Why do you say that the weather on solstice starts to get cold in winter?
Counting nine does not start from the solstice in winter, but from the second day of the solstice in winter.
second
The weather is not cold on the solstice in winter. Since autumn, the weather is getting colder every day.
As for why the winter of solstice is not the coldest day.
Like the highest angle of the sun at noon one day.
But the highest temperature is two hours in the afternoon.
Similarly, although the lowest day in a year is the winter solstice, the coldest day is not the winter solstice.
In summer, the sun is scorching the earth, and the accumulated heat should be distributed bit by bit.
Therefore, the change of temperature and the change of sun height are not synchronous, but slightly delayed.
Moreover, it is the height of the sun that affects the temperature, and atmospheric circulation is also very important.
Combining these factors, the day with the lowest sun height is not the coldest day.
Similarly, the day with the highest sun height is not the hottest day.