annual magnetic variation

例句：

1. 1. The annual magnetic variation is a significant factor in the Earth's magnetic field.
   年度磁变化是地球磁场的一个重要因素。
2. 2. The scientists were able to predict the annual magnetic variation based on their observations.
   科学家们能够根据他们的观察预测年度磁变化。
3. 3. The study of annual magnetic variation has important implications for understanding the Earth's magnetic field.
   年度磁变化的研究表明，对理解地球磁场具有重要意义。