase and identify features of magnetopause shadowing during both the net-loss and the net-acceleration storm phases. We also highlight two distinct types of shadowing; 'indirect', where electrons are lost through ULF wave driven radial transport towards the magnetopause boundary, and 'direct', where electrons are lost as their orbit intersects the magnetopause.

Oblique whistler mode waves are observed frequently in dayside and dawnside of the Earth’s magnetosphere around the outer radiation belt. Through the nonlinear trapping, by coherent chorus waves, energetic resonant electrons (tens keV) can be accelerated rapidly and become relativistic electrons (a few MeV). Electron acceleration of velocity perpendicular to the background magnetic field of resonant electrons plays an essential role in both cyclotron and Landau resonances. Green’s functions are treated as the results of wave-particle interactions between the target waves and the given electrons. We build up a database of Green’s functions for a great number of electrons interacting with oblique whistler mode chorus emissions. The formation processes of the outer radiation belt electron fluxes interacting with consecutive chorus emissions are traced by applying the convolution integrals for the Green’s functions. We trace the evolution of the radiation belt electron fluxes for a few minutes and find that MeV electrons are generated promptly due to the combination of cyclotron resonance and Landau resonance with oblique chorus waves. We compare the formation processes among waves with different wave normal angles, and the results show that chorus waves with larger wave normal angles can accelerate 10-30 keV electrons to MeV faster. We further compare the precipitation fluxes between parallel and oblique chorus emissions. Our simulation result reveals that oblique chorus emissions lead to more electron precipitation than parallel chorus emissions. Multiple resonances effect in the oblique whistler mode wave-particle interactions is the reason for the greater precipitation.

Suprathermal electrons (~0.1-10 keV) in the inner magnetosphere are usually observed in a 90°-peaked pitch angle distribution, formed due to the conservation of the first and second adiabatic invariants as they are transported from the plasma sheet. We report a peculiar field-aligned suprathermal electron (FASE) distribution measured by Van Allen Probes, where parallel fluxes are one order of magnitude higher than perpendicular fluxes. Those FASEs are found to be closely correlated with large-amplitude hiss waves, and are observed around the Landau resonant energies. We demonstrate, using quasilinear diffusion simulations, that hiss waves can rapidly accelerate suprathermal electrons through Landau resonance, and create the observed FASE population. The proposed mechanism potentially has broad implications for suprathermal electron dynamics as well as whistler mode waves in the Earth’s magnetosphere, and has been demonstrated in the Jovian magnetosphere.

The triggering process of whistler-mode rising-tone emissions such as chorus in the Earth’s magnetosphere is studied by one-dimensional electromagnetic simulations [1]. We assume a parabolic magnetic field and energetic electrons forming an anisotropic subtracted bi-Maxwellian momentum distribution function. We inject a large amplitude triggering waves at the magnetic equator by oscillating currents with a constant frequency 0.3 of the electron cyclotron frequency externally. By separating forward and backward waves based on the spatial helicity of the whistler-mode waves, we find that the generation region of triggered rising-tone emissions moves upstream of the triggering waves as a self-sustaining process. Being separated from the triggering wave with a constant frequency, a series of triggered wave packets are formed with frequencies gradually increasing from 0.3 to 0.75 of the electron cyclotron frequency. The wave growth of the first triggered wave packet is smooth over the frequency range 0.3-0.5 of the electron cyclotron frequency. Subsequently, the triggered wave packets with short durations are observed with the frequency range 0.5-0.7 of the electron cyclotron frequency. We observe formation of electron holes in the spatial range with the inhomogeneity factor |S| less than 1. The electron hole position continuously moves to smaller absolute values of parallel velocity in velocity phase space, resulting in smooth wave growth and frequency increase in the first triggered wave packet. When a modulation of the first subpacket with a short duration appears in the wave amplitude, some density modulations of the untrapped resonant electrons are observed around the electron holes. Those density modulations cause fluctuations of the resonant current, which enhance the formation of subpackets in space and time. [1] T. Nogi, S. Nakamura, and Y. Omura, “Full particle simulation of whistler‐mode triggered falling‐tone emissions in the magnetosphere”, Journal of Geophysical Research: Space Physics, 125, e2020JA027953, 2020.

In order to analyze the large volume of wave data returned from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) investigation on NASA’s Van Allen Probes, we have developed computational methods to find key characteristics of waves in the Earth’s inner magnetosphere. Using novel signal processing techniques, we have developed autonomous algorithms that can analyze Van Allen Probes waveform observations to determine the characteristics of individual chorus elements. In particular, the methods allow us to determine each individual chorus element as a function of frequency and time. With this characterization, we can derive the frequency/time sweep rate of chorus elements for a large number of events without the need for manual identification of the elements. This enables statistical studies of the properties of the individual chorus elements which has been limited in the past to small numbers of events identified and analyzed by hand. We present the basics of the automated detection technique, describing its current state of evolution as well performance metrics. We also show results of the statistics on the range and character of chorus element sweep rate. In addition we show how chorus power varies with radial position, magnetic latitude, and magnetic local time as well the relation between chorus power and sweep