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Waves which couple to energetic electrons are particularly important in space weather, as they drive rapid changes in the topology and intensity of Earth’s outer radiation belt during geomagnetic storms. This includes Ultra Low Frequency (ULF) waves that interact with electrons via radial diffusion which can lead to electron dropouts and rapid acceleration and inward transport of electrons during. In radiation belt simulations, the strength of this interaction is specified by ULF wave radial diffusion coefficients. In this paper we detail the development of new models of electric and magnetic radial diffusion coefficients derived from in-situ observations of the azimuthal electric field and compressional magnetic field. The new models use L* as it accounts for adiabatic changes due to the dynamic magnetic field coupled with an optimized set of four components of solar wind and geomagnetic activity, Bz, V, Pdyn and Sym-H, as independent variables (inputs). These independent variables are known drivers of ULF waves and offer the ability to calculate diffusion coefficients at a higher cadence then existing models based on Kp. We investigate the performance of the new models by characterizing the model residuals as a function of each independent variable and by comparing to existing radial diffusion models during a quiet geomagnetic period and through a geomagnetic storm. We find that the models developed here perform well under varying levels of activity and have a larger slope or steeper gradient as a function of L* as compared to existing models (higher radial diffusion at higher L* values).

In this study, we report the statistical properties of whistler mode low hybrid (LH) emissions in the ionosphere, which have structureless spectra with a lower frequency boundary that matches the variation of the local lower hybrid resonance frequency fLHR. A potential source for the low hybrid emissions is identified as the high-frequency plasmaspheric hiss (HFPH) in the magnetosphere. We use DEMETER and Van Allen Probes data to perform a statistical study of the wave power distribution of the LH emissions and HFPH. Both LH and HFPH emissions show a similar frequency range, a similar invariant magnetic latitude range, and have similar trends in magnetic local time (MLT) (stronger wave intensity on the dayside) and in the AE index (stronger wave intensity for higher AE condition). A ray tracing simulation is also performed to demonstrate the propagation of HFPH waves from the magnetosphere into the ionosphere as LH waves.

We conduct a global survey of magnetosonic waves and compute the associated bounce and drift averaged diffusion coefficients, taking into account co-located measurements of fpe/fce, to assess the role of magnetosonic waves in radiation belt dynamics. The average magnetosonic wave intensities increase with increasing geomagnetic activity and decreasing relative frequency with the majority of the wave power in the range fcp < f < 0.3fLHR during active conditions. In the region 4.0 ≤ L* ≤ 5.0, the bounce and drift averaged energy diffusion rates due to magnetosonic waves never exceed those due to whistler mode chorus, suggesting that whistler mode chorus is the dominant mode for electron energisation to relativistic energies in this region. Further in, in the region 2.0 ≤ L* ≤ 3.5, the bounce and drift averaged pitch angle diffusion rates due to magnetosonic waves can exceed those due to plasmaspheric hiss and very low frequency (VLF) transmitters over energy-dependent ranges of intermediate pitch angles. We compute electron lifetimes by solving the 1D pitch angle diffusion equation including the effects of plasmaspheric hiss, VLF transmitters and magnetosonic waves. We find that magnetosonic waves can have a significant effect on electron loss timescales in the slot region reducing the loss timescales during active times from 5.6 to 1.5 days for 500 keV electrons at L* = 2.5 and from 140.4 days to 35.7 days for 1 MeV electrons at L* = 2.0.

During magnetospheric storms, radiation belt electrons are produced and then removed by collisions with the lower atmosphere on varying timescales. An efficient loss process is microbursts, strong, transient precipitation of electrons over a wide energy range, from tens of keV to sub-relativistic and relativistic energies (100s keV and above). However, the detailed generation mechanism of microbursts, especially over sub-relativistic and relativistic energies, remains unknown. Here we show that these energetic electron microbursts may be caused by ducted whistler-mode lower-band chorus waves. Using observations of equatorial chorus waves nearby low-altitude precipitation as well as data-driven simulations, we demonstrate that the observed microbursts are the result of resonant interaction of electrons with ducted chorus waves rather than nonducted ones. Revealing the physical mechanism behind the microbursts advances our understanding of radiation belt dynamics and its impact on the lower atmosphere and space weather.

Owing to the ever-present solar wind, our vast solar system is full of plasmas. The turbulent solar wind, together with sporadic solar eruptions, introduces various space plasma processes and phenomena in the solar atmosphere all the way to the Earth's ionosphere and atmosphere and outward to interact with the interstellar media to form the heliopause and termination shock. Remarkable progress has been made in space plasma physics in the last 65 years, mainly due to sophisticated in-situ measurements of plasmas, plasma waves, neutral particles, energetic particles, and dust via space-borne satellite instrumentation. Additionally high technology ground-based instrumentation has led to new and greater knowledge of solar and auroral features. As a result, a new branch of space physics, i.e., space weather, has emerged since many of the space physics processes have a direct or indirect influence on humankind. After briefly reviewing the major space physics discoveries before rockets and satellites, we aim to review all our updated understanding on coronal holes, solar flares and coronal mass ejections, which are central to space weather events at Earth, solar wind, storms and substorms, magnetotail and substorms, emphasizing the role of the magnetotail in substorm dynamics, radiation belts/energetic magnetospheric particles, structures and space weather dynamics in the ionosphere, plasma waves, instabilities, and wave-particle interactions, long-period geomagnetic pulsations, auroras, geomagnetically induced currents (GICs), planetary magnetospheres and solar/stellar wind interactions with comets, moons and asteroids, interplanetary discontinuities, shocks and waves, interplanetary dust, space dusty plasmas and solar energetic particles and shocks, including the heliospheric termination shock. This paper is aimed to provide a panoramic view of space physics and space weather., Accepted for publication in IEEE Transactions on Plasma Science (2022)

Whistler-mode chorus waves are critical for driving resonant scattering and loss of radiation belt relativistic electrons into the atmosphere. The resonant energies of electrons scattered by chorus waves increase at increasingly higher magnetic latitudes. Propagation of chorus waves to middle and high latitudes is hampered by wave divergence and Landau damping but is promoted otherwise if ducted by density irregularities. Although ducting theories have been proposed since the 1960’s, no conjugate observation of ducted chorus propagation from the equatorial magnetosphere to the ionosphere has been observed so far. Here we provide such an observation, for the first time, using conjugate spacecraft measurements. Ducted chorus waves maintain significant wave power upon reaching the ionosphere, which is confirmed by ray tracing simulations. Our results suggest that ducted chorus waves may be an important driver for relativistic electron precipitation.

Increasing numbers of satellites are orbiting through the Earth's radiation belts, and the range of orbits being commonly used is also growing. As a result, there is an increasing need for services to help protect satellites from space weather. The Satellite RIsk prediction and radiation Forecast (SaRIF) system provides reconstructions and forecasts of the high-energy electron flux throughout the outer radiation belt and translates these predictions into charging currents, dose rates, total ionizing dose and risk indicators. SaRIF both informs satellite operators of current and expected conditions and provides a tool to aid in post-event analysis. The reconstructions and forecasts are provided by the British Antarctic Survey Radiation Belt Model (BAS-RBM) running as part of an automatic system using real-time data to specify the boundary conditions and drive processes within the physics-based model. If SaRIF is to provide a useful tool, then the accuracy of the reconstructions and forecasts needs to be understood. Here we assess the accuracy of the simulations for geostationary orbit by comparing the model output with measurements made by the GOES 14 spacecraft for the period March–September 2019. No GOES 14 data was used to create the reconstruction or forecasts. We show that, with some improvements to the original system, the reconstructions have a prediction efficiency of 0.82 for >800 keV electrons and 0.87 for >2 MeV electrons, with corresponding prediction efficiencies of 0.59 and 0.78 for the forecasts.

The interactions between electromagnetic ion cyclotron (EMIC) waves and relativistic electrons are influential in diffusing radiation belt electrons into the loss code from which the electrons are lost into the atmosphere. These wave-particle interactions between EMIC waves and electrons with energies of a few MeV or more, depend strongly on wave spectra and plasma properties. Here we study the variability in wave spectra and plasma properties as a function of L* found during Van Allen Probe EMIC observations. These results are used to calculate statistical bounce and drift average diffusion coefficients that include the variation in wave spectra and plasma density as a function of L* and activity by averaging observation specific diffusion coefficients. The diffusion coefficients are included into global radiation belt simulations and the effect of the EMIC waves is explored. The distribution in the plasma frequency to electron gyrofrequency ratio decreases to lower values as L* decreases. As a result, few EMIC waves are able to resonate with 2-3MeV electrons at L* ≤ 3.75 while electrons of the same energy at larger L* are diffused by EMIC waves in high density regions. In comparison, a sufficient number of EMIC waves are able to resonate with higher energy electrons, urn:x-wiley:21699380:media:jgra56873:jgra56873-math-0001MeV, at L* ≥ 3.25 to significantly effect the decay in electron flux. EMIC wave parametrisations of electron diffusion by EMIC waves are compared and solar wind dynamic pressure is found to give the best agreement with Van Allen Probe observations.

Extreme ultraviolet images taken by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory make it possible to use deep vision techniques to forecast solar wind speed—a difficult, high‐impact, and unsolved problem. At a 4 day time horizon, this study uses attention‐based models and a set of methodological improvements to deliver an 11.1% lower RMSE and a 17.4% higher prediction correlation compared to the previous work testing on the period from 2010 to 2018. Our analysis shows that attention‐based models combined with our pipeline consistently outperform convolutional alternatives. Our study shows a large performance improvement by using a 30 min as opposed to a daily sampling frequency. Our model has learned relationships between coronal holes' characteristics and the speed of their associated high‐speed streams, agreeing with empirical results. Our study finds a strong dependence of our best model on the phase of the solar cycle, with the best performance occurring in the declining phase.

The high energy electron population in Earth's outer radiation belt is extremely variable, changing by multiple orders of magnitude on timescales that vary from under an hour to several weeks. These changes are typically linked to geomagnetic activity such as storms and substorms. In this study, we seek to understand how coherent changes in the radiation belt are across all radial distances, in order to provide a spatial insight into apparent global variations. We do this by calculating the correlation between fluxes on different L* measured by the PET instrument aboard the SAMPEX spacecraft for times associated with 15 large storms. Our results show that during these times, variations in the > 0.63 MeV electron flux are coherent outside the minimum plasmapause location and also coherent inside the minimum plasmapause location, when flux is present. However, variations in the electron fluxes inside the plasmapause show little correlation with those outside the plasmapause. During storm recovery and possibly main phases, flux variations are coherent across all L * regardless of plasmapause location, due to a rapid decrease, followed by an increase in radiation belt fluxes across all L*.

In the Outer Radiation Belt, the acceleration and loss of high‐energy electrons is largely controlled by wave‐particle interactions. Quasilinear diffusion coefficients are an efficient way to capture the small‐scale physics of wave‐particle interactions due to magnetospheric wave modes such as plasmaspheric hiss. The strength of quasilinear diffusion coefficients as a function of energy and pitch‐angle depends on both wave parameters and plasma parameters such as ambient magnetic field strength, plasma number density and composition. For plasmaspheric hiss in the magnetosphere, observations indicate large variations in the wave intensity and wavenormal angle, but less is known about the simultaneous variability of the magnetic field and number density. We use in‐situ measurements from the Van Allen Probe mission to demonstrate the variability of selected factors that control the size and shape of pitch‐angle diffusion coefficients: wave intensity, magnetic field strength and electron number density. We then compare with the variability of diffusion coefficients calculated individually from co‐located and simultaneous groups of measurements. We show that the distribution of the plasmaspheric hiss diffusion coefficients is highly non‐Gaussian with large variance, and that the distributions themselves vary strongly across the three phase‐space bins studied. In most bins studied, the plasmaspheric hiss diffusion coefficients tend to increase with geomagnetic activity, but our results indicate that new approaches that include natural variability may yield improved parameterizations. We suggest methods like stochastic parameterization of wave‐particle interactions could use variability information to improve modelling of the Outer Radiation Belt.

Signals from man‐made Very Low Frequency (VLF) transmitters, used for communications with submarines, can leak into space and contribute to the dynamics of energetic electrons in the inner radiation belt and slot region. In this study we use ∼5 years of plasma wave data from the Van Allen Probe A satellite to construct new models of the observed wave power from VLF transmitters both as a function of L* and magnetic local time and geographic location. Average power peaks primarily on the nightside of the Earth for the VLF transmitters at low geographic latitudes. At higher latitudes the peak average power extends further in magnetic local time due to more extensive periods of nighttime in the winter months. Nighttime power is typically orders of magnitude more than that observed near noon, implying that loss rates from a given VLF transmitter will also maximize in this region. The observed power from any given VLF transmitter is tightly confined in longitude, with the nightside peak power typically falling by a factor of 10 within 10° longitude of the location of the peak signal. We show that the total average wave power from all VLF transmitters lies in the range 3–9 pT2 in the region 1.3

Signals from very low frequency (VLF) transmitters can leak from the Earth‐ionosphere wave guide into the inner magnetosphere, where they propagate in the whistler mode and contribute to electron dynamics in the inner radiation belt and slot region. Observations show that the waves from each VLF transmitter are highly localized, peaking on the nightside in the vicinity of the transmitter. In this study we use ∼5 years of Van Allen Probes observations to construct global statistical models of the bounce‐averaged pitch angle diffusion coefficients for each individual VLF transmitter, as a function of L*, magnetic local time (MLT), and geographic longitude. We construct a 1‐D pitch angle diffusion model with implicit longitude and MLT dependence to show that VLF transmitter waves weakly scatter electrons into the drift loss cone. We find that global averages of the wave power, determined by averaging the wave power over MLT and longitude, capture the long‐term dynamics of the loss process, despite the highly localized nature of the waves in space. We use our new model to assess the role of VLF transmitter waves, hiss waves, and Coulomb collisions on electron loss in the inner radiation belt and slot region. At moderate relativistic energies, E∼500 keV, waves from VLF transmitters reduce electron lifetimes by an order of magnitude or more, down to the order of 200 days near the outer edge of the inner radiation belt. However, VLF transmitter waves are ineffective at removing multi–megaelectron volt electrons from either the inner radiation belt or slot region.

The recent introduction of all‐electric propulsion on geosynchronous satellites enables lower‐cost access to space by replacing chemical propellant. However, the time period required to initially raise the satellite to geostationary orbit (GEO) is around 200 days. During this time the satellite can be exposed to dynamic increases in trapped flux which are challenging to model. To understand the potential penalty of this new technique in terms of radiation exposure, the influence of several key parameters on solar cell degradation during the electric orbit raising period has been investigated. This is achieved by calculating the accumulation of non‐ionising dose through time for a range of approaches. We demonstrate the changes in degradation caused by launching during a long‐lived (100s of days) enhancement in MeV trapped proton flux for three different electric orbit raising scenarios and three different thicknesses of coverglass. Results show that launching in an active environment can increase solar cell degradation due to trapped protons by ~5% before start of service compared with a quiet environment. The crucial energy range for such enhancements in proton flux is 3‐10MeV (depending on shielding). Further changes of a few percent can occur between different trajectories, or when a 50μm change in coverglass thickness is applied.

The magnetopause marks the outer edge of the Earth's magnetosphere and a distinct boundary between solar wind and magnetospheric plasma populations. In this letter, we use global magnetohydrodynamic simulations to examine the response of the terrestrial magnetopause to fast-forward interplanetary shocks of various strengths and compare to theoretical predictions. The theory and simulations indicate the magnetopause response can be characterised by three distinct phases; an initial acceleration as inertial forces are overcome, a rapid compressive phase comprising the majority of the distance travelled, and large-scale damped oscillations with amplitudes of the order of an Earth radius. The two approaches agree in predicting subsolar magnetopause oscillations with frequencies 2-13 mHz but the simulations notably predict larger amplitudes and weaker damping rates. This phenomenon is of high relevance to space weather forecasting and provides a possible explanation for magnetopause oscillations observed following the large interplanetary shocks of August 1972 and March 1991., 9 pages, 3 figures, 1 table. Accepted as a Geophysical Research Letter on 09 July 2021

Signals from very-low-frequency transmitters on the ground are known to induce energetic electron precipitation from the Earth's radiation belts. The effectiveness of this mechanism depends on the propagation characteristics of those signals in the magnetosphere, and in particular whether the signals are ducted or nonducted along channels of enhanced plasma density, analogous to optical fibers. Here we perform a statistical analysis of in-situ waveform data collected by the Van Allen Probes satellites that shows that nonducted propagation dominates over ducted propagation in both the occurrence and intensity of the waves. Ray tracing confirms that the latitudinal distribution of wavevectors corresponds to nonducted as opposed to ducted propagation. Our results show the dominant mode of propagation needed to quantify transmitter-induced precipitation and improve the forecast of electron radiation belt dynamics for the safe operation of satellites.

The plasmasphere is a vast torus shape region of the inner magnetosphere, filled with dense $\left(\sim 1-10^{6} \# / \text{cm}^{-3}\right)$ and cold (less than $10 \text{eV})$ ions and electrons. The outer boundary of the plasmasphere, called plasmapause, is a sharp plasma density boundary that separates closed and open drift paths for cold plasmas. Distinct plasmapause with sharp density variations are only 16% of the observed plasmapause and are preferred to occur at the post-midnight and dawnside than the duskside. Most of the plasmapause, however, is accompanied by significant density irregularities. These density irregularities are thought to play an important role in wave excitation and propagation, such as the excitation of the electromagnetic ion cyclotron (EMIC) waves and magnetosonic (MS) waves, and the propagation of EMIC wave and MS waves.

The impact of radial diffusion in storm time radiation belt dynamics is well‐debated. In this study we quantify the changes and variability in radial diffusion coefficients during geomagnetic storms. A statistical analysis of Van Allen Probes data (2012 − 2019) is conducted to obtain measurements of the magnetic and electric power spectral densities for Ultra Low Frequency (ULF) waves, and corresponding radial diffusion coefficients. The results show global wave power enhancements occur during the storm main phase, and continue into the recovery phase. Local time asymmetries show sources of wave power are both external solar wind driving and internal sources from coupling with ring current ions and substorms. Wave power enhancements are also observed at low L values (L < 4). The accessibility of wave power to low L is attributed to a depression of the Alfvén continuum. The increased wave power drives enhancements in both the magnetic and electric field diffusion coefficients by more than an order of magnitude. Significant variability in diffusion coefficients is observed, with values ranging over several orders of magnitude. A comparison to the Kp parameterised empirical model of Ozeke et al. (2014) is conducted and indicates important differences during storm times. Although the electric field diffusion coefficient is relatively well described by the empirical model, the magnetic field diffusion coefficient is approximately ∼ 10 times larger than predicted. We discuss how differences could be attributed to dataset limitations and assumptions. Alternative storm‐time radial diffusion coefficients are provided as a function of L* and storm phase.

Pc1 geomagnetic pulsations, equivalent to electromagnetic ion cyclotron waves in the magnetosphere, display a specific amplitude modulation, though the region of the modulation remains an open issue. To classify whether the amplitude modulation has a magnetospheric or ionospheric origin, an isolated proton aurora (IPA), which is a proxy of Pc1 wave–particle interactions, is compared with the associated Pc1 waves for a geomagnetic conjugate pair, Halley Research Base in Antarctica and Nain in Canada. The temporal variation of an IPA shows a higher correlation coefficient (0.88) with Pc1 waves in the same hemisphere than that in the opposite hemisphere. This conjugate observation reveals that the classic cyclotron resonance is insufficient to determine the amplitude modulation. We suggest that direct wave radiation from the ionospheric current by IPA should also contribute to the amplitude modulation.

Proton flux measurements from the Proton Telescope instrument aboard the CRRES satellite are revisited, and used to drive a radial diffusion model of the inner proton belt at 1.1 ≤ L ≤ 1.65. Our model utilises a physics‐based evaluation of the cosmic ray albedo neutron decay (CRAND) source, and coulomb collisional loss is driven by a drift averaged density model combining results from the International Reference Ionosphere, NRLMSIS‐00 atmosphere and Radio Plasma Imager plasmasphere models, parameterised by solar activity and season. We drive our model using time‐averaged data at L = 1.65 to calculate steady state profiles of equatorial phase space density, and optimise our choice of radial diffusion coefficients based on four defining parameters to minimise the difference between model and data. This is first performed for a quiet period when the belt can be assumed to represent steady state. Additionally, we investigate fitting steady state solutions to time averages taken during active periods where the data exhibits limited deviation from steady state, demonstrated by CRRES measurements following the 24th March 1991 storm. We also discuss a way to make the optimisation process more reliable by excluding periods of variability in plasmaspheric density from any time average. Lastly, we compare our resultant diffusion coefficients to those derived via a similar process in previous work, and diffusion coefficients derived for electrons from ground and in situ observations. We find that higher diffusion coefficients are derived compared with previous work, and suggest more work is required to derive proton diffusion coefficients for different geomagnetic activity levels.

It is important to understand the variability of plasma processes across many different timescales in order to successfully model plasma in the inner magnetosphere. In this presentation, we focus on the interplay between the variability cold plasmaspheric plasma, whistler-mode wave activity, and the efficacy of wave-particle interactions in the inner magnetosphere. We use in-situ observations to quantify the amount and timescales of variability in pitch-angle diffusion due to plasmaspheric hiss in Earth’s inner magnetosphere, and suggest reasons for the variability. We then use a stochastic parameterization scheme to investigate the consequences of that variability in a numerical diffusion model. The results from the stochastic parameterization are contrasted with the standard approach of constructing averaged diffusion coefficients. We demonstrate that even when the average diffusion rates are the same, different timescales of variability in the wave-particle interactions lead to different end results in numerical diffusion models. We discuss the implications of our results for the modelling of wave-particle interactions in magnetospheres, and suggest quantifications that are vital for accurate modelling.

Ultra Low Frequency (ULF) waves drive radial diffusion of radiation belt electrons, where this process contributes to and, at times, dominates energisation, loss, and large scale transport of the outer radiation belt. In this study we quantify the changes and variability in ULF wave power during geomagnetic storms, through a statistical analysis of Van Allen Probes data for the time period spanning 2012 – 2019. The results show that global wave power enhancements occur during the main phase, and continue into the recovery phase of storms. Local time asymmetries show sources of ULF wave power are both external solar wind driving as well as internal sources from coupling with ring current ions and substorms.The statistical analysis demonstrates that storm time ULF waves are able to access lower L values compared to pre-storm conditions, with enhancements observed within L = 4. We assess how magnetospheric compressions and cold plasma distributions shape how ULF wave power propagates through the magnetosphere. Results show that the Earthward displacement of the magnetopause is a key factor in the low L enhancements. Furthermore, the presence of plasmaspheric plumes during geomagnetic storms plays a crucial role in trapping ULF wave power, and contributes significantly to large storm time enhancements in ULF wave power.The results have clear implications for enhanced radial diffusion of the outer radiation belt during geomagnetic storms. Estimates of storm time radial diffusion coefficients are derived from the ULF wave power observations, and compared to existing empirical models of radial diffusion coefficients. We show that current Kp-parameterised models, such as the Ozeke et al. [2014] model, do not fully capture the large variability in storm time radial diffusion coefficients or the extent of enhancements in the magnetic field diffusion coefficients.

Fast-forward interplanetary interplanetary shocks, as occur at the forefront of interplanetary coronal mass ejections and at corotating interaction regions, can rapidly compress the magnetopause inside the drift paths of electrons and protons, and expose geosynchonous satellites directly to the solar wind. Here, we use Gorgon Global-MHD simulations to study the response of the magnetopause to different fast-forward interplanetary shocks, with strengths extending from the median shocks observed during solar minimum up to that representing an extreme space weather event. The subsequent magnetopause response can be characterised by three distinct phases; an initial acceleration as inertial forces are overcome, a rapid compression well-represented by a power law, and large-scale damped oscillatory motion of the order of an Earth radius, prior to reaching pressure-balance equilibrium. The subsolar magnetopause is found to oscillate with notable frequencies in the range of 2–13 mHz over several periods of diminishing amplitudes. These results provide an explanation for similar large-scale magnetopause oscillations observed previously during the extreme events of August 1972 and March 1991 and highlight why static magnetopause models break down during periods of strong solar wind driving.

Electromagnetic ion cyclotron (EMIC) waves play an important role in relativistic electron losses in the radiation belts through diffusion via resonant wave-particle interactions. We present a new statistical model of electron diffusion by EMIC waves calculated, using Van Allen Probe observations, by averaging observation specific diffusion coefficients. The resulting diffusion coefficients therefore capture a wider range of wave-particle interactions than previous average models which are calculated using average observations. These calculations, and their role in radiation belt simulations, are then compared against existing diffusion models. The new diffusion coefficients are found to significantly improve the agreement between the calculated decay of relativistic electrons and Van Allen Probes data.