ST2.5

Auroral precipitation plays an important role in magnetosphere-ionosphere-thermosphere (MIT) coupling by enhancing ionospheric ionization and conductivity at high latitudes. Diffuse electron precipitation refers to scattered electrons from the plasma sheet that are lost in the ionosphere. Diffuse precipitation makes the largest contribution to the total precipitation energy flux and is expected to have substantial impacts on the ionospheric conductance and affect the electrodynamic coupling between the magnetosphere and ionosphere-thermosphere. Kinetic theory and observational analysis also demonstrate that diffuse precipitation is subject to multiple reflection effects, i.e. secondary electrons produced by the primary precipitation are reflected between the north and south hemispheres multiple times before they are fully lost in the atmosphere. In this study, we make use of the newly developed Multiscale Atmosphere-Geospace Environment (MAGE) model developed at the NASA DRIVE Science Center for Geospace Storms (CGS) to explore the role of diffuse electron precipitation in MIT coupling. Diffuse precipitation in MAGE is derived from the electron distribution in the Rice Convection Model (RCM), a ring current model that solves for energy dependent drifts of electrons and ions. Diffuse precipitation, together with mono-energetic electron precipitation based on parameterization of the magnetohydrodynamic (MHD) parameters from the Grid Agnostic MHD with Extended Research Applications (GAMERA) magnetosphere model, are input to the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) to calculate the ionospheric ionization rate and conductivity and height-integrated conductance. With controlled numerical experiments, we investigate 1. how the diffuse precipitation affects the location and structure of a mesoscale ionospheric convection process, i.e., subauroral polarization streams (SAPS); 2. How multiple reflection effects impact the ionosphere-thermosphere and their coupling with the magnetosphere. Our study demonstrates that diffuse electron precipitation plays a critical role in determining the location and structure of SAPS. The multiple reflection effects make diffuse precipitation number flux and energy flux a few times higher than the unmodified precipitation, resulting in a greatly enhanced auroral ionospheric conductance, lower cross polar cap potential,  higher total field-aligned currents, and changes in global thermospheric winds and temperature. Therefore, diffuse electron precipitation has both local and global impacts on MIT coupling.

How to cite: Lin, D., Wang, W., Merkin, V., Pham, K., Bao, S., Sorathia, K., Toffoletto, F., Shi, X., Meers, O., Khazanov, G., Michael, A., Lyon, J., Garretson, J., and Anderson, B.: Diffuse electron precipitation in magnetosphere-ionosphere-thermosphere coupling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6342, https://doi.org/10.5194/egusphere-egu21-6342, 2021.

Neutral winds have long been viewed as a driver of Jupiter’s radiation belts. On the other hand, the impact of thermospheric neutral winds in driving plasma dynamics in the Earth’s inner magnetosphere is yet to be quantified. We now have the appropriate combination of data and physics-based model to address this fundamental science question.

In this work, we revisit the local time asymmetry of the equatorial electron intensity observed in the innermost radiation belt (L=1.30). We combine in-situ field and particle observations, together with a physics-based coupled model, RCM-CTIPe, to determine whether the dynamo electric fields produced by tidal motion of upper atmospheric winds flowing across the Earth’s magnetic field lines are the main drivers of the drift-shell distortion observed in the Earth’s inner radiation belt.

Our results provide a first quantification of the contribution of the neutral wind in transporting the trapped energetic particles of the Earth’s inner radiation belt.

How to cite: Lejosne, S., Maruyama, N., Selesnick, R. S., and Fedrizzi, M.: Thermospheric Neutral Winds: A Driver of the Earth’s Inner Radiation Belt to Be Reckoned With, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2071, https://doi.org/10.5194/egusphere-egu21-2071, 2021.

In this study, we use the Van Allen Probes data statistically to investigate the features of magnetic dips by the means of superposed epoch analysis. Based on the different max values of electron and proton plasma betas, we categorize the dips into two types: electron-driven dips and proton-driven dips. Superposed epoch analysis on two types of magnetic dips suggests the correlation between the magnetic fluctuations and plasma betas. Moreover, the occurrence of the butterfly distributions of relativistic electrons driven by the magnetic dips is confirmed by the statistical results. Our results reveal the statistical characteristics of magnetic dips and build up the relationship among the magnetic fluctuations and several parameters, indicating the potentially important role of magnetic dips in the dynamics of the inner magnetosphere.

How to cite: Zhu, H. and Chen, L.: Superposed Epoch Analyses of electron-driven and proton-driven magnetic dips, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9315, https://doi.org/10.5194/egusphere-egu21-9315, 2021.

Whistler mode chorus emissions in the Earth’s magnetosphere cause energetic electron precipitation and the associated pulsating aurora. First-order cyclotron resonance in parallel whistler mode wave-particle interactions is the main mechanism of the precipitation. Not only cyclotron resonance but also Landau resonance and higher-order cyclotron resonances occur in the oblique whistler mode wave-particle interactions. Especially, electrons can be accelerated and scattered to lower equatorial pitch angles rapidly via Landau resonance. We apply test particle simulation and the Green’s function method to check the energetic electron precipitation caused by oblique chorus emissions. We simulate the wave-particle interactions around L=4.5 for electron ranges from 10 keV to a few MeV. We further compare the precipitation fluxes between parallel and oblique chorus emissions. Our simulation result reveals that oblique chorus emissions lead to more electron precipitation than parallel chorus emissions. At kinetic energy E < 100 keV, the electron precipitation ratio (oblique case/parallel case) is about 1.3. At 100 keV < E < 0.5 MeV, the ratio is greater than 2. At E > 0.5 MeV, the ratio is greater than 2 orders. Multiple resonances effect in the oblique whistler mode wave-particle interactions is the reason for the greater precipitation.

How to cite: Hsieh, Y. and Omura, Y.: Energetic electron precipitation via oblique whistler mode chorus emissions in the outer radiation belt, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15306, https://doi.org/10.5194/egusphere-egu21-15306, 2021.

Interplanetary (IP) shock driven sudden compression produces disturbances in the polar ionosphere. Various studies have investigated the effects of IP shock using imagers and radars. However, very few studies have reported the plasma flow reversal and a sudden vertical plasma drift motion following a CME driven IP shock. We report on the cusp ionospheric features following an IP shock impingement on 16 June 2012, using SuperDARN radar and digisonde from the Antarctic Zhongshan Station (ZHO). SuperDARN ZHO radar observed instant strong plasma flow reversal during the IP shock driven sudden impulse (SI) with a suppression in the number of backscatter echoes. Besides, we also report on a “Doppler Impulse” phenomenon, an instant and brief downward plasma motion, were observed by the digisonde in response to the SI and discuss the possible physical causes. Geomagnetic disturbance and convection patterns indicate the flow reversal was generated by the downward field-aligned current (FAC). We speculate that sudden enhancement in ionization associated with SI is responsible for generating the Doppler Impulse phenomenon.

How to cite: Liu, J.: Transient cusp ionospheric disturbances caused by a solar wind dynamic pressure enhancement, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-634, https://doi.org/10.5194/egusphere-egu21-634, 2021.

How to cite: Wang, H., He, Y., and Luehr, H.: Local time and longitudinal differences in the occurrence frequency of ionospheric EMIC waves during magnetic storm periods, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-821, https://doi.org/10.5194/egusphere-egu21-821, 2021.

The temporal and spatial evolution of electromagnetic ion cyclotron (EMIC) waves during
the magnetic storm of 21–29 June 2015 was investigated using high-resolution magnetic field observations
from Swarm constellation in the ionosphere and Van Allen Probes in the magnetosphere. Magnetospheric
EMIC waves had a maximum occurrence frequency in the afternoon sector and shifted equatorward during
the expansion phase and poleward during the recovery phase. However, ionospheric waves in subauroral
regions occurred more frequently in the nighttime than during the day and exhibited less obvious
latitudinal movements. During the main phase, dayside EMIC waves occurred in both the ionosphere
and magnetosphere in response to the dramatic increase in the solar wind dynamic pressure. Waves were
absent in the magnetosphere and ionosphere around the minimum SYM-H. During the early recovery
phase, He⁺ band EMIC waves were observed in the ionosphere and magnetosphere. During the late
recovery phase, H⁺ band EMIC waves emerged in response to enhanced earthward convection during
substorms in the premidnight sector. The occurrence of EMIC waves in the noon sector was affected by
the intensity of substorm activity. Both ionospheric wave frequency and power were higher in the summer
hemisphere than in the winter hemisphere. Waves were confined to an MLT interval of less than 5 hr with a
duration of less than 186 min from coordinated observations. The results could provide additional insights
into the spatial characteristics and propagation features of EMIC waves during storm periods

How to cite: He, Y., Wang, H., Hermann, L., Lynn, K., Anthony, S., Eric, L., and Ma, S.: Storm Time EMIC Waves Observed by Swarm and Van Allen Probe Satellites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1156, https://doi.org/10.5194/egusphere-egu21-1156, 2021.

Nonlinear resonance between energetic electrons and chorus waves is widely used to explain the frequency sweep of chorus, which predicts that rising tone elements are comprised by multiple subpackets with the frequency gradually increasing. Here we report two events that subelements with their frequencies downward chirping occur in rising tone chorus. The duration of those subelements is comparable with the regular subpackets, and their frequency sweep rates 6-12 kHz/s are consistent with previous theory and observations. Waveform of the subelement shows similar morphology to regular chorus element, consisting several finer structures "hyper-subpackets". We propose a possible scenario that the falling tone subelements are formed by nonlinear process with much shorter timescale. The starting frequency of each subelement controlled by the linear growth phase increases may because the electron distribution varies fast. This study provides new insight on chorus generation and also brings challenges.

How to cite: Liu, S. and Gao, Z.: Unexpected frequency-sweep reverse of subelements in chorus rising tone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1444, https://doi.org/10.5194/egusphere-egu21-1444, 2021.

Based on data from the ZH-1 satellites, companied with Van Allen Probes and NOAA observations, we analyze the high energy particle evolutions in radiation belts, slot region and SAA during August 2018 major geomagnetic storm (minimum Dst ≈ −190 nT). 

  1) Relativistic electron enhancements in extremely low L-shell regions (reaching L ∼ 3) were observed during storm. 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.

2) A robust evidence is clearly demonstrated that the energetic electron flux with energy 30∼600 keV are increased by 2∼3 times in the inner radiation belt near equator and SAA region on dayside during the major geomagnetic storm. This is the first time that the 100s keV electron flux enhancement is reported to be potentially induced by the interaction with magnetosonic waves in extremely low L-shells (L<2) observed by Van Allen Probes. Proton loss in outer boundary of inner radiation belt takes place in energy of 2~220 MeV extensively during the occurrence of this storm but the loss mechanism is energy dependence which is consistent with some previous studies. It is confirmed that the magnetic field line curvature scattering plays a significant role in the proton loss phenomenon in energy 30-100 MeV during this storm. This work provides a beneficial help to comprehensively understand the charged particles trapping and loss in SAA region and inner radiation belt dynamic physics.

How to cite: Zhang, Z.: Electron filling and proton loss in radiation belts and SAA during 2018 storm based on ZH-1 satellite observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1529, https://doi.org/10.5194/egusphere-egu21-1529, 2021.

Recently, attention was drawn [1] that after geomagnetic storms that cause formation of new radiation belts in slot region or in the inner magnetosphere, after about 2 months, there is an increase in seismic activity near the footprints of geomagnetic lines of new radiation belts. More detailed studies showed [2] that on May 30, 1991, an earthquake M=7.0 occurred in Alaska with (54.57N, 161.61E) near the footprint of geomagnetic line L = 2.69 belonging to new radiation belt, which was observed by the CRRES satellite [3] around geomagnetic lines 2<L<3 after geomagnetic storm on March 24, 1991. After geomagnetic storm on September 3, 2012, the Van Allen Probes satellites observed new radiation belt around 3.0≤L≤3.5 [4], and about 2 months later, on October 28, 2012, earthquake M=7.8 occurred off the coast of Canada (52.79N, 132.1W) near the footprint of geomagnetic line L=3.32 belonging to the new radiation belt. Also, Van Allen Probes observed new radiation belt around L=1.5-1.8 after geomagnetic storm on June 23, 2015 [5], and ~2 months later, in September 2015, seismic activity noticeably increased near the footprint of these geomagnetic lines. We consider variations in seismic activity in connection with the strongest geomagnetic storms in 2003 with Dst~- 400 nT (Halloween Storm) and the formation of a belt of relativistic electrons in the inner magnetosphere around L~1.5 existed until the end of 2005 as observed SAMPEX [6]. Analysis of data from the USGS global seismological catalog showed that near the footprint of geomagnetic lines L=1.4-1.6 the number of earthquakes with M≥4.5 increased in 2003-2004 by ~70% compared with their number in two previous years. On the Northern Tien Shan, on December 1, 2003 a strong for the region earthquake M=6.0 occurred on the border of Kazakhstan and China (42.9N, 80.5E) near the footprint of L = 1.63, adjacent to the new radiation belt.

How to cite: Toyshiev, N., Khachikyan, G., and Zhumabayev, B.: Increase in seismic activity near the footprints of new radiation belts forming after geomagnetic storms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2149, https://doi.org/10.5194/egusphere-egu21-2149, 2021.

Electron cyclotron harmonic (ECH) and whistler-mode chorus waves can contribute significantly to the magnetospheric dynamics. In the frequency-time spectrogram, ECH usually appears as a series of harmonic structureless bands, while chorus often exhibits successive discrete elements. Here, we present surprising observations by Van Allen Probes of lag-correlated rising tones of ECH and upper-band chorus waves. The time lags of ECH elements with respect to chorus elements range from 0.05 to 0.28 s, negatively correlated with the chorus peak amplitudes. The ECH elements seemingly emerge only when the chorus elements are sufficiently intense (peak amplitude >3 mV/m), and their peak amplitudes are positively correlated. Our data and modeling suggest that upper-band chorus may promote the generation of ECH through rapidly precipitating the ~keV electrons near the loss cone. This phenomenon implies that ECH and chorus may not grow independently but competitively or collaboratively gain energy from hot electrons.

How to cite: Gao, Z.: Lag-correlated rising tones of electron cyclotron harmonic and whistler-mode upper-band chorus waves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2459, https://doi.org/10.5194/egusphere-egu21-2459, 2021.

Electromagnetic waves observed in the inner magnetosphere at frequencies between about 0.5 and 4 kHz sometimes exhibit a quasiperiodic (QP) time modulation of the wave intensity with modulation periods from tens of seconds up to a few minutes. Such waves are typically termed “QP emissions” and their origin is still not fully understood. We use a large set of more than 2,000 of these events identified in the low-altitude DEMETER spacecraft data to analyze how the wave properties (modulation period, intensity) depend on relevant controlling factors. Moreover, in-situ measurements of energetic electron precipitation are used to check for precipitation peaks matching the individual QP elements. We successfully identified several such events and we perform their detailed analysis. Most importantly, while the waves may propagate unducted across L-shells, the precipitating particles follow magnetic field lines from the interaction region down to the observation point. They can thus be used to deduce important information about the location and spatial extent of the anticipated generation region of the emissions.

How to cite: Nemec, F., Hajoš, M., Bezděková, B., Santolík, O., and Parrot, M.: Quasiperiodic emissions and related particle precipitation bursts observed by the DEMETER spacecraft, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2775, https://doi.org/10.5194/egusphere-egu21-2775, 2021.

Wave intensity measured in the very low frequency (VLF) range (up to 20 kHz) is typically represented using frequency-time spectrograms. Since the characterization of spectrogram main features and/or their direct comparison is a challenging task, we transform the measurements of the low-altitude DEMETER spacecraft using the principal component analysis (PCA). The present study is focused on both the physical interpretation of the first two principal components and their application to real physical problems. To understand the physical meaning of the first principal components, their scatter plot is constructed and discussed. Moreover, the dependence of the first principal component (PC1) coefficients on the geomagnetic activity and their seasonal/longitudinal variations are analyzed. The obtained distributions are well comparable with those obtained by previous studies for average wave intensities, indicating that the PC1 coefficients are directly related to the overall wave intensity. Furthermore, the variations of PC1 coefficients around interplanetary (IP) shock arrivals are analyzed, suggesting that the fast forward shock occurrence has the most significant effect. It is shown that the wave intensity variations depend on the wave intensity detected before the shock arrival. The shock strength and interplanetary magnetic field orientation are also important. To further demonstrate the adaptability of PCA, we use a similar method to analyze also ground-based VLF measurements performed by the Kannuslehto station located in northern Finland.

How to cite: Bezděková, B., Němec, F., Parrot, M., Manninen, J., Krupařová, O., and Krupař, V.: Variations of VLF Wave Intensity Analyzed via Principal Component Analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2805, https://doi.org/10.5194/egusphere-egu21-2805, 2021.

Measurements from the Van Allen Probes mission clearly demonstrated that the radiation belts cannot be considered as a bulk population above approximately electron rest mass. Ultra-relativistic electrons (~>4Mev) form a new population that shows a very different morphology (e.g. very narrow remnant belts) and slow but sporadic acceleration.

We show that acceleration to multi-MeV energies can not only result of a two-step processes consisting of local heating and radial diffusion but occurs locally due to energy diffusion by whistler mode waves. Local heating appears to be able to transport electrons in energy space from 100s of keV all the way to ultra-relativistic energies (>7MeV). Acceleration to such high energies occurs only for the conditions when cold plasma in the trough region is extremely depleted down to the values typical for the plasma sheet.

There is also a clear difference between the loss mechanisms at MeV and multi MeV energies The difference between the loss mechanisms at MeV and multi-MeV energies is due to EMIC waves that can very efficiently scatter ultra-relativistic electrons, but leave MeV electrons unaffected.

We also present how the new understanding gained from the Van Allen Probes mission can be used to produce the most accurate data assimilative forecast. Under the recently funded EU Horizon 2020 Project Prediction of Adverse effects of Geomagnetic storms and Energetic Radiation (PAGER) we will study how ensemble forecasting from the Sun can produce long-term probabilistic forecasts of the radiation environment in the inner magnetosphere.

How to cite: Shprits, Y., Allison, H., Drozdov, A., Wang, D., Aseev, N., Zhelavskaya, I., and Usanova, M.: Acceleration and Loss of Ultra-relativistic Electrons in the Earth Van Allen Radiation Belts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3120, https://doi.org/10.5194/egusphere-egu21-3120, 2021.

The Earth’s inner energetic electron belt typically exhibits one-peak radial structure with high flux intensities at radial distances < ~2.5 Earth radii. Recent studies suggested that human-made very-low-frequency (VLF) transmitters leaked into the inner magnetosphere can efficiently scatter energetic electrons, bifurcating the inner electron belt. In this study, we use 6-year electron flux data from Van Allen Probes to comprehensively analyze the statistical distributions of the bifurcated inner electron belt and their dependence on electron energy, season, and geomagnetic activity, which is crucial to understand when and where VLF transmitters can efficiently scatter electrons in addition to other naturally occurring waves. We reveal that bifurcation can be frequently observed for tens of keV electrons under relatively quiet geomagnetic conditions, typically after significant flux enhancements that elevate fluxes at L = 2.0 – ~2.5 providing the prerequisite for the bifurcation. The bifurcation typically lasts for a few days until interrupted by substorm injections or inward radial diffusion. The L-shells of bifurcation dip decrease with increasing electron energy, and the occurrence of bifurcation is higher during northern hemisphere winter than summer, supporting the important role of VLF transmitter waves in energetic electron loss in near-Earth space.

How to cite: Hua, M., Ni, B., Li, W., Ma, Q., Gu, X., Fu, S., Cao, X., Guo, Y., and Liu, Y.: Statistical Distribution of Bifurcation of Earth's Inner Energetic Electron Belt at tens of keV, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6003, https://doi.org/10.5194/egusphere-egu21-6003, 2021.

Whistler-mode electromagnetic waves, especially natural emissions of chorus and hiss, have been shown to transfer energy between different electron populations in the inner magnetosphere via quasi-linear or nonlinear wave particle interactions. Average or median intensities of chorus and hiss emissions have been found to increase with increasing levels of geomagnetic activity but their stochastic variations in individual spacecraft measurements at the same location are usually comparable to these large-scale temporal effects. Statistical properties of variations of wave power directly influence results of quasi-linear diffusion models.

We use the survey measurements of the Waves instruments of the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) onboard two Van Allen Probes to asses the probability distribution function of these stochastic variations. We take advantage of the entire data set of these measurements with a nearly 100% coverage from August 31, 2012 till October 13, 2019 (2600 days) for spacecraft A, and from  September 1, 2012 till July 16, 2019 (2510 days) for spacecraft B. 

How to cite: Santolik, O., Kurth, W. S., and Kletzing, C. A.: Variability of natural whistler-mode emissions in the inner magnetosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10735, https://doi.org/10.5194/egusphere-egu21-10735, 2021.

Chorus waves with extremely low frequency (ELF) below 0.1 f_ce are proposed to be a potential mechanism of scattering losses of relativistic electrons in the radiation belt. However, the generation of ELF chorus is still an open question. Here we report three interesting events that the occurrence of ELF chorus waves shows evident correlation with the increase of background plasma density while the disturbance of ambient magnetic field is negligible. We calculate the growth rate of chorus waves by using the correlated data of waves and particles form the Van Allen Probes. The calculated growth rates agree well with the wave along the satellite orbit. The current study suggests that the plasma density may play an important role on controlling the wave frequency during the chorus generation process.

How to cite: He, Q. and Liu, S.: The generatin of extremely low-frequency chorus waves associated with plasma density enhancement, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7748, https://doi.org/10.5194/egusphere-egu21-7748, 2021.