@article{ShpritsAllisonWangetal.2022, author = {Shprits, Yuri Y. and Allison, Hayley J. and Wang, Dedong and Drozdov, Alexander and Szabo-Roberts, Matyas and Zhelavskaya, Irina and Vasile, Ruggero}, title = {A new population of ultra-relativistic electrons in the outer radiation zone}, series = {Journal of geophysical research : Space physics}, volume = {127}, journal = {Journal of geophysical research : Space physics}, number = {5}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9380}, doi = {10.1029/2021JA030214}, pages = {34}, year = {2022}, abstract = {Van Allen Probes measurements revealed the presence of the most unusual structures in the ultra-relativistic radiation belts. Detailed modeling, analysis of pitch angle distributions, analysis of the difference between relativistic and ultra-realistic electron evolution, along with theoretical studies of the scattering and wave growth, all indicate that electromagnetic ion cyclotron (EMIC) waves can produce a very efficient loss of the ultra-relativistic electrons in the heart of the radiation belts. Moreover, a detailed analysis of the profiles of phase space densities provides direct evidence for localized loss by EMIC waves. The evolution of multi-MeV fluxes shows dramatic and very sudden enhancements of electrons for selected storms. Analysis of phase space density profiles reveals that growing peaks at different values of the first invariant are formed at approximately the same radial distance from the Earth and show the sequential formation of the peaks from lower to higher energies, indicating that local energy diffusion is the dominant source of the acceleration from MeV to multi-MeV energies. Further simultaneous analysis of the background density and ultra-relativistic electron fluxes shows that the acceleration to multi-MeV energies only occurs when plasma density is significantly depleted outside of the plasmasphere, which is consistent with the modeling of acceleration due to chorus waves.}, language = {en} } @article{LandisSaikinZhelavskayaetal.2022, author = {Landis, D. A. and Saikin, Anthony and Zhelavskaya, Irina and Drozdov, Alexander and Aseev, Nikita and Shprits, Yuri Y. and Pfitzer, Maximilian F. and Smirnov, Artem G.}, title = {NARX Neural Network Derivations of the Outer Boundary Radiation Belt Electron Flux}, series = {Space Weather: the international journal of research and applications}, volume = {20}, journal = {Space Weather: the international journal of research and applications}, number = {5}, publisher = {American Geophysical Union}, address = {Washington}, issn = {1542-7390}, doi = {10.1029/2021SW002774}, pages = {18}, year = {2022}, abstract = {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.}, language = {en} } @article{RipollLoridanDentonetal.2019, author = {Ripoll, Jean-Francois and Loridan, Vivien and Denton, Michael H. and Cunningham, Gregory and Reeves, G. and Santolik, O. and Fennell, Joseph and Turner, Drew L. and Drozdov, Alexander and Villa, Juan Sebastian Cervantes and Shprits, Yuri Y. and Thaller, Scott A. and Kurth, William S. and Kletzing, Craig A. and Henderson, Michael G. and Ukhorskiy, Aleksandr Y.}, title = {Observations and Fokker-Planck Simulations of the L-Shell, Energy, and Times}, series = {Journal of geophysical research : Space physics}, volume = {124}, journal = {Journal of geophysical research : Space physics}, number = {2}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9380}, doi = {10.1029/2018JA026111}, pages = {1125 -- 1142}, year = {2019}, abstract = {The evolution of the radiation belts in L-shell (L), energy (E), and equatorial pitch angle (alpha(0)) is analyzed during the calm 11-day interval (4-15 March) following the 1 March 2013 storm. Magnetic Electron and Ion Spectrometer (MagEIS) observations from Van Allen Probes are interpreted alongside 1D and 3D Fokker-Planck simulations combined with consistent event-driven scattering modeling from whistler mode hiss waves. Three (L, E, alpha(0)) regions persist through 11 days of hiss wave scattering; the pitch angle-dependent inner belt core (L similar to <2.2 and E < 700 keV), pitch angle homogeneous outer belt low-energy core (L > similar to 5 and E similar to < 100 keV), and a distinct pocket of electrons (L similar to [4.5, 5.5] and E similar to [0.7, 2] MeV). The pitch angle homogeneous outer belt is explained by the diffusion coefficients that are roughly constant for alpha(0) similar to <60 degrees, E > 100 keV, 3.5 < L < L-pp similar to 6. Thus, observed unidirectional flux decays can be used to estimate local pitch angle diffusion rates in that region. Top-hat distributions are computed and observed at L similar to 3-3.5 and E = 100-300 keV.}, language = {en} }