Displays

Earth’s magnetotail plasma sheet plays a crucial role in the variability of Earth’s outer electron radiation belt. Typically, injections of energetic electrons from Earth’s magnetotail into the outer radiation belt and inner magnetosphere during periods of substorm activity are not observed exceeding ~300 keV.  Consistent with that, phase space density radial distributions of electrons typically indicate that for electrons below ~300 keV, there is a source of electrons in the plasma sheet while for electrons with energies above that, there is a local source within the outer radiation belt itself.  However, here we ask the question: is this always the case or can the plasma sheet provide a direct source of relativistic (> ~500 keV) electrons into Earth’s outer radiation belt via substorm injection? Using phase space density analysis for fixed values of electron first and second adiabatic invariants, we use energetic electron data from NASA’s Van Allen Probes and Magnetospheric Multiscale (MMS) missions during periods in which MMS observed energetic electron injections in the plasma sheet while Van Allen Probes concurrently observed injections into the outer radiation belt. We report on cases that indicate there was a sufficient source of up to >1 MeV electrons in the electron injections in the plasma sheet as observed by MMS, yet Van Allen Probes did not see those energies injected inside of geosynchronous orbit.  From global insight with recent test-particle simulations in global, dynamic magnetospheric fields, we offer an explanation for why the highest-energy electrons might not be able to inject into the outer belt even while the lower energy (< ~300 keV) electrons do. Two other intriguing points that we will discuss concerning these results are: i) what acceleration mechanism is capable of producing such abundance of relativistic electrons at such large radial distances (X-GSE < -10 RE) in Earth’s magnetotail? and ii) during what conditions (if any) might injections of relativistic electrons be able to penetrate into the outer belt?

How to cite: Turner, D., Cohen, I., Sorathia, K., Ukhorskiy, S., Reeves, G., Ripoll, J.-F., Gabrielse, C., Fennell, J., and Blake, J. B.: Substorm Injections as a Source of Relativistic Electrons in Earth’s Outer Radiation Belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5801, https://doi.org/10.5194/egusphere-egu2020-5801, 2020.

Low frequency (LF) ~22 Hz to 200 Hz plasmaspheric hiss was studied using a year of Polar
plasma wave data occurring during solar cycle minimum. The waves are found to be most intense in the noon and early dusk sectors. When only the most intense LF (ILF) hiss was examined, they are found to be substorm dependent and most prominent in the noon sector. The noon sector ILF waves were also determined to be independent of solar wind ram pressure. The ILF hiss intensity is independent of magnetic latitude. ILF hiss is found to be highly coherent in nature. ILF hiss propagates at all angles relative to
the ambient magnetic field. Circular, elliptical, and linear/highly elliptically polarized hiss have been detected, with elliptical polarization the dominant characteristic. A case of linear polarized ILF hiss that occurred deep in the plasmasphere during geomagnetic quiet was noted. The waveforms and polarizations of ILF hiss are similar to those of intense high frequency hiss. We propose the hypothesis that ~10–100 keV substorm injected electrons gradient drift to dayside minimum B pockets close to the magnetopause to generate LF chorus. The closeness of this chorus to low altitude entry points into the plasmasphere will minimize wave damping and allow intense noon‐sector ILF hiss. The coherency of ILF hiss leads the authors to predict energetic electron precipitation into the midlatitude ionosphere and the electron slot formation during substorms. Several means of testing the above hypotheses are discussed.
 
References
[1] Tsurutani, B.T., S.A. Park, B.J. Falkowski, J. Bortnik, G.S. Lakhina, A. Sen, J.S. Pickett, R. Hajra, M. Parrot, and P. Henri (2020), Low frequency (f < 200 Hz) Polar plasmasheric hiss: Coherent and intense, J. Geophys. Res. Spa. Phys., in press. 

How to cite: Tsurutani, B., Park, S. A., Pickett, J., Lakhina, G., and Sen, A.: The Detection and Consequences of Coherent Electromagnetic Plasma Waves: Prediction of Rapid L = 2-3 Electron Slot Formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2729, https://doi.org/10.5194/egusphere-egu2020-2729, 2020.

Substorms are a highly dynamic process that results in the global redistribution of energy within the magnetosphere. The occurrence of a substorm can provide the inner magnetosphere with hot ions and consequently intensify the ring current population. However, substorms are a highly variable phenomenon that can occur as an isolated event or as part of a sequence. In this study we investigate how substorms shape the energy content, anisotropy, and storm time behaviour of the ring current population.

Using ion observations (H+, O+, and He+) from the RBSPICE and HOPE instruments onboard the Van Allen Probes, we quantify how the total ring current energy content and ring current anisotropy changes during the substorm process. A statistical analysis demonstrates the impact of a typical substorm energises the ring current by 12% on average. The features of the energy enhancement correlate well with the expected properties of particle injections into the inner magnetosphere, and large enhancements in the O+ contribution to the energy content suggest important compositional variations.

Analysis also shows that the ring current ions experience significant isotropisation following substorm onset. Although previously attributed to enhanced EMIC wave activity, a consideration of different drivers of the isotropisation identifies that although EMIC wave activity plays a role, the properties of the injected and convected population is the dominant driver.

Finally, we explore the storm time variations of the ring current, revealing important information on the role of substorms in storm dynamics. A superposed epoch analysis of ring current energy content shows large enhancements particularly in the premidnight sector during the main phase, and a reduction in both local time asymmetry and intensity during the recovery phase. A comparison with estimated energy content using the Sym-H index was conducted. In agreement with previous results, the Sym-H index significantly overestimates energy content. A new finding is an observed temporal discrepancy, where estimates maximise ~ 12 hours earlier than the in-situ observations. We assert that an observed enhancement in substorm activity coincident with the Sym-H recovery is responsible. The results highlight the drawbacks of ring current indices and emphasise the impacts of substorms on the ring current population.

How to cite: Sandhu, J., Rae, J., Walach, M.-T., Watt, C., Freeman, M., Gkioulidou, M., Forsyth, C., Reeves, G., Spence, H., Hartley, D., Meredith, N., and Ross, J.: The Impacts of Substorms on the Ring Current, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18091, https://doi.org/10.5194/egusphere-egu2020-18091, 2020.

Particle injections transport particles from the Earth’s magnetotail to the inner magnetosphere. During this process, ions in the injections are substantially energized. The physical processes behind this energization are still under debate. Recent results from the Van Allen Probes mission at radial distances < 6 R_E have shown that higher mass ions (helium and oxygen) with high charge states are often found at substantially higher energies than protons (up to MeV energies compared to a couple hundred keV) in the inner magnetosphere. Here we present results from the Magnetospheric Multiscale (MMS) mission over a broad range of radial distances (between 7-25 R_E) where the energization of injected ions is charge state dependent. We demonstrate with these observations that injected ions exhibit behavior which is well ordered by energy per charge due to the gradient/curvature drift’s impact on particle trajectories as they drift in the direction of transient electric fields. The charge state dependent energization leads to the dominance of multiple charge state heavy ions, as opposed to H⁺, above ~250 keV throughout the Earth’s inner and middle magnetosphere. Additionally, there are also cases with hints of non-adiabatic energization observed in O⁺ between ~100-250 keV, where O⁺ potentially gets some extra-energization compared to H⁺ due differences in their respective gyroradii. However, the highest energy ions (> 300 keV oxygen and helium) are still likely of solar wind origin and primarily accelerated due to their higher charge-state. In the process of these results we demonstrate the utility of a technique for deducing ion charge-states using instrumentation that does not directly discriminate by charge state.

How to cite: Bingham, S., Cohen, I., Mauk, B., Mitchell, D., Turner, D., and Fuselier, S.: MMS Observations of the Charge State and Mass Dependent Energization of Heavy Ions During Injections in the Earth’s Magnetotail, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11657, https://doi.org/10.5194/egusphere-egu2020-11657, 2020.

Correlations between chorus waves and plasmaspheric hiss have been directly observed, leading to the proposition that the two wave modes are causally linked. Ray tracing simulations have confirmed that chorus waves can propagate into the plasmasphere and be a source of plasmaspheric hiss, but only for a specific set of initial conditions, particularly relating to the orientation of the wave vector at the chorus source. In this study, both survey and burst mode observations from the Van Allen Probes EMFISIS Waves instrument are coupled with ray tracing simulations to determine the fraction of chorus wave power that exists with the conditions required to enter the plasmasphere. In general, it is found that only a small fraction (< 2%) of chorus wave power exists with the required wave vector orientation. An exception is found when the chorus source is located close to a plasmaspheric plume. Here, azimuthal density gradients modify the wave propagation to permit a large fraction, up to 94%, of chorus wave power to access the plasmasphere. Therefore plasmaspheric plumes are identified as an important access region if a significant fraction of chorus wave power is to enter the plasmasphere and be a source of plasmaspheric hiss. To provide context, we note that plumes are most commonly observed on the dusk side whereas chorus wave power typically peak on the dawn side. The post-noon sector, where these two statistical distributions overlap, appears to be key for observing correlations between chorus and hiss. As such, particular attention is devoted to this region.

How to cite: Hartley, D. P., Chen, L., Kletzing, C., Horne, R., and Santolik, O.: The Angular Distribution of Whistler-Mode Chorus and the Importance of Plumes in the Chorus-Hiss Mechanism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-279, https://doi.org/10.5194/egusphere-egu2020-279, 2020.

Signals from man-made 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 through wave-particle interactions. These inner regions of the magnetosphere are becoming increasingly important from a satellite perspective. For instance, the newly populated Medium Earth Orbits pass though the slot region, and satellites launched via electric orbit raising are exposed to the inner belt and slot region for extended periods of time.

We have calculated diffusion coefficients associated with wave-particle interactions between radiation belt electrons and waves from each of the strongest VLF transmitters using Van Allen Probe observations. These coefficients are included into global models of the radiation belts to assess the importance of the effects of VLF transmitters individually and collectively on electron populations.

How to cite: Ross, J., Glauert, S., Horne, R., Meredith, N., and Clilverd, M.: Global models of the inner electron radiation belt and slot region investigating the effects of VLF transmitter waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4642, https://doi.org/10.5194/egusphere-egu2020-4642, 2020.

Electron scattering by chorus and hiss waves is an important mechanism that can lead to fast electron acceleration and loss in the inner magnetosphere. Making use of Van Allen Probes measurements, we present the factors found recently to affect the efficiency and control the predominance of the precipitation or acceleration regimes. The dependence of VLF waves frequency on latitude [1], so that the relative wave frequency goes down, leads to decreasing the electron scattering resonance latitudes. This provides an effective increase of wave amplitude due to whistler-mode wave amplitude distribution on latitude. High latitude wave extent and wave amplitude distribution on latitude determine the regime of scattering (higher latitudes) or acceleration (lower latitudes). Wave normal angle distribution and the existence of the significant oblique whistler population influence efficiency of electron scattering affects significantly the scattering rates and potentially shifts the wave-particle interaction regime during geomagnetic storms from mostly scattering to mostly acceleration [2]. Dynamics of plasma characteristics during disturbed periods, such as ω_pe/Ω_ce decreases (especially in the night sector) sometimes leading to very short time scales for quasi‐linear MeV electron acceleration in agreement with Van Allen Probes observations [3].  ω_pe/Ω_ce dynamics in the plasmasphere increases the efficiency of electron scattering by hiss.

References

[1] Agapitov et al. (2018) Journal of Geophysical Research, https://doi.org/10.1002/2017JA024843

[2] Artemyev et al., (2016). Space Science Reviews, https://doi.org/10.1007/s11214-016-0252-5

[3] Agapitov et al., (2019) Geophysical Research Letters, https://doi.org/10.1029/2019GL083446

How to cite: Agapitov, O., Mourenas, D., Artemyev, A., Mozer, F., and Bonnell, J.: Timescales of electrons wave-particle interactions with chorus and hiss in the outer radiation belts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12580, https://doi.org/10.5194/egusphere-egu2020-12580, 2020.

Dynamics of energetic and relativistic particles have received a lot of attention in recent years. Significant efforts have been focused on the understanding of the acceleration and loss processes of relativistic electrons and their dynamic evolution, as well as the understanding of ring-current injections in variable magnetic and electric fields. More recently, observations have been used systematically with the aid of data assimilation tools that allow to reconstruct the state of the system by blending models and various observations, and also allow to infer unknown physics and quantify various physical processes. In this study, we present an overview of recent modeling efforts with the VERB-3D and VERB-4D codes. We also show data assimilation from ring current to multi-MeV energies. We present a systematic comparative analysis of the dominant acceleration and loss processes for ring current, relativistic, and ultra-relativistic electrons and compare them. In particular, modeling and data assimilation reveal the missing physical processes at these three ranges of energies. Sensitivity simulations show that the background plasma density, location of the magnetopause, accurate description of electric and magnetic fields, and the description of the not well sampled high latitude wave environment play a crucial role for the dynamics of various electron populations in the inner magnetosphere. In summary, we present the recently funded EU Horizon 2020 project led by GFZ that will produce a chain of probabilistic modeling forecasts from the Sun to the inner magnetosphere.

How to cite: Shprits, Y., Aseev, N., Drozdov, A., Cervantes Villa, J. S., Castillo Tibocha, A. M., Zhelavskaya, I., Vasile, R., Effenberger, F., Soergel, D., Michaelis, I., and Saikin, A.: Modeling and Data Assimilation of the Ring Current, Relativistic and Ultra-relativistic Electrons in the Inner Magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3354, https://doi.org/10.5194/egusphere-egu2020-3354, 2020.

Coronal mass ejection (CME) driven sheath regions are one of the key structures driving strong magnetospheric disturbances, in particular at high latitudes. Sheaths are turbulent and compressed regions that exhibit large-amplitude magnetic field variations and high and variable dynamic pressure. They thus put the magnetosphere under particularly strong solar wind forcing. We show here the results of our recent studies that have investigated the response of inner magnetosphere plasma waves, energy and L-shell resolved outer belt electron variations and precipitation of high-energy electrons to the upper atmosphere during sheath regions. The data come primarily from Van Allen Probes and ground-based riometers. Our results reveal that sheaths drive intense “wave storms” in the inner magnetosphere (ULF, EMIC, chorus, hiss). Lower-energy electron fluxes (source and seed populations) are typically enhanced due to frequent and strong substorms injecting fresh electrons, while relativistic electrons are effectively depleted at wide L-ranges due to scattering by wave-particle interactions and magnetopause shadowing playing in concert. We found that even non-geoeffective sheaths can drive significant wave activity and dramatic changes in the outer belt electron fluxes. The “complex ejecta”, however, that consist of multiple sheaths and distorted CME ejecta can lead to sustained chorus and ULF waves, and as a consequence, effective electron acceleration to high energies. We also report some distinct characteristics in the intensity and Magnetic Local Time distribution of precipitation during sheaths when compared to other large-scale solar wind driver structures. The different precipitation responses likely stem from driver specific characteristics in their ability to excite inner magnetosphere plasma waves.

How to cite: Kilpua, E., Kalliokoski, M., Juusola, L., Grandin, M., Kero, A., Turner, D., Jaynes, A., Asikainen, T., Dubyagin, S., George, H., Hietala, H., Koskinen, H., Osmane, A., Palmroth, M., Partamies, N., Pulkkinen, T., Raita, T., Turc, L., and Vainio, R.: Differences in inner magnetospheric wave activity, outer Van Allen belt electron dynamics and atmospheric precipitation during CME sheaths and flux ropes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6034, https://doi.org/10.5194/egusphere-egu2020-6034, 2020.

Two wave packets of second harmonic poloidal Pc 4 waves with a wave frequency of ~7 mHz were detected by Van Allen Probe A at a radial distance of ~5.8 R_E and magnetic local time of 13 hr near the magnetic equator, where plasmaspheric refilling was in progress. Proton butterfly distributions with energy dispersions were also measured at the same time; the proton fluxes at 10–30 keV oscillated with the same frequency as the Pc 4 waves. Using the ion sounding technique, we find that the Pc 4 waves propagated eastward with an azimuthal wave number (m number) of ~220 and ~260 for each wave packet, respectively. Such eastward propagating high‐m (m > 100) waves were seldom reported in previous studies. The condition of drift‐bounce resonance is well satisfied for the estimated m numbers in both events. Proton phase space density was also examined to understand the wave excitation mechanism. We obtained temporal variations of the energy and radial gradient of the proton phase space density and find that temporal intensification of the radial gradient can generate the two wave packets. The cold electron density around the spacecraft apogee was >100 cm⁻³ in the present events, and hence the eigenfrequency of the Pc 4 waves became lower. This causes the increase of the m number which satisfies the resonance condition of drift‐bounce resonance for 10–30 keV protons and meets the condition for destabilization due to gyrokinetic effect.

How to cite: Yamamoto, K., Nosé, M., Keika, K., Hartley, D., Smith, C., MacDowall, R., Lanzerotti, L., Mitchell, D., Spence, H., Reeves, G., Wygant, J., Bonnell, J., and Oimatsu, S.: Eastward Propagating Second Harmonic Poloidal Waves Triggered by Temporary Outward Gradient of Proton Phase Space Density: Van Allen Probe A Observation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9575, https://doi.org/10.5194/egusphere-egu2020-9575, 2020.

It has recently been demonstrated through simulations and observations that flux oscillations of hundreds-keV electrons are produced in the magnetosphere in association with broadband Ultra Low Frequency (ULF) waves (Sarris et al., JGR, 2017). These oscillations are observed in the form of drift-periodic flux fluctuations, but are not associated with drift echoes following storm- or substorm-related energetic particle injections. They are observed in particular during quiet times, and it has been shown that they could indicate ongoing radial transport processes caused by ULF waves. It has also been shown that the width of electron energy channels is a critical parameter affecting the observed amplitude of flux oscillations, with narrower energy channel widths enabling the observation of higher-amplitude flux oscillations; this potentially explains why such features were not observed regularly before the Van Allen Probes era, as previous spacecraft generally had lower energy resolution. We extend these initial results by investigating the association between the observed flux oscillations with the amplitude of electric and magnetic fluctuations in the ULF range and with Phase Space Density gradients, both of which are expected to also affect radial transport rates.

How to cite: Li, X., Sarris, T., Temerin, M., Zhao, H., Khoo, L. Y., Turner, D., Liu, W., and Claudepierre, S.: Observations and simulations of electron flux oscillations in response to broadband ULF waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22404, https://doi.org/10.5194/egusphere-egu2020-22404, 2020.

Wave-particle interactions play a key role in radiation belt dynamics. Traditionally, Ultra-Low Frequency (ULF) wave-particle interaction is parameterised statistically by a small number of controlling factors for given solar wind driving conditions or geomagnetic activity levels. Here, we investigate solar wind driving of ultra-low frequency (ULF) wave power and the role of the magnetosphere in screening that power from penetrating deep into the inner magnetosphere. We demonstrate that, during enhanced ring current intensity, the Alfvén continuum plummets, allowing lower frequency waves to penetrate deeper into the magnetosphere than during quiet periods. With this penetration, ULF wave power is able to accumulate closer to the Earth than characterised by statistical models. During periods of enhanced solar wind driving such as coronal mass ejection driven storms, where ring current intensities maximise, the observed penetration provides a simple physics-based reason for why storm-time ULF wave power is different compared to non-storm time waves. We demonstrate statistically that the ring current plays a pivotal role in allowing ULF wave energy to access the inner magnetosphere and show a new parameterisation of ULF wave power for radiation belt research purposes that is specifically tuned for geomagnetic storms.

How to cite: Rae, J., Murphy, K., Watt, C., Sandhu, J., Wharton, S., Degeling, A., Georgiou, M., Forsyth, C., Bentley, S., Staples, F., and Shi, Q.: Understanding the controlling factors of Ultra-Low Frequency waves and their penetration during geomagnetic storms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11063, https://doi.org/10.5194/egusphere-egu2020-11063, 2020.

Probabilistic modelling is used heavily in weather and climate models to accurately represent the full range of possible physical states, thereby improving forecasts and capturing the uncertainty inherent in a complex system. Here, we begin to apply probabilistic modelling to ULF waves. Eventually, we aim to better determine the impact of ULF waves on Earth’s radiation belts; by representing the full probability distribution of radial diffusion coefficients we will represent physical reality more faithfully than solely using the mean or median.

However, to construct such a model, we first need to determine the probability distributions of the radial diffusion coefficient, which varies with the power in the underlying ULF waves. Therefore we present an analysis of the distributions of wave power spectral density for both ground-based magnetometers (CARISMA) and the corresponding in situ observations. We compare these distributions, examine the relationships between them and comment on the new physical insights this probabilistic approach reveals. Differences between distributions seen on the ground and in space give us new insights into the generation and propagation of ULF waves in the magnetosphere. We comment on the consequences of these types of distributions for probabilistic modelling. We also discuss how these distributions change with the driving solar wind; in particular, whether upper and lower bounds of power at the ground determined by the solar wind are seen in space. These bounds may indicate a limit to the ability of the magnetosphere to support ULF waves, and therefore limits on the resulting radial diffusion.

How to cite: Bentley, S., Watt, C., and Thompson, R.: Probabilistic ULF models: how do they improve our understanding of the physics?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5642, https://doi.org/10.5194/egusphere-egu2020-5642, 2020.

Using data from the NASA Mars Atmosphere and Voltatile EvolutioN (MAVEN) and ESA Mars Express spacecraft, we show that transient phenomena in the foreshock and solar wind can directly inject energy into the ionosphere of Mars. We demonstrate that the impact of compressive Ultra-Low Frequency (ULF) waves in the solar wind on the induced magnetospheres drive compressional, linearly polarized, magnetosonic ULF waves in the ionosphere, and a localized electromagnetic "ringing" at the local proton gyrofrequency. The pulsations heat and energize ionospheric plasmas. A preliminary survey of events shows that no special upstream conditions are required in the interplanetary magnetic field or solar wind. Elevated ion densities and temperatures in the solar wind near to Mars are consistent with the presence of an additional population of Martian ions, leading to ion-ion instablities, associated wave-particle interactions, and heating of the solar wind. The phenomenon was found to be seasonal, occurring when Mars is near perihelion. Finally, we present simultaneous multipoint observations of the phenomenon, with the Mars Express observing the waves upstream, and MAVEN observing the response in the ionosphere. When these new observations are combined with decades of previous studies, they collectively provide strong evidence for a previously undemonstrated atmospheric loss process at unmagnetized planets: ionospheric escape driven by the direct impact of transient phenomena from the foreshock and solar wind.

How to cite: Collinson, G., Wilson III, L., Omidi, N., Sibeck, D., Espley, J., Fowler, C., Mitchell, D., Grebowsky, J., Mazelle, C., Ruhunusiri, S., Halekas, J., Jakosky, B., and Harada, Y.: Solar Wind induced waves in the skies of Mars: Ionospheric compression, energization, and escape resulting from the impact of ultra-low frequency magnetosonic waves generated upstream of the Martian bow shock, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1966, https://doi.org/10.5194/egusphere-egu2020-1966, 2020.

The Earth’s electron radiation belts are a dynamic environment and can change dramatically on short timescales. From Van Allen Probes observations, we see storm time drop-out events followed by a rapid recovery of the electron flux over a broad range of energies. Substorms can supply a seed population of new electrons to the radiation belt region, which are then energised by a number of processes, rebuilding the belts. However, how the electron flux is replenished across energy space, and the sequence of events leading to flux enhancements, remains an open question. Here we use a 3-D radiation belt model to explore how the seed population is accelerated to 1 MeV on realistic timescales, comparing the output to Van Allen Probes observations. By using a low energy boundary condition derived by POES data we encompass the whole radiation belt region, employing an open outer boundary condition. This approach isolates the contribution of seed population changes and allows electron flux variations over a broad range of L* to be studied. Using the model, we explore the contribution of both local acceleration and radial diffusion and demonstrate that the timing and duration of these two processes, particularly in relation to one another, is important to determine how the radiation belt rebuilds.

How to cite: Allison, H., Shprits, Y., Glauert, S., Horne, R., and Wang, D.: Modelling the Rebuilding the Radiation Belt Following a Drop-out Event from Acceleration of the Seed Population, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18264, https://doi.org/10.5194/egusphere-egu2020-18264, 2020.

Local acceleration driven by whistler-mode chorus waves is fundamentally important for the acceleration of seed electrons in the outer radiation belt to relativistic energies. Τhis mechanism strongly depends on substorm activity and on the source electron population injected by the substorms into the inner magnetosphere. In our work we use Van Allen Probes data to investigate the features of source electrons, seed electrons and chorus waves for events of enhancement versus events of depletion of relativistic electrons in the outer Van Allen belt. To that end we calculate the electron phase space density (PSD) for five values of the first adiabatic invariant corresponding to source and seed electrons, and we perform a superposed epoch analysis of 28 geomagnetic disturbance events, out of which, 20 result in enhancement and 8 in depletion of relativistic electron PSD. Our results indicate that events resulting in significant enhancement of relativistic electron PSD in the outer radiation belt are characterized by statistically stronger and more prolonged storm and substorm activity, leading to more efficient injections of source but mostly seed electrons to the inner magnetosphere, and also to more pronounced and long-lasting chorus and Pc5 wave activity. The effect of these parameters in the acceleration of electrons seems to be determined by the abundance of seed electrons at the region of L*=4-5.

How to cite: Nasi, A., Daglis, I. A., Katsavrias, C., and Li, W.: Association of chorus waves and source/seed electrons with the enhancement of relativistic electrons in the outer Van Allen belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1014, https://doi.org/10.5194/egusphere-egu2020-1014, 2020.

Energetic Electron Precipitation (EEP) associated with substorm injections typically occurs when magnetospheric waves, particularly whistler-mode waves, resonantly interact with electrons to affect their equatorial pitch angle. This can be considered as a diffusion process that scatters particles into the loss cone. In this study, we investigate whistler-mode wave generation in conjunction with electron injections using in-situ wave measurements by the Themis mission. We calculate the pitch angle diffusion coefficient exerted by the observed wave activity using the quasi-linear diffusion approximation and estimate scattering efficiency in the substorm injection region to constrain where and how much scattering happens typically during these events.

How to cite: Ghaffari, R. and Cully, C.: Statistical Study of Pitch Angle Diffusion during Substorm Injections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12266, https://doi.org/10.5194/egusphere-egu2020-12266, 2020.

Proton and electron spectra in the plasma sheet usually consist of spectral core and high energy tail. These two populations are formed by different processes, driven by the various combinations of the solar wind parameters.These processes include different time delays and may act differently on protons or electrons. In this work we evaluate empirically the magnitude and the time delay of the impact of different solar wind parameter combinations on the protons and electrons with energies (30-300 keV) and reveal the mechanisms behind these impacts. To do this we build a model of the fluxes at different energy channels in the transition region (nightside central plasma sheet between 6 and 15 Re) for the THEMIS spacecraft observations in 2007-2018. We use normalized values of solar wind parameter combinations (incl. speed, density, pressure, electric field, etc) as inputs of the model, with regression coefficients indicating their impact magnitudes. We investigate different time delays up to 16 hours. The model obtained shows that protons and electrons are controlled differently by solar wind parameters: dynamic pressure is important for protons, whereas solar wind speed and VBs are important for electrons. Larger time delays are required to describe higher energy electron fluxes.

How to cite: Nikita, S., Sergeev, V., Sormakov, D., Dubyagin, S., and Runov, A.: Proton and electron fluxes in the plasma sheet transition region and their dependence on the solar wind parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6892, https://doi.org/10.5194/egusphere-egu2020-6892, 2020.

Plasma injections from Earth’s magnetotail to high-latitude ionosphere pro-
vided by substorm activity are known to play a key role in the MeV-electron
acceleration mechanism by resonating interaction of very-low-frequency (VLF)
chorus waves with seed electrons. On the other hand, non-adiabatic motion
of plasma-sheet protons related to current sheet scattering (CSS) causes pitch-
angle diffusion and precipitation to the ionosphere, inducing the formation of
a characteristic energy-latitude dispersion pattern at the equatorward side of
the auroral isotropy boundary (IB), which gets significantly altered during geo-
magnetic storms due to particle precipitation triggered by electromagnetic ion
cyclotron (EMIC) waves.
For these last two years, a moderate geomagnetic storm activity has been affect-
ing the Earth’s environment, with the notable case of Aug 2018 G3-class storm.
The effects of such disturbances - especially in case of prolonged substorm ac-
tivity during the recovery phase - have been clearly spotted by the entire suite
of detectors on board the China Seismo-Electromagnetic Satellite (CSES-01), a
low-Earth-orbit (LEO) mission launched on Feb 2, 2018.
Here, we present long-term storm-time observations by particle, e.m.-field, and
plasma instrumentation on board CSES-01, namely the High-Energy Particle
Detector (HEPD), the Electric Field Detector (EFD), and the High Precision
Magnetometer (HPM), either developed or data-validated by the Italian LI-
MADOU Collaboration. Thanks to magnetosphere-to-ionosphere mapping, re-
sults from HEPD, EFD, and HPM data analysis help track substorm plasma
injections and consequent magnetosphere re-arrangement on a statistical basis.
This further inscribes CSES-01 into the thematic area of space-weather and
space-climate exploration and modeling, which is especially important in a pe-
riod when many key space-weather instruments have been quit or operate well
beyond the end of their scheduled lifetimes.

How to cite: Parmentier, A., Martucci, M., Piersanti, M., and CSES-Limadou Collaboration, T.: CSES monitoring of the interplay between current-sheet and EMIC-wave driven scattering as a proxy of substorm activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2330, https://doi.org/10.5194/egusphere-egu2020-2330, 2020.

The ionosphere is greatly influenced by ionizing radiation including both electromagnetic flux and energetic particles. The ionosphere is immersed in a magnetic field and the interactions of radio waves with the ionosphere are complex and exhibit the following properties: anisotropy, absorption, dispersion, birefringent. The ionospheric effects on radiowave systems depend upon the focus of the treatment. The development of inhomogeneous electron density structures is responsible for radiowave signal fluctuations. A comprehensive treatment of radiowaves propagation in the ionospheric plasma is based on the investigation of the statistical moments of both amplitude and phase fluctuations of scattered radiation. In this paper analytical calculations of the statistical characteristics in the conductive collision magnetized ionospheric plasma have been carried out for the first time using the complex geometrical optics approximation. Stochastic wave equation of the phase fluctuations includes both dielectric permittivity and conductivity tensors which are random functions of the spatial coordinates and time. Using the boundary conditions correlation function of the phase fluctuations has been obtained for arbitrary second order statistical moment of electron density fluctuations (large and small ionospheric plasmonic structures); observation points are spaced at small distance. The index of refraction contains both ordinary and extraordinary waves. Angular power spectrum (broadening, shift of its maximum) of scattered electromagnetic waves is investigated. It was shown that Hall’s, Pedersen, and longitudinal conductivities have a substantial influence on the frequency fluctuation of an incident wave. Doppler spread associated with random ionospheric structure, and Doppler shifts associated with relative motion of the ray path with respect to the elongated plasmonic structures. Spatial-temporal broadening of the spatial spectrum depends on the anisotropy factor of elongated plasma irregularities, inclination angle with respect to the lines of forces of geomagnetic field, collision frequency between plasma particles, conductivity fluctuations, and the movement of ionospheric plasmonic irregularities. Shift of the spectral maximum changes the sign depending on the anisotropy factor of elongated plasma irregularities, inclination angle with respect to the lines of forces of geomagnetic field and conductivity fluctuations. Numerical calculations and spatial-temporal modeling are carried out for both large and small-scale ionospheric plasma irregularities using experimental data and experimentally observing power-law spectrum of electron density fluctuations. The obtained results are useful for solving the reverse problem restoring plasma parameters, in satellite communication and navigation systems that operate in the earth-space regime. The influence of the conductivity fluctuations on the second order statistical moments will open new horizons in understanding and forecasting new phenomena in the upper ionosphere caused due to spatial-temporal parameters fluctuations.

How to cite: Jandieri, G., Ishimaru, A., and Pistora, J.: Second order statistical moments of scattered electromagnetic waves in the conductive magnetized ionospheric plasma, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1284, https://doi.org/10.5194/egusphere-egu2020-1284, 2020.

Since 2000 the four Cluster spacecraft have crossed the Earth's plasmasphere along a polar orbit every 2.5 days, with various perigee altitudes (from 1.5 to 4 R_E), different configurations (string of pearls, tetrahedron) and changing separations (from 10 to 100 000 km). The resulting dataset allows different types of inner magnetosphere studies and provides insight in plasmasphere dynamics, including changes in plasmapause position. Plasmaspheric plumes can also be studied on a case-by-case basis, in a statistical manner and in relation with wave activity (EMIC, electromagnetic rising tone, whistler waves).

Moreover, data from an old mission, Dynamics Explorer-1, have recently become available. In particular, densities and temperatures for many ions (H⁺, He⁺, He⁺⁺, O⁺, and O⁺⁺) have been derived from the RIMS (Retarding Ion Mass Spectrometer) instrument and are available from October 1981 to January 1985. Such composition data, not available from the Cluster satellites, allow in particular to analyze the distributions of those ions in the plasmasphere boundary layer, as a function of magnetic local time and geomagnetic activity.

Finally, since 2012, the two Van Allen Probes satellites are orbiting the inner magnetosphere in the magnetic equatorial plane and with a low perigee, allowing a crossing of the plasmasphere every 9 hours. The EMFISIS (Electric and Magnetic Field Instrument Suite and Integrated Science) instrument onboard both spacecraft can determine the electron density in a very large density range (up to 3000 cm^-3) using several methods. This gives a different opportunity to analyze the plasmapause and plasmaspheric plumes from a different perspective.

How to cite: Darrouzet, F., De Keyser, J., Décréau, P., Gallagher, D., Verbanac, G., and Bandic, M.: Plasmasphere observations with Cluster data supplemented with data from the Dynamics Explorer-1 and Van Allen Probes missions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18386, https://doi.org/10.5194/egusphere-egu2020-18386, 2020.

Frequency-latitude plots of electromagnetic wave intensity in the very low frequency range (VLF, up to about 20 kHz) observed by the low altitude DEMETER spacecraft are analyzed. Apart from electromagnetic waves generated by plasma instabilities in the magnetosphere, a significant portion of the detected wave intensity comes from ground-based lightning activity and VLF military transmitters. These whistler mode waves are observed not only close to source locations, but also close to their geomagnetically conjugated points. There appears to be an upper frequency limit of such emissions, where the wave intensity substantially decreases. Its frequency roughly corresponds to half of the equatorial electron cyclotron frequency at a respective magnetic field line, suggesting a relation to wave ducting in ducts with enhanced density. However, it seems to exhibit a non-negligible longitudinal dependence and it is different during the day than during the night. We use a realistic model of the Earth’s magnetic field to explain the observed variations. We interpret the observations in terms of ducted/unducted wave propagation, and we compare the wave intensities in the source hemisphere with those measured in the hemisphere geomagnetically conjugated.

How to cite: Nemec, F., Santolík, O., and Parrot, M.: On the upper frequency limit of whistler mode waves observed by low-altitude spacecraft, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2432, https://doi.org/10.5194/egusphere-egu2020-2432, 2020.

The Space Application of Timepix Radiation Monitor (SATRAM) on board the Proba-V satellite of the European Space Agency (ESA) was launched in May 2013 into a sun-synchronous orbit with an altitude of about 820 km. This technology demonstration payload is based on the Timepix technology developed by the CERN-based Medipix2 Collaboration. It is equipped with a 300 um thick silicon sensor with a pixel pitch of 55 um in a 256 x 256 pixel matrix. The device is sensitive to X-rays and all charged particles. A Monte Carlo simulation was conducted to determine the detector response to electrons (0.5–7 MeV) and protons (10–400 MeV) taking into account the shielding of the detector housing and the satellite. With the help of the simulation, a strategy was developed to estimate omnidirectional electron, proton, and ion fluxes around Earth using stopping power, maximum energy deposition per pixel of the particle track, and the shape of the particle tracks in the sensor. Presented are typical overall dose rates as well as fluxes of individual particle species. A superposed epoch analysis is used to analyze variations of particle fluxes related to geomagnetic storms and interplanetary shock arrivals as a function of time and L-shell.

How to cite: Gohl, S., Němec, F., Bergmann, B., and Pospíšil, S.: Energetic particle flux variations detected at low altitudes by Space Application of Timepix Radiation Monitor (SATRAM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2435, https://doi.org/10.5194/egusphere-egu2020-2435, 2020.

Earth’s radiation belts comprise complex and dynamic systems, depending substantially on solar activity. The pitch angle distributions (PADs) play an important role for radiation belts modelling, as they yield information on the particle transport, source and loss processes. Yet, many missions flying in the radiation belts provide omni-directional or uni-directional electron flux measurements and do not resolve pitch angles. We propose an empirical model of the equatorial PADs and a method to retrieve PADs from omni-directional flux measurements at different energies and locations along the inclined orbits. We use the entire dataset of MagEIS and REPT instruments aboard the Van Allen Probes (RBSP) mission to analyze the equatorial pitch angle distributions in the energy range from 30 keV to 6.2 MeV. The fitting method resolves all main types of PADs, including butterfly and cap distributions, and the resulting coefficients are directly related to the PAD shapes. The developed model can be used to obtain pitch angle resolved fluxes for GPS, Arase and other missions. The proposed algorithm is applied to the GPS electron flux data set to obtain the pitch-angle resolved fluxes, which are compared to the RBSP data at a number of GPS-RBSP conjunctions. The proposed model also allows one to reconstruct the pitch-angle resolved data using LEO measurements. The dynamics of the fitting coefficients based on solar activity is discussed with respect to AE, Kp, Dst indices and solar wind parameters: velocity, density and dynamic pressure.

How to cite: Smirnov, A., Shprits, Y., Allison, H., and Aseev, N.: Equatorial pitch angle distributions in Earth's radiation belts: an empirical model from Van Allen Probes data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11503, https://doi.org/10.5194/egusphere-egu2020-11503, 2020.

Based on data from the Van Allen Probes and ZH-1 satellites, relativistic electron enhancements in extremely low L-shell Regions (reaching L~3) were observed during major geomagnetic storm (minimum Dst`-190 nT).  Contrary to what occurs in the outer belt, such an intense and deep electron penetration event is rare and more interesting. Strong whistler-mode (chorus and hiss) waves, with amplitudes 81-126 pT, were also observed in the extremely low L-shell simultaneously (reaching L~2.5) where the plasmapause was suppressed. The bounce-averaged diffusion coefficient calculations support that the chorus waves can play a significantly important role in diffusing and accelerating the 1-3 MeV electrons even in such low L-shells during storms. This is the first time that the electron acceleration induced by chorus waves in the extremely low L-shell region is reported. This new finding will help to deeply understand the electron acceleration process in radiation belt physics.

How to cite: Zhang, Z., Chen, L., Liu, S., Xiong, Y., Li, X., and Shen, X.: Chorus acceleration of relativistic electrons in extremely low L-shell during geomagnetic storm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2055, https://doi.org/10.5194/egusphere-egu2020-2055, 2020.

The last decade has shown the prime importance of wave-particle interaction for the accurate modelling of the dynamics of energetic electrons trapped in the Earth’s radiation belts, as well as for other planets, such as Jupiter or Saturn. They have been therefore added in the sum of physical processes modeled in radiation belt codes such as Salammbô, with conclusive results. However, this upgrade of the physical representation is not straightforward and comes at the price of degrading the numerical resolution. In particular, computational instabilities and odd phase space density profiles are observed, impacting the code’s accuracy and its physical relevance. This challenging issue requires the development of a numerical scheme which supports in particular wave-particle cross diffusion terms. Thus, we will present in this talk the new dedicated numerical scheme we have developed and implemented in Salammbô. Then we will focus on quantifying the effect of wave-particle cross diffusion terms on the dynamics of highly energetic trapped electrons, in presenting results for real case storms.

How to cite: Dahmen, N., Maget, V., and Rogier, F.: Evaluating the effect of wave-particle cross diffusion in radiation belts modelling using an innovative and robust numerical scheme, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3562, https://doi.org/10.5194/egusphere-egu2020-3562, 2020.

The flux of highly energetic electrons in the outer radiation belt show a high variability during geomagnetically disturbed conditions. Wave-particle interaction with VLF chorus waves play a significant role in the flux variation of these particles, and quantification of the effects from these interactions is crucially important for accurately modeling the global dynamics of the outer radiation belt and for providing a comprehensive description of electron flux variations over a wide energy range (from the source population of keV electrons to the relativistic core population of the outer radiation belt).  In this study, we use the synthetic model based on the combined database from the Van Allen Probes and Cluster spacecraft VLF measurements (including the recent findings of wave amplitude dependence on geomagnetic latitude, wave normal angle distribution, and variations of wave frequency with latitude) to develop a comprehensive parametric model of electron lifetime in the outer radiation belt as a function of geomagnetic activity, L-shell, and magnetic local time. Results show high local scattering rates during moderate and active conditions, local scattering is higher on the dawn and night side compared to day side, and electron lifetime is short during active conditions. 

How to cite: Aryan, H., Agapitov, O., Artemyev, A., Balikhin, M., Mourenas, D., and Boynton, R.: The model of outer radiation belt electron lifetimes based on combined Van Allen Probes and Cluster VLF wave measurements , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18676, https://doi.org/10.5194/egusphere-egu2020-18676, 2020.

This research develops forecast models of the spatiotemporal evolution of emissions throughout the inner magnetosphere between L=2-6 and at all MLT. The system identification, or machine learning, technique based on Nonlinear AutoRegressive Moving Average eXogenous (NARMAX) models is employed to deduce the forecasting models of the lower band chorus, Hiss, and magnetosonic waves using solar wind and geomagnetic indices as inputs. It is difficult to develop machine leaning based spatiotemporal models of the waves in the inner magnetosphere as the data is sparse and machine learning techniques require large amounts of data to deduce a model. To solve this problem, the spatial co-ordinates at the time of the measurements are included as inputs to the model along with time lags of the solar wind and geomagnetic indices, while the measurement of the waves by the Van Allen Probes are used as the output to train the models. The estimates of the resultant models are compared with separate data to the training data to assess the performance of the models. The models are then used to reconstruct the spatiotemporal waves over the inner magnetosphere, as the waves respond to changes in the solar wind and geomagnetic indices.  

How to cite: Boynton, R., Aryan, H., Simon, W., and Balikhin, M.: System identification models for waves in the inner magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16544, https://doi.org/10.5194/egusphere-egu2020-16544, 2020.

In situ measurements of electron scale fluctuations by the Van Allen Probes and MMS have demonstrated the ubiquitous occurrence of phase-space holes and various kinetic nonlinear structures in the Earth's magnetosphere. However it remains an open question whether phase-space holes have to be incorporated into global magnetospheric models describing the energisation and acceleration of electrons. In this communication we will review current wave-particle models of electron phase-space holes interacting with energetic electrons (e.g. >1 keV in the Earth's radiation belts)  and present new theoretical results showing that finite correlation times of phase-space holes results in enhanced pitch-angle scattering. The pitch-angle scattering by phase-space holes is shown to be on par with that produced by chorus waves, and in some instances outgrows the chorus contribution. 

How to cite: Osmane, A.: Effect of finite correlation time on the wave-particle interactions of nonlinear electrostatic structures with electrons in the Earth's radiation belts., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21856, https://doi.org/10.5194/egusphere-egu2020-21856, 2020.

We compare the simultaneous magnetometer, SuperDARN radar, and GPS observations during Pc5 wave event on March 02, 2002. A possible correspondence between those instruments may help to determine the mechanism of the ionosphere modulation by magnetospheric disturbances. Transient Pc5 pulsations (2.6 mHz) in the morning sector, stimulated by the solar wind density jumps, have been detected simultaneously by ground magnetometers and the Kodiak and King Salmon SuperDARN radars.  Besides that, pulsations with the same periodicity have been found in the rate of total electron content (TEC), dTEC/dt (ROT), variations in several GPS radio paths. The ratio between the spectral amplitudes of the Doppler velocities and magnetic pulsations (X component) on the ground are Vx/Bx~7-12 (m/s)/nT and Vy/Bx~27 (m/s)/nT. The ratio between the oscillation amplitudes of ROT and ionospheric Doppler meridional (Vx) and azimuthal (Vy) velocities are ROT/Vx~0.02-0.07 (dTECu/min)/(m/s) and ROT/Vy~0.004 (dTECu/min)/(m/s). The correspondence between simultaneous periodic variations of the ionospheric Doppler velocity and geomagnetic field can be reasonably well interpreted quantitively on the basis of theory of Alfven wave interaction with the thin ionospheric layer. However, order-of-magnitudes estimates of possible TEC modulation mechanisms show that a responsible mechanism which can interpret the observed ratios has not been found yet. 

How to cite: Pilipenko, V., Kozyreva, O., Bland, E., and Baddeley, L.: Periodic modulation of the upper ionosphere by ULF waves as observed by SuperDARN radars and GPS/TEC technique, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2039, https://doi.org/10.5194/egusphere-egu2020-2039, 2020.

A midlatitude coherent decameter radar installed near Ekaterinburg, Russia (EKB radar) has been operating since 2012. It is aimed at monitoring dynamics of the ionosphere–magnetosphere system in Eastern Siberia. A special operation mode is used at the radar to study ULF wave activity: three adjacent beams oriented approximately along the magnetic meridian are surveyed with time resolution of 18 s each. A number of wave observation events registered with the radar was analyzed and discussed in several papers. An overview of the main results from these studies is presented here.

A statistical study of more than 30 waves observed in the nightside ionosphere revealed that in the majority of the cases their frequencies are considerably lower than those of field line resonance (FLR) for appropriate magnetic shells and longitudinal sectors (FLR fundamental frequencies for each case were estimated based on spacecraft data). Thus, these waves cannot be associated with the Alfvén mode. It was assumed that at least part of them should be identified with the drift compressional mode. Indeed, in individual cases oscillations exhibited signatures of this mode: in one of the events a linear dependence of frequency on azimuthal wave number m at a fixed magnetic shell was found. Only the drift compressional mode can feature such dependence in the inner magnetosphere. For two other cases merging of drift compressional and Alfvén modes at some critical value of m was shown. A case of simultaneous spacecraft and radar wave observation accompanied by increases in energetic particle fluxes was shown. A modulation with the frequency of this wave was found for flux intensity of those energetic protons, whose phase velocity is close to that of the wave. This implies that the source of the wave was a drift resonance with the substorm injected protons.

How to cite: Chelpanov, M., Mager, O., Mager, P., and Klimushkin, D.: ULF waves registered with the Ekaterinburg radar: Statistical analysis and case studies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6901, https://doi.org/10.5194/egusphere-egu2020-6901, 2020.

The GOES-16 spacecraft, launched in November 2016, is the first of the GOES-R series next generation NOAA weather satellites. The spacecraft has a similar suite of space weather instruments to previous GOES satellites but with improved magnetometer sampling rate and wider energy range of particle flux observations. Presented are observations of simultaneously occurring Pc 4/5 ULF waves and electromagnetic ion cyclotron (EMIC) waves with a discussion on the relationship between the two wave modes including possible generation mechanisms. The waves were also observed in the particle data and we discuss both adiabatic and non-adiabatic wave-particle effects. Relativistic electron fluxes showed strong adiabatic motion with the magnetic field ULF waves. Estimates of Pc 4/5 ULF wave m-numbers suggest they were high, while ring current energy ion fluxes showed ULF variations with non-zero phasing relative to magnetic field ULF wave. This suggests ULF wave drift resonance with ring current ions. In one event we observed EMIC variations in the ion fluxes around energies that can drift resonate with simultaneously observed Pc 5 waves, suggesting that one particle population may be responsible for generating and/or modifying both observed Pc 5 and EMIC waves. ULF variations were also observed in electron/ion fluxes at lower energies down to 30 eV. We looked into ULF bounce resonance with 30 eV electrons, but the resonance condition did not match the observations. We will also discuss future plans to expand this study of ULF waves and wave-particle interactions using the two newest GOES satellites.

How to cite: Loto'aniu, P.: Observations of simultaneously occurring ULF and Ion Cyclotron Waves by the GOES-16 satellite magnetometer and particle detectors at geostationary orbit, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6164, https://doi.org/10.5194/egusphere-egu2020-6164, 2020.

We use  multipoint magnetic field, plasma  and particle observations to study the spatial, temporal  and spectral characteristics of Pc 4-5 pulsations   observed  in the recovery phase of a strong magnetic storm on January 1, 2016.   The magnetosphere was compressed and periodic increases of the total magnetic field strength occurred every 20-40 min at the times of generation of the pulsations.  The frequencies of the Pc4 pulsations varied  from 14 mHz to 25 mHz with radial distance. An explanation for this behavior can be given in terms of standing Alfvén waves along resonant field lines.  By contrast, Fourier analysis of the magnetic field observations  shows that the compressional  Pc5 pulsations  exhibited  similar spectra at different radial distances.  The long duration of the Pc5 pulsations and their nearly constant frequencies indicate that the plasma conditions in the morning sector of magnetosphere were stable for more than two hours.  The Pc4 and Pc5   pulsations displayed wave properties consistent with the second harmonic waves. The energetic particles   observed by Van Allen Probes and GOES 15  exhibited  a regular periodicity over a  broad range of energies from tens of eV to 2 MeV  with periods  corresponding to  those of the compressional component   of the  ULF magnetic field.   We searched for possible solar wind triggers and discussed generation mechanisms for the compressional Pc5 pulsations  in terms of drift mirror instability and  drift bounce resonance. 

How to cite: Korotova, G., Sibeck, D., and Engebretson, M.: Multipoint observations of spatial and temporal characteristics of Pc 4-5 pulsations in the dayside magnetosphere and particle signatures. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20948, https://doi.org/10.5194/egusphere-egu2020-20948, 2020.

We studied O⁺drift-bounce resonance using Magnetospheric Multiscale (MMS) data. A case study of an event on 17 February 2016 shows that O⁺ flux oscillations at ~10–30 keV occurred at MLT ~ 5 hr and L~ 8–9 during a storm recovery phase. These flux oscillations were accompanied by a toroidal Pc5 wave and a high-speed solar wind (~550 km/s). The azimuthal wave number (m-number) of this Pc5 wave was found to be approximately –2. The O⁺/H⁺ flux ratio was enhanced at ~10–30 keV corresponding to the O⁺ flux oscillations without any clear variations of H⁺ fluxes, indicating the selective acceleration of O⁺ ions by the drift-bounce resonance. A search for the similar events in the time period from September 2015 to March 2017 yielded 12 events. These events were mainly observed in the dawn to the afternoon region at L~ 7–12 when the solar wind speed is high, and all of them were simultaneously identified on the ground, indicating low m-number. Correlation analysis revealed that the O⁺/H⁺ energy density ratio has the highest correlation coefficient with peak power of the electric field in the azimuthal component (E_a). This statistical result supports the selective acceleration of O⁺ due to the N = 2 drift-bounce resonance.

How to cite: Oimatsu, S., Nosé, M., Le, G., Fuselier, S. A., Ergun, R. E., Lindqvist, P.-A., and Sormakov, D.: Selective acceleration of O+ by drift-bounce resonance in the Earth’s magnetosphere: MMS observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2832, https://doi.org/10.5194/egusphere-egu2020-2832, 2020.

How to cite: Li, B.: Magnetospheric Multiscale (MMS) Observations of ULF Waves and Correlated Low-Energy IonMonoenergetic Acceleration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6858, https://doi.org/10.5194/egusphere-egu2020-6858, 2020.

Several observational studies have shown that ULF oscillations of the solar wind dynamic pressure can drive periodic fluctuations in magnetic field measurements at corresponding frequencies. In this study, we use multi-spacecraft (Cluster, GOES, THEMIS and Van Allen Probes) mission measurements to investigate the propagation of pressure fluctuations-driven pulsations within the Pc5 and Pc4 frequency range (from ~0.5 to 25 mHz) into the magnetosphere. During intervals of slow solar wind — to exclude waves generated by velocity shear at the magnetopause — common periodicities in electromagnetic fields in the magnetosphere and the solar wind driver are first detected in Lomb-Scargle periodograms. Then, using the cross-wavelet transform, we examine the causal relationship and specifically, in cross-wavelet spectra and wavelet transform coherence. Lastly, spatial and temporal variations of wave properties are mapped from beyond the magnetopause to the inner magnetosphere through frequency, polarisation and power signatures of waves detected at the various probes. The observed dependence of wave properties on their localisation offers an excellent source for verification of the role that solar wind dynamic pressure oscillations as driver of ULF waves propagating through the magnetosheath into the dayside and nightside magnetosphere.

How to cite: Georgiou, M., Katsavrias, C., Daglis, I., and Balasis, G.: Ultra-Low Frequency (ULF) waves originating in solar wind dynamic pressure oscillations and propagating through the magnetosheath to the inner magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21129, https://doi.org/10.5194/egusphere-egu2020-21129, 2020.

Using global magnetohydrodynamic simulations we investigate the recently discovered eigenmode of the magnetopause surface – the natural response of the boundary to impulsive solar wind transients. We show that following the directly driven motion of the magnetopause by a pressure pulse, decaying oscillations of the boundary follow in agreement with theoretical predications and previous simulations of the magnetopause surface eigenmode. Across the equatorial magnetosphere these oscillations originate at the subsolar point and maintain a near-constant frequency through all local times, though into the flanks a secondary higher-frequency signal emerges consistent with the expectations of Kelvin-Helmholtz generated surface waves. Focusing only on the eigenmode shows its amplitude grows with local time away from the subsolar point, with the waves showing no azimuthal propagation in the region 9-15h MLT – surprising given the convecting effect downtail of the magnetosheath flow.  In the noon-midnight meridian the eigenmode is confined to the dayside magnetosphere. Comparing these results to MHD theory, we propose how the structure of the magnetopause surface eigenmode is determined by the properties of the magnetospheric system and how it may influence global dynamics during impulsive events.

How to cite: Archer, M., Hartinger, M., Plaschke, F., and Rastaetter, L.: Wave Propagation and Global Implications of Magnetopause Surface Eigenmodes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3146, https://doi.org/10.5194/egusphere-egu2020-3146, 2020.

Observational studies have demonstrated that ULF waves excited in the ion foreshock are a main source of Pc3-4 ULF waves detected in the magnetosphere. However, quantitative understanding of the propagation of the waves is not easy, because the waves are generated through a kinetic process in the foreshock, pass through the turbulent magnetosheath, and propagate as fast mode waves and couple to shear Alfven waves within the magnetosphere.  Recent advancement of hybrid numerical simulations of foreshock dynamics motivated us to analyze observational data from multiple sources and compare the results with simulation results. We have selected the time interval 1000-1200 UT on 20 July 2016, when the THEMIS, GOES, and Van Allen Probe spacecraft covered the solar wind, foreshock, magnetosheath, and magnetosphere. The EMMA magnetometers (L=1.6-6.5) were located near noon. We found that the spectrum of the magnetic field magnitude (Bt) in the foreshock exhibits a peak near 90 mHz, which agrees with the theoretical prediction assuming an ion beam instability in the foreshock.  A similar Bt spectrum is found in the dayside outer magnetosphere but not in the magnetosheath or in the nightside magnetosphere.  On the ground, a 90 mHz spectral peak was detected in the H component only at L=2-3. The numerical simulation using the VLASIATOR code shows that the foreshock is formed on the prenoon sector but that the effect of the upstream waves in the magnetosphere is most pronounced at noon. The Bt spectrum of the simulated waves in the outer magnetosphere exhibits a peak at 90 mHz, which is consistent with the observation.

How to cite: Takahashi, K., Turc, T., Kilpua, E., Takahashi, N., Dimmock, A., Kajdic, P., Palmroth, M., Pfau-Kempf, Y., Soucek, J., Singer, H., Motoba, T., and Kletzing, C.: Observation and Numerical Simulation of Propagation of ULF Waves From the Ion Foreshock Into the Magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5562, https://doi.org/10.5194/egusphere-egu2020-5562, 2020.