The Effect of Plasma Boundaries on the Dynamic Evolution of Relativistic Radiation Belt Electrons

Abstract

Understanding the dynamic evolution of relativistic electrons in the Earth's radiation belts during both storm and nonstorm times is a challenging task. The U.S. National Science Foundation's Geospace Environment Modeling (GEM) focus group "Quantitative Assessment of Radiation Belt Modeling" has selected two storm time and two nonstorm time events that occurred during the second year of the Van Allen Probes mission for in-depth study. Here, we perform simulations for these GEM challenge events using the 3D Versatile Electron Radiation Belt code. We set up the outer L * boundary using data from the Geostationary Operational Environmental Satellites and validate the simulation results against satellite observations from both the Geostationary Operational Environmental Satellites and Van Allen Probe missions for 0.9-MeV electrons. Our results show that the position of the plasmapause plays a significant role in the dynamic evolution of relativistic electrons. The magnetopause shadowing effect is included by using last closed drift shell, and it is shown to significantly contribute to the dropouts of relativistic electrons at high L * . We perform simulations using four different empirical radial diffusion coefficient models for the GEM challenge events, and the results show that these simulations reproduce the general dynamic evolution of relativistic radiation belt electrons. However, in the events shown here, simulations using the radial diffusion coefficients from Brautigam and Albert (2000) produce the best agreement with satellite observations. Key Points:• We investigate the effect of different plasmapause positions and radial diffusion coefficients during the four GEM challenge events • Including the magnetopause shadowing effect by using the last closed drift shell helps to reproduce the dropouts • The three-dimensional Versatile Electron Radiation Belt code reproduces the general dynamics of relativistic electrons during GEM challenge events Supporting Information:• Supporting Information S1 , et al. (2020). The effect of plasma boundaries on the dynamic evolution of relativistic radiation belt electrons.

The Role of Hiss, Chorus, and EMIC Waves in the Modeling of the Dynamics of the Multi‐MeV Radiation Belt Electrons

“…Brautigam and Albert's (2000) parameterization is used for the radial diffusion. This model is chosen because it produces the best agreement with the observations (e.g., Drozdov, Shprits, Aseev et al, 2017; Wang et al, 2020). The statistics from Spasojevic et al (2015) and Orlova et al (2016) are used for the hiss waves (considering realistic spectrum from Li et al (2015) that takes into account low‐frequency hiss), and the model presented in Zhu et al (2019) is used for chorus waves.…”

A Comparison of Radial Diffusion Coefficients in 1‐D and 3‐D Long‐Term Radiation Belt Simulations

“…To quantify the agreement between model output and Van Allen Probes observations, we use the normalized difference (ND) of the electron flux ( j): This metric has been used previously by Subbotin and Shprits (2009), Drozdov, and Wang et al (2020) and provides the difference between observations ( obs j ) and model output ( model j ) at a particular energy, * L , eq  , and time. The result is normalized by the maximum flux in the heart of the belt and is therefore particularly useful to determine how well the simulation reproduces the observed flux peaks, as well as the behavior around the maximum.…”

Reconstruction of the Radiation Belts for Solar Cycles 17–24 (1933–2017)

“…The simulation by Wang et al. (2019) used the more comprehensive plasmasphere model Plasma density in the Inner magnetosphere Neural network‐based Empirical (PINE) (Zhelavskaya et al., 2017), provided better agreement with the observations in comparisons to the Carpenter and Anderson (1992) model. Accurate modeling of the radiation belt in the slot region and the inner belt would require more accurate qualification of the scattering process near the Earth below 2 R E (Albert et al., 2020).…”

“…Future endeavors into radiation belt modeling may want to consider using a metric for the plasmasphere location which incorporates a more complicated and in-depth description such as O' Brien and Moldwin (2003). The simulation by Wang et al (2019) Table 9 The Logged First and Second Moment Distributions of Flux Values Figure 10. Total integrated flux by percentile (5th, 10th, 25th, 50th, 75th, 90th, 95th) over each solar cycle for the 0.5, 1.0, and 2.0 MeV 85° pitch angle electrons (panels a, b, and c, respectively).…”