In China folklore, it is believed that after a solar term, the spirit of the sun rises and the earth warms up. What is this solar term?

The winter solstice is the coldest time, with the lowest temperature, the strongest yin and the weakest yang. The cathode is Yang, and then the earth gradually warms, the Yin gradually decreases, and the Yang gradually increases. Everything in nature began to revive. Plants began to sprout, buds began to open, and animals scrambled to reproduce. . . All this presents a thriving scene. At the same time, human beings also feel the warmth of the earth. The carnival of the Spring Festival heralds the beginning of the coming year.