Analytic expressions for ULF wave radiation belt radial diffusion coefficients.
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We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L).There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV-even though the model does not include the effects of local internal acceleration sources.Analytic expressions for the radial diffusion coefficients are presentedThe coefficients do not dependent on energy or wave m valueThe electric field diffusion coefficient dominates over the magnetic.
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PubMed Central - PubMed
Affiliation: Department of Physics, University of Alberta Edmonton, Alberta, Canada.
ABSTRACT
: We present analytic expressions for ULF wave-derived radiation belt radial diffusion coefficients, as a function of L and Kp, which can easily be incorporated into global radiation belt transport models. The diffusion coefficients are derived from statistical representations of ULF wave power, electric field power mapped from ground magnetometer data, and compressional magnetic field power from in situ measurements. We show that the overall electric and magnetic diffusion coefficients are to a good approximation both independent of energy. We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L). There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV-even though the model does not include the effects of local internal acceleration sources. Our results highlight not only the importance of correct specification of radial diffusion coefficients for developing accurate models but also show significant promise for belt specification based on relatively simple models driven by solar wind parameters such as solar wind speed or geomagnetic indices such as Kp. Key points: Analytic expressions for the radial diffusion coefficients are presentedThe coefficients do not dependent on energy or wave m valueThe electric field diffusion coefficient dominates over the magnetic. No MeSH data available. Related in: MedlinePlus |
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Mentions: The outer boundary flux is specified at L = 7 from the CRRES MEA flux measurements at each of the MEA energy channels by taking the median electron flux value during each orbit over the time interval when the spacecraft is within 0.1 RE of L = 7. Examples of the electron flux used for the outer boundary condition over a 90 day period are illustrated in Figure 11. Note that for times between CRRES apogees, the data are interpolated in the model to provide outer boundary conditions with the hourly resolution of the radial diffusion model runs. At the inner boundary L = 1 we set the electron flux to be 0, representing loss to the ionosphere. Analytic expressions for the electron lifetime, τ outside the plasmasphere as a function of Kp, L shell and energy are given in Shprits et al. [2007], and these electron lifetimes are used to produce the results presented in Figure 9. However, Y. Y. Shprits (personal communication, 2013) state that these electron lifetimes need to be multiplied by a factor of 2, and we use these corrected electron lifetimes in the simulations illustrated in Figure 10. Inside the plasmasphere we set the electron lifetime, τ, to 10 days, which is the approach used in Shprits et al. [2005]. The plasmapause location is estimated using the approximation given in Carpenter and Anderson [1992]. The electron flux simulations are driven purely by the time series of Kp, which is shown in Figures 9a and 10a. |
View Article: PubMed Central - PubMed
Affiliation: Department of Physics, University of Alberta Edmonton, Alberta, Canada.
: We present analytic expressions for ULF wave-derived radiation belt radial diffusion coefficients, as a function of L and Kp, which can easily be incorporated into global radiation belt transport models. The diffusion coefficients are derived from statistical representations of ULF wave power, electric field power mapped from ground magnetometer data, and compressional magnetic field power from in situ measurements. We show that the overall electric and magnetic diffusion coefficients are to a good approximation both independent of energy. We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L). There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV-even though the model does not include the effects of local internal acceleration sources. Our results highlight not only the importance of correct specification of radial diffusion coefficients for developing accurate models but also show significant promise for belt specification based on relatively simple models driven by solar wind parameters such as solar wind speed or geomagnetic indices such as Kp.
Key points: Analytic expressions for the radial diffusion coefficients are presentedThe coefficients do not dependent on energy or wave m valueThe electric field diffusion coefficient dominates over the magnetic.
No MeSH data available.