Is it seasonal because of natural yearly weather seasons, or is it because of the growth dynamics?! Most curves look a lot like an explosion that burns out loc

Is it seasonal because of natural yearly weather seasons, or is it because of the growth dynamics?! Most curves look a lot like an explosion that burns out locally too fast to sustain a continuous fire. This could lead to some kind of seasonal dynamics without external factors. One exception is maybe Argentina. Since the beginning it was more like a continuous burning fire - until they stopped. What did they do?