Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Rd, Laurel, Maryland 20723, USA.
New Jersey Institute of Technology, 141 Summit St, Newark, New Jersey 07103, USA.
Nature. 2014 Mar 20;507(7492):338-40. doi: 10.1038/nature13046.
Structured features on top of nominally smooth distributions of radiation-belt particles at Earth have been previously associated with particle acceleration and transport mechanisms powered exclusively by enhanced solar-wind activity. Although planetary rotation is considered to be important for particle acceleration at Jupiter and Saturn, the electric field produced in the inner magnetosphere by Earth's rotation can change the velocity of trapped particles by only about 1-2 kilometres per second, so rotation has been thought inconsequential for radiation-belt electrons with velocities of about 100,000 kilometres per second. Here we report that the distributions of energetic electrons across the entire spatial extent of Earth's inner radiation belt are organized in regular, highly structured and unexpected 'zebra stripes', even when the solar-wind activity is low. Modelling reveals that the patterns are produced by Earth's rotation. Radiation-belt electrons are trapped in Earth's dipole-like magnetic field, where they undergo slow longitudinal drift motion around the planet because of the gradient and curvature of the magnetic field. Earth's rotation induces global diurnal variations of magnetic and electric fields that resonantly interact with electrons whose drift period is close to 24 hours, modifying electron fluxes over a broad energy range into regular patterns composed of multiple stripes extending over the entire span of the inner radiation belt.
在地球辐射带中原本平滑分布的粒子上方，存在着结构特征，这些特征以前与仅由增强的太阳风活动驱动的粒子加速和输运机制有关。尽管行星旋转被认为对木星和土星的粒子加速很重要，但地球旋转在内部磁层中产生的电场只能使被捕获的粒子的速度改变约 1-2 公里每秒，因此旋转对于速度约为 100,000 公里每秒的辐射带电子来说是微不足道的。在这里，我们报告说，即使在太阳风活动较弱的情况下，整个地球内辐射带的高能电子的分布呈现出规则的、高度结构化的、出人意料的“斑马条纹”模式。模型表明，这些模式是由地球的旋转产生的。辐射带电子被捕获在地球的偶极子状磁场中，由于磁场的梯度和曲率，它们在行星周围经历缓慢的纵向漂移运动。地球的旋转引起磁场和电场的全球日变化，与漂移周期接近 24 小时的电子发生共振相互作用，将广泛能量范围内的电子通量修改成由多个条纹组成的规则图案，这些条纹延伸到整个内辐射带。
