TY  - JOUR
A1  - Shprits, Yuri Y.
A1  - Drozdov, Alexander
A1  - Spasojevic, Maria
A1  - Kellerman, Adam C.
A1  - Usanova, Maria E.
A1  - Engebretson, Mark J.
A1  - Agapitov, Oleksiy V.
A1  - Zhelavskaya, Irina
A1  - Raita, Tero J.
A1  - Spence, Harlan E.
A1  - Baker, Daniel N.
A1  - Zhu, Hui
A1  - Aseev, Nikita
T1  - Wave-induced loss of ultra-relativistic electrons in the Van Allen radiation belts
JF  - Nature Communications
Y1  - 2016
U6  - https://doi.org/10.1038/ncomms12883
SN  - 2041-1723
VL  - 7
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Aseev, Nikita
A1  - Shprits, Yuri Y.
A1  - Wang, Dedong
A1  - Wygant, John
A1  - Drozdov, Alexander
A1  - Kellerman, Adam C.
A1  - Reeves, Geoffrey D.
T1  - Transport and loss of ring current electrons inside geosynchronous orbit during the 17 March 2013 storm
JF  - Journal of geophysical research : Space physics
N2  - Ring current electrons (1–100 keV) have received significant attention in recent decades, but many questions regarding their major transport and loss mechanisms remain open. In this study, we use the four‐dimensional Versatile Electron Radiation Belt code to model the enhancement of phase space density that occurred during the 17 March 2013 storm. Our model includes global convection, radial diffusion, and scattering into the Earth's atmosphere driven by whistler‐mode hiss and chorus waves. We study the sensitivity of the model to the boundary conditions, global electric field, the electric field associated with subauroral polarization streams, electron loss rates, and radial diffusion coefficients. The results of the code are almost insensitive to the model parameters above 4.5 RERE, which indicates that the general dynamics of the electrons between 4.5 RE and the geostationary orbit can be explained by global convection. We found that the major discrepancies between the model and data can stem from the inaccurate electric field model and uncertainties in lifetimes. We show that additional mechanisms that are responsible for radial transport are required to explain the dynamics of ≥40‐keV electrons, and the inclusion of the radial diffusion rates that are typically assumed in radiation belt studies leads to a better agreement with the data. The overall effect of subauroral polarization streams on the electron phase space density profiles seems to be smaller than the uncertainties in other input parameters. This study is an initial step toward understanding the dynamics of these particles inside the geostationary orbit.
KW  - ring current electrons
KW  - magnetospheric convection
KW  - ensemble modeling
KW  - inner magnetosphere
KW  - electron transport
KW  - wave-particle interactions
Y1  - 2019
U6  - https://doi.org/10.1029/2018JA026031
SN  - 2169-9380
SN  - 2169-9402
VL  - 124
IS  - 2
SP  - 915
EP  - 933
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Smirnov, Artem
A1  - Shprits, Yuri Y.
A1  - Allison, Hayley
A1  - Aseev, Nikita
A1  - Drozdov, Alexander
A1  - Kollmann, Peter
A1  - Wang, Dedong
A1  - Saikin, Anthony
T1  - Storm-Time evolution of the Equatorial Electron Pitch Angle Distributions in Earth's Outer Radiation Belt
JF  - Frontiers in astronomy and space sciences
N2  - In this study we analyze the storm-time evolution of equatorial electron pitch angle distributions (PADs) in the outer radiation belt region using observations from the Magnetic Electron Ion Spectrometer (MagEIS) instrument aboard the Van Allen Probes in 2012-2019. The PADs are approximated using a sum of the first, third and fifth sine harmonics. Different combinations of the respective coefficients refer to the main PAD shapes within the outer radiation belt, namely the pancake, flat-top, butterfly and cap PADs. We conduct a superposed epoch analysis of 129 geomagnetic storms and analyze the PAD evolution for day and night MLT sectors. PAD shapes exhibit a strong energy-dependent response. At energies of tens of keV, the PADs exhibit little variation throughout geomagnetic storms. Cap PADs are mainly observed at energies < 300 keV, and their extent in L shrinks with increasing energy. The cap distributions transform into the pancake PADs around the main phase of the storm on the nightside, and then come back to their original shapes during the recovery phase. At higher energies on the dayside, the PADs are mainly pancake during pre-storm conditions and become more anisotropic during the main phase. The quiet-time butterfly PADs can be observed on the nightside at L> 5.6. During the main phase, butterfly PADs have stronger 90 degrees-minima and can be observed at lower L-shells (down to L = 5), then transitioning into flat-top PADs at L similar to 4.5 - 5 and pancake PADs at L < 4.5. The resulting PAD coefficients for different energies, locations and storm epochs can be used to test the wave models and physics-based radiation belt codes in terms of pitch angle distributions.
KW  - pitch angle
KW  - pitch angle distributions
KW  - electrons
KW  - radiation belts
KW  - magnetosphere
KW  - van alien probes
Y1  - 2022
U6  - https://doi.org/10.3389/fspas.2022.836811
SN  - 2296-987X
VL  - 9
PB  - Frontiers Media
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Drozdov, Alexander
A1  - Aseev, Nikita
A1  - Effenberger, Frederic
A1  - Turner, Drew L.
A1  - Saikin, Anthony
A1  - Shprits, Yuri Y.
T1  - Storm Time Depletions of Multi-MeV Radiation Belt Electrons Observed at Different Pitch Angles
JF  - Journal of geophysical research : Space physics
N2  - During geomagnetic storms, the rapid depletion of the high-energy (several MeV) outer radiation belt electrons is the result of loss to the interplanetary medium through the magnetopause, outward radial diffusion, and loss to the atmosphere due to wave-particle interactions. We have performed a statistical study of 110 storms using pitch angle resolved electron flux measurements from the Van Allen Probes mission and found that inside of the radiation belt (L* = 3 - 5) the number of storms that result in depletion of electrons with equatorial pitch angle alpha(eq) = 30 degrees is higher than number of storms that result in depletion of electrons with equatorial pitch angle alpha(eq) = 75 degrees. We conclude that this result is consistent with electron scattering by whistler and electromagnetic ion cyclotron waves. At the outer edge of the radiation belt (L* >= 5.2) the number of storms that result in depletion is also large (similar to 40-50%), emphasizing the significance of the magnetopause shadowing effect and outward radial transport.
Y1  - 2019
U6  - https://doi.org/10.1029/2019JA027332
SN  - 2169-9380
SN  - 2169-9402
VL  - 124
IS  - 11
SP  - 8943
EP  - 8953
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Castillo, Angelica M.
A1  - Shprits, Yuri Y.
A1  - Ganushkina, Natalia
A1  - Drozdov, Alexander
A1  - Aseev, Nikita
A1  - Wang, Dedong
A1  - Dubyagin, Stepan
T1  - Simulations of the inner magnetospheric energetic electrons using the IMPTAM-VERB coupled model
JF  - Journal of Atmospheric and Solar-Terrestrial Physics
N2  - In this study, we present initial results of the coupling between the Inner Magnetospheric Particle Transport and Acceleration Model (IMPTAM) and the Versatile Electron Radiation Belt (VERB-3D) code. IMPTAM traces electrons of 10-100 keV energies from the plasma sheet (L = 9 Re) to inner L-shell regions. The flux evolution modeled by IMPTAM is used at the low energy and outer L* computational boundaries of the VERB code (assuming a dipole approximation) to perform radiation belt simulations of energetic electrons. The model was tested on the March 17th, 2013 storm, for a six-day period. Four different simulations were performed and their results compared to satellites observations from Van Allen probes and GOES. The coupled IMPTAM-VERB model reproduces evolution and storm-time features of electron fluxes throughout the studied storm in agreement with the satellite data (within similar to 0.5 orders of magnitude). Including dynamics of the low energy population at L* = 6.6 increases fluxes closer to the heart of the belt and has a strong impact in the VERB simulations at all energies. However, inclusion of magnetopause losses leads to drastic flux decreases even below L* = 3. The dynamics of low energy electrons (max. 10s of keV) do not affect electron fluxes at energies >= 900 keV. Since the IMPTAM-VERB coupled model is only driven by solar wind parameters and the Dst and Kp indexes, it is suitable as a forecasting tool. In this study, we demonstrate that the estimation of electron dynamics with satellite-data-independent models is possible and very accurate.
KW  - Electron populations
KW  - Radiation belts
KW  - IMPTAM
KW  - VERB
Y1  - 2019
U6  - https://doi.org/10.1016/j.jastp.2019.05.014
SN  - 1364-6826
SN  - 1879-1824
VL  - 191
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Aseev, Nikita
A1  - Shprits, Yuri Y.
A1  - Drozdov, Alexander
A1  - Kellerman, Adam C.
A1  - Usanova, Maria E.
A1  - Wang, D.
A1  - Zhelavskaya, Irina
T1  - Signatures of Ultrarelativistic Electron Loss in the Heart of the Outer Radiation Belt Measured by Van Allen Probes
JF  - Journal of geophysical research : Space physics
N2  - Up until recently, signatures of the ultrarelativistic electron loss driven by electromagnetic ion cyclotron (EMIC) waves in the Earth's outer radiation belt have been limited to direct or indirect measurements of electron precipitation or the narrowing of normalized pitch angle distributions in the heart of the belt. In this study, we demonstrate additional observational evidence of ultrarelativistic electron loss that can be driven by resonant interaction with EMIC waves. We analyzed the profiles derived from Van Allen Probe particle data as a function of time and three adiabatic invariants between 9 October and 29 November 2012. New local minimums in the profiles are accompanied by the narrowing of normalized pitch angle distributions and ground&#8208;based detection of EMIC waves. Such a correlation may be indicative of ultrarelativistic electron precipitation into the Earth's atmosphere caused by resonance with EMIC waves.
Y1  - 2017
U6  - https://doi.org/10.1002/2017JA024485
SN  - 2169-9380
SN  - 2169-9402
VL  - 122
SP  - 10102
EP  - 10111
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Aseev, Nikita
A1  - Shprits, Yuri Y.
T1  - Reanalysis of ring current electron phase space densities using van allen probe observations, convection model, and log‐normal kalman filter
JF  - Space weather : the international journal of research and applications
N2  - Models of ring current electron dynamics unavoidably contain uncertainties in boundary conditions, electric and magnetic fields, electron scattering rates, and plasmapause location. Model errors can accumulate with time and result in significant deviations of model predictions from observations. Data assimilation offers useful tools which can combine physics-based models and measurements to improve model predictions. In this study, we systematically analyze performance of the Kalman filter applied to a log-transformed convection model of ring current electrons and Van Allen Probe data. We consider long-term dynamics of mu = 2.3 MeV/G and K = 0.3 G(1/2) R-E electrons from 1 February 2013 to 16 June 2013. By using synthetic data, we show that the Kalman filter is capable of correcting errors in model predictions associated with uncertainties in electron lifetimes, boundary conditions, and convection electric fields. We demonstrate that reanalysis retains features which cannot be fully reproduced by the convection model such as storm-time earthward propagation of the electrons down to 2.5 R-E. The Kalman filter can adjust model predictions to satellite measurements even in regions where data are not available. We show that the Kalman filter can adjust model predictions in accordance with observations for mu = 0.1, 2.3, and 9.9 MeV/G and constant K = 0.3 G(1/2) R-E electrons. The results of this study demonstrate that data assimilation can improve performance of ring current models, better quantify model uncertainties, and help deeper understand the physics of the ring current particles.
Y1  - 2019
U6  - https://doi.org/10.1029/2018SW002110
SN  - 1542-7390
VL  - 17
IS  - 4
SP  - 619
EP  - 638
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Cervantes Villa, Juan Sebastian
A1  - Shprits, Yuri Y.
A1  - Aseev, Nikita
A1  - Allison, Hayley J.
T1  - Quantifying the effects of EMIC wave scattering and magnetopause shadowing in the outer electron radiation belt by means of data assimilation
JF  - Journal of geophysical research : Space physics
N2  - In this study we investigate two distinct loss mechanisms responsible for the rapid dropouts of radiation belt electrons by assimilating data from Van Allen Probes A and B and Geostationary Operational Environmental Satellites (GOES) 13 and 15 into a 3-D diffusion model. In particular, we examine the respective contribution of electromagnetic ion cyclotron (EMIC) wave scattering and magnetopause shadowing for values of the first adiabatic invariant mu ranging from 300 to 3,000 MeV G(-1). We inspect the innovation vector and perform a statistical analysis to quantitatively assess the effect of both processes as a function of various geomagnetic indices, solar wind parameters, and radial distance from the Earth. Our results are in agreement with previous studies that demonstrated the energy dependence of these two mechanisms. We show that EMIC wave scattering tends to dominate loss at lower L shells, and it may amount to between 10%/hr and 30%/hr of the maximum value of phase space density (PSD) over all L shells for fixed first and second adiabatic invariants. On the other hand, magnetopause shadowing is found to deplete electrons across all energies, mostly at higher L shells, resulting in loss from 50%/hr to 70%/hr of the maximum PSD. Nevertheless, during times of enhanced geomagnetic activity, both processes can operate beyond such location and encompass the entire outer radiation belt.
Y1  - 2020
U6  - https://doi.org/10.1029/2020JA028208
SN  - 2169-9380
SN  - 2169-9402
VL  - 125
IS  - 8
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Aseev, Nikita
A1  - Shprits, Yuri Y.
A1  - Drozdov, Alexander
A1  - Kellerman, Adam C.
T1  - Numerical applications of the advective-diffusive codes for the inner magnetosphere
JF  - Space Weather: The International Journal of Research and Applications
N2  - In this study we present analytical solutions for convection and diffusion equations. We gather here the analytical solutions for the one-dimensional convection equation, the two-dimensional convection problem, and the one- and two-dimensional diffusion equations. Using obtained analytical solutions, we test the four-dimensional Versatile Electron Radiation Belt code (the VERB-4D code), which solves the modified Fokker-Planck equation with additional convection terms. The ninth-order upwind numerical scheme for the one-dimensional convection equation shows much more accurate results than the results obtained with the third-order scheme. The universal limiter eliminates unphysical oscillations generated by high-order linear upwind schemes. Decrease in the space step leads to convergence of a numerical solution of the two-dimensional diffusion equation with mixed terms to the analytical solution. We compare the results of the third- and ninth-order schemes applied to magnetospheric convection modeling. The results show significant differences in electron fluxes near geostationary orbit when different numerical schemes are used.
KW  - advective-diffusive codes
KW  - inner magnetosphere
KW  - numerical schemes
Y1  - 2016
U6  - https://doi.org/10.1002/2016SW001484
SN  - 1542-7390
VL  - 14
SP  - 993
EP  - 1010
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Landis, Daji August
A1  - Saikin, Anthony
A1  - Zhelavskaya, Irina
A1  - Drozdov, Alexander
A1  - Aseev, Nikita
A1  - Shprits, Yuri Y.
A1  - Pfitzer, Maximilian F.
A1  - Smirnov, Artem G.
T1  - NARX Neural Network Derivations of the Outer Boundary Radiation Belt Electron Flux
JF  - Space Weather: the international journal of research and applications
N2  - We present two new empirical models of radiation belt electron flux at geostationary orbit. GOES-15 measurements of 0.8 MeV electrons were used to train a Nonlinear Autoregressive with Exogenous input (NARX) neural network for both modeling GOES-15 flux values and an upper boundary condition scaling factor (BF). The GOES-15 flux model utilizes an input and feedback delay of 2 and 2 time steps (i.e., 5 min time steps) with the most efficient number of hidden layers set to 10. Magnetic local time, Dst, Kp, solar wind dynamic pressure, AE, and solar wind velocity were found to perform as predicative indicators of GOES-15 flux and therefore were used as the exogenous inputs. The NARX-derived upper boundary condition scaling factor was used in conjunction with the Versatile Electron Radiation Belt (VERB) code to produce reconstructions of the radiation belts during the period of July-November 1990, independent of in-situ observations. Here, Kp was chosen as the sole exogenous input to be more compatible with the VERB code. This Combined Release and Radiation Effects Satellite-era reconstruction showcases the potential to use these neural network-derived boundary conditions as a method of hindcasting the historical radiation belts. This study serves as a companion paper to another recently published study on reconstructing the radiation belts during Solar Cycles 17-24 (Saikin et al., 2021, ), for which the results featured in this paper were used.
KW  - radiation belts
KW  - forecasting (1922, 4315, 7924, 7964)
KW  - machine learning (0555)
Y1  - 2022
U6  - https://doi.org/10.1029/2021SW002774
SN  - 1542-7390
VL  - 20
IS  - 5
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Shprits, Yuri Y.
A1  - Kellerman, Adam C .
A1  - Aseev, Nikita
A1  - Drozdov, Alexander
A1  - Michaelis, Ingo
T1  - Multi-MeV electron loss in the heart of the radiation belts
JF  - Geophysical research letters
N2  - Significant progress has been made in recent years in understanding acceleration mechanisms in the Earth's radiation belts. In particular, a number of studies demonstrated the importance of the local acceleration by analyzing the radial profiles of phase space density (PSD) and observing building up peaks in PSD. In this study, we focus on understanding of the local loss using very similar tools. The profiles of PSD for various values of the first adiabatic invariants during the previously studied 17 January 2013 storm are presented and discussed. The profiles of PSD show clear deepening minimums consistent with the scattering by electromagnetic ion cyclotron waves. Long-term evolution shows that local minimums in PSD can persist for relatively long times. During considered interval of time the deepening minimums were observed around L* = 4 during 17 January 2013 storm and around L* = 3.5 during 1 March 2013 storm. This study shows a new method that can help identify the location, magnitude, and time of the local loss and will help quantify local loss in the future. This study also provides additional clear and definitive evidence that local loss plays a major role for the dynamics of the multi-MeV electrons.
Y1  - 2017
U6  - https://doi.org/10.1002/2016GL072258
SN  - 0094-8276
SN  - 1944-8007
VL  - 44
IS  - 3
SP  - 1204
EP  - 1209
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Smirnov, Artem
A1  - Berrendorf, Max
A1  - Shprits, Yuri Y.
A1  - Kronberg, Elena A.
A1  - Allison, Hayley J.
A1  - Aseev, Nikita
A1  - Zhelavskaya, Irina
A1  - Morley, Steven K.
A1  - Reeves, Geoffrey D.
A1  - Carver, Matthew R.
A1  - Effenberger, Frederic
T1  - Medium energy electron flux in earth's outer radiation
belt (MERLIN)
BT  - a Machine learning model
JF  - Space weather : the international journal of research and applications
N2  - The radiation belts of the Earth, filled with energetic electrons, comprise complex and dynamic systems that pose a significant threat to satellite operation. While various models of electron flux both for low and relativistic energies have been developed, the behavior of medium energy (120-600 keV) electrons, especially in the MEO region, remains poorly quantified. At these energies, electrons are driven by both convective and diffusive transport, and their prediction usually requires sophisticated 4D modeling codes. In this paper, we present an alternative approach using the Light Gradient Boosting (LightGBM) machine learning algorithm. The Medium Energy electRon fLux In Earth's outer radiatioN belt (MERLIN) model takes as input the satellite position, a combination of geomagnetic indices and solar wind parameters including the time history of velocity, and does not use persistence. MERLIN is trained on >15 years of the GPS electron flux data and tested on more than 1.5 years of measurements. Tenfold cross validation yields that the model predicts the MEO radiation environment well, both in terms of dynamics and amplitudes o f flux. Evaluation on the test set shows high correlation between the predicted and observed electron flux (0.8) and low values of absolute error. The MERLIN model can have wide space weather applications, providing information for the scientific community in the form of radiation belts reconstructions, as well as industry for satellite mission design, nowcast of the MEO environment, and surface charging analysis.
KW  - machine learning
KW  - radiation belts
KW  - electron flux
KW  - empirical modeling
KW  - magnetosphere
KW  - electrons
Y1  - 2020
U6  - https://doi.org/10.1029/2020SW002532
SN  - 1542-7390
VL  - 18
IS  - 11
PB  - American geophysical union, AGU
CY  - Washington
ER  - 
TY  - JOUR
A1  - Cervantes Villa, Juan Sebastian
A1  - Shprits, Yuri Y.
A1  - Aseev, Nikita
A1  - Drozdov, Alexander
A1  - Castillo Tibocha, Angelica Maria
A1  - Stolle, Claudia
T1  - Identifying radiation belt electron source and loss processes by assimilating spacecraft data in a three-dimensional diffusion model
JF  - Journal of geophysical research : Space physics
N2  - Data assimilation aims to blend incomplete and inaccurate data with physics-based dynamical models. In the Earth's radiation belts, it is used to reconstruct electron phase space density, and it has become an increasingly important tool in validating our current understanding of radiation belt dynamics, identifying new physical processes, and predicting the near-Earth hazardous radiation environment. In this study, we perform reanalysis of the sparse measurements from four spacecraft using the three-dimensional Versatile Electron Radiation Belt diffusion model and a split-operator Kalman filter over a 6-month period from 1 October 2012 to 1 April 2013. In comparison to previous works, our 3-D model accounts for more physical processes, namely, mixed pitch angle-energy diffusion, scattering by Electromagnetic Ion Cyclotron waves, and magnetopause shadowing. We describe how data assimilation, by means of the innovation vector, can be used to account for missing physics in the model. We use this method to identify the radial distances from the Earth and the geomagnetic conditions where our model is inconsistent with the measured phase space density for different values of the invariants mu and K. As a result, the Kalman filter adjusts the predictions in order to match the observations, and we interpret this as evidence of where and when additional source or loss processes are active. The current work demonstrates that 3-D data assimilation provides a comprehensive picture of the radiation belt electrons and is a crucial step toward performing reanalysis using measurements from ongoing and future missions.
KW  - acceleration
KW  - code
KW  - density
KW  - emic waves
KW  - energetic particle
KW  - mechanisms
KW  - reanalysis
KW  - ultrarelativistic electrons
KW  - weather
Y1  - 2019
U6  - https://doi.org/10.1029/2019JA027514
SN  - 2169-9380
SN  - 2169-9402
VL  - 125
IS  - 1
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Drozdov, Alexander
A1  - Shprits, Yuri Y.
A1  - Usanova, Maria E.
A1  - Aseev, Nikita
A1  - Kellerman, Adam C.
A1  - Zhu, H.
T1  - EMIC wave parameterization in the long-term VERB code simulation
JF  - Journal of geophysical research : Space physics
N2  - Electromagnetic ion cyclotron (EMIC) waves play an important role in the dynamics of ultrarelativistic electron population in the radiation belts. However, as EMIC waves are very sporadic, developing a parameterization of such wave properties is a challenging task. Currently, there are no dynamic, activity-dependent models of EMIC waves that can be used in the long-term (several months) simulations, which makes the quantitative modeling of the radiation belt dynamics incomplete. In this study, we investigate Kp, Dst, and AE indices, solar wind speed, and dynamic pressure as possible parameters of EMIC wave presence. The EMIC waves are included in the long-term simulations (1year, including different geomagnetic activity) performed with the Versatile Electron Radiation Belt code, and we compare results of the simulation with the Van Allen Probes observations. The comparison shows that modeling with EMIC waves, parameterized by solar wind dynamic pressure, provides a better agreement with the observations among considered parameterizations. The simulation with EMIC waves improves the dynamics of ultrarelativistic fluxes and reproduces the formation of the local minimum in the phase space density profiles.
KW  - radiation belts
KW  - VERB code
KW  - EMIC
Y1  - 2017
U6  - https://doi.org/10.1002/2017JA024389
SN  - 2169-9380
SN  - 2169-9402
VL  - 122
SP  - 8488
EP  - 8501
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Smirnov, Artem G.
A1  - Kronberg, Elena A.
A1  - Latallerie, F.
A1  - Daly, Patrick W.
A1  - Aseev, Nikita
A1  - Shprits, Yuri Y.
A1  - Kellerman, Adam C.
A1  - Kasahara, Satoshi
A1  - Turner, Drew L.
A1  - Taylor, M. G. G. T.
T1  - Electron Intensity Measurements by the Cluster/RAPID/IES Instrument in Earth's Radiation Belts and Ring Current
JF  - Space Weather: The International Journal of Research and Applications
N2  - Plain Language Summary Radiation belts of the Earth, which are the zones of charged energetic particles trapped by the geomagnetic field, comprise enormous and dynamic systems. While the inner radiation belt, composed mainly of high-energy protons, is relatively stable, the outer belt, filled with energetic electrons, is highly variable and depends substantially on solar activity. Hence, extended reliable observations and the improved models of the electron intensities in the outer belt depending on solar wind parameters are necessary for prediction of their dynamics. The Cluster mission has been measuring electron flux intensities in the radiation belts since its launch in 2000, thus providing a huge dataset that can be used for radiation belts analysis. Using 16 years of electron measurements by the Cluster mission corrected for background contamination, we derived a uniform linear-logarithmic dependence of electron fluxes in the outer belt on the solar wind dynamic pressure.
Y1  - 2019
U6  - https://doi.org/10.1029/2018SW001989
SN  - 1542-7390
VL  - 17
IS  - 4
SP  - 553
EP  - 566
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wang, Dedong
A1  - Shprits, Yuri Y.
A1  - Zhelayskaya, Irina S.
A1  - Agapitov, Oleksiy
A1  - Drozdov, Alexander
A1  - Aseev, Nikita
T1  - Analytical chorus wave model derived from van Allen Probe Observations
JF  - Journal of geophysical research : Space physics
N2  - Chorus waves play an important role in the dynamic evolution of energetic electrons in the Earth's radiation belts and ring current. Using more than 5 years of Van Allen Probe data, we developed a new analytical model for upper‐band chorus (UBC; 0.5fce < f < fce) and lower‐band chorus (LBC; 0.05fce < f < 0.5fce) waves, where fce is the equatorial electron gyrofrequency. By applying polynomial fits to chorus wave root mean square amplitudes, we developed regression models for LBC and UBC as a function of geomagnetic activity (Kp), L, magnetic latitude (λ), and magnetic local time (MLT). Dependence on Kp is separated from the dependence on λ, L, and MLT as Kp‐scaling law to simplify the calculation of diffusion coefficients and inclusion into particle tracing codes. Frequency models for UBC and LBC are also developed, which depends on MLT and magnetic latitude. This empirical model is valid in all MLTs, magnetic latitude up to 20°, Kp ≤ 6, L‐shell range from 3.5 to 6 for LBC and from 4 to 6 for UBC. The dependence of root mean square amplitudes on L are different for different bands, which implies different energy sources for different wave bands. This analytical chorus wave model is convenient for inclusion in quasi‐linear diffusion calculations of electron scattering rates and particle simulations in the inner magnetosphere, especially for the newly developed four‐dimensional codes, which require significantly improved wave parameterizations.
KW  - chorus waves
KW  - radiation belt electrons
KW  - ring current electrons
KW  - analytical model
KW  - wave-particle interactions
KW  - diffusion coefficients
Y1  - 2019
U6  - https://doi.org/10.1029/2018JA026183
SN  - 2169-9380
SN  - 2169-9402
VL  - 124
IS  - 2
SP  - 1063
EP  - 1084
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Smirnov, Artem
A1  - Shprits, Yuri Y.
A1  - Allison, Hayley
A1  - Aseev, Nikita
A1  - Drozdov, Alexander
A1  - Kollmann, Peter
A1  - Wang, Dedong
A1  - Saikin, Anthony
T1  - An empirical model of the equatorial electron pitch angle distributions in earth's outer radiation belt
JF  - Space Weather: the International Journal of Research and Applications
N2  - In this study, we present an empirical model of the equatorial electron pitch angle distributions (PADs) in the outer radiation belt based on the full data set collected by the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard the Van Allen Probes in 2012-2019. The PADs are fitted with a combination of the first, third and fifth sine harmonics. The resulting equation resolves all PAD types found in the outer radiation belt (pancake, flat-top, butterfly and cap PADs) and can be analytically integrated to derive omnidirectional flux. We introduce a two-step modeling procedure that for the first time ensures a continuous dependence on L, magnetic local time and activity, parametrized by the solar wind dynamic pressure. We propose two methods to reconstruct equatorial electron flux using the model. The first approach requires two uni-directional flux observations and is applicable to low-PA data. The second method can be used to reconstruct the full equatorial PADs from a single uni- or omnidirectional measurement at off-equatorial latitudes. The model can be used for converting the long-term data sets of electron fluxes to phase space density in terms of adiabatic invariants, for physics-based modeling in the form of boundary conditions, and for data assimilation purposes.
KW  - pitch angle
KW  - radiation belt
KW  - model
KW  - magnetosphere
KW  - van allen probes;
KW  - electrons
Y1  - 2022
U6  - https://doi.org/10.1029/2022SW003053
SN  - 1542-7390
VL  - 20
IS  - 9
PB  - American Geophysical Union
CY  - Washington, DC
ER  - 
TY  - JOUR
A1  - Smirnov, Artem G.
A1  - Kronberg, Elena A.
A1  - Daly, Patrick W.
A1  - Aseev, Nikita
A1  - Shprits, Yuri Y.
A1  - Kellerman, Adam C.
T1  - Adiabatic Invariants Calculations for Cluster Mission: A Long-Term Product for Radiation Belts Studies
JF  - Journal of Geophysical Research: Space Physics
N2  - The Cluster mission has produced a large data set of electron flux measurements in the Earth's magnetosphere since its launch in late 2000. Electron fluxes are measured using Research with Adaptive Particle Imaging Detector (RAPID)/Imaging Electron Spectrometer (IES) detector as a function of energy, pitch angle, spacecraft position, and time. However, no adiabatic invariants have been calculated for Cluster so far. In this paper we present a step-by-step guide to calculations of adiabatic invariants and conversion of the electron flux to phase space density (PSD) in these coordinates. The electron flux is measured in two RAPID/IES energy channels providing pitch angle distribution at energies 39.2-50.5 and 68.1-94.5 keV in nominal mode since 2004. A fitting method allows to expand the conversion of the differential fluxes to the range from 40 to 150 keV. Best data coverage for phase space density in adiabatic invariant coordinates can be obtained for values of second adiabatic invariant, K, similar to 10(2), and values of the first adiabatic invariant mu in the range approximate to 5-20 MeV/G. Furthermore, we describe the production of a new data product "LSTAR," equivalent to the third adiabatic invariant, available through the Cluster Science Archive for years 2001-2018 with 1-min resolution. The produced data set adds to the availability of observations in Earth's radiation belts region and can be used for long-term statistical purposes.
KW  - L-Asterisk
KW  - magnetosphere
KW  - electrons
KW  - model
Y1  - 2019
VL  - 125
IS  - 2
PB  - John Wiley & Sons, Inc.
CY  - New Jersey
ER  -