Dmitriy Subbotin

Energetic, relativistic, and ultrarelativistic electrons: Comparison of long‐term VERB code simulations with Van Allen Probes measurements

In this study, we compare long-term simulations performed by the Versatile Electron Radiation Belt (VERB) code with observations from the Magnetic Electron Ion Spectrometer and Relativistic Electron-Proton Telescope instruments on the Van Allen Probes satellites. The model takes into account radial, energy, pitch angle and mixed diffusion, losses into the atmosphere, and magnetopause shadowing. We consider the energetic (>100 keV), relativistic (~0.5–1 MeV), and ultrarelativistic (>2 MeV) electrons. One year of relativistic electron measurements (μ = 700 MeV/G) from 1 October 2012 to 1 October 2013 are well reproduced by the simulation during varying levels of geomagnetic activity. However, for ultrarelativistic energies (μ = 3500 MeV/G), the VERB code simulation overestimates electron fluxes and phase space density. These results indicate that an additional loss mechanism is operational and efficient for these high energies. The most likely mechanism for explaining the observed loss at ultrarelativistic energies is scattering by the electromagnetic ion cyclotron waves.

Profound change of the near-Earth radiation environment caused by solar superstorms

locally accelerated. Modeling, which now includes transport with resonant acceleration and loss processes and mixed diffusion, shows a rather good correspondence with observations. In this study, we use the same version of the VERB code to model a storm stronger than the Halloween storms, which most likely occurred in the past and may occur in the future. Our simulations indicate that during such a strong event, electrons will be transported into the heart of the inner zone, where they will be accelerated by chorus waves. When the plasmapause extends to larger distances, electrons accelerated by resonant wave‐particle interactions in the inner radiation belt will find themselves in a very different plasma environment and strong fluxes may persist for several years after such a storm. Such intensification of the near‐Earth plasma environment would substantially decrease satellite lifetimes at LEO. The radiation mitigation strategy for satellites operating in the inner belt should include a consideration of the potential for a dramatic increase in the near‐Earth radiation. Such intensification of the near‐Earth radiation environment may be truly devastating and would substantially decrease the lifetimes of meteorological, communication, and military satellites.

Three‐dimensional data assimilation and reanalysis of radiation belt electrons: Observations of a four‐zone structure using five spacecraft and the VERB code

Obtaining the global state of radiation belt electrons through reanalysis is an important step toward validating our current understanding of radiation belt dynamics and for identification of new physical processes. In the current study, reanalysis of radiation belt electrons is achieved through data assimilation of five spacecraft with the 3-D Versatile Electron Radiation Belt (VERB) code using a split-operator Kalman filter technique. The spacecraft data are cleaned for noise, saturation effects, and then intercalibrated on an individual energy channel basis, by considering phase space density conjunctions in the T96 field model. Reanalysis during the CRRES era reveals a never-before-reported four-zone structure in the Earths radiation belts during the 24 March 1991 shock-induced injection superstorm: (1) an inner belt, (2) the high-energy shock-injection belt, (3) a remnant outer radiation belt, and (4) a second outer radiation belt. The third belt formed near the same time as the second belt and was later enhanced across keV to MeV energies by a second particle injection observed by CRRES and the Northern Solar Terrestrial Array riometer network. During the recovery phase of the storm, the fourth belt was created near L*=4RE, lasting for several days. Evidence is provided that the fourth belt was likely created by a dominant local heating process. This study outlines the necessity to consider all diffusive processes acting simultaneously and the advantage of supporting ground-based data in quantifying the observed radiation belt dynamics. It is demonstrated that 3-D data assimilation can resolve various nondiffusive processes and provides a comprehensive picture of the electron radiation belts.

Simulation of high‐energy radiation belt electron fluxes using NARMAX‐VERB coupled codes

This study presents a fusion of data-driven and physics-driven methodologies of energetic electron flux forecasting in the outer radiation belt. Data-driven NARMAX (Nonlinear AutoRegressive Moving Averages with eXogenous inputs) model predictions for geosynchronous orbit fluxes have been used as an outer boundary condition to drive the physics-based Versatile Electron Radiation Belt (VERB) code, to simulate energetic electron fluxes in the outer radiation belt environment. The coupled system has been tested for three extended time periods totalling several weeks of observations. The time periods involved periods of quiet, moderate, and strong geomagnetic activity and captured a range of dynamics typical of the radiation belts. The model has successfully simulated energetic electron fluxes for various magnetospheric conditions. Physical mechanisms that may be responsible for the discrepancies between the model results and observations are discussed.