Modeling cross L shell impacts of magnetopause shadowing and ULF wave radial diffusion in the Van Allen belts

Abstract

We present simulations of the outer electron radiation belt using a new ULF wave-driven radial diffusion model, including empirical representations of loss due to chorus and plasmaspheric hiss. With an outer boundary condition constrained by in situ electron flux observations, we focus on the impacts of magnetopause shadowing and outward radial diffusion in the heart of the radiation belt. Third invariant conserving solutions are combined to simulate the L shell and time dependence of the differential flux at a fixed energy. Results for the geomagnetically quiet year of 2008 demonstrate not only remarkable cross L shell impacts from magnetopause shadowing but also excellent agreement with the in situ observations even though no internal acceleration source is included in the model. Our model demonstrates powerful utility for capturing the cross-L impacts of magnetopause shadowing with significant prospects for improved space weather forecasting. The potential role of the plasmasphere in creating a third belt is also discussed.

Time‐Integral Correlations of Multiple Variables With the Relativistic‐Electron Flux at Geosynchronous Orbit: The Strong Roles of Substorm‐Injected Electrons and the Ion Plasma Sheet

“…The sign of the correlation of d mp with F e1.2 for this physical process should be positive, with more radiation‐belt loss when d mp is smaller (cf. Table ). Enhanced ULF wave‐driven radial diffusion is thought to act in concert with magnetopause shadowing to transport radiation‐belt electrons outward to the magnetopause to be lost (e.g., Ozeke et al, ; Shprits et al, ; Yu, Koller, & Morley, ). A controlling variable for this processes is S geo , the amplitude of ULF fluctuations at geosynchronous orbit.…”

How quickly, how deeply, and how strongly can dynamical outer boundary conditions impact Van Allen radiation belt morphology?

“…Many such ULF wave‐particle interactions are then considered to be combined stochastically within the radial diffusion paradigm. This produces transport and energization which can be specified by the magnitude of the radial diffusion coefficient ( D LL ), itself proportional to the ULF wave power driving the diffusion [e.g., Fälthammar , ; Fei et al ., , and references therein; Ozeke et al ., , , ]. The significant point is that the effects of intense ULF wave power on the dynamics of the radiation belts can be totally and completely different depending upon the boundary conditions and in particular the strength and presence or absence of a suitable source population at the outer edge of the outer zone.…”

“…[], respectively, as discussed, for example, in Ozeke et al . []. The only input to the simulations, besides these Kp ‐driven diffusion coefficients and loss timescales, is the observed flux as a function of energy at the outer boundary assumed to lie at L = 6.…”

Accurately characterizing the importance of wave‐particle interactions in radiation belt dynamics: The pitfalls of statistical wave representations

“…To quantify the relative contribution of electron loss and acceleration by various wave modes requires detailed studies of the electron and wave dynamics as well as global radiation belt modeling during geomagnetic storms. In general, empirical ultralow frequency (ULF) [ Brautigam and Albert , ; Ozeke et al ., ; Ali et al ., ] and very low frequency (VLF) wave models [ Meredith et al ., ; Summers , ; Li et al ., ] characterized by geomagnetic indices are used as inputs for radiation belt models [ Bourdarie et al ., ; Shprits and Thorne , ; Shprits et al ., ; Albert et al ., ; Subbotin et al ., ; Reeves et al ., ; Tu et al ., ; Ozeke et al ., , ]. The relative importance of ULF and VLF wave modes in radiation belt dynamics is then inferred from the modeled response as compared to in situ observations.…”