Three‐dimensional VERB radiation belt simulations including mixed diffusion

Subbotin, D.; Shprits, Yuri; Ni, Binbin

doi:10.1029/2009ja015070

Cited by 101 publications

(133 citation statements)

References 62 publications

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“…Results indicate that during the small but representative storm events, the drift loss to the magnetopause (i.e, magnetopause shadowing) together with outward radial diffusion is mainly responsible for the electron loss, contributing approximately 93-99 % of the total loss near the geosynchronous orbit (L * > 5.0), but with the inner region (L * ≤ 5.0) requiring some additional loss mechanisms (only 60 % can be explained by the above coupled mechanism). Future studies will be directed to quantify relative contributions of other individual or mixed loss mechanisms, such as pitch angle and energy diffusions, which can be included within multidimensional models to represent wave-particle interactions (e.g., Beutier and Boscher, 1995;Albert et al, 2009;Su et al, 2010;Subbotin et al, 2010;Tu et al, 2013).…”

Section: Discussionmentioning

confidence: 99%

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Koller

Morley

2013

Ann. Geophys.

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Abstract. Energetic radiation belt electron fluxes can undergo sudden dropouts in response to different solar wind drivers. Many physical processes contribute to the electron flux dropout, but their respective roles in the net electron depletion remain a fundamental puzzle. Some previous studies have qualitatively examined the importance of magnetopause shadowing in the sudden dropouts either from observations or from simulations. While it is difficult to directly measure the electron flux loss into the solar wind, radial diffusion codes with a fixed boundary location (commonly utilized in the literature) are not able to explicitly account for magnetopause shadowing. The exact percentage of its contribution has therefore not yet been resolved. To overcome these limitations and to determine the exact contribution in percentage, we carry out radial diffusion simulations with the magnetopause shadowing effect explicitly accounted for during a superposed solar wind stream interface passage, and quantify the relative contribution of the magnetopause shadowing coupled with outward radial diffusion by comparing with GPS-observed total flux dropout. Results indicate that during high-speed solar wind stream events, which are typically preceded by enhanced dynamic pressure and hence a compressed magnetosphere, magnetopause shadowing coupled with the outward radial diffusion can explain about 60-99 % of the main-phase radiation belt electron depletion near the geosynchronous orbit. While the outer region (L * > 5) can nearly be explained by the above coupled mechanism, additional loss mechanisms are needed to fully explain the energetic electron loss for the inner region (L * ≤ 5). While this conclusion confirms earlier studies, our quantification study demonstrates its relative importance with respect to other mechanisms at different locations.

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Section: Discussionmentioning

confidence: 99%

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Koller

Morley

2013

Ann. Geophys.

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“…Compared to the other parameters, the wave normal angle information during the propagation of EMIC waves is difficult to acquire directly from in situ observations. Although EMIC waves are believed to become more and more oblique during their propagation to higher latitudes mainly due to the geomagnetic field gradient and curvature, previous studies have commonly adopted a parallel or quasi-parallel propagation assumption to determine the resonant scattering rates of EMIC waves [e.g., Summers and Thorne, 2003;Summers, 2005;Summers et al, 2007;Li et al, 2007;Ukhorskiy et al, 2010;Subbotin et al, 2010;Kersten et al, 2014;Ma et al, 2015]. The major purpose of this study is to evaluate the quantitative role of EMIC waves in driving scattering loss of outer radiation belt relativistic electrons and its sensitivity to wave normal angle distribution.…”

Section: Introductionmentioning

confidence: 99%

Resonant scattering of outer zone relativistic electrons by multiband EMIC waves and resultant electron loss time scales

et al. 2015

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To improve our understanding of the role of electromagnetic ion cyclotron (EMIC) waves in radiation belt electron dynamics, we perform a comprehensive analysis of EMIC wave‐induced resonant scattering of outer zone relativistic (>0.5 MeV) electrons and resultant electron loss time scales with respect to EMIC wave band, L shell, and wave normal angle model. The results demonstrate that while H+‐band EMIC waves dominate the scattering losses of ~1–4 MeV outer zone relativistic electrons, it is He+‐band and O+‐band waves that prevail over the pitch angle diffusion of ultrarelativistic electrons at higher energies. Given the wave amplitude, EMIC waves at higher L shells tend to resonantly interact with a larger population of outer zone relativistic electrons and drive their pitch angle scattering more efficiently. Obliquity of EMIC waves can reduce the efficiency of wave‐induced relativistic electron pitch angle scattering. Compared to the frequently adopted parallel or quasi‐parallel model, use of the latitudinally varying wave normal angle model produces the largest decrease in H+‐band EMIC wave scattering rates at pitch angles < ~40° for electrons > ~5 MeV. At a representative nominal amplitude of 1 nT, EMIC wave scattering produces the equilibrium state (i.e., the lowest normal mode under which electrons at the same energy but different pitch angles decay exponentially on the same time scale) of outer belt relativistic electrons within several to tens of minutes and the following exponential decay extending to higher pitch angles on time scales from <1 min to ~1 h. The electron loss cone can be either empty as a result of the weak diffusion or heavily/fully filled due to approaching the strong diffusion limit, while the trapped electron population at high pitch angles close to 90° remains intact because of no resonant scattering. In this manner, EMIC wave scattering has the potential to deepen the anisotropic distribution of outer zone relativistic electrons by reshaping their pitch angle profiles to “top‐hat.” Overall, H+‐band and He+‐band EMIC waves are most efficient in producing the pitch angle scattering loss of relativistic electrons at ~1–2 MeV. In contrast, the presence of O+‐band EMIC waves, while at a smaller occurrence rate, can dominate the scattering loss of 5–10 MeV electrons in the entire region of the outer zone, which should be considered in future modeling of the outer zone relativistic electron dynamics.

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“…The Salammbo model (Beutier and Boscher, 1995) is an early example of such. More recent 3-D diffusion models now include cross-diffusion terms and have shown that such terms can be important to the evolution of the radiation belts (Xiao et al, 2010;Subbotin et al, 2010). The Dynamic Radiation Environment Assimilation Model (DREAM, Reeves et al, 2005) incorporates data assimilation to drive radial diffusion results towards more realistic values (Koller et al, 2007).…”

Section: T Welling Et Al: Radbelt Verificationmentioning

confidence: 99%

Verification of SpacePy's radial diffusion radiation belt model

2012

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Abstract. Model verification, or the process of ensuring that the prescribed equations are properly solved, is a necessary step in code development. Careful, quantitative verification guides users when selecting grid resolution and time step and gives confidence to code developers that existing code is properly instituted. This work introduces the RadBelt radiation belt model, a new, open-source version of the Dynamic Radiation Environment Assimilation Model (DREAM) and uses the Method of Manufactured Solutions (MMS) to quantitatively verify it. Order of convergence is investigated for a plethora of code configurations and source terms. The ability to apply many different diffusion coefficients, including time constant and time varying, is thoroughly investigated. The model passes all of the tests, demonstrating correct implementation of the numerical solver. The importance of D LL and source term dynamics on the selection of time step and grid size is also explored. Finally, an alternative method to apply the source term is examined to illustrate additional considerations required when non-linear source terms are used.

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Three‐dimensional VERB radiation belt simulations including mixed diffusion

Cited by 101 publications

References 62 publications

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Resonant scattering of outer zone relativistic electrons by multiband EMIC waves and resultant electron loss time scales

Verification of SpacePy's radial diffusion radiation belt model

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