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arXiv 2403.06706astro-ph.SRphysics.plasm-phphysics.space-ph
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太阳风中散射高能粒子的动力学:磁流体力学与试验粒子模拟

Dynamics of energetic particles scattered in the solar wind : Magnetohydrodynamics and test-particle simulations

Houeibib Ahmed, Pantellini Filippo, Griton Lea

AI总结:

该研究结合三维 MHD 太阳风模拟与相对论导心试验粒子计算,引入沿磁场散射平均自由程,揭示 SEP 电子的俯仰角分布及绝热冷却与漂移能量损失的时间转换机制。

摘要:

我们对太阳高能粒子(SEPs)在太阳风中的输运进行建模。我们在一个稳态三维太阳风磁流体力学模拟的磁场中传播相对论性试验粒子。太阳风模拟使用 MPI-AMRVAC 代码,并采用一种新的三阶精度预测-校正时间积分方案来积分相对论性导心方程。通过引入恒定的沿磁场散射平均自由程 $λ_\parallel$,我们考虑了粒子轨迹在速度空间中由湍流引起的散射。我们考察了在日心距离 0.28 AU、磁纬 $24^{\circ}$ 处注入太阳风的 81 keV 中程 SEP 电子。当 $λ_\parallel=0.5$ AU 时,模拟得到的速度俯仰角分布与 1 AU 处的原位测量在定性上吻合良好。更一般地,在 $λ_\parallel$ 为 0.1 至 1 AU 的范围内,观测到与速度漂移相关的能量损失率约为每天 10%。这种能量损失可归因于电子的磁曲率和梯度诱导极向漂移逆着电场主要分量运动。在我们代表平均太阳风条件的案例研究中,观测到的漂移诱导能量损失率在日心距离约 1.2 AU 附近最快。我们强调,在传播的最初 1.5 小时内,绝热冷却是主导机制;只有在更晚的时候,与漂移相关的损失率才占据主导。

英文摘要:

We model the transport of solar energetic particles (SEPs) in the solar wind. We propagated relativistic test particles in the field of a steady three-dimensional magnetohydrodynamic simulation of the solar wind. We used the code MPI-AMRVAC for the wind simulations and integrated the relativistic guiding center equations using a new third-order-accurate predictor-corrector time-integration scheme. Turbulence-induced scattering of the particle trajectories in velocity space was taken into account through the inclusion of a constant field-aligned scattering mean free path $λ_\parallel$. We considered mid-range SEP electrons of $81\:{\rm keV}$ injected into the solar wind at a heliocentric distance of 0.28 AU and a magnetic latitude of $24^{\circ}$. For $λ_\parallel =0.5\:{\rm AU}$, the simulated velocity pitch angle distributions agree qualitatively well with in situ measurements at 1 AU. More generally, for $λ_\parallel$ in the range 0.1 to 1\:AU, an energy-loss rate associated with the velocity drift of about $10\%$ per day is observed. The energy loss is attributable to the magnetic curvature and gradient-induced poleward drifts of the electrons against the dominant component of the electric field. In our case study, which is representative of the average solar wind conditions, the observed drift-induced energy-loss rate is fastest near a heliocentric distance of 1.2 AU. We emphasize that adiabatic cooling is the dominant mechanism during the first 1.5 hours of propagation. Only at later times does the drift-associated loss rate become dominant.

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