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Enhanced radial transport and energization of radiation belt electrons due to drift orbit bifurcations.

Ukhorskiy AY, Sitnov MI, Millan RM, Kress BT, Smith DC - J Geophys Res Space Phys (2014)

Bottom Line: We use a test particle approach which captures anomalous effects such as drift orbit bifurcations.Even at quiet time fluctuations in dynamic pressure, radial transport at large pitch angles exhibits strong deviations from the diffusion approximation.The radial transport rates are much lower at small pitch angle values which results in a better agreement with the diffusion approximation.

View Article: PubMed Central - PubMed

Affiliation: Applied Physics Laboratory, Johns Hopkins University Laurel, Maryland, USA.

ABSTRACT

[1]Relativistic electron intensities in Earth's outer radiation belt can vary by multiple orders of magnitude on the time scales ranging from minutes to days. One fundamental process contributing to dynamic variability of radiation belt intensities is the radial transport of relativistic electrons across their drift shells. In this paper we analyze the properties of three-dimensional radial transport in a global magnetic field model driven by variations in the solar wind dynamic pressure. We use a test particle approach which captures anomalous effects such as drift orbit bifurcations. We show that the bifurcations lead to an order of magnitude increase in radial transport rates and enhance the energization at large equatorial pitch angles. Even at quiet time fluctuations in dynamic pressure, radial transport at large pitch angles exhibits strong deviations from the diffusion approximation. The radial transport rates are much lower at small pitch angle values which results in a better agreement with the diffusion approximation.

No MeSH data available.


Related in: MedlinePlus

Radial transport in test particle simulations of electrons with small equatorial pitch angles (LM=6.5, αeq=15°). Similar to Figure 3, black lines show 80 sample trajectories, while red lines correspond to average values computed with all trajectories in the simulation. Figure 4a shows the transport during the entire simulation, while Figures 4b and 4c zoom in on the first 8 and 2 h correspondingly.
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fig04: Radial transport in test particle simulations of electrons with small equatorial pitch angles (LM=6.5, αeq=15°). Similar to Figure 3, black lines show 80 sample trajectories, while red lines correspond to average values computed with all trajectories in the simulation. Figure 4a shows the transport during the entire simulation, while Figures 4b and 4c zoom in on the first 8 and 2 h correspondingly.

Mentions: [24]Radial transport of particles with small equatorial pitch angles not susceptible to drift orbit bifurcations is shown in Figure 4. Figure 4a shows the transport over the entire simulation. It is evident that the transport rates are much slower than in the previously considered case of the near-equatorial particles. Over 20 h, particles with small equatorial pitch angles expanded only over a small fraction of the outer belt, which was covered by the near-equatorial particles over less than 1.5 h. Since the transport is much slower, the drift-phase correlations among particles of the ensemble decay well before the particles expand over the entire system. Consequently, radial transport on the time scales of is in a much better agreement with radial diffusion, which is evident in nearly linear scaling of in Figure 4a.


Enhanced radial transport and energization of radiation belt electrons due to drift orbit bifurcations.

Ukhorskiy AY, Sitnov MI, Millan RM, Kress BT, Smith DC - J Geophys Res Space Phys (2014)

Radial transport in test particle simulations of electrons with small equatorial pitch angles (LM=6.5, αeq=15°). Similar to Figure 3, black lines show 80 sample trajectories, while red lines correspond to average values computed with all trajectories in the simulation. Figure 4a shows the transport during the entire simulation, while Figures 4b and 4c zoom in on the first 8 and 2 h correspondingly.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497472&req=5

fig04: Radial transport in test particle simulations of electrons with small equatorial pitch angles (LM=6.5, αeq=15°). Similar to Figure 3, black lines show 80 sample trajectories, while red lines correspond to average values computed with all trajectories in the simulation. Figure 4a shows the transport during the entire simulation, while Figures 4b and 4c zoom in on the first 8 and 2 h correspondingly.
Mentions: [24]Radial transport of particles with small equatorial pitch angles not susceptible to drift orbit bifurcations is shown in Figure 4. Figure 4a shows the transport over the entire simulation. It is evident that the transport rates are much slower than in the previously considered case of the near-equatorial particles. Over 20 h, particles with small equatorial pitch angles expanded only over a small fraction of the outer belt, which was covered by the near-equatorial particles over less than 1.5 h. Since the transport is much slower, the drift-phase correlations among particles of the ensemble decay well before the particles expand over the entire system. Consequently, radial transport on the time scales of is in a much better agreement with radial diffusion, which is evident in nearly linear scaling of in Figure 4a.

Bottom Line: We use a test particle approach which captures anomalous effects such as drift orbit bifurcations.Even at quiet time fluctuations in dynamic pressure, radial transport at large pitch angles exhibits strong deviations from the diffusion approximation.The radial transport rates are much lower at small pitch angle values which results in a better agreement with the diffusion approximation.

View Article: PubMed Central - PubMed

Affiliation: Applied Physics Laboratory, Johns Hopkins University Laurel, Maryland, USA.

ABSTRACT

[1]Relativistic electron intensities in Earth's outer radiation belt can vary by multiple orders of magnitude on the time scales ranging from minutes to days. One fundamental process contributing to dynamic variability of radiation belt intensities is the radial transport of relativistic electrons across their drift shells. In this paper we analyze the properties of three-dimensional radial transport in a global magnetic field model driven by variations in the solar wind dynamic pressure. We use a test particle approach which captures anomalous effects such as drift orbit bifurcations. We show that the bifurcations lead to an order of magnitude increase in radial transport rates and enhance the energization at large equatorial pitch angles. Even at quiet time fluctuations in dynamic pressure, radial transport at large pitch angles exhibits strong deviations from the diffusion approximation. The radial transport rates are much lower at small pitch angle values which results in a better agreement with the diffusion approximation.

No MeSH data available.


Related in: MedlinePlus