Chorus-driven resonant scattering of diffuse auroral electrons in nondipolar magnetic fields
Chorus-driven resonant scattering of diffuse auroral electrons in nondipolar magnetic fields
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DOI：
10.1029/2011ja016453
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发表时间：
2011-06
影响因子：
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通讯作者：
B. Ni;R. Thorne;Y. Shprits;K. Orlova;N. Meredith
中科院分区：
文献类型：
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作者：
B. Ni;R. Thorne;Y. Shprits;K. Orlova;N. Meredith
我们使用各种非偶极Tsyganenko磁场模型，对00:00 MLT沿赤道交叉6 RE的磁场线存在的斜夜侧合唱发射的漫射极光电子的共振散射进行了全面分析。利用T89、T96和T01s模型对中度和主动扰动地磁条件下的反弹平均准线性扩散系数进行了评估。结果表明，加入非偶极磁场后，200 eV ~ 10 keV等离子体片电子的俯俯角和动量扩散的弹跳平均速率发生了显著变化。与使用偶极子场的结果相比，使用Tsyganenko模型获得的200 eV电子在所有共振螺距角下的俯仰角扩散速率都有所提高。相比之下，对于500 eV至10 keV的电子，俯仰角散射率在中间和/或高俯仰角处增强，但在损耗锥附近往往相当低，因此与偶极子场相比，减少了沉淀损失。在200 eV至2 keV的电子中，上带合唱是散射损失的主要原因，而在5-10 keV的电子中，下带合唱散射主要存在，这与偶极子模型的结果一致。一阶回旋共振和朗道共振是等离子体薄片电子在斜合唱波作用下的净散射率的主要原因，也是使用Tsyganenko模型引入的反射平均扩散系数差异的主要原因。随着地磁活动的增加，散射率与偶极子结果的差异也相应增加。Tsyganenko模型之间的扩散速率也出现不可忽略的差异，特别是在高俯仰角时，这表明随着地磁活动水平的增加而增加，并依赖于Tsyganenko模型场之间的差异。反弹平均准线性散射率对所采用的全球磁场模型和地磁活动水平的强烈依赖表明，在未来的模拟工作中应纳入现实的磁场模型，以准确量化磁层合唱在驱动弥漫性极光降水和电子薄饼分布形成中的作用。
[1] We perform a comprehensive analysis of resonant scattering of diffuse auroral electrons by oblique nightside chorus emissions present along a field line with an equatorial crossing of 6 RE at 00:00 MLT, using various nondipolar Tsyganenko magnetic field models. Bounce-averaged quasi-linear diffusion coefficients are evaluated for both moderately and actively disturbed geomagnetic conditions using the T89, T96, and T01s models. The results indicate that inclusion of nondipolar magnetic field leads to significant changes in bounce-averaged rates of both pitch angle and momentum diffusion for 200 eV to 10 keV plasma sheet electrons. Compared to the results using a dipole field, the rates of pitch angle diffusion obtained using the Tsyganenko models are enhanced at all resonant pitch angles for 200 eV electrons. In contrast, for 500 eV to 10 keV electrons the rates of pitch angle scattering are enhanced at intermediate and/or high pitch angles but tend to be considerably lower near the loss cone, thus reducing the precipitation loss compared to that in a dipole field. Upper band chorus acts as the dominant cause for scattering loss of 200 eV to 2 keV electrons, while lower band chorus scattering prevails for 5–10 keV electrons, consistent with the results using the dipole model. The first-order cyclotron resonance and the Landau resonance are mainly responsible for the net scattering rates of plasma sheet electrons by oblique chorus waves and also primarily account for the differences in bounce-averaged diffusion coefficients introduced by the use of Tsyganenko models. As the geomagnetic activity increases, the differences in scattering rates compared to the dipole results increase accordingly. Nonnegligible differences also occur particularly at high pitch angles for the diffusion rates between the Tsyganenko models, showing an increase with geomagnetic activity level and a dependence on the discrepancy between the Tsyganenko model fields. The strong dependence of bounce-averaged quasi-linear scattering rates on the adopted global magnetic field model and geomagnetic activity level demonstrates that realistic magnetic field models should be incorporated into future modeling efforts to accurately quantify the role of magnetospheric chorus in driving the diffuse auroral precipitation and the formation of electron pancake distributions.