ST2.8

Via cyclotron resonant interactions, electromagnetic ion cyclotron (EMIC) waves play an important role in the loss of ring current protons. In this study, by calculating the proton bounce-averaged pitch angle diffusion coefficients using both the cold and hot plasma dispersion relations, we investigate the hot plasma effects on the EMIC wave-induced scattering loss of ring current protons. Our results show that, for H⁺ band (He⁺ band) EMIC waves, inclusion of hot protons results in significant decrease of pitch angle diffusion coefficients of ~ 10 - 60 keV (4 - 30 keV) protons, while the scattering efficiency of higher energy protons increases at low pitch angles and decreases at relatively high pitch angles. We also find that the cold plasma approximation seriously underestimates the loss timescales of protons at energies from a few keV to tens of keV but overestimate that of higher energy protons. The differences in proton loss timescales caused by hot plasmas are generally less than a factor of ~ 5 for H⁺ band but can exceed an order of magnitude for He⁺ band, showing a strong dependence on ,  and L-shell. This study confirms that hot plasma effects play a crucial role in the EMIC wave driven loss of ring current protons and should be included in future modeling of ring current dynamics.

How to cite: Zhu, Q., Cao, X., Ni, B., Gu, X., and Ma, X.: Hot Plasma Effects on the Pitch-Angle Scattering of Ring Current Protons by EMIC Waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2106, https://doi.org/10.5194/egusphere-egu22-2106, 2022.

Low-energy ring current electrons of up to 50 keV represent a major threat to spacecrafts within the inner magnetosphere since they are one of the main causes of spacecraft surface charging. Furthermore, they can provide a seed population for relativistic radiation belt electrons during geomagnetic storms. In this work, we report the first results of coupling the Versatile Electron Radiation Belt (VERB) code with a fully MLT resolved physics-based plasmasphere model to investigate the loss mechanisms of low energy electrons. Our four dimensional ring current model used in this study includes radial diffusion, convection, and loss due to whistler-mode chorus and hiss waves. The physics-based model of the plasmasphere includes convection of cold plasma and refilling from the ionosphere.
We simulate two storm events from the Van Allen Probes' era and compare results of cold plasma density and electron flux against measurements from the twin Van Allen Probe satellites. Our plasmasphere model is not only capable of predicting the plasmapause location but also the formation of plasmaspheric plumes, where plume whistler mode waves propagate. Including the plume region, which usually has very restricted spatial coverage, allows us to examine the effect of plume whistler mode waves on the loss of ring current electrons during these two events. These plasma boundaries show significant dynamics during the main and recovery phase of storms and are crucial to correctly predict electron loss.
By using the extracted plasma boundaries to determine the spatial extent of different waves species, we find better agreement of electron flux results with measurements, especially during the main phase of storms. We also report on the first ring current simulation results including the loss introduced by spatially localised whistler-wave scattering in plasmaspheric plumes.

How to cite: Haas, B., Shprits, Y., Wutzig, M., Allison, H., and Wang, D.: The Effect of Plasmaspheric Plumes on the Loss of Ring Current Electrons, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7570, https://doi.org/10.5194/egusphere-egu22-7570, 2022.

Energetic electron scattering by electromagnetic ion cyclotron (EMIC) waves is one of the most effective mechanisms of electrons losses in the inner magnetosphere. Such resonant scattering has been traditionally considered as a controlling process for the dynamics of relativistic electron fluxes in the Earth’s radiation belts. EMIC wave generation is mainly associated with the ring current ion population injected from the plasma sheet. These ions are drifting westward and generate the most intense EMIC waves on the dusk flank. In this work, we consider an alternative mechanism of EMIC wave generation due to local plasma compression by strong ultra-low-frequency (ULF) waves that modulate a quasi-periodical ion anisotropy responsible for EMIC excitation. Using THEMIS spacecraft observations of simultaneous EMIC waves and compressional ULF waves, we investigate the statistical properties of such quasi-periodic EMIC emission. We show spatial distributions of ULF-modulated EMIC waves, statistics of their amplitudes and typical frequencies. We also discuss the associated measurements of ULF-modulated hot ion populations responsible for EMIC wave generation.

How to cite: Shahid, M., Bashir, M. F., Artemyev, A., Zhang, X., Angelopoulos, V., and Murtaza, G.: Properties of quasi-periodical emission of electromagnetic ion cyclotron waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11316, https://doi.org/10.5194/egusphere-egu22-11316, 2022.

Magnetopause perturbations by solar wind transients drive a wide variety of ultra-low-frequency (ULF) waves in the Earth’s magnetosphere. Compressional ULF waves modulate thermal and energetic electron fluxes, changing their flux anisotropy. Such modulation may move electron distributions beyond the threshold of instabilities and drive the generation of electron cyclotron harmonic (ECH) and whistler-mode waves. Given the importance of ECH and whistler-mode waves for electron scattering into the atmosphere, we statistically investigate the main characteristics of ULF-modulated ECH and whistler-mode waves. We find two main types of events: with the correlation of whistler-mode and ECH waves and with their anti-correlation. We present the spatial distribution of these two types of events and examine correlations of background plasma/magnetic field characteristics with properties of whistler and ECH waves modulated by ULF waves.

How to cite: Waheed, A., Bashir, M. F., Artemyev, A., and Zhang, X.: Whistler and electron cyclotron harmonic waves at the near-Earth dayside plasma sheet: statistics of modulation by ultra-low frequency waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11179, https://doi.org/10.5194/egusphere-egu22-11179, 2022.

In this study, we present in-situ measurement by Van Allen Probes showing that surface wave could oscillate the plasmapause and modulate hiss and electron cyclotron harmonic (ECH) waves. Plasmapause sur-face wave (PSW) in Ps6 band was observed during an intense substorm on 16 July 2017, accompanied with quasi-periodic emissions of hiss (positively correlated to plasma density) and ECH waves (anticorrelated to the density). Phase relation between magnetic field and velocity perturbations indicatesthat the PSW was an eigenmode between southern and northern ionosphere. Measurements from ground-based magnetometers suggest that such PSW propagates sunward at dusk flank and were excited around the expansion phase of an intense substorm. Addiational cases of PSWs are also presented to demonstrate that such waves are commonly observed near plasmapause and are likely to be related to substorm activities.

How to cite: Hao, Y., Zong, Q., Yue, C., Zhou, X., Zhang, H., Pu, Z., and Shprits, Y.: Plasmapause Surface Waves Triggered by Substorms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11579, https://doi.org/10.5194/egusphere-egu22-11579, 2022.

The plasma properties in the inner magnetosphere play critical roles in plasma dynamics by changing magnetic field configurations and generating the ring current. Geomagnetic substorms, especially intense substorms can significantly influence inner magnetosphere. This study presents our preliminary statistical results of plasma properties and their substorm dependence at the equatorial plane based on the Van Allen Probe observations. We find that both H+ and O+ pressure increases significantly during substorms, and the pressure ratio of O+ to H+ also increases. The peak of H+ pressure is almost fixed around L=4, while that of O+ moves inward as the substorm intensifies. In addition, substorms can significantly change the ion energy distributions. They will increase the proportion of pressure provided by the lower energy components of H+ (E < ~100keV), especially in lower L-shells. At the same time, they decrease the contribution to the plasma pressure from lower energy components of O+, which shows almost no L-shell dependence. During quiet times, the perpendicular current density distributes roughly symmetrically, with negative value inside (L < ~4.5) and positive value outside. During substorms, the current density enhances and shows asymmetry with higher current density from the pre-dusk to the post-midnight. The parallel current density caused by the pressure gradient also increases with substorms. These field-aligned currents (FACs) enter the ionosphere at dusk and move upward at dawn, as region II FAC.

How to cite: Fu, H., Yue, C., Zong, Q., and Zhou, X.: Substorm influences on plasma properties distributions in the inner magnetosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9045, https://doi.org/10.5194/egusphere-egu22-9045, 2022.

During July-October of 2019, a sequence of Corotating Interaction Regions (V_SW ≥ 600 km/s) impacted the magnetosphere, for four consecutive solar rotations. Even though the series of CIRs resulted in relatively weak geomagnetic storms (SYM-H_min ≈ -60 nT, Kp_max ≈ 5), the net effect of the outer radiation belt during each disturbance was different, depending on the electron energy. During the August-September CIR, intense substorm activity was recorded (SML_min ≈ - 2000 nT), as well as significant enhancement of ultra-relativistic electrons.

We exploit coordinated and cross-calibrated particle measurements from the Van Allen Probes, Arase and Galileo 207, 215 satellites, to investigate the relative contribution of radial diffusion and gyro-resonant acceleration, using both electron fluxes and Phase Space Density (PSD) radial profiles, also compared with a 1D Fokker-Planck simulation.

Additionally, we use chorus wave amplitude and radial diffusion coefficient (D_LL) estimations, from the SafeSpace D_LL database, density measurements from the GFZ-Potsdam database, as well as solar wind and geomagnetic parameters, for a detailed investigation of these events.

This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870437 for the SafeSpace project.

How to cite: Nasi, A., Daglis, I. A., Katsavrias, C., Sandberg, I., Li, W., Allison, H., Miyoshi, Y., Imajo, S., Mitani, T., Hori, T., Shprits, Y., Kasahara, S., Yokota, S., Keika, K., Shinohara, I., Matsuoka, A., and Kasahara, Y.: Coordinated observations of relativistic electron enhancements following the arrival of consecutive Corotating Interaction Regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-536, https://doi.org/10.5194/egusphere-egu22-536, 2022.

Subauroral polarization streams (SAPS) typically refer to an enhanced westward plasma flow channel in the duskside subauroral ionosphere. SAPS overlap with the low-latitude part of downward Region-2 field-aligned currents (FACs). The relatively low subauroral conductance in this region requires a strong electric field for current closure, which drives the fast sunward plasma flow. Observations have shown dynamic variability of SAPS under various solar wind and interplanetary magnetic field (IMF) conditions, which are related to the variability of FACs and auroral precipitation, as well as their source regions in the ring current and plasmasheet. In this study, we use satellite observations and numerical simulations with the state-of-the-art Multiscale Atmosphere Geospace Environment (MAGE) model to investigate: 1) The role of diffuse electron precipitation in the formation of SAPS; 2) SAPS variability under IMF B_Y; and 3) Dawnside (as opposed to the more conventional duskside) SAPS as a unique feature of major geomagnetic storms. With data-model comparison, we will demonstrate that SAPS result from the different behaviors of ring current ions and plasma sheet electrons, and the corresponding self-consistent response of the ionosphere-thermosphere system via electrodynamic and particle coupling with the magnetosphere. We conclude that SAPS distribution and variability represent a fundamental feature of the geospace response to solar disturbances during storm time.

How to cite: Lin, D., Wang, W., Merkin, V., Wiltberger, M., Sorathia, K., Pham, K., Bao, S., Michael, A., Shi, X., Huang, C., Wu, Q., Zhang, Y., Oppenheim, M., Toffoletto, F., Lyon, J., Garretson, J., and Anderson, B.: Subauroral polarization streams (SAPS): Intrinsic response of geospace during storm time, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6869, https://doi.org/10.5194/egusphere-egu22-6869, 2022.

Chorus waves can cause the loss of energetic electrons in the Earth's radiation belts and ring current via pitch-angle diffusion. To quantify the effect of chorus waves on energetic electrons, we calculated the bounce-averaged quasi-linear diffusion coefficients. In this study, using these diffusion coefficients, we parameterize the lifetime of the electrons with an energy range from 1 keV to 2 MeV. In each magnetic local time (MLT), we calculate the lifetime for each energy and L-shell using two different methods. By applying polynomial fits, we parameterize the electron lifetime as a function of L-shell and electron kinetic energy (Ek) in each MLT and geomagnetic activity (Kp). The parameterized electron lifetimes show a strong functional dependence on L-shell and electron energy. During storm time, the lifetimes for higher energy (> 100 keV) electrons range from hours to days in the heart of the radiation belts. In contrast, the lifetimes for electrons with lower energy (< 100 keV) range from minutes to hours. This parameterization of electron lifetime is convenient for inclusion in simulations in the inner magnetosphere. 

How to cite: Wang, D., Shprits, Y., and Haas, B.: Parameterized Lifetime of Energetic Electrons due to Interactions with Chorus Waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1546, https://doi.org/10.5194/egusphere-egu22-1546, 2022.

Properly characterizing fast relativistic electron losses in the terrestrial Van Allen belts remains a significant challenge for accurately simulating their dynamics. In particular, magnetopause shadowing losses can deplete the radiation belt within hours or even minutes but can have long-lasting impacts on the subsequent belt dynamics. By statistically analyzing seven years of data from the entire Van Allen Probes mission in the context of the last closed drift shell, here we show how these losses are much more organized and predictable than previously thought. Once magnetic storm electron dynamics are properly analyzed in terms of the location of the last closed drift shell, not only is the loss shown to be repeatable but its energy-dependent spatio-temporal evolution is also revealed to follow a very similar pattern from storm to storm. Employing an energy-dependent ULF wave radial diffusion model, we further show for the first time how the similar and repeatable fractional loss of the pre-storm electron population in each storm can be reproduced and explained. Empirical characterization of this loss may open a pathway toward improved radiation belt specification and forecast models. This is especially important since underestimates of loss can also create unrealistic sources in models, creating phantom electron radiation and leading to the prediction of an overly harsh radiation environment.

How to cite: Olifer, L., Mann, I., Ozeke, L., Claudepierre, S., Baker, D., and Spence, H.: On the Similarity and Repeatability of Fast Magnetopause Shadowing Loss, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8799, https://doi.org/10.5194/egusphere-egu22-8799, 2022.

We present a machine-learning-based model of relativistic electron fluxes >1.8 MeV using a neural network approach in the Earth's outer radiation belt. The Outer RadIation belt Electron Neural net model for Relativistic electrons (ORIENT-R) uses only solar wind conditions and geomagnetic indices as input. For the first time, we show that the state of the outer radiation belt can be determined using only solar wind conditions and geomagnetic indices, without any initial and boundary conditions. The most important features for determining outer radiation belt dynamics are found to be AL, solar wind flow speed and density, and SYM-H indices. ORIENT-R reproduces out-of-sample relativistic electron fluxes with a correlation coefficient of 0.95 and an uncertainty factor of ∼2. ORIENT-R reproduces radiation belt dynamics during an out-of-sample geomagnetic storm with good agreement to the observations. In addition, ORIENT-R was run for a completely out-of-sample period between March 2018 and October 2019 when the AL index ended and was replaced with the predicted AL index (lasp.colorado.edu/home/personnel/xinlin.li). It reproduces electron fluxes with a correlation coefficient of 0.92 and an out-of-sample uncertainty factor of ∼3. Furthermore, ORIENT-R captured the trend in the electron fluxes from low-earth-orbit (LEO) SAMPEX, which is a completely out-of-sample data set both temporally and spatially. In sum, the ORIENT-R model can reproduce transport, acceleration, decay, and dropouts of the outer radiation belt anywhere from short timescales (i.e., geomagnetic storms) and very long timescales (i.e., solar cycle) variations.

How to cite: Chu, X., Ma, D., Bortnik, J., Tobiska, W. K., Cruz, A., Bouwer, S. D., Zhao, H., Ma, Q., Zhang, K., Baker, D. N., Li, X., Spence, H., and Reeves, G. D.: A Neural Network-Based Model of the Relativistic Electrons Fluxes in the Outer Radiation Belt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6611, https://doi.org/10.5194/egusphere-egu22-6611, 2022.

Pitch angle distributions (PADs) of trapped particles play an important role in understanding the processes driving the dynamics of Earth’s radiation belts and ring current. The Van Allen Probes mission has provided electron observations of PADs with an unprecedented coverage in energy (from tens of keV to several MeV) and pitch angles during the mission’s lifespan. We approximate the equatorial electron PADs using the Fourier sine series expansion up to degree 5. The corresponding coefficients can be directly related to the main PAD shapes (pancake, butterfly, flat-top and cap), and the approximated PADs can be easily integrated and converted to omnidirectional flux. Using the entire Van Allen Probes MagEIS data set in 2012-2019, we analyze the response of the equatorial electron PAD shapes to 129 geomagnetic storms with minimum Dst< -50nT. At lower energies (<100 keV), the PADs are stable throughout geomagnetic storms and mainly exhibit a pancake shape. At higher energies, the storm-time PAD evolution depends on the magnetic local time (MLT). At dayside, the pancake distributions become steeper during the main phase and then recover to their original broader form during recovery phase, likely due to the inward radial diffusion. At nightside MLT, the butterfly distributions become more pronounced during the main phase due to the combination of drift-shell splitting and magnetopause shadowing. We present a simple polynomial regression model of PAD shapes driven by the solar wind dynamic pressure. The model allows reconstructions of the full equatorial PADs based on uni-directional measurements at low equatorial pitch angles (applicable to LEO satellite data), as well as from omnidirectional electron flux observations and significantly outperforms the standard sin(alpha) approximation.

How to cite: Smirnov, A., Shprits, Y., Allison, H., Aseev, N., Drozdov, A., Kollmann, P., Wang, D., and Saikin, A.: Equatorial electron pitch angle distributions in Earth's outer radiation belt: Storm-time evolution and empirical modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7732, https://doi.org/10.5194/egusphere-egu22-7732, 2022.

Electromagnetic ion cyclotron (EMIC) wave plays an important role in precipitating relativistic electrons. In this study, we analyze an EMIC wave event on 6 November 2015 that extended over 6 hours in local time and the amplitude of this EMIC wave is about 3nT. Solar wind dynamic pressure enhancement excites EMIC waves, and whistler mode chorus waves are observed at the same time. When the EMIC wave occurs, the flux of relativistic electrons with pitch angle around 90° increases and the flux of small-pitch-angle relativistic electrons decreases. We calculate the electron PSD, which proves that EMIC wave leads to relativistic electron precipitation. Our result indicates that the large-amplitude EMIC wave will lead to nonlinear wave-particle interaction, thus leading to relativistic electron precipitation. When the wave amplitude is larger, the nonlinear wave-particle interaction becomes stronger.

How to cite: Yan, Y. and Yue, C.: EMIC Waves Induced by the Enhancement of Solar Wind Dynamic Pressure and Subsequent Relativistic Electron Precipitation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9034, https://doi.org/10.5194/egusphere-egu22-9034, 2022.

Interplanetary (IP) shocks in general have strong impact on particles and electromagnetic field. In this study, we have examined the dynamics of cross-energy ions and plasma waves observed by the Van Allen Probe B satellite which was located near the equator at the noon sector after the impact of an IP shock on 27 Feb, 2014. We found that the ULF waves and electromagnetic waves are induced and the differential fluxes of protons with different energies increased or decreased after the IP shock arrival. For low energy ions (10-100eV), the perpendicular flux increased intensively due to ExB drift and betatron acceleration. These adiabatic processes also accounted for the special behavior of 10~200 keV ions, which are due to the positive gradient in phase space density before the IP shock arrival. In addition, the short-lived ultra-low frequency waves triggered by the IP shock interacted with the ~100 keV protons and resulting in the stripes in pitch angle distribution. Meanwhile, the anisotropic ions of ~50-300 keV generate EMIC wave at higher L shell after the shock arrival. This study reveals that an IP shock event can cause comprehensive responses of different energy ions and drive several plasma waves at the same time.

How to cite: Li, Y., Yue, C., Zong, Q., and Zhou, X.: Simultaneous Cross-energy Ion Response and Wave Generation after An Interplanetary Shock: A Case Study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9648, https://doi.org/10.5194/egusphere-egu22-9648, 2022.

Auroral kilometric radiations (AKR) are existed by suprathermal (1-10keV) electrons, which are accelerated by parallel electric fields and pitch angle scattered by magnetic field gradients. Here, using observations of the Arase satellite and Van Allen Probes from 23 March 2017 to 31 July 2019, we present the first statistical study of AKR distribution characteristic in the region of λ = 0°−40°and L = 3.0−9.0. Results (totally 32,043 samples) show that southern AKR on the nightside (12,853 samples) are positioned to the east relative to their northern conjugates (13,630 samples), the wave frequencies and amplitudes of AKR in the southern hemisphere are greater than those in the northern hemisphere. Further studies suggest that SYM-H indexes and interplanetary magnetic field (IMF) have different distributions in the northern and southern hemispheres. The probable reason is that different IMF conditions cause asymmetric Field-aligned currents between the northern and southern hemispheres, then yield the asymmetry of AKR and auroras. This study helps to provide more information on the magnetosphere-ionosphere-atmosphere coupling.

How to cite: Tang, J., Xiao, F., Liu, S., and Zhang, S.: Asymmetry of Auroral Kilometric Radiation in the Northern and Southern hemispheres, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3288, https://doi.org/10.5194/egusphere-egu22-3288, 2022.

A localized flux tube with reduced entropy (PV^5/3, where P and V stand for the plasma pressure and flux tube volume, respectively) as compared to its neighbors is defined as a plasma-sheet bubble. Bubbles are susceptible to interchange instability. The interchange instability plays a key role in the transport of plasma from the magnetotail to the near-Earth region. A strong dawn-to-dusk electric field is formed inside the bubble which creates a shear flow. The E×B drift causes the bubble to grow earthward and the magnetic tension force drives it towards the equilibrium location where its total entropy matches the entropy of the surrounding area. According to the Vasyliunas equation, when the angle (α) between ∇V and ∇PV^5/3 is either 0 (being parallel) or 180^° (being antiparallel), the Birkeland current cannot be flown between the plasma sheet and the ionosphere. In this study, using the linear instability analysis we investigate the excitation and development of interchange modes in the low-beta plasma sheet (β<<1) when 0<α<180^°. To this end, a boundary layer (with thickness δ) separating regions of higher and lower entropy is assumed in a small region of the ionosphere. The first-order electric potential (Φ) within this layer is numerically calculated based on time-sequence technique. The complete analytical solution for the temporal variation of Φ clearly shows that the unstable interchange modes with large wavelengths compared to the boundary layer (i.e., λ>>δ) can be generated.

How to cite: Sadeghzadeh, S., Yang, J., and Mousavi, A.: Interchange instability analysis based on magnetosphere-ionosphere coupling theory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2109, https://doi.org/10.5194/egusphere-egu22-2109, 2022.

The Van Allen Probe B satellite simultaneously observed electromagnetic ion cyclotron (EMIC) and fast magnetosonic (MS) waves in a magnetic dip on April 29, 2017. During the magnetic dip, we found the coexistence of flux enhancements of ring current protons (∼11.2–∼51.7 keV) and flux reductions of relativistic electrons (∼1 MeV), which are identified as typical signatures of a magnetic dip in the inner magnetosphere. Based on linear theoretical calculations and observational analysis, the observed ring current protons show an anisotropic temperature distribution and partial shell distribution for different energies during the magnetic dip to provide free energies for the generation of EMIC and MS waves, respectively. Our findings indicate that the complex unstable distribution in the velocity phase space of ring current protons during the magnetic dip can trigger the simultaneous generation of EMIC and MS waves in the inner magnetosphere.

How to cite: Huang, Z., Yuan, Z., Yu, X., Xue, Z., and Ouyang, Z.: Simultaneous Generation of EMIC and MS Waves During the Magnetic Dip in the Inner Magnetosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1678, https://doi.org/10.5194/egusphere-egu22-1678, 2022.

 In this letter, we report an electromagnetic ion cyclotron (EMIC) harmonic event observed by the Van Allen Probe B, whose generation is demonstrated to result from nonlinear wave-wave resonances through the bicoherence analysis. Hybrid simulation shows that the second to sixth harmonics could be excited in sequence after a pump EMIC wave is initially injected, which is in consistent with the observations of EMIC harmonic. It indicates the important role of the second harmonic in the generation of higher harmonics. Finally, the statistical distribution for the amplitude of EMIC second harmonic waves indicates that the energy transfer rate from the fundamental wave to the second harmonic is mainly less than 2%, which might be too low to result in third and other higher harmonics above the observational level. Our results will give some new insights into the excitation of EMIC harmonic waves in the inner magnetosphere.

How to cite: Deng, D., Yuan, Z., Huang, S., Xue, Z., Huang, Z., and Yu, X.: Electromagnetic Ion Cyclotron Harmonic Waves Generated via Nonlinear Wave-Wave couplings, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1623, https://doi.org/10.5194/egusphere-egu22-1623, 2022.

Using observations of Van Allen Probes, we present a statistical study of plasmaspheric plumes in the inner magnetosphere. Plasmaspheric plumes tend to occur during the recovery phase of geomagnetic storms. Furthermore, the results imply that the occurrence rate of observed plasmaspheric plume in the inner magnetosphere is larger during stronger geomagnetic activity. This statistical result is different from the observations of the Cluster satellite with much higher L-shells in most orbital period, which suggest that the plasmaspheric plume near the magnetopause tends to be observed during moderate geomagnetic activity (Lee et al., 2016). In the following, the dynamic evolutions of plasmaspheric plumes during a moderate geomagnetic storm in February 2013 and a strong geomagnetic storm in May 2013 are simulated through group test particle simulation. It is obvious that the plasmaspheric particles drift out on open convection paths due to sunward convection during both geomagnetic storms. It seems that the outer plasmaspheric particles exhaust sooner and the plasmasphere shrinks faster during strong geomagnetic storms. As a result, the longitudinal width of the plume is narrower and the plume is limited to lower L-shells during the recovery phase of strong geomagnetic storm. The simulated evolutions may provide a possible interpretation for the occurrence rates: Van Allen Probes tend to observe plumes during stronger geomagnetic storms, and the Cluster satellite with higher L-shells tends to observe plumes during moderate geomagnetic storms. 

How to cite: Li, H.: Statistical Study and Corresponding Evolution of Plasmaspheric Plumes under Different Levels of Geomagnetic Storms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1081, https://doi.org/10.5194/egusphere-egu22-1081, 2022.

Bounce-resonant diffusion coefficients of radiation belt energetic electrons induced by extremely low-frequency (ELF) chorus waves are comprehensively evaluated using Van Allen Probes observations on 22 December 2014. ELF chorus waves can efficiently scatter 85° < _eq < 89° electrons with bounce resonance pitch angle scattering rates above 10^-4/s and energy scattering rates above 10^-7/s. By comparing diffusion coefficients due to bounce resonance with those due to cyclotron and Landau resonances, we found that bounce resonance diffusion rates have slight energy dependence for >100 keV electrons while Landau-resonant scattering rates decrease significantly in the MeV energy range. These findings suggest that bounce resonances by ELF chorus waves have potentially significant contributions to the dynamics of energetic electrons and should be considered in the further modeling of Earth’s radiation belts.

How to cite: Guo, D., Xiang, Z., Ni, B., Cao, X., Fu, S., Zhou, R., Gu, X., Yi, J., Guo, Y., and Jiao, L.: Bounce Resonance Scattering of Radiation Belt Energetic Electrons by Extremely Low-Frequency Chorus Waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2136, https://doi.org/10.5194/egusphere-egu22-2136, 2022.

Throat auroras frequently observed near local noon have been confirmed to correspond to magnetopause indentations, but the generation mechanisms for these indentations and the detailed properties of throat aurora are both not fully understood. Using all‐sky camera and magnetometer observations, we reported some new observational features of throat aurora as follows. (1) Throat auroras can occur under stable solar wind conditions and cause clear geomagnetic responses. (2) These geomagnetic responses can be simultaneously observed at conjugate geomagnetic meridian chains in the Northern and Southern Hemispheres. (3) The initial geomagnetic responses of throat aurora show concurrent onsets that were observed at all stations along the meridians. (4) Immediately after the concurrent onsets, poleward moving signatures and micropositive bays were observed in the X components at higher‐ and lower‐latitude stations, respectively. We argue that these observations provide evidence for throat aurora being generated by low‐latitude magnetopause reconnection. We suggest that the concurrent onsets reflect the instantaneous responses of the reconnection signal arriving at the ionosphere, the followed poleward moving signatures reflect the antisunward dragging of the footprint of newly opened field lines, and the micropositive bays may result from a pair of field‐aligned currents generated during the reconnection. This study may shed new light on the geomagnetic transients observed at cusp latitude near magnetic local noon.

How to cite: Feng, H.-T., Han, D., Chen, X., Liu, J., and Xu, Z.: Interhemispheric Conjugacy of Concurrent Onset and Poleward Traveling Geomagnetic Responses for Throat Aurora Observed Under Quiet Solar Wind Conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1143, https://doi.org/10.5194/egusphere-egu22-1143, 2022.

Electron cyclotron harmonic (ECH) waves which mainly observed in the first harmonic band are believed to play a part in scattering diffuse aurora electrons in the Earth's magnetosphere. Here we report two enhanced ECH emission events with nominal wave magnitudes exceeding 1mV/m in higher bands ( up to the 4^th harmonic bands) observed from Van Allen Probes mission during geomagnetic disturbance periods in the low density area. Based on actual measurements sampled by Van Allen Probes, we model the electron distribution using a superposition of bi-Maxwellian functions and then numerically evaluate the local growth rates and diffuse coefficients. These differences in frequency distribution for two events can be explained by differences in the loss cone feature of hot electron components. The scattering properties in the first four bands for two events are debated, these results suggest ECH waves in higher band can still cause efficient pitch angle scattering which are similar to ECH waves in the first band. This work broadens our understanding in the formation of diffuse aurora contributed by ECH waves.

How to cite: Qiwu, Y., Fuliang, X., Qinghua, Z., Si, L., Zhonglei, G., Yihua, H., Sai, Z., Zhoukun, D., and Jiawen, T.: Observations of Higher-band ECH waves and its impact on radiation belt energetic electrons, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6712, https://doi.org/10.5194/egusphere-egu22-6712, 2022.