Geomagnetic activity, the natural variations in Earth'smagneticfield, it fluctuates in 11-year cycles.
地磁活动是地球磁场的自然变化，其波动周期为11年。
2
At the Earth's surface, these tempests can be detected by changes in the strength of the Earth'smagneticfield.
在地球表面，可以通过改变地球磁场强度来检测这些风暴。
3
The Earth'smagneticfield is generated as the molten iron of the Earth's outer core revolves around its solid inner core; when surges in the molten iron occur, magnetic tempests are created.