地球变化磁场（variation of geomagnetic field）是起源于地球外部并叠加在基本磁场上的各种短期的变化磁场
地磁活动是地球磁场的自然变化，其波动周期为11年。
Geomagnetic activity, the natural variations in Earth's magnetic field, it fluctuates in 11-year cycles.
显然，试图解释和预测磁场变化的地球物理学家必须了解外核发生了什么。
Clearly, geophysicists who seek to explain and forecast changes in the field must understand what happens in the outer core.
地球磁场不同的变化会造成它们不同的自旋方式，每种方式都会让罗盘的化学状态表现出细微的差异。
Variations in Earth’s magnetic field cause them to spin in different ways, each of which leaves the compass in a slightly different chemical state.
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