periodic variation

例句：

1. 1. The temperature inthe area varies periodically due to theweather patterns.
   该地区的温度因天气模式而周期性变化。
2. 2. The population of the city has beenundergoing periodic variations in recent years.
   近年来，该市的人口经历了周期性的变化。
3. 3. The growthrate of the economy is influenced by periodicvariations in demand and supply.
   经济的增长受到需求和供给周期性变化的影响。