We present an analytic theory to demonstrate that electrons with an initially asymmetric spatial distribution would form an Archimedean spiral distribution in the inner magnetosphere. Such evolution is a result of the gradient/curvature drift, whose angular velocity decreases with radial distance. It has been known for a long time that spectrograms of energetic electrons in Earth's inner radiation belt exhibit time-varying organized peaks and valleys. Recent observations from Van Allen Probes have shown that such regular patterns are ubiquitous and are referred to as “zebra stripes”. Our theory can predict zebra stripes accurately. We also use the Rice Convection Model (RCM) to simulate zebra stripes. For the simplest situation with the dipolar magnetic field model, the analytic theory perfectly matches with the RCM simulation. In a realistic simulation, the RCM reproduces the time-dependent structures and evolution of the zebra stripes, which are in good consistency with Van Allen Probes observations.

How to cite: Sun, W., Yang, J., Wang, W., and Cui, J.: Archimedean Spiral Distribution of Electrons in Earth Inner Magnetosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4064, https://doi.org/10.5194/egusphere-egu23-4064, 2023.

Changes in pitch angle distributions can be a useful indicator of various changes in the radiation belts. Many methods of observing pitch angle distributions are qualitative. We present a method of studying pitch angle distributions that allows for a quantitative analysis of pitch angle distributions over time and energy channels, which allows for closer monitoring of spatial and temporal changes in the radiation belts. We use Van Allen Probes data from both spacecraft in fit pitch angle distributions with the form J₀sinⁿα, tracking ‘n’ over time. We use this method of tracking pitch angle distributions to establish a connection between very localized wave particle interactions and particle scattering.

How to cite: Greeley, A., Kanekal, S., and Schiller, Q.: Using pitch angle index to quantify anisotropies in the outer radiation belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9976, https://doi.org/10.5194/egusphere-egu23-9976, 2023.

Novel analysis of phase space densities at multiple energies allows for differentiation between various acceleration mechanisms at ultra‐relativistic energies. This method allows us to trace how particles are being accelerated at different energies and show how long it takes for acceleration to reach particular energy. This method clearly demonstrates the importance of local acceleration and also demonstrates the importance of outward radial diffusion in transporting electrons to GEO.

Acceleration to such high energies occurs only when cold plasma in the trough region is extremely depleted, down to the values typical for the plasma sheet. We perform event and statistical analysis of these depletions and show that the ultra‐relativistic energies are reached for each such depletion that is accompanied by the intensification of ~2MeV. VERB‐2D simulations are then used to explain these observations. There is also a clear difference between the loss mechanisms at MeV and multi‐MeV energies due to EMIC waves that can very efficiently scatter ultra‐relativistic electrons but leave MeV electrons unaffected.

Modelling and observations clearly show that cold plasma has a controlling effect over the ultra‐ relativistic electrons that are 10^6‐10^7 times more energetic. We also present how the new understanding gained from the Van Allen Probes mission can be used to produce the most accurate data assimilative forecast. Under the recently funded EU Horizon 2020 Project Prediction of Adverse effects of Geomagnetic storms and Energetic Radiation (PAGER) we study how ensemble forecasting from the Sun can produce long‐term probabilistic forecasts of the radiation environment in the inner magnetosphere.

How to cite: Shprits, Y., Allison, H., Drozdov, A., and Wang, D.: The controlling effect of the cold plasma density over the acceleration and loss of ultra‐relativistic electrons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3482, https://doi.org/10.5194/egusphere-egu23-3482, 2023.

We present a robust assessment of the formation and evolution of the cold H+ population produced via charge-exchange processes between ring current ions and exospheric neutral hydrogen in the inner magnetosphere, inferred via numerical simulations of the near-Earth plasma using a drift kinetic model of the ring current-plasmasphere system.

We evaluate the flow of mass and energy through the inner magnetospheric system and show that the production and evolution of the cold H+ population can be primarily driven by the plasma sheet conditions and dynamics and has the potential to reshape the plasmasphere and enhance the early-stage plasmaspheric refilling. We present evidence that the plasma sheet heavy ion composition is the primary controlling factor in the formation of the cold H+ via charge exchange with the geocorona, while the neutral density plays a much smaller role.

How to cite: Ilie, R., Liu, J., Liemohn, M., and Borovky, J.: A new mechanism for early time plasmaspheric refilling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17001, https://doi.org/10.5194/egusphere-egu23-17001, 2023.

One of the key assumptions of radiation belt modeling based on a three-dimensional Fokker-Planck equation is that trapped particle fluxes do not depend on the drift phase (i.e., the azimuthal angle, or magnetic local time, MLT). It is usually considered that MLT-dependent structures (such as particle injection signatures and subsequent drift echoes) are rapidly smoothed out by drift phase mixing. Yet, the characteristic times for radiation belt drift phase mixing are not well known.

In this presentation, we show the existence of a naturally occurring phase mixing process in the presence of field fluctuations. This process complements the observational phase mixing due to the finite resolution of the measuring instrument.

We present a first quantification for the characteristic time of natural phase mixing and we discuss the implications in terms of radiation belt modeling.

How to cite: Lejosne, S. and Albert, J. M.: Characteristic Times for Radiation Belt Drift Phase Mixing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10180, https://doi.org/10.5194/egusphere-egu23-10180, 2023.

Observations and magnetohydrodynamic simulations show that not all plasma injections from reconnection in the tail reach the inner magnetosphere to populate the ring current. We have used a self-consistent three-dimension particle-in-cell (PIC) simulation one way coupled to a global magnetohydrodynamic (MHD) simulation of the solar wind-magnetosphere-ionosphere system to investigate the population of the ring current during storm time substorms. This model includes a large fraction of the inner magnetosphere and the near-Earth tail. It allows us to study of the injection of particles from the tail and the interaction of the particles with plasma waves. The calculation begins with electrons and ions propagating earthward from the tail reconnection region. The particle distributions that enter the inner magnetosphere (R < 10 R_E) from the magnetotail have a suprathermal component which acts as a seed population for the ring current. We imposed a steady southward IMF with a magnitude of 8 nT at the upstream boundary of the MHD simulation domain for more than three hours. The solar wind number density was 6 cm^-3, the thermal pressure was 16 pPa, and the velocity was 530 km/s in the X direction toward Earth.  After we ran the MHD simulation, we chose an interval to examine during which there were several earthward flow channels and dipolarization fronts. Then, we used the output from this time to populate a large PIC simulation domain in the inner magnetosphere. In GSM coordinates, this domain extends over -22 R_E <X < 12.5 R_E, -13 R_E < Y <13 R_E, -5 R_E < Z < 5 R_E. The mass ratio was 256 with realistic ions and more massive electrons. In an initial simulation, we ran the code for 16,000 cycles and found that a ring current developed. We will discuss the reasons why some particles from the tail reach the inner magnetosphere, and some do not by examining how the particles are accelerated and lost.    

How to cite: El Alaoui, M., Lapenta, G., Rusaitis, L., and Walker, R.: Study of Ion Injection into the Inner Magnetosphere Using an Implicit Particle in Cell Simulation Driven by A Global MHD simulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10216, https://doi.org/10.5194/egusphere-egu23-10216, 2023.

During geomagnetically active periods plasma is transported from the magnetotail into the inner magnetosphere to become the ring current. The transpot of plasma into the ring current occurs at different spatial and temporal scales, from global quasi-steady convection to bursty bulk flows (BBFs), with typical cross-tail extents of 1-3 Earth radii. During its enhancement, the ring current plays a critical role in magnetosphere-ionosphere coupling. Ring current ions build up plasma pressure in the inner magnetosphere and will drive field-aligned currents which must close in the ionosphere, while electrons will lead to diffuse precipitation and enhanced ionospheric conductance which shape the ionospheric path of current closure. Current closure in the ionosphere will couple to the thermospheric neutral population, via Joule heating, and alter the dynamics of the plasmasphere, via the penetration electric field in the inner magnetosphere. 

Understanding the relative role of convection at different spatial scales in both the buildup of the ring current and its broader effects on geospace coupling is an area of active interest and one of the core science questions of the Center for Geospace Storms. In this talk I will describe how addressing this question has informed the development of the Multiscale Atmosphere Geospace Environment (MAGE) model and highlight several recent modeling studies which illustrate the central role of mesoscale processes.

How to cite: Sorathia, K., Michael, A., Sciola, A., Bao, S., Lin, D., Merkin, S., Ukhorskiy, S., Roedig, C., and Garretson, J.: Global modeling of the mesoscale buildup of the ring current and its role in magnetosphere-ionosphere coupling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3445, https://doi.org/10.5194/egusphere-egu23-3445, 2023.

Solar wind variations and transients are the main driver of the dynamics of the Earth’s magnetosphere. Interplanetary coronal mass ejections (ICME) cause the largest variations in the near-Earth space, but significant geomagnetic activity can also be driven by high-speed streams (HSSs) and stream interaction regions (SIRs). Solar wind – magnetosphere interactions drive fluctuations in the inner magnetosphere and impact the electrons in the outer radiation belt. Ultra low frequency (ULF) waves in the Pc5 range (2-7mHz) can accelerate electrons in the inner magnetosphere via drift resonance and cause changes in the electron flux up to several orders of magnitude. The different solar wind structures, ICMEs and HSSs/SIRs have been found to have different impact on the ULF waves and electrons in the inner magnetosphere. In this study we use mutual information from information theory to study the statistical dependency of the ULF waves and radiation belt electrons on the solar wind parameters and fluctuations over the solar cycle 23. Unlike Pearson correlation coefficient mutual information can also be used to investigate non-linear statistical dependencies between different parameters. We calculate correlation coefficients separately for each year and find that the non-linearity between the solar wind parameters and some magnetospheric parameters is higher during solar maximum when most of the geomagnetic activity is driven by ICMEs, while the non-linearity decreases during the declining phase, as larger portion of the geomagnetic activity is driven by HSSs and SIRs. To investigate further if the change of the ratio of ICMEs and HSSs is the possible cause of the changes in the non-linearity during the solar cycle, we calculate the correlation coefficients separately during ICMEs, HSSs/SIRs and quiet solar wind.

How to cite: Hoilijoki, S., Lipsanen, V., Osmane, A., Kalliokoski, M., George, H., Turc, L., and Kilpua, E.: Impact of the solar activity on the non-linearity of the statistical dependency between solar wind and the inner magnetosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8906, https://doi.org/10.5194/egusphere-egu23-8906, 2023.

Electromagnetic ion cyclotron (EMIC) waves are important because of their essential role in reducing the amount of radiation in the Earth's radiation belts under geomagnetic storm conditions. In this presentation, we show results from a new simulation model of EMIC waves and compare them with SWARM satellite data and ground-based observations [I. P. Pakhotin et al., Geophys. Res. Lett., 2022, doi:10.1029/2022GL098249]. The EMIC wave model is a first-of-a-kind in accounting for wave propagation in the magnetosphere and a realistic ionosphere specified using the IRI and MSIS empirical models. The inclusion of a realistic ionosphere in the model enables new pathways to the upper atmosphere to be identified, which is crucial for understanding the waves detected on the ground. We show using a model-data comparison that EMIC wave energy is reflected at different locations in the ionosphere toward the equator to form standing waves. This is a new resonance phenomenoncreated by interference of waves that produces an amplitude peak in the upper atmosphere at lower latitudes, far from the location of the initial source. Understanding such pathways is crucial for correctly diagnosing the location of EMIC wave populations in space, and assessing their role in radiation belt loss.

How to cite: Rankin, R., Sydorenko, D., and Mann, I. R.: New pathways for EMIC wave propagation within the ionosphere: SWARM observations and modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17213, https://doi.org/10.5194/egusphere-egu23-17213, 2023.

Space plasmas are often characterized by non-thermal particle distributions that are generally characterized by a high-energy tail that follows a power law for large velocity arguments. For modelling purposes, these are often described by kappa-type distributions (Livadiotis, 2017). Over the past few decades, the kappa distribution has been adopted in interpretations of observations in various space plasma contexts including the solar wind (Chotoo et al., 2000), planetary magnetospheres (Collier and Hamilton, 1995), the outer heliosphere (Decker and Krimigis, 2003) and the inner heliosheath (Livadiotis and McComas, 2012) and also in theoretical models (Hellberg et al., 2009). An abundance of data from the Cassini and Voyager missions has established in Saturn's magnetosphere the coexistence of non-thermal electron populations (of different characteristics). Schippers et al. (2008) analysed the radial distribution of electron populations in Saturn's magnetosphere by using an ad hoc two-kappa model, thus establishing the relevance of multi-kappa models with respect to electron populations in Saturn's magnetosphere. This coexistence of electron clouds (at distinct temperatures) is a key element in our work.

Electrostatic Solitary Waves (ESWs), generally associated with bipolar electric field waveforms observed alongside propagating density disturbances, are known to occur in Saturn's magnetosphere (Pickett et al., 2015). In this study, we have relied on a multi-fluid plasma model to investigate the significance of suprathermal electron populations in determining the characteristics of different types of solitary wave solutions. Our investigation reveals that the spectral index (i.e. the  parameter value related to the cold electron population mainly) is crucial in explaining the difference among different types of nonlinear structures. A comparison with spacecraft observations suggests that our theoretical estimations may be relevant in the interpretation of ESW observations in Saturn's magnetosphere.

References

Chotoo, K., Schwadron, N.A., Mason, G.M., Zurbuchen, T.H., Gloeckler, G., Posner, A., Fisk, L.A., Galvin, A.B., Hamilton, D.C., Collier, M.R., 2000. J. Geophys. Res. Space Phys. 105, 23107–23122. https://doi.org/10.1029/1998JA000015

Collier, M.R., Hamilton, D.C., 1995. Geophys. Res. Lett. 22, 303–306. https://doi.org/10.1029/94GL02997

Decker, R.B., Krimigis, S.M., 2003. Adv. Space Res. 32, 597–602. https://doi.org/10.1016/S0273-1177(03)00356-9

Hellberg, M.A., Mace, R.L., Baluku, T.K., Kourakis, I. and Saini, N.S., 2009. Physics of Plasmas, 16(9), p.094701

Livadiotis, G., 2017. Kappa Distributions - Theory and Applications in Plasmas (Elsevier).

Livadiotis, G., McComas, D.J., 2012. Astrophys. J. 749, 11. https://doi.org/10.1088/0004-637X/749/1/11

Pickett, J.S., Kurth, W.S., Gurnett, D.A., Huff, R.L., Faden, J.B., Averkamp, T.F., Píša, D. and Jones, G.H., 2015. Journal of Geophysical Research: Space Physics, 120(8), pp.6569-6580.

Schippers, P., Blanc, M., André, N., Dandouras, I., Lewis, G.R., Gilbert, L.K., Persoon, A.M., Krupp, N., Gurnett, D.A., Coates, A.J., Krimigis, S.M., Young, D.T., Dougherty, M.K., 2008. J. Geophys. Res. Space Phys. 113, https://doi.org/10.1029/2008JA013098

How to cite: Varghese, S. S. and Kourakis, I.: On the role of suprathermal electrons on the characteristics of electrostatic solitary waves in Saturn’s magnetosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4797, https://doi.org/10.5194/egusphere-egu23-4797, 2023.

There is a growing body of observational, theoretical and experimental evidence to indicate that a proper description of radiation belt charged particle transport will require new mathematical models, i.e. new partial differential equations. One leading candidate is to extend the ‘standard diffusion equation’ to a more general Fokker-Planck equation in order to include advection coefficients. Ideally, these advection (first-order transport) coefficients should be parameterized by plasma and VLF/ELF electromagnetic wave parameters in a similar manner to that used for the diffusion coefficients. To the authors' knowledge, this goal has not yet been achieved - at least not to obtain an equation that can be/has been implemented into operational global scale numerical models.

In general, advection coefficients are in fact a combination of both ‘drift coefficients’ and derivatives of the diffusion coefficients. In the standard quasilinear formalism, this combination produces advection coefficients that are identically zero because of specific constraints imposed via the Hamiltonian structure, with a derivation often attributed to Landau/Lichtenberg & Lieberman [1].

In this paper [2] we present a new theory that incorporates and builds upon the ‘weak turbulence/quasilinear results’ of [3,4] and demonstrates the breaking of the ‘Landau-Lichtenberg-Liebermann condition’ for the case of high wave amplitudes, or equivalently small timescales.

We therefore obtain:
(i) the standard quasilinear results for small wave amplitudes and long timescales;
(ii) and non-zero advection coefficients - as well as diffusion coefficients - that are valid for short timescales (high wave amplitudes).

These limiting timescales are determined by the electromagnetic wave amplitude. This also demonstrates that one can use what may be considered ‘quasilinear methods’ to obtain interesting new results for ‘nonlinear/high-amplitude’ waves in radiation belt modelling. We verify the results using high-performance test-particle experiments.

References

[1] A.J. Lichtenberg, and M.A. Lieberman, “Regular and Chaotic Dynamics”, 2nd Ed., Springer, 1991

[2] O. Allanson et al (in prep)

[3] D.S. Lemons, PoP, 19, 012306, 2012

[4] O. Allanson, T. Elsden, C. Watt, and T. Neukirch, Frontiers Aston. Space Sci., 8:805699, 2022

How to cite: Allanson, O., Bortnik, J., Ma, D., Osmane, A., and Albert, J.: Radiation belt particle diffusion, drift and advection via cyclotron interactions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8925, https://doi.org/10.5194/egusphere-egu23-8925, 2023.

The dynamics of Earth's outer electron radiation belt is, in part, driven by interactions with whistler-mode chorus waves.  Chorus can cause rapid acceleration of electrons up to relativistic energies, as well as drive precipitation of particles into the atmosphere causing both microbursts and diffuse aurora.  Chorus can propagate in such a way that it crosses the plasmapause boundary and may contribute to the possible sources of plasmaspheric hiss, which itself can cause atmospheric losses of particles and the formation of the slot region between the inner and outer radiation belts.  The direction of the wave vector relative to the background magnetic field is a key parameter for quantifying these processes, since it determines the propagation trajectory of the wave, and is required for calculating the resonance condition of the wave-particle interaction.

The orientation of the wave vector is investigated using both survey mode data and high-resolution burst mode observations from the EMFISIS Waves instrument on the Van Allen Probes spacecraft.  Spatial coverage beyond the Van Allen Probes orbit is provided by burst-mode observations from the FIELDS instrument suite on Magnetospheric Multiscale (MMS).  The polar and azimuthal wave vector angles are considered using both spectral analysis, where the frequency-time structure can be resolved, and instantaneous values, which can be used to identify variations within individual chorus subpackets.  We compare the results from each of these different timescales.  Near strong plasma density gradients, such as those which occur on the boundaries of plasmaspheric plumes, we identify that the wave vector becomes more oblique than the general case where no density gradients are present.  The obliquity of the wave vector is shown to directly relate to both the magnitude of the density gradient, and its proximity to the spacecraft.  

How to cite: Hartley, D. P., Christopher, I., Chen, L., Santolik, O., Kletzing, C., Argall, M., and Ahmadi, N.: The Angular Distribution of Whistler-Mode Chorus Wave Vector Directions from Van Allen Probes and MMS Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7785, https://doi.org/10.5194/egusphere-egu23-7785, 2023.

Whistler mode waves interact with different magnetospheric particle populations in the inner magnetosphere and significantly influence particle fluxes in the Earth's radiation belts. Using recently acquired large databases of spacecraft measurements from the Van Allen Probes and Cluster missions we construct new empirical models of whistler mode waves in the inner magnetosphere. We pay special attention to the off-equatorial region, which is often under-sampled in the currently existing models, and to the inter-calibration of data from different spacecraft missions. We take into account the effects of instrumental noise and other artifacts which influence the quality of data at the input of the modeling procedure. Our results show that dawn chorus occurs most often around noon, while its peak average amplitudes are observed during the local night. We also show that off-equatorial plasmaspheric hiss has a strong obliquely propagating component. We further confirm the influence of low plasma density regions on the intensity of chorus.

How to cite: Santolik, O., Kolmasova, I., Taubenschuss, U., Turcicova, M., and Hanzelka, M.: An Empirical Model of Whistler Mode Waves in the Radiation Belt Region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7524, https://doi.org/10.5194/egusphere-egu23-7524, 2023.

Whistler-mode waves propagating in the Earth’s inner magnetosphere sometimes appear as a set of nearly constant frequency elements separated by a fixed frequency. Such events are typically called line radiation, and they can have two distinct origins. First, events with narrow spectral lines and the frequency spacing corresponding to the base power system frequency (50/100 or 60/120 Hz) are generated by electromagnetic radiation from electric power systems on the ground (power line harmonic radiation, PLHR). Second, waves with broader spectral lines, whose frequency spacing does not correspond to the power system frequency, are believed to be generated by plasma instabilities in the magnetosphere (magnetospheric line radiation, MLR).

Frequencies of line radiation events are typically on the order of a few kHz, while their frequency spacing is on the order of a hundred Hz. Relevant spacecraft observations at larger radial distances are thus very sparse due to the typically low frequency resolution of available measurements, not sufficient to distinguish the line structure. We use high-resolution multicomponent wave measurements performed by the EMFISIS instrument on board the Van Allen Probes during the burst mode to fill this observational gap. We systematically identify the line radiation events and analyze their occurrence and properties. Detailed wave propagation analysis allows us to reveal wave propagation throughout the magnetosphere. We further show that the frequency spacing of MLR events appears to be related to an electrostatic wave observed at the corresponding frequency (≈100 Hz). Finally, conjugate observations performed by the Kannuslehto station in Finland are used to estimate the spatial extent of the events.

How to cite: Nemec, F., Santolík, O., Manninen, J., Hospodarsky, G. B., and Kurth, W. S.: Line radiation events: Properties, generation, and propagation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3188, https://doi.org/10.5194/egusphere-egu23-3188, 2023.

The Relativistic Electron and Proton Telescope (REPT), consisting of a stack of nine aligned silicon detectors onboard Van Allen Probes, has contributed a great number of discoveries based its nominal data. However, the REPT Pulse Height Analysis (PHA) data set, which was taken every 12 milliseconds (ms), including the pulse height that is proportional to the energy deposit of each individual particle from all nine REPT detectors, has been seldom-tapped. Here we show that this data set actually provides higher energy resolution particle measurements than the typical binned data from REPT. Geant4 simulations are used to extend and improve the electron detecting capabilities of REPT using the PHA data. After replicating the nominal characteristics of REPT in the Geant4 toolbox, new channels for REPT, going from 12 electron channels to 47 and lowering the minimum energy to ~1 MeV, have been formulated. The deep storm-time penetration of MeV electrons into the slot region (2<L<3) and inner belt (L<2) has been investigated. Clear dynamic variations of MeV electrons in these regions are revealed and substantiated by quantitative analysis. This is only an example of how the REPT PHA data will enable us to quantitatively address many more various science questions.

How to cite: Li, X., O'Brien, D., and Baker, D.: Observations and Analysis of Deep Penetrations of MeV Electrons from REPT PHA Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8693, https://doi.org/10.5194/egusphere-egu23-8693, 2023.

Magnetospheric ultra-low frequency (ULF) waves are known to cause radial diffusion and transport of hundreds-keV to few-MeV electrons in the radiation belts, as the range of drift frequencies of such electrons overlaps with the frequencies of the waves, leading to resonant interactions. Numerous expressions have been derived to quantitatively describe radial diffusion, so that they can be incorporated in global models of radiation belt electrons; however, most expressions of the radial diffusion rates are derived only for equatorially mirroring electrons, and are based on estimates of the power of ULF waves that are obtained either from spacecraft close to the equatorial plane or from the ground. Recent studies using the Van Allen Probes and Arase have shown that the wave power in magnetic fluctuations is significantly enhanced away from the magnetic equator, consistent with models simulating the natural modes of oscillation of magnetospheric field lines. This has significant implications for the estimation of radial diffusion rates, as higher pitch angle electrons will experience considerably higher ULF wave fluctuations than equatorial electrons. In this talk, we present recent results on the distribution of the magnetic field wave power as a function of magnetic latitude in different local time sectors and under different solar and geomagnetic conditions. Furthermore, using analytic functions of wave amplitudes in 3D test particle simulations, we simulate the change in L over time for particles of different pitch angles; this change in L can be translated to novel analytic diffusion coefficients with pitch-angle, L and energy dependence. In this talk we discuss the potential implications for the radial diffusion rates as currently estimated.

How to cite: Sarris, T., Li, X., Zhao, H., Papadakis, K., Liu, W., Tu, W., Angelopoulos, V., Glassmeier, K.-H., Miyoshi, Y., Matsuoka, A., Shinohara, I., and Imajo, S.: Observations of Off-Equatorial ULF Waves and Simulations of their effects on Radial Diffusion in the Radiation Belts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15611, https://doi.org/10.5194/egusphere-egu23-15611, 2023.

Whistler-Mode Chorus (WMC) waves are an important contributor to the dynamics of the magnetosphere, not only for their prevalence in measured observations of near-Earth space but also for their dominant role in transporting energy and particles throughout it. It is therefore of key importance to space weather modelling that we understand how WMC waves are generated, how they subsequently evolve and how they interact with the particle populations that they transport. There are also fundamental physics question to answer as WMC waves display nonlinear phenomena rarely seen in other fields, including their ability to raise and lower their frequency repeatedly and rapidly leading to rising and falling tone waves respectively. Are the interactions between the wave and the particles driving such phenomena, and if so to what degree are they doing so?

In this talk, we revisit the nonlinear evolution of WMC waves from a theoretical perspective.  Wave-particle interactions are shown to be a key driver of the modulational instabilities that lead to element and subelement formation which are well represented by an extension of the well-known Nonlinear Schrodinger equation. Simulations of this yields power spectrum reminiscent of the rising and falling tone emissions observed in mission data from the Van Allen probes, THEMIS, MMS and Cluster and determines that that wave-particle interactions are the primary cause of this effect. As a result, this nonlinear theory indicates regimes in which these frequency sweeps can be enhanced or dampened, and suggests why the WMC band gap at half the gyrofrequency exists.

How to cite: Ratliff, D. and Allanson, O.: Nonlinear wave-particle interactions in Whistler-Mode Chorus waves: modulation as a route to rising and falling tones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3375, https://doi.org/10.5194/egusphere-egu23-3375, 2023.

The wave-particle resonant interaction is a key process controlling energetic electron flux dynamics in the Earth’s radiation belts. All existing radiation belt codes are Fokker-Planck models relying on the quasi-linear diffusion theory to describe the impact of wave-particle interactions. However, in the outer radiation belt, spacecraft often detect waves sufficiently intense to interact resonantly with electrons in the nonlinear regime.

We propose an approach to (1) estimate the contribution of such nonlinear resonant interactions, and (2) include them into diffusion-based radiation belt models. Using statistics of chorus wave-packet amplitudes and sizes (number of wave periods within one packet), we provide a rescaling factor for the quasi-linear diffusion rates to account for the contribution of nonlinear interactions in long-term electron flux dynamics. Such nonlinear effects may speed up 0.1-1 MeV electron diffusive acceleration by a factor of x2-3 during disturbed periods.

How to cite: Vainchtein, D., Artemyev, A., Mourenas, D., and Zhang, X.: Quantifying the Contribution of Nonlinear Resonant Effects to Diffusion Rates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4471, https://doi.org/10.5194/egusphere-egu23-4471, 2023.