The coldest days of winter are here! How cold were they in the past? The answer is in the song of the coldest days of winter →

my country has officially entered the coldest days of the year, which is considered the coldest time of the year. This can be felt from the songs about getting rid of the cold that our creative ancestors composed...

The weather conditions during the 39th day of the 9th month in various versions of the “99th day of the 9th month song to get rid of the cold”

my country has a vast territory and great differences in climate across regions. The temperature difference in the "Three Nines" is also relatively large, but words such as "cold", "ice" and "wind" are definitely high-frequency words at this time. We enter the ice and snow world of various places through the "Nine Nines to Dispel the Cold Songs"

Beijing version: Walking on the ice during the 39th and 49th days of the year

Research shows that, generally speaking, the first ice on Beijing rivers begins in late November or early December, and ends in mid-February to late March. The ice period is generally 80-100 days, with a minimum of 74 days and a maximum of 122 days. The freezing period of rivers is generally 40-70 days. Of course, it depends on the situation. The north freezes earlier than the south, the mountains freeze earlier than the plains, and the reservoirs freeze earlier than the rivers. The thickness of the ice varies, ranging from 0.28 to 0.56 meters.

That is to say, the rivers in Beijing begin to freeze around December every year, and by the 39th day of the coldest winter, the river surface may be completely frozen.

The river is frozen (Source: Tuchong Creative)

Since the river is frozen, can we fish by chipping ice or go ice skating on the river to have a good time? Here we need to remind everyone that the thickness of the ice surface varies in different regions and river conditions, which poses a great safety hazard. Please act cautiously and ensure safety.

Changsha version: 3927, pen hanging upside down in front of the eaves

The pen here refers to "icicles". In the morning of winter, you can see icicles hanging on the eaves. How are they formed? There must be snowfall. When there is snow on the roof, it will melt under the sun and drip down the eaves. When night falls, the melted snow water still flows down, but the temperature is already very low, so it freezes. After a certain period of accumulation, icicles are formed.

Icicles are crystal clear under the sunlight. Some children will break them off to play with them. In fact, this is a very dangerous action. Icicles are very sharp and can easily hurt themselves or their friends. Icicles have a certain degree of hardness, but they are relatively brittle. When they hit an obstacle, they will break and fly out, which may hurt people. Therefore, everyone must not ignore safety for the sake of playing.

Icicles under the eaves (Source: Tuchong Creative)

Icicles look very "clean", so some children will eat them, which is not advisable. Snow falls with impurities in the air during the falling process, and when it melts, the impurities will also remain on the icicles. Many of these impurities may be industrial waste gas and automobile exhaust. Eating them together with ice water is not good for health.

Zhejiang version: 3927, playing the flute at the fence

The 篥 is a "筚篥" (bìlì), a reed wind instrument from the Han Dynasty. It is shaped like a trumpet, with a bamboo tube and a reed mouthpiece. The tube body is made of wood with seven sound holes and a reed whistle inserted on it. There are single-tube and double-tube types. It is popular in the Korean areas in northern my country and is also popular in Fujian.

Bixiao (Source: Tuchong Creative)

During the coldest days of winter, in addition to low temperatures and snowfall, there are also strong winds. The strong winds blowing through the fences make a loud noise, just like playing a 筚篥. The flute, Xiao, and 筚篥 are all wind instruments, which are a kind of sound-generating phenomenon formed by the narrow tube effect. When the wind is strong enough and the wind direction is appropriate, the fence will also produce a narrow tube effect and make a loud sound. Therefore, this reflects the ancient people's description of the strong winds during the coldest days of winter.

The winter solstice has passed, why is it getting colder?

Why is the 39th day of winter the coldest period of the year?

We know that solar radiation is the ultimate source of the earth's heat energy, and the coldest days of the year are related to the sun.

On the winter solstice, the daytime is the shortest in the whole year, the angle between the direct sun and the ground is the smallest, and the intensity of sunlight received per unit area is the smallest. The smallest angle and the shortest exposure time, therefore, the ground receives the least solar heat every day, and the daily heat deficit on the ground has not yet reached its maximum value.

After the winter solstice, the daytime hours begin to get longer, so the temperature should start to rise, but why does it continue to drop?

1. From the winter solstice to the "Three Nines", the average time increases by only about one minute per day, and the solar radiation in one minute is very limited;

2. The angle between the sun's direct angle and the ground is indeed increasing, but very slowly, and the intensity of sunlight is still relatively small;

3. The surface of the earth is not iron with very small specific heat, but water or land with relatively large specific heat. The release and absorption of energy is a relatively slow process;

4. The earth absorbs the heat from the sun during the day and radiates it at night. The heat balance of the ground is still in a deficit. Not only can it not store heat every day, but it also has to dissipate some of the heat stored in the summer. The surface continues to lose heat and the ground temperature continues to drop.

5. Around the "Three Nines", the Earth's heat storage is the least in a year, and the total heat deficit reaches its maximum, so it is also the coldest time;

6. Around the "Three Nines", the cold air mass in Siberia developed to an extremely strong stage, and strong cold air frequently invaded my country, which was also one of the reasons for the low temperature;

7. During the coldest days of winter, there will usually be large areas of snowfall or snow accumulation in many places on the surface. Snow is white and will reflect some of the solar radiation. The melting of snow will also dissipate some of the heat.

It is precisely because of the above reasons that the 39th day of winter becomes the coldest time of the year.

When the coldest days of winter meet global warming

The 39th day of the coldest period is indeed the coldest time in my country, but global warming has become an indisputable fact. We use Beijing's temperature change curve throughout the year to illustrate: the lowest temperatures in December, January and February are -5℃, -6℃ and -4℃ respectively. These are the three coldest months of the year, which is Beijing's winter. The lowest temperatures in the remaining months are all above 0℃. January is the month with the lowest temperature in Beijing in a year.

Research results from the National Climate Center show that the annual average surface temperature deviation in China from 1901 to 2020 has generally shown an upward trend.

Therefore, the three coldest days of winter are now very different from those in the past. The term "warm winter" frequently appears in the news media, which brings us many questions, such as:

Heavy fog frequently occurs in many places, affecting traffic safety and flight takeoffs and landings;

Bacteria in the air grow and multiply due to warm temperatures, which poses a threat to human health and increases the incidence of disease;

The survival rate of pest eggs and pathogens in the soil increases, and the probability of pests and diseases occurring in the following year increases.

How to spend the coldest days of winter? The ancients have given a good suggestion, that is, "winter storage", which is not hibernation. Reduce unnecessary outings (hiding), and keep warm when going out. At the same time, you should also take good care of your health during the coldest days of winter from the aspects of diet, exercise, and sleep. Eat warm and easily digestible food appropriately, choose appropriate exercise methods such as yoga and jogging, and ensure adequate sleep and a regular work and rest schedule to maintain the balance of yin and yang in the human body, nourish the positive energy, and prevent diseases.

Author: Wang Yuanhong, Senior Weather and Climate Engineer

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.