Nature2014-06-24 4:01 PM

地球辐射带中的“斑马线” Rotationally driven ‘zebra stripes’ in Earth’s inner radiation belt


地球的辐射带有很多电子和离子,它们被一个磁场束缚在原位。这些带中的结构化特征以前被归因于增强的太阳风活动。虽然行星转动被认为在驱动木星和土星周围的带动态中起重要作用,但这一直被人为对地球的辐射带无足轻重——地球辐射带中所涉及的力要小得多。对来自Van Allen Probes任务的 数据所做的一项新的分析显示,地球内辐射带整个空间的高能电子分布是以规则的、高度结构化的、出乎意料的 “斑马线”形式组织的,甚至当太阳风活动强度低时也是如此。模拟显示,这种模式是由行星转动产生的,后者诱导与漂移周期接近24小时的电子以共振式发生相互作用的磁场和电场发生全球性的日间变化。


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.






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