Fu Cha Dunchong's "Yanjing Year" said: "It is difficult to have three or nine days in winter." It means that it has entered the coldest stage in cold weather since March 9. Jing Fang Yi Zhan of the Western Han Dynasty said, "It is extremely cold on the 30th after winter on the solstice." "The third day after beginning of winter is the coldest day in December from solstice." It means that March 9 is the coldest day.
By May of 969, the coldest time had passed, the weather began to get warmer, and the branches of willow trees began to sprout green buds. In July and September, the snow and ice will begin to melt, and the frozen river will slowly thaw. In August and September, swallows will fly back from the south to build nests. By 1999, the weather was warmer than before, and there was a spring thunder gradually. When most parts of China enter the spring ploughing season, you will see cows everywhere.