Why do extratropical cyclones occur in spring and autumn?

The extratropical cyclone, also known as "extratropical depression" or "frontal cyclone", is an elliptical baroclinic cyclone, which is active in the temperate middle and high latitudes. Structurally speaking, the extratropical cyclone is a cold center system, that is, the central pressure of the extratropical cyclone is lower than that around it, which has the nature of a cold center. In terms of scale, temperate cyclones are generally larger than tropical cyclones, ranging in diameter from several hundred kilometers to 3,000 kilometers, with an average diameter of 1000 kilometers. Temperate cyclones appear with the front, and sometimes 2-5 temperate cyclones are formed one after another on the same front, advancing from west to east in turn, which is called "cyclone family". The whole life cycle of extratropical cyclones from generation, development to extinction is generally 2-6 days.

1. The extratropical cyclone is developed from waves on the front. Due to some reasons, waves are formed on the front, and a closed isobar appears near the peak of the waves, which gradually develops into a complete cyclone.

2. In spring and autumn, cold air and warm air meet most frequently, and it is most likely to form an extratropical cyclone in this season.