Abstract—

This paper analyzes the effect of azimuthal proton drift from the nighttime sector of the Earth’s magnetosphere on the characteristics of the pitch-angle anisotropy of proton fluxes in the daytime sector. The drift in the magnetic field caused by curvature of the field lines and the magnetic field gradient, in the absence of external forces, has been considered. The external geomagnetic field has been described with Tsyganenko’s T96 model. The proton drift has been calculated in the approximation of the guiding center motion in the equatorial magnetosphere plane, i.e., after averaging over the bounce oscillations of particles between the mirror points. The influence of two effects on the anisotropy value has been studied. The first effect is related to changes in the proton pitch angle in the course of azimuthal drift. This effect can significantly (up to approximately six times, depending on the T96 model input parameters) increase the transverse anisotropy of protons when they drift from the nighttime to the daytime side. The second effect is caused by drift-shell splitting, as a result of which protons from the nighttime sector from different radial distances come to the same field line on the daytime side: the lower the pitch angle of the particle is, the larger is the distance it starts to drift from. As a result, the radial proton flux gradient on the magnetosphere nighttime side can lead to a pitch-angle anisotropy of fluxes in the daytime sector that is sufficient to generate electromagnetic ion cyclotron (EMIC) waves, even if the fluxes in the nighttime sector were isotropic in the pitch angles. The dependence of this anisotropy on the radial proton flux gradient on the nighttime side has been studied. The maximum anisotropy in the daytime sector due to the longitudinal drift in the geomagnetic field can be achieved at a distance of 5.3–10 R_E depending on the Т96 model input parameters.

中文翻译：

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非偶极子磁场中粒子漂移引起的白天磁层高能质子的螺距角各向异性特征

摘要—

本文分析了来自地球磁气圈夜间区域的质子漂移对白天区域质子通量俯仰角各向异性特征的影响。已经考虑了在没有外力的情况下由磁力线的曲率和磁场梯度引起的磁场漂移。使用Tsyganenko的T96模型描述了外部地磁场。质子漂移是根据赤道磁层平面中的引导中心运动的近似值来计算的，即，在对镜点之间的粒子的反弹振动进行平均之后。研究了两种效应对各向异性值的影响。第一个效应与质子俯仰角在方位角漂移过程中的变化有关。当质子从夜间漂移到白天时，这种效应会显着增加（最多约六倍，具体取决于T96模型的输入参数），从而增加质子的横向各向异性。第二个影响是由漂移壳分裂引起的，其结果是来自不同径向距离的夜间扇区的质子到达白天侧的同一场线：粒子的俯仰角越小，则其越大。它开始漂移的距离。结果，在磁层夜间的径向质子通量梯度会导致白天扇区通量的俯仰角各向异性，即使夜间扇区中的通量为，也足以产生电磁离子回旋加速器（EMIC）波。各向同性的俯仰角。已经研究了这种各向异性对夜间径向质子通量梯度的影响。由于地磁场的纵向漂移，白天扇区的最大各向异性可以在5.3–10的距离处实现R _E取决于Т96模型输入参数。