Modeling the loss of inner belt protons by magnetic field line curvature scattering
Modeling the loss of inner belt protons by magnetic field line curvature scattering
复制标题
通过磁场线曲率散射模拟内带质子的损失
DOI：
10.1002/2014ja019864
复制
发表时间：
2014
期刊：
影响因子：
--
通讯作者：
K. Liu
中科院分区：
文献类型：
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作者：
W. Tu;M. Cowee;K. Liu
在地磁风暴期间观察到内辐射带中高能质子的突然损失。据推测，这种突然损失的发生是由于地磁场配置的变化导致第一个绝热不变量 μ 在称为磁场线曲率散射或 μ 散射的过程中崩溃。然而，将观察结果与μ散射引起的损失的各种分析模型预测进行比较却产生了差异。为了更好地了解分析模型预测质子损失的效果，对各种磁场配置进行了测试粒子模拟。尽管我们的模拟结果与单个 μ 散射事件的解析模型非常吻合，但累积 μ 散射后的结果可能与基于解析模型的理论预测存在显着差异。特别是，我们发现预测初始 δμ/μ > 0.01 或 ε > 0.1 的质子最终丢失的假设高估了质子损失。基于测试粒子模拟结果，我们开发了一个新的经验模型，称为“ε-onset”模型，以预测 ε 的最小值，在该最小值下，可以假设给定螺距角和能量的所有质子因 μ 散射而损失。通过应用我们的ε-起始模型作为捕获和去捕获之间的可变截止条件，我们在一系列Kp的理论预测和模拟结果之间获得了非常好的一致性，这表明与之前使用的固定值截止条件相比，ε-起始模型可以作为μ散射引起的内带质子损失的易于使用且更可靠的预测器。
The sudden loss of energetic protons in the inner radiation belt has been observed during geomagnetic storms. It is hypothesized that this sudden loss occurs because of changes in the geomagnetic field configuration which lead to a breakdown of the first adiabatic invariant, μ, in a process called magnetic field line curvature scattering or μ scattering. Comparison of observations to various analytic model predictions for μ scattering induced loss has, however, yielded discrepancies. To better understand how well the analytic models predict the proton loss, test particle simulations are carried out for various magnetic field configurations. Although our simulation results agree well with the analytic models for single μ‐scattering events, the results after cumulative μ scattering can show significant disagreement with the theoretical predictions based on analytic models. In particular, we find the assumption that protons with predicted initial δμ/μ > 0.01 or ε > 0.1 are ultimately lost overestimates the proton loss. Based on the test particle simulation results, we develop a new empirical model, called the “ε‐onset” model, to predict the minimum value of ε at which all protons of a given pitch angle and energy can be assumed to be lost due to μ scattering. By applying our ε‐onset model as the variable cutoff condition between trapping and detrapping, we obtain very good agreement between theoretical predictions and the simulation results for a range of Kp, suggesting that the ε‐onset model can potentially serve as an easy‐to‐use and more reliable predictor of inner belt proton loss due to μ scattering than the previously used fixed‐valued cutoff conditions.