ST2.5

Satellite observations show that electrons in the Van Allen radiation belts can have energies in excess of 7 MeV. The Van Allen Probes mission not only provided measurements of ultra-relativistic radiation belt electrons, but also simultaneous observations of plasma waves, allowing for the routine inference of total plasma number density. Based on a year of observations from 2015, we show that the electron plasma density has a controlling effect over local chorus acceleration to ultra-relativistic energies, which occurs only when the plasma number density drops down to very low values (~10 cm^-3). Results from a Versatile Electron Radiation Belt (VERB) simulation show that a reduced electron plasma density allows chorus waves to efficiently resonate with electrons up to ultra-relativistic energies, producing enhancements from 100s of keV up to >7 MeV via local diffusive acceleration. We analyse statistically the observed chorus wave power during ultra-relativistic enhancement events, considering the contribution from both upper and lower band chorus waves. The Versatile Electron Radiation Belt (VERB) model is also used to recreate an ultra-relativistic electron acceleration event and simulation results are compared to observations, showing close agreement in the evolution when the reduction in electron plasma density is taken into account. The PINE density model allows for the investigation of global magnetospheric density changes during this event. We therefore analyze the how the global cold plasma density changes during ultra-relativistic enhancement events and compare to in-situ point measurements of the plasma density.

How to cite: Allison, H., Shprits, Y., Wang, D., Zhelavskaya, I., and Smirnov, A.: Chorus acceleration of ultra-relativistic radiation belt electrons during periods of low plasma density, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2880, https://doi.org/10.5194/egusphere-egu22-2880, 2022.

Energetic electron acceleration and precipitation in the Earth's outer radiation belt are highly related to whistler mode chorus waves. We perform test particle simulations to investigate electron dynamics interacting with both parallel and oblique chorus emissions at L=4.5. We build up a database of the Green's functions for a large number of electrons interacting with whistler mode chorus emissions. The loss process of electron fluxes interacting with consecutive chorus emissions in the outer radiation belt is traced by applying the convolution integrals of distribution functions and the Green's functions. Oblique chorus emissions lead to more electron precipitation than that led by parallel chorus emissions. By checking the resonance condition and resonant energies at loss cone angle, we find that the nonlinear scattering via cyclotron resonance is the main process that pushes energetic electrons into the loss cone. Electrons are difficult to be scattered into the loss cone directly by Landau resonance, but Landau resonance helps electrons moving toward the loss cone. We propose a 2-step precipitation process for oblique chorus emissions that contributes to more electron loss: (1) During the first chorus emission, the nonlinear trapping of Landau resonance accelerates an electron close to the loss cone. (2) During the second emission, the nonlinear scattering of cyclotron resonance scatters the electron into the loss cone. The combination of Landau resonance and cyclotron resonance by oblique chorus emissions results in a higher precipitation rate than the single cyclotron resonance by purely parallel chorus emissions.

How to cite: Hsieh, Y. and Omura, Y.: Energetic electron loss process associating with oblique chorus emissions in the outer radiation belt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6, https://doi.org/10.5194/egusphere-egu22-6, 2022.

How to properly describe resonant interactions between electrons and quasi-coherent chorus waves is still an open question. Previous studies have progressed from modeling chorus as a single wave to considering effects such as amplitude modulation or phase decoherence in wave particle resonance. However, incorporating realistic features of chorus waves in test particle calculations has always been a challenging but critically important step to evaluate their nonlinear effects. In this work, we use a chorus wave packet generated by a particle-in-cell simulation in test-particle simulations. The used chorus wave naturally has features including amplitude modulation, phase decoherence and dynamic evolution during propagation. Our results suggest that, while being latitudinal dependent, realistic features of chorus generally lead to significant suppression of nonlinear effects. This result should be important to understand phase space transport of electrons due to interactions with chorus waves.

How to cite: An, Z., Wu, Y., and Tao, X.: Electron Dynamics in a Chorus Wave Field Generated from Particle-in-Cell Simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7259, https://doi.org/10.5194/egusphere-egu22-7259, 2022.

Ionospheric-originating cold ions are difficult to measure throughout Earth's magnetosphere due to spacecraft charging limiting our ability to measure this low energy population, thus complicating investigations into how these cold ions participate in the growth of electromagnetic ion cyclotron (EMIC) waves. While these cold ion populations pose measurement challenges for most missions, recent event studies have shown that, at times, the Magnetospheric Multiscale (MMS) mission is capable of directly measuring both the low-energy cold populations as well as the hot ion composition, enabling improved understanding of EMIC wave generation, propagation, and wave polarization properties [1, 2, 3, 4]. These studies demonstrated the utility of considering the full ion composition for improving our understanding of different aspects of EMIC waves in the outer magnetosphere. We applied our experience analyzing the combined ion composition and EMIC wave data from event studies and conducted a statistical analysis of MMS datasets during the Prime Mission dayside intervals, with plans to expand the analysis to later mission phases and other magnetospheric regions. Out of approximately 6000 dayside wave intervals identified, around 25% of the intervals also contained simultaneous measurements of the cold ion composition needed to conduct more accurate modeling of linear wave growth in the outer magnetosphere, where the free energy source of EMIC waves may also be modulated by solar wind pressure pulses. This paper will discuss observations and progress on the statistical analysis and possible implications for studies on inner magnetospheric EMIC waves.

References
1.    Vines, S. K., Allen, R. C., Anderson, B. J., Engebretson, M. J., Fuselier, S. A., Russell, C. T., et al. (2019). EMIC Waves in the Outer Magnetosphere: Observations of an Off-Equator Source Region. Geophys. Res. Lett. 46, 5707–5716. doi:10.1029/2019GL082152
2.    Lee, J. H., Turner, D. L., Toledo-Redondo, S., Vines, S. K., Allen, R. C., Fuselier, S. A., et al. (2019). MMS Measurements and Modeling of peculiar Electromagnetic Ion Cyclotron Waves. Geophys. Res. Lett. 46, 11622–11631. doi:10.1029/2019GL085182
3.    Lee, J. H., Turner, D. L., Vines, S. K., Allen, R. C., Toledo-Redondo, S., Bingham, S. T., et al. (2021). Application of Cold and Hot Plasma Composition Measurements to Investigate Impacts on Dusk-Side Electromagnetic Ion Cyclotron Waves. J. Geophys. Res. Space Phys. 126, e2020JA028650. doi:10.1029/2020JA028650
4.    Toledo-Redondo, S., Lee, J. H., Vines, S. K., Turner, D. L., Allen, R. C., André, M., et al. (2021). Kinetic Interaction of Cold and Hot Protons with an Oblique EMIC Wave Near the Dayside Reconnecting Magnetopause. Geophys. Res. Lett. 48, e2021GL092376. doi:10.1029/2021GL092376

How to cite: Lee, J., Toledo-Redondo, S., Cohen, I., Turner, D., Vines, S., and Allen, R.: Statistical analysis of ion composition and effects on EMIC waves in the outer magnetosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6643, https://doi.org/10.5194/egusphere-egu22-6643, 2022.

We report the first statistical survey of the oxygen ion cyclotron harmonic waves observed by Van Allen Probes throughout the mission. An example event observed on 19 February 2014 after a strong magnetic storm and a substorm was first presented to demonstrate the general properties of OCH waves. The observed waves have multiple spectral peaks around harmonics of the oxygen ion gyrofrequency. During the event, oxygen ionsof 10s keV had a ring-like partial shell velocity distribution which might have driven the wave excitation through the oxygen ion Bernstein instability. On the other hand, the phase space densities of He⁺ and O⁺ less than a few hundred eV were larger around 90° pitch angle, indicating transverse heating of these ions. Our statistical study shows that the waves occurred over 2 < L < 6 and across all magnetic local time. More than 50% of the events were observed just outside the plasmapause, and the typical wave amplitude is between ~0.1 and several nT. The frequency spacing between two consecutive wave harmonics decreases with increasing L but stabilizes when L > 5. The frequency spacing is larger than the local oxygen ion gyrofrequency for many events, especially those observed at larger L, suggesting that these waves propagated there from lower L shell regions. The waves are mainly on the dayside at L > 4 under quiet geomagnetic conditions, but can occur at lower L shells with a more uniform MLT distribution under more active geomagnetic conditions.

How to cite: Wang, Y., Liu, K., Min, K., Yao, F., Xiong, Y., Cheng, K., Liu, Y., Zheng, X., and Zhou, J.: Statistical study of oxygen ion cyclotron harmonic waves observed by Van Allen Probes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1458, https://doi.org/10.5194/egusphere-egu22-1458, 2022.

Radial diffusion driven by Ultra Low Frequency (ULF) waves is very important for magnetospheric dynamics, because it contributes to relativistic electron enhancements and losses in the outer Van Allen radiation belt. Previous studies have investigated the dependence of ULF wave power spectral density and radial diffusion coefficients (D_LL) on solar wind parameters. However, a conclusive correlation between the type of interplanetary drivers (such as Interplanetary Coronal Mass Ejections (ICMEs) and Stream Interaction Regions (SIRs)), ULF wave power spectral density and radial diffusion coefficients D_LL is still an open topic. In this study, we use the "SafeSpace" database (https://synergasia.uoa.gr/modules/document/?course=PHYS120), which includes radial diffusion coefficients D_LL and ULF wave power spectral density. This database was created using magnetic and electric field measurements by the THEMIS satellites for a 9-year period (2011- 2019). We conduct a statistical analysis of radial diffusion coefficients D_LL, which contributes to relativistic electron radial diffusion quantification, and ULF wave power spectral density, to find out their dependence on ICMEs (25 events) and SIRs (46 events). In addition, we study how the parameters of these solar wind drivers influence the growth of ULF waves and  the behavior of radial diffusion coefficients.

How to cite: Thanasoula, K., Katsavrias, C., Nasi, A., Daglis, I. A., Balasis, G., and Sarris, T.: Magnetospheric ULF wave dependence on Interplanetary Coronal Mass Ejections and Stream Interaction Regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-475, https://doi.org/10.5194/egusphere-egu22-475, 2022.

We report observations of a magnetosheath jet followed by a period of decelerated background plasma. During this period, THEMIS-A magnetometer showed abrupt disturbances which, in the wavelet spectrum, appeared as prominent and irregular pulsations in two frequency bands (7.6–9.2 and 12–17 mHz) within the Pi2 range. The observations suggest—for the first time to our knowledge— that these pulsations were locally generated by the abrupt magnetic field changes driven by the jet’s interaction with the ambient magnetosheath plasma. Furthermore, similar pulsations, detected by THEMIS-D inside the magnetosphere with a 140 s time-lag (which corresponds to the propagation time of a disturbance traveling with Alfvénic speed), are shown to be directly associated with the ones in the magnetosheath, which raises the question of how exactly these pulsations are propagated through the magnetopause.

This research is co-financed by the Greece and the European Union (European Social Fund - ESF) through the Operational Program “Human Resources Development, Education and Lifelong Learning 2014–2020” in the context of the project ULFpulse (MIS: 5048130). C. Katsavrias and I.A. Daglis aknowledge the European Union's Horizon 2020 research and innovation programme “SafeSpace” under grant agreement No 870437. S. Raptis and T. Karlsson acknowledge support from SNSA grant 90/17.

How to cite: Katsavrias, C., Raptis, S., Daglis, I., Karlsson, T., Georgiou, M., and Balasis, G.: On the Generation of Pi2 Pulsations due to Plasma Flow Patterns Around Magnetosheath Jets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5502, https://doi.org/10.5194/egusphere-egu22-5502, 2022.

How to cite: George, H., Osmane, A., Kilpua, E., Lesjone, S., Kalliokoski, M., and Hoilijoki, S. and the Vlasiator team: Estimating radial diffusion using a hybrid-Vlasov simulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4497, https://doi.org/10.5194/egusphere-egu22-4497, 2022.

Zebra stripes are structured peaks and valleys observed on spectrograms of protons and energetic electrons trapped in the inner radiation belts. They have been observed since the 1960s and even though they are transient structures, statistical studies have shown that they are commonly observed and correlated with geomagnetic Kp and Dst indices. Since their discovery, various mechanisms relying on wave-particle interactions have been suggested to explain the formation of zebra stripes. More recently, Lejosne and Roederer (JGR, 121, 2016) have presented a kinematic argument (supported with numerical results) with less constraints than models relying on drift-orbit mechanisms. In this communication, we present a theoretical derivation of zebra stripes from first principles and demonstrate that 1) their formation has a kinematic origin, and 2) that it does not require the presence of electric or magnetic field fluctuations. However, we show that the inclusion of electric or magnetic field fluctuations does not prevent the formation of zebra stripes, and our analysis therefore provides an explanation as to why simulations of drift orbit processes have been able to reproduce zebra stripes patterns.

How to cite: Osmane, A.: Theoretical explanation for the formation of zebra stripes in the inner radiation belts despite the absence of electric or magnetic field fluctuations., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4560, https://doi.org/10.5194/egusphere-egu22-4560, 2022.

Ground-based VLF transmitters located around the world generate signals that leak through the bottom side of the ionosphere in the form of whistler mode waves.  Wave and particle measurements on satellites have observed that these man-made VLF waves can be strong enough to scatter trapped energetic electrons into low pitch angle orbits, causing loss by absorption in the lower atmosphere.  This precipitation loss process is greatly enhanced by intentional amplification of the whistler waves in the ionosphere using a newly discovered process called Rocket Exhaust Driven Amplification (REDA).  Satellite measurements of REDA have shown between 30 and 50 dB intensification of VLF waves in space using a 60-second burn of the 150 g/s thruster on the Cygnus satellite that services the International Space Station (ISS) [Bernhardt et al. 2021; Bernhardt 2021].  This controlled amplification process is adequate to deplete the energetic particle population in the radiation belts in a few minutes rather than the multi-day period it would take naturally.  Numerical simulations of the pitch angle diffusion for radiation belt particles use the UCLA quasi-linear Fokker Planck model (QLFP) to assess the impact of REDA on radiation belt remediation (RBR) of newly injected energetic electrons [Bernhardt et al., 2022].  The simulated precipitation fluxes of energetic electrons are applied to models of D-region electron density and bremsstrahlung x-rays for predictions of the modified environment that can be observed with satellite and ground-based sensors.   

References:

Bernhardt, P.A., et al., Strong Amplification of ELF/VLF Signals in Space Using Neutral Gas Injections from a Satellite Rocket Engine (2021), Radio Science, 56(2), e2020RS007207, https://doi.org/10.1029/ 2020RS007207.

Bernhardt, P.A., The Whistler Traveling Wave Parametric Amplifier (WTWPA) Driven by an Ion Ring-Beam Distribution from a Neutral Gas Injection in Space Plasmas (2021), IEEE Transactions on Plasma Science. 49, 6, 1983-1996, DOI: 10.1109/TPS.2021.3079130.

Bernhardt, P.A., et al., Active Precipitation of Radiation Belt Electrons using Rocket Exhaust Driven Amplification (REDA) of Man-Made Whistlers, Submitted to the Journal of Geophysical Research, 2022.

How to cite: Bernhardt, P., Hua, M., Bortnik, J., Ma, Q., Verronen, P., McCarthy, M., Golkowski, M., Cohen, M., Howarth, A., James, G., and Meredith, N.: Active Control of the Radiation Belt Particle Populations with Ionospheric Amplification of VLF Waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2836, https://doi.org/10.5194/egusphere-egu22-2836, 2022.