@article{SmirnovBerrendorfShpritsetal.2020,
  author    = {Smirnov, Artem and Berrendorf, Max and Shprits, Yuri Y. and Kronberg, Elena A. and Allison, Hayley J. and Aseev, Nikita and Zhelavskaya, Irina and Morley, Steven K. and Reeves, Geoffrey D. and Carver, Matthew R. and Effenberger, Frederic},
  title     = {Medium energy electron flux in earth's outer radiation belt (MERLIN)},
  series = {Space weather : the international journal of research and applications},
  volume    = {18},
  journal   = {Space weather : the international journal of research and applications},
  number    = {11},
  publisher = {American geophysical union, AGU},
  address   = {Washington},
  issn      = {1542-7390},
  doi       = {10.1029/2020SW002532},
  pages     = {20},
  year      = {2020},
  abstract  = {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.},
  language  = {en}
}
@misc{SmirnovKronbergDalyetal.2020,
  author    = {Smirnov, Artem G. and Kronberg, Elena A. and Daly, Patrick W. and Aseev, Nikita and Shprits, Yuri Y. and Kellerman, Adam C.},
  title     = {Adiabatic Invariants Calculations for Cluster Mission: A Long-Term Product for Radiation Belts Studies},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {2},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-52391},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-523915},
  pages     = {14},
  year      = {2020},
  abstract  = {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.},
  language  = {en}
}
@article{SmirnovKronbergDalyetal.2020,
  author    = {Smirnov, Artem G. and Kronberg, Elena A. and Daly, Patrick W. and Aseev, Nikita and Shprits, Yuri Y. and Kellerman, Adam C.},
  title     = {Adiabatic Invariants Calculations for Cluster Mission: A Long-Term Product for Radiation Belts Studies},
  series = {Journal of Geophysical Research: Space Physics},
  volume    = {125},
  journal   = {Journal of Geophysical Research: Space Physics},
  number    = {2},
  publisher = {John Wiley \& Sons, Inc.},
  address   = {New Jersey},
  pages     = {12},
  year      = {2020},
  abstract  = {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.},
  language  = {en}
}
@article{SmirnovShpritsAllisonetal.2022,
  author    = {Smirnov, Artem and Shprits, Yuri Y. and Allison, Hayley and Aseev, Nikita and Drozdov, Alexander and Kollmann, Peter and Wang, Dedong and Saikin, Anthony},
  title     = {Storm-Time evolution of the Equatorial Electron Pitch Angle Distributions in Earth's Outer Radiation Belt},
  series = {Frontiers in astronomy and space sciences},
  volume    = {9},
  journal   = {Frontiers in astronomy and space sciences},
  publisher = {Frontiers Media},
  address   = {Lausanne},
  issn      = {2296-987X},
  doi       = {10.3389/fspas.2022.836811},
  pages     = {15},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{SmirnovShpritsAllisonetal.2022,
  author    = {Smirnov, Artem and Shprits, Yuri Y. and Allison, Hayley and Aseev, Nikita and Drozdov, Alexander and Kollmann, Peter and Wang, Dedong and Saikin, Anthony},
  title     = {An empirical model of the equatorial electron pitch angle distributions in earth's outer radiation belt},
  series = {Space Weather: the International Journal of Research and Applications},
  volume    = {20},
  journal   = {Space Weather: the International Journal of Research and Applications},
  number    = {9},
  publisher = {American Geophysical Union},
  address   = {Washington, DC},
  issn      = {1542-7390},
  doi       = {10.1029/2022SW003053},
  pages     = {17},
  year      = {2022},
  abstract  = {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.},
  language  = {en}
}
@article{HaasShpritsAllisonetal.2022,
  author    = {Haas, Bernhard and Shprits, Yuri Y. and Allison, Hayley and Wutzig, Michael and Wang, Dedong},
  title     = {Which parameter controls ring current electron dynamics},
  series = {Frontiers in astronomy and space sciences},
  volume    = {9},
  journal   = {Frontiers in astronomy and space sciences},
  publisher = {Frontiers Media},
  address   = {Lausanne},
  issn      = {2296-987X},
  doi       = {10.3389/fspas.2022.911002},
  pages     = {11},
  year      = {2022},
  abstract  = {Predicting the electron population of Earth's ring current during geomagnetic storms still remains a challenging task. In this work, we investigate the sensitivity of 10 keV ring current electrons to different driving processes, parameterised by the Kp index, during several moderate and intense storms. Results are validated against measurements from the Van Allen Probes satellites. Perturbing the Kp index allows us to identify the most dominant processes for moderate and intense storms respectively. We find that during moderate storms (Kp < 6) the drift velocities mostly control the behaviour of low energy electrons, while loss from wave-particle interactions is the most critical parameter for quantifying the evolution of intense storms (Kp > 6). Perturbations of the Kp index used to drive the boundary conditions at GEO and set the plasmapause location only show a minimal effect on simulation results over a limited L range. It is further shown that the flux at L \& SIM; 3 is more sensitive to changes in the Kp index compared to higher L shells, making it a good proxy for validating the source-loss balance of a ring current model.},
  language  = {en}
}