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Energetic electron flux measured by SOPA from LANL satellites 1990-095, 1991-080, 1994-084, and LANL-97A. The vertical dotted line of each panel indicates local midnight. The nine traces correspond to each energy; 50-75 keV, 75-105 keV, 105-150 keV, 150-225 keV, 225-315 keV, 315500 keV, 500-750 keV, 750-1100 keV, and 1100-1500 keV, respectively.
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1] We examined and simulated the dynamics of energetic electrons during the October 2001 magnetic storm with the relativistic RAM electron model for a wide range of energies. The storm had a rapid main phase followed by a day of strong geomagnetic activity that produced a second Dst minimum and then a very quiet recovery phase. During the main phas...
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Dynamical variations of radiation belt trapped electron fluxes are examined to better understand the variability of enhancements linked to substorm clusters. Analysis is undertaken using the Substorm Onsets and Phases from Indices of the Electrojet substorm cluster algorithm for event detection. Observations from low earth orbit are complemented by...
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... When the convective electric field induced by the solar wind enhances, a significant number of electrons move from the magnetotail to the inner magnetosphere, which is recognized as convection. Besides, electron flux enhancement due to convection in the inner magnetosphere exhibits an MLT (magnetic local time) asymmetry (e.g., Miyoshi et al., 2006). When the MLT is divided into two major sectors, this asymmetry shows higher electron fluxes in the dawn sector and lower electron fluxes in the dusk sector. ...
... Simultaneously, the electron flux increased in the dawn sector near the heart of the external outer belt (L ∼ 6.5) and gradually increased in the dusk sector after about an hour, leading to a significant dawn-dusk asymmetry of the electron flux during this period with a dawn-to-dusk ratio up to two orders of magnitude ( Figure 6e). In addition, from 12:00 UT to 18:00 UT, this asymmetry is predominantly distributed at higher L (e.g., L > 6), which is consistent with the observed signature of convective activity (Miyoshi et al., 2006). Therefore, the analysis in this section provides evidence that convection could also be an important mechanism for the formation of the external outer belt in the sub-relativistic electron three-belt structure, alongside the substorm injections observed in Section 3.4. ...
The Van Allen Probes mission contributed to the discovery of the relativistic (∼500 keV–2 MeV) and ultra‐relativistic (∼>2 MeV) electron three‐belt structure in Earth's radiation belts. This structure results from the partial depletion of the preexisting outer belt and the replenishment of a new outer belt. Ultra‐low frequency and very‐low frequency waves are believed to play important roles in these processes, and substorm injections are usually not responsible for the formation of the external outer belt. In this study, based on observations from the Arase and NOAA‐18 (National Oceanic and Atmospheric Administration‐18) satellites, we report an electron three‐belt event in the energy range of ∼100–200 keV (i.e., sub‐relativistic electrons). According to the evolution of the phase space density and the dawn‐dusk asymmetric flux enhancement during this event, we conclude that the depletion of the upper part of the original outer belt was due to outward radial diffusion accompanied by magnetopause shadowing effect and convection, and the formation of the external outer belt was due to increased electron flux from convection as well as substorm injections. This discovery and its preliminary explanation may help understand the electron three‐belt structure in radiation belts more comprehensively.
... The outer boundary of RAM needs particle flux distributions (in energy and pitch angle). For many scientific studies, these are derived from geosynchronous observations (e.g., Jordanova et al., 2016;Miyoshi et al., 2006). To avoid potential issues with data availability or data processing for the boundary, we use the Kp-parameterized model of Denton et al. (2015) that was developed using LANL geosynchronous particle data. ...
The Ring current–Atmosphere interactions Model (RAM) with Self‐Consistent magnetic (B) field (SCB) combines a large‐scale kinetic model of ring current plasma with a three‐dimensional (3‐D) force‐balanced model of the terrestrial magnetic field. RAM‐SCB simulates the evolution of major ion species (H⁺, O⁺, and He⁺ by default) and electrons as a function of azimuth, radial distance, energy, and pitch angle. Simulation outputs include the Dst index, and pressure and differential flux of the modeled species, thus providing benefit as a science code and to inform surface charging hazard within the model domain. Version 2.2 of this open‐source simulation code has now—as of 8 August 2023—been made available for Runs‐On‐Request via the Community Coordinated Modeling Center.
... The D LL is obtained from the empirical radial diffusion coefficient from Brautigam and Albert (2000), which was derived up to Kp = 6 and for equatorially mirroring electrons. Here it is also applied to Kp > 6 intervals and to electrons at all pitch angles due to the unresolved pitch angle dependence of D LL (e.g., Li et al., 2016;Miyoshi et al., 2006;Sarris et al., 2022). To represent the magnetopause shadowing loss, electron lifetimes outside the LCDS are assumed to be on the order of electron drift periods. ...
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Magnetopause shadowing has been recognized as a significant loss mechanism contributing to the rapid dropouts of radiation belt electrons. The last closed drift shell (LCDS), a critical input in modeling the magnetopause shadowing loss, is typically calculated by tracing magnetic field lines with constant second adiabatic invariant and magnetic field strength at particle's mirror point (Bm). However, the effects of drift orbit bifurcation (DOB) have not been realistically incorporated into the LCDS estimation for dropout modeling. DOB occurs when the local maximum of the magnetic field strength on the equator exceeds Bm, causing particles to be trapped in one hemisphere and leading to the violation of the second adiabatic invariant. To evaluate the effects of DOB on shadowing loss, we implemented three different LCDS calculations, that is, tracing field lines ignoring DOB, tracing test particles rejecting field lines with DOB, and tracing test particles including field lines with DOB, in a one‐dimensional radial diffusion model. By reproducing the electron dropout observed at high L* during the geomagnetic storm in May 2017, we discovered, for the first time, that physically incorporating DOB effects into the LCDS calculation via test particle tracing can best capture the observed electron loss at high L*.
... The ring current ion composition during active and quiet times is well studied using in situ observations and modeling Ebihara et al., 2002;Jordanova et al., 1996Jordanova et al., , 1998Jordanova et al., , 2006Jordanova et al., , 2012Kistler et al., 1989Kistler et al., , 2016Miyoshi et al., 2006). However, there have been limited studies on the electron contribution to the ring current. ...
Using Arase observations of the inner magnetosphere during 26 CIR‐driven geomagnetic storms with minimum Sym‐H between −33 and −86 nT, we investigated ring current pressure development of ions (H⁺, He⁺, O⁺) and electron during prestorm, main, early recovery and late recovery phases as a function of L‐shell and magnetic local time. It is found that during the main and early recovery phase of the storms the ion pressure is asymmetric in the inner magnetosphere, leading to a strong partial ring current. The ion pressure becomes symmetric during the late recovery phase. H⁺ ions with energies of ∼20–50 keV and ∼50–100 keV contribute more to the ring current pressure during the main phase and early/late recovery phase, respectively. O⁺ ions with energies of ∼10–20 keV contribute significantly during main and early recovery phase. These are consistent with previous studies. The electron pressure was found to be asymmetric during the main, early recovery and late recovery phase. The electron pressure peaks from midnight to the dawn sector. Electrons with energy of <50 keV contribute to the ring current pressure during the main and early recovery phase of the storms. Overall, the electron contribution to the total ring current is found to be ∼11% during the main and early recovery phases. However, the electron contribution is found to be significant (∼22%) in the 03–09 MLT sector during the main and early recovery phase. The results indicate an important role of electrons in the ring current build up.
... For the diffusion coefficients considered in this paper, the pitch-angle scaling factor given by Equation 21 can be applied to BA LL D , as its derivation follows the Fälthammar (1965) methodology, consistent with Schulz and Lanzerotti (1974). This approach is taken by Miyoshi et al. (2006) ; (g-i) Similar to panels (g-i) but for the simulations on panels (j-l) and measurements. ...
Radial diffusion is one of the dominant physical mechanisms driving acceleration and loss of radiation belt electrons. A number of parameterizations for radial diffusion coefficients have been developed, each differing in the data set used. Here, we investigate the performance of different parameterizations by Brautigam and Albert (2000), https://doi.org/10.1029/1999ja900344, Brautigam et al. (2005), https://doi.org/10.1029/2004ja010612, Ozeke et al. (2014), https://doi.org/10.1002/2013ja019204, Ali et al. (2015), https://doi.org/10.1002/2014ja020419; Ali et al. (2016), https://doi.org/10.1002/2016ja023002; Ali (2016), and Liu et al. (2016), https://doi.org/10.1002/2015gl067398 on long‐term radiation belt modeling using the Versatile Electron Radiation Belt (VERB) code, and compare the results to Van Allen Probes observations. First, 1‐D radial diffusion simulations are performed, isolating the contribution of solely radial diffusion. We then take into account effects of local acceleration and loss showing additional 3‐D simulations, including diffusion across pitch‐angle, energy, and mixed diffusion. For the L* range studied, the difference between simulations with Brautigam and Albert (2000), https://doi.org/10.1029/1999ja900344, Ozeke et al. (2014), https://doi.org/10.1002/2013ja019204, and Liu et al. (2016), https://doi.org/10.1002/2015gl067398 parameterizations is shown to be small, with Brautigam and Albert (2000), https://doi.org/10.1029/1999ja900344 offering the smallest averaged (across multiple energies) absolute normalized difference with observations. Using the Ali et al. (2016), https://doi.org/10.1002/2016ja023002 parameterization tended to result in a lower flux than both the observations and the VERB simulations using the other coefficients. We find that the 3‐D simulations are less sensitive to the radial diffusion coefficient chosen than the 1‐D simulations, suggesting that for 3‐D radiation belt models, a similar result is likely to be achieved, regardless of whether Brautigam and Albert (2000), https://doi.org/10.1029/1999ja900344, Ozeke et al. (2014), https://doi.org/10.1002/2013ja019204, and Liu et al. (2016), https://doi.org/10.1002/2015gl067398 parameterizations are used.
... The physics based numerical model used in the present study is the ring current-atmosphere interactions model (RAM) coupled with a SC magnetic field (B) (Jordanova & Miyoshi, 2005;Jordanova et al., 1996Jordanova et al., , 1997Jordanova et al., , 2006Jordanova et al., , 2010Jordanova et al., , 2016Miyoshi et al., 2006;Yu et al., 2012Yu et al., , 2017Zaharia et al., 2006). RAM-SCB solves numerically the bounce averaged kinetic equation for the phase distribution function Q R E t ...
Understanding the physical processes that control the dynamics of energetic particles in the inner magnetosphere is important for both space‐borne and ground‐based assets essential to the modern society. The storm time distribution of ring current particles in the inner magnetosphere depends strongly on their transport in the evolving electric and magnetic fields along with particle acceleration and loss. In this study, we investigated the ring current particle variations using observations and simulations. We compared the ion (H⁺, He⁺, and O⁺) and electron flux and plasma pressure variations from Arase observations with the self‐consistent inner magnetosphere model: Ring current Atmosphere interactions Model with Self Consistent magnetic field (RAM‐SCB) during the 7–8 November 2017 geomagnetic storm. We investigated the contribution of the different species (ions and electrons) to the magnetic field deformation observed at ground magnetic stations (09°–45° MLat) using RAM‐SCB simulations. The results show that the ions are the major contributor with ∼88% and electrons contribute ∼12% to the total ring current pressure. It is also found that the electron contribution is non‐negligible (∼18%) to the ring current in dawn‐side during the main phase of the storm. Thus, the electron contribution to the storm time ring current is important and should not be neglected.
... Magnetopause shadowing describes the loss of trapped particles on drift trajectories that intersect the magnetopause following sudden compressions of the magnetosphere (e.g., K. C. Kim et al., 2008). Losses at lower L-shells than those that directly interact with the magnetopause can occur as electrons are driven toward the magnetopause boundary by outward radial transport resulting from perturbations to the PSD radial distribution by ultralow frequency wave activity that violates the third adiabatic invariant (e.g., Loto'aniu et al., 2010;Miyoshi et al., 2006;Shprits et al., 2006;. Rapid deceleration due to nonlinear wave-particle interactions (e.g., Tao et al., 2012) could also contribute to dropouts, but has yet to be thoroughly investigated. ...
Radiation belt flux dropout events are sudden and often significant reductions in high‐energy electrons from Earth's outer radiation belts. These losses are theorized to be due to interactions with the dayside magnetopause and possibly connected to observations of escaping magnetospheric particles. This study focuses on radiation belt losses during a moderate‐strength, nonstorm dropout event on November 21, 2016. The potential loss mechanisms and the linkage to dayside escape are investigated using combined energetic electron observations throughout the dayside magnetosphere from the Magnetospheric Multiscale and Van Allen Probes spacecraft along with global magnetohydrodynamic and test particle simulations. In particular, this nonstorm‐time event simplifies the magnetospheric conditions and removes ambiguity in the interpretation of results, allowing focus on subsequent losses from enhanced outward radial transport that can occur after initial compression and relaxation of the magnetopause boundary. The evolution of measured phase space density profiles suggest a total loss of approximately 60% of the initial radiation belt content during the event. Together the in situ observations and high‐resolution simulations help to characterize the loss by bounding the following parameters: (a) the duration of the loss, (b) the relative distribution of losses and surface area of the magnetopause over which loss occurs, and (c) the escaping flux (i.e., loss) rate across the magnetopause. In particular, this study is able to estimate the surface area of loss to less than 2.9 × 10⁶ RE² and the duration of loss to greater than 6 h, while also demonstrating the magnetic local time‐dependence of the escaping flux and energy spectrum.
... Each event has been studied at least once in previous work. (Miyoshi et al., 2006;Yermolaev et al., 2008;Pulkkinen et al., 2011;Honkonen et al., 2013). All global models have been executed through the CCMC website (http://ccmc.gsfc.nasa.gov/) ...
The performance of three global magnetohydrodynamic (MHD) models in estimating the Earth's magnetopause location and ionospheric cross polar cap potential (CPCP) have been presented. Using the Community Coordinated Modeling Center's Run-on-Request system and extensive database on results of various magnetospheric scenarios simulated for a variety of solar weather patterns, the aforementioned model predictions have been compared with magnetopause standoff distance estimations obtained from six empirical models, and with cross polar cap potential estimations obtained from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) Model and the Super Dual Auroral Radar Network (SuperDARN) observations. We have considered a range of events spanning different space weather activity to analyze the performance of these models. Using a fit performance metric analysis for each event, the models' reproducibility of magnetopause standoff distances and CPCP against empirically-predicted observations were quantified, and salient features that govern the performance characteristics of the modeled magnetospheric and ionospheric quantities were identified. Results indicate mixed outcomes for different models during different events, with almost all models underperforming during the extreme-most events. The quantification also indicates a tendency to underpredict magnetopause distances in the absence of an inner magnetospheric model, and an inclination toward over predicting CPCP values under general conditions.
... The lifetime due to wave-particle interactions as a empirical function of the geomagnetic activity index Kp 6 we shall determine according to work [4] ...
... Since T wp (Kp = 0) was not determined in [4], the following formula for calculation is offered ...
Modeling of pitch angle scattering of ring current protons at interaction with electromagnetic ion cyclotron waves during a nonstorm period was considered very seldom. Therefore it is used correlated observation of enhanced electromagnetic ion cyclotron (EMIC) waves and dynamic evolution of ring current proton flux collected by Cluster satellite near the location L = 4.5 during March 26–27, 2003, a nonstorm period (Dst > –10 nT). Energetic (5–30 keV) proton fluxes are found to drop rapidly (e.g., a half hour) at lower pitch angles, corresponding to intensified EMIC wave activities. As mathematical model is used the non-stationary one-dimensional pitch angle diffusion equation which allows to compute numerically density of phase space or pitch angle distribution of the charged particles in the Earth’s magnetosphere. The model depends on time t, a local pitch angle and several parameters (the mass of a particle, the energy, the McIlwain parameter, the magnetic local time or geomagnetic eastern longitude, the geomagnetic activity index, parameter of the charged particle pitch angle distribution taken for the 90 degrees pitch angle at t = 0, the lifetime due to wave–particle interactions). This model allows numerically to estimate also for different geophysical conditions a lifetime due to wave–particle interactions. It is shown, that EMIC waves can yield decrements in proton flux within 30 minutes, consistent with the observational data. The good consent is received. Comparison of results on full model for the pitch angle range from 0 up to 180 degrees and on the model for the 90 degrees pitch angle is lead. For a perpendicular differential flux of the Earth’s ring current protons very good consent with the maximal relative error approximately 3.23 % is received
... This process indicated by the decrease of ΔL to zero in Figure 3 is typically within half a day. The enhancement of energetic electrons in the slot region and the outer radiation belt during the storm main phase have been deeply investigated, especially in the era of Van Allen Probes, including the radial transport by the enhanced convection electric field Thorne et al., 2007;Zhao et al., 2017) and ULF waves (Elkington, 2003;Miyoshi et al., 2006;Ripoll et al., 2016), local acceleration by chorus waves (Horne, 2005;Ma et al., 2018;Thorne et al., 2007), and the relationship between the initial enhancement of energetic electrons and the innermost plasmapause locations (Khoo et al., 2018(Khoo et al., , 2019. ...
We investigate the shapes of the inner boundary of the outer radiation belt during different geomagnetic storm phases using energetic electron observations from Van Allen Probes. The case of two consecutive but isolated storms in April 2016 shows that (a) the inner boundary, as a function of L shell and energy, exhibits a “V‐shaped” form with the energetic electrons showing a kappa‐like energy spectrum (electron flux steeply falling with increasing energies), whereas it is in a “S‐shaped” form as the energetic electrons show a reversed energy spectrum (electron flux going up with increasing energies from hundreds of keV to ∼1 MeV); (b) the boundary is abruptly transformed from S to V shape during the storm main phase and retains in V shape for several days until it evolves into S shape during the late recovery phase. The main statistical results from 37 isolated geomagnetic storms between 2013 and 2017 present that (a) the more SYM‐H drops, the closest to Earth the transition from V to S shape starts, with a linear correlation coefficient of ∼0.7; (b) the minimum energy at which the transition starts is between 100 and 550 keV (typically, less than 250 keV); (c) the transition from V to S shape typically occurs in the plasmasphere.
