What solar term did the cold weather start from?

Counting nine cold days begins with the solar terms from winter to sun.

The ancients believed that the winter solstice is an important solar term for the transformation of Yin and Yang, representing the beginning of the next cycle and a day of good luck, and "counting nine" also began from then on. From the solstice in winter to nine, every nine days is a "nine". By "99", the weather turned warmer, and most parts of the country had entered spring, also known as "99 sunny day".

Jiujiu, also called Jiujiu in winter, is a folk method in China to calculate the flowering date in cold weather and warm spring. Generally, March and April are the coldest time, which is the coldest time of the year. When you count to nine "nine days" (998 1 day), spring will be deep and warm, and everything will be full of vitality. It's time for spring ploughing. The number nine method is passed down from mouth to mouth among the people in our country, which has a history and lacks records. As for when it originated, there is no exact information. In traditional culture, nine is the extreme number, the "supreme yang" number and the largest number. The accumulation of "Zhiyang" means that Yin Qi is decreasing day by day, and it is tired to the end, which means that the cold is getting warmer and "the spring is deep".