Dynamics of Energetic Electrons in the Slot Region During Geomagnetically Quiet Times: Losses Due to Wave‐Particle Interactions Versus a Source From Cosmic Ray Albedo Neutron Decay (CRAND)
Dynamics of Energetic Electrons in the Slot Region During Geomagnetically Quiet Times: Losses Due to Wave‐Particle Interactions Versus a Source From Cosmic Ray Albedo Neutron Decay (CRAND)
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DOI：
10.1029/2020ja028042
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发表时间：
2020-09
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通讯作者：
Z. Xiang;Xinlin Li;B. Ni;M. Temerin;Hong Zhao;Kun Zhang;L. Khoo
中科院分区：
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作者：
Z. Xiang;Xinlin Li;B. Ni;M. Temerin;Hong Zhao;Kun Zhang;L. Khoo
位于外辐射带和内辐射带之间的地球狭缝区域被认为是由于波引起的向内径向扩散和俯仰角(PA)散射之间的平衡。然而，最近的卫星观测和模拟研究表明，宇宙射线反照率中子衰变(CRAND)也可能在缝隙区域的高能电子动力学中发挥重要作用。在这项研究中，使用漂移扩散源模型，我们研究了2014年7月期间，所有有效波和CRD对狭缝区高能电子动力学的相对贡献，这是一个延长的平静地磁活动时期。根据拟线性理论计算了三种波(嘶嘶声、闪电哨声和甚低频发射器)的反弹平均PA扩散系数，而CRAND源则遵循向等人的结果。(2019年，https://doi.org/10.1029/2018GL081730).仿真结果表明，LGW和VLF发射波均能增强损耗，减弱由HISS波引起的TOP-HAT功率分布。对于L=2.5时的470keV电子，没有CRAND的模拟结果比Van Allen探测器的观测结果要快得多。在计入CRAND之后，模拟的电子通量变化再现了卫星观测，表明CRAND是缝隙区域在平静时期数百keV电子的重要来源。声源和波粒相互作用造成的损耗之间的平衡为狭缝区的相对论电子通量提供了一个下限，在保证真实本底能级的情况下，它可以作为仪器校准的一个重要参考点。
Earth's slot region, lying between the outer and inner radiation belts, has been identified as due to a balance between inward radial diffusion and pitch angle (PA) scattering induced by waves. However, recent satellite observations and modeling studies indicate that cosmic ray albedo neutron decay (CRAND) may also play a significant role in energetic electron dynamics in the slot region. In this study, using a drift‐diffusion‐source model, we investigate the relative contribution of all significant waves and CRAND to the dynamics of energetic electrons in the slot region during July 2014, an extended period of quiet geomagnetic activity. The bounce‐averaged PA diffusion coefficients from three types of waves (hiss, lightning‐generated whistlers [LGW], and very low frequency [VLF] transmitters) are calculated based on quasi‐linear theory, while the CRAND source follows the results in Xiang et al. (2019, https://doi.org/10.1029/2018GL081730). The simulation results indicate that both LGW and VLF transmitter waves can enhance loss and weaken the top hat PA distribution induced by hiss waves. For 470 keV electrons at L = 2.5, simulation results without CRAND show a much quicker decrease than observations from the Van Allen Probes. After including CRAND, simulated electron flux variations reproduce satellite observations, suggesting that CRAND is an important source for hundreds of keV electrons in the slot region during quiet times. The balance between the CRAND source and loss due to wave‐particle interactions provides a lower limit to relativistic electron fluxes in the slot region, which can act as an important reference point for instrument calibration when a true background level is warranted.