糖心TV

	Title	Talk Abstracts
Daniel Ratliff	When, Where and How Do Non-Gaussian Chorus Wave Statistics Emerge?	The statistics of Chorus waves underpin contemporary space weather modelling, as the wave-particle interactions they mediate are a fundamental driver of particle acceleration in the Earth鈥檚 radiation belts. These effects are captured within diffusion coefficients utilised for large/long scale particle dynamics, which require a (statistical) model of the Chorus frequency spectrum for a given environment. These are typically Gaussian, due to their analytic tractability and the body of such statistical models developed from mission data. However, the observed Chorus spectrum can be considerably non-Gaussian, presenting asymmetry, heavy-tailedness or multimodality, features which a Gaussian cannot describe. Recent studies highlight that such non-Gaussian spectra have a significant impact on the resulting diffusion coefficients and thus our predictions of radiation belt dynamics. This therefore prompts the question – where and when should one expect Chorus wave statistics to transition from the Gaussian statistical picture to a non-Gaussian one? To answer this question, we adapt a Wave Action Model framework utilised within oceanography, where the transition from Gaussian to non-Gaussian statistics is well understood. This Whistler Action Model (WhAM) allows us to extract the Benjamin-Feir index (BFI) that predicts non-Gaussian spectra whenever BFI>1/2. Global maps of this index using statistical surveys of wave properties and plasma environments indicate this threshold is surpassed for waves in the night and dawn sectors during high AE activity in line with spacecraft observations. We then explore a burst-mode event measured by Van Allen A on the 1st March 2013 to understand the emergent shape of the resulting non-Gaussian spectral profiles, finding an array of spectral shapes can be produced by the WhAM, including multimodal, heavy-tailed and asymmetric power spectra. The predictions of the WhAM give reasonable agreement with the Van Allen observations, providing initial validation of the framework as a dynamic model for realistic Chorus spectra.
Sarah Glauert	Modelling the radiation belts with quasi-linear theory	Understanding the behaviour of the Earth鈥檚 radiation belts is important because many of the satellites on which society now depends orbit through the belts. Damage to these satellites, both temporary and permanent, is known to be associated with enhanced levels of high energy electrons. The electron flux in the belts is highly variable, with order of magnitude changes seen on a timescale of hours, so understanding, and ultimately being able to predict, this variability is an important step to safeguarding our satellite infrastructure. Fokker-Planck based radiation belt models use quasi-linear theory to account for the effects wave-particle interactions within the belts and can provide simulations of days to years to help understand the behaviour of the belts. This talk will explain our recent approach to combining quasi-linear theory with wave observations to derive diffusion coefficients for radiation belt models. We will show how these diffusion coefficients perform in simulations, highlighting both simulations that successfully reproduce observations and those where further research is required. Finally, we will discuss the role that non-linear interactions may play in the cases when the simulations fail to reproduce observations.
Clare Watt	The consequences of temporal variability of quasi-linear diffusion in Earth's magnetosphere	Kinetic wave-particle interactions in Earth鈥檚 outer radiation belt energize and scatter high-energy electrons, playing an important role in the dynamic variation of the extent and intensity of the outer belt. It is possible to model the effects of wave-particle interactions across long length and time scales using quasi-linear theory, leading to a Fokker-Planck equation to describe the effects of the waves on the high energy electrons. This powerful theory renders the efficacy of the wave-particle interaction in a diffusion coefficient that not only varies with the phase-space coordinates of the model, but also varies in time. In this talk we will explore the important consequences of the temporal variation of wave-particle interactions using numerical Fokker-Planck experiments. The experiments are constrained using observational clues from in situ observations that indicate how wave-particle interactions vary on a range of timescales spanning the duration of individual wave packets, to much longer timescales associated with geomagnetic activity.
James W S Cook	Estimating fusion fuel ion spin depolarisation by wave-particle interactions.	Fusion reaction rates arising from deuterium and tritium fuel ions with isotropically distributed quantum spin-states, i.e. those that occur without intervention, are consequently diminished by 1/3. Aligning spin states, an every day occurrence in MRI for example, offers a boost in reactivity, which could have a significant impact on the power output of fusion power plants. However, initially advantageously aligned fuel ion spin states may be made isotropic by wave induced depolarisation thereby reducing reactivity rates to their natural baseline. This work explores several aspects of advanced spin-polarised fuel: the anisotropic birth of alpha-particles and neutrons; subsequent excitation of waves due to the extra free energy; estimates of the spin-wave resonance width associated with depolarisation; the danger posed to spin polarised fuel by normal waves in the system; and finally an estimate of the robustness of spin-polarised fuel in the presence of tokamak eigenmode-like structures over collisional timescales.
Oliver Allanson	What is a Nonlinear Wave-Particle Interaction? How do I know When an Interaction is Nonlinear? What Can I do About it? What Questions Remain Un-Answered?	Interactions between electromagnetic plasma waves and energetic charged particles give rise to charged particle acceleration, transport and loss in position and velocity space. One of the most tractable methods to model the statistical evolution (acceleration, transport and loss) of charged particles in response to perturbations by these waves is the quasilinear diffusion theory. This paradigm predominates in our understanding of the inner magnetosphere (radiation belts), and has further utility for solar wind and cosmic ray turbulence. Within the last two decades there has been a sustained resurgence in the study of nonlinear wave-particle interactions. This was essentially (re-)motivated by the discovery of high-amplitude electromagnetic waves (e.g. amplitudes of tens-hundreds picoTesla thorugh to multiple nanoTesla) in the inner magnetosphere by burst-mode resolution spacecraft waveform measurements. Tremendous advances have been made in those two decades regarding observation, theory and modelling of these nonlinear wave-particle interactions. But, it is (probably) fair to say that there remains an outstanding challenge in two-way knowledge transfer of key results and outstanding challenges, i.e. 'what do observers and modellers need from theorists?' And vice-versa. We aim to try and bridge the gap by answering as best as possible the following questions: 1. What is a nonlinear wave-particle interaction? 2. How do I know when an interaction is nonlinear? 3. What can I do about it? 4. What questions remain un-answered? Time permitting we will also share some very recent new results regarding nonlinear wave particle interactions.
Ravindra Desai	Simulating extreme events in the radiation belts	The Van Allen radiation belts exhibit flux variations spanning multiple orders of magnitude due to a complex balance of production and loss processes. Extreme space-weather events can push the radiation belt into extreme regimes that provide a unique opportunity to distinguish individual mechanisms responsible for generating hazardous relativistic electron populations. Based upon the major storm of March 1991 and 鈥渘ear-miss鈥� of July 2012, we show that large interplanetary shock-driven magnetospheric compression at the the sudden commencement phase of geomagnetic storms can rapidly remove the entire outer radiation belt while simultaneously accelerating a distinct third belt deep within the slot region. For the strongest shocks, with speeds exceeding 2,000 km/s, electron energies in the slot region surpass 50 MeV, consistent with the unprecedented observations from March 1991 and representing the first physics-based simulation of such extreme belt formation. We then focus on the evolution of the radiation belts after the initial shock. Using the British Antarctic Survey radiation belt model, we show that immediately after the shock the multi-MeV electrons from the slot region are transported into the inner belt by radial diffusion and that the enhanced inner belt will then persist for months. The outer radiation belt will rebuild during the days following the storm and the main mechanism for this is the acceleration of low energy electrons by chorus waves, rather than inward radial diffusion.
Yoshiharu Omura	Nonlinear Growth of Whistler Mode Waves in Magnetospheres	Whistler mode waves in magnetospheres originate from thermal fluctuations and grow by receiving energy from energetic electrons through pitch angle diffusion toward lower pitch angles. This initial amplification is well described by the linear growth rate. When the wave amplitude becomes sufficiently large to nonlinearly trap resonant electrons, a distinct nonlinear growth process begins: nonlinear resonant currents form, producing simultaneous frequency variation and additional wave amplification. Depending on the shape of the electron velocity distribution near the resonant velocity, either electron holes or electron hills develop, leading to rising tone or falling tone emissions. Both the frequency variation and the spatial gradient of the background magnetic field play crucial roles in controlling this nonlinear growth [1]. To clarify the transition from linear to nonlinear growth, we perform full particle simulations with varying levels of thermal fluctuations and different gradients of a parabolic background magnetic field [2]. Our results show that coherent waves with frequency variation emerge from waves initially growing according to the linear growth rate. These coherent waves are further amplified as they propagate through an optimal parabolic magnetic field configuration. Remarkably, even in a uniform background magnetic field and in the absence of positive linear growth rates, small coherent wave packets can form from electromagnetic thermal fluctuations through nonlinear growth driven by frequency variation. Several coherent waves may coexist with nonlinear trapping potentials at different velocities in phase space, corresponding to different frequencies. Multiple nonlinear growth processes occurring simultaneously at different frequencies can generate hiss emissions inside Earth鈥檚 plasmasphere. In contrast, outside the plasmapause, where plasma density is lower, nonlinear wave growth driven by frequency variation occurs sequentially near the magnetic equator, producing rising tone or falling tone chorus emissions. References [1] Omura, Y., Nonlinear wave growth theory of whistler mode chorus and hiss emissions in the magnetosphere. Earth Planets Space 73:95, 2021. [2] Yin, Z., Simulation study on whistler mode hiss emissions in the magnetosphere, Master鈥檚 thesis, Department of Electrical Engineering, Kyoto University, 2025.
Colin Forsyth	Variations of ULF wave power inside the outside the plasmapause	It has been well-established that the location of some of the wave populations that influence radiation belt dynamics, namely hiss and chorus-mode wave populations, are strongly constrained by the location of the plasmapause. It has also been demonstrated that the variability in electron fluxes differs inside and outside the plasmapause. However, for ULF waves, the typically used diffusion coefficients make no distinction between waves inside and outside the plasmasphere. Storm-time case studies have shown that the location of the plasmasphere impacts the ability of ULF waves to penetrate to lower L-shells. Here, using in-situ observations , we demonstrate that: (1) the variation of magnetic ULF wave power against L-shell is almost flat inside the plasmasphere and increases with L-shell outside the plasmasphere; and (2) that the electric ULF wave power is very similar for most measure of geomagnetic activity or solar wind driving, save Kp. These observations such that our current empirical models of DLL are insufficient and will not capture differences in radial diffusion inside and outside the plasmapause.

Posters

	Title	Poster Abstract
Emily Grant	Quantifying the variability of chorus wave and plasma properties outside the plasmasphere	Diffusion coefficients derived from quasi-linear theory are central to modeling the behaviour of high-energy electrons in Earth's outer radiation belt, governing the rates of pitch-angle and energy diffusion driven by wave-particle interactions. However, existing models commonly rely on averaged wave and plasma properties, often parameterised by geomagnetic indices such as Kp. Previous studies suggest that this approach fails to capture the extreme values of key variables that disproportionately drive electron dynamics. Characterising the full underlying distributions of these properties, rather than their mean behaviour, is essential to create models of diffusion coefficients that appropriately capture their variation in time and space. The outer radiation belt is a highly dynamic environment, with wave and plasma conditions exhibiting considerable spatiotemporal variability. This variability means that diffusion coefficients can span several orders of magnitude depending on local conditions, and models that rely on bulk averages risk systematically underrepresenting the most impactful physical regimes. Appropriately capturing this variability — and distinguishing between its spatial and temporal components — is therefore a prerequisite for improving both the accuracy and the physical interpretability of diffusion-based models. Using observational data from RBSP-A, we examine the statistical properties of several variables known to influence diffusion coefficients: chorus wave power across multiple frequency bands, local electron number density, magnetic field strength, and the ratio of the electron plasma frequency to electron gyrofrequency (蠅pe/蠅ce). A key methodological consideration is the selection of an appropriate spatial grid size for the variability analysis. An optimal grid must be fine enough to resolve localised dynamics and separate spatial from temporal variability in satellite observations, while remaining broad enough to capture the statistical structure of the inner magnetosphere. We fit suitable probability distribution functions to the data at smaller spatial scales and characterise their parameters across distinct regions of the inner magnetosphere, investigating whether systematic regional patterns emerge. By capturing the tail behaviour of key wave and plasma properties, this approach better represents the conditions that most strongly influence electron dynamics and the resulting diffusion coefficients, supporting improved radiation belt models and more robust conclusions drawn from them.