When will it snow heavily in Beijing?

Every year around September 23rd, when the sun reaches longitude 180 degrees, it is the autumnal equinox solar term.

"Autumnal equinox" means that on the day of the autumnal equinox, the sun shines directly on the equator, and the length of day and night is almost equal, and day and night are 12 hour respectively.

After the autumnal equinox, the direct sunlight crossed the equator and moved to the southern hemisphere. The northern hemisphere gets less and less solar radiation and the temperature drops gradually. The average daily temperature in the Yangtze River basin and its vast area to the north drops below 22℃, and it enters a cool autumn. The influence of cold air mass in the north continued to increase, and activities began to be frequent. The warm air that originally occupied the mainland quickly withdrew southward and was filled by the cold air in the north.

At the autumnal equinox, the autumn rain period has basically ended, and the rainfall in most parts of China has decreased significantly. The average precipitation in the middle and lower reaches of the Yangtze River is about 20 mm, which is half or even two-thirds less than that in the middle. The average annual rainfall in Shanghai in late September is 18.3 mm, which is 49.9 mm less than that in mid-September, and the climate of "autumn dryness" begins to appear, so it is necessary to prevent autumn dryness at this time.

After the autumnal equinox, the autumn is crisp and the crabs are fat and yellow, which is a beautiful and pleasant season; The autumnal equinox is also an important season for agricultural production, when cotton bolls and late rice begin to mature.

Cold Dew

Every year around 65438+10.8, when the sun reaches 195 degrees, it is a cold dew solar term. The book "Twenty-four Solar Terms" says, "In September and a half, the dew is cold and will condense." Cold dew "means that the air temperature at this time is lower than the Millennium solar terms, and the original white and crystal dew on the ground is about to condense into frost."

In the cold dew season, Nanling and the vast areas in northern China have entered autumn, and the northeast and northwest regions have entered winter or are about to enter winter. At this time, the influence of cold air in the north has been strengthened and it has been invading the south. In some years, the cold air is particularly strong, which makes the temperature in the south of the Yangtze River drop below 16℃, forming a "cold dew wind", which is very harmful to the double-cropping late rice in the south, resulting in empty grain and a substantial reduction in grain production. Therefore, we should always pay attention to listening to the weather forecast to prevent the harm of "cold dew wind"

After the cold dew, most parts of China are under the control of cold and high pressure, and the rainy season is over. The weather is often warm during the day and cool at night. The clear sky in Wan Li is very beneficial to the autumn harvest. Therefore, at this time, we must seize the sunny weather to harvest cotton and achieve a bumper harvest.

Frost reduction

Frost falling is a solar term, which means that the temperature drops and the water vapor near the surface freezes into frost. Every year, around1October 23rd, 10, the sun starts when it reaches longitude 2 10 degrees. The book "Seventy-two Days of the Month" said: "In mid-September, the gas stagnated and the dew became frost." It can be seen that falling frost means starting to see frost.

"After autumn, the north wind is tight and the night is still frosty." In the first frost season, the temperature has dropped relatively low. At this time, as long as there is strong cold air going south in the north, the temperature will drop sharply. When the local surface temperature drops to 0℃ or below, the water vapor in the air attached to the stratum will reach saturation and condense into tiny ice crystals to form frost.

China has a vast territory, and the climate varies greatly from place to place. "first frost began in time" reflects the climate characteristics of the Yellow River Basin. Heilongjiang and Inner Mongolia in the north entered the first frost period in the middle and late September, and the first frost appeared in 65438+February south of Nanling. The first frost in Shanghai usually occurs in the middle of 1 1 year, and the early frost occurs in the late of 1 year, and the final frost usually lasts until the late March of the following year.

The appearance of frost shows that the minimum ground temperature has dropped below 0℃, which will have a certain impact on crops. The earlier frost appears, the greater the harm to crops, because plants can not only absorb external water, but also freeze their own water into ice, which will cause crops to suffer from freezing damage.

During the first frost season, most areas in China are in drought, the precipitation is obviously reduced, and the air is relatively dry, which is easy to cause fires. Therefore, we should attach great importance to fire prevention.

"If you don't cut the grain in the first frost, you lose a reed a day." In the first frost season, when the late rice is ripe, you should pay close attention to harvesting, otherwise it will lead to a reduction in grain production due to bird damage and grain falling.

Beginning of Winter

Every year around 1 1.7, the solar term in beginning of winter is when the sun reaches 225 degrees of the yellow meridian. Beginning of winter is one of the solar terms reflecting seasonal changes, and beginning of winter is the beginning of winter in China. The book "The Seventy-Two Days of the Month" says: "The beginning also stands" and "the winter also ends, and everything is harvested".

In fact, China is a vast country, and winter doesn't always start at the same time. According to the standard of dividing four seasons by climatology, if the average climate temperature is lower than 10℃ for winter, then the statement that "beginning of winter is beginning of winter" only conforms to the climate law of Huanghuai area. Mohe, the northernmost part of China, and the area north of Daxinganling have entered the winter in early September, and Beijing has entered the winter in late June at 65438+ 10, while the winter in the Yangtze River basin will not really start until around the "light snow" solar term. In Shanghai 165438+ 10, the average temperature in the first five months was above 10℃, and in the last period it dropped below 10℃, so the winter in Shanghai lasted until the last period165438+1.

In early winter, although there is less and less solar radiation in the northern hemisphere, there is still some heat storage on the surface in summer, so it is generally not too cold. When the weather is clear and cloudless, there is always warm and comfortable "Xiaoyangchun" weather. At this time, the cold air in the north also has a strong force, often invading the south, forming a strong wind, cooling down and accompanied by rain and snow. Therefore, in the early winter season, the weather is cold and warm, and cold and warm alternate frequently, which has adverse effects on people's lives, human health and agricultural production. Therefore, we should pay more attention to listening to the weather forecast, adjust clothes according to the weather changes, ensure good health, and take anti-freezing measures for crops to prevent freezing damage.

There are folk sayings such as "beginning of winter has no rain and sunny winter, beginning of winter has rainy winter and rainy winter" and "beginning of winter has a northwest wind and a bumper harvest in the coming year", which shows that the weather in beginning of winter has a great influence on the future climate and needs attention.

Minor Snow

Every year, before165438+1October 22nd, the solar term when the sun reaches 240 degrees of the yellow meridian is "light snow". Light snow means the beginning of snow, but it is not very heavy. The book "seventy-two days of the month" said: "In mid-October, it rained and was cold and thin, so it condensed into snow. The words of the villain are not prosperous. "

In the light snow season, the first snow began to appear in the Yellow River basin, while the first snow day in the Yangtze River basin was delayed by about one month. The average first snow day in Shanghai is 65438+1early October, but the earliest year can be 65438+February, and the earliest first snow appears on165438+1October 2.

When the near-surface temperature is lower than 0℃, the small ice crystals in the cloud will fall to the ground in the form of snowflakes, so the near-surface temperature is lower than or close to 0℃, which is an important condition for snowfall. This shows that after the light snow festival, the air activity in most parts of China is mainly cold air with strong intensity. For example, the average temperature of Shanghai 1 1 in late October was 9.6℃, and that of 1 in early February dropped by 2.2℃.

The agricultural production season in the middle and lower reaches of the Yangtze River generally begins with "fright" and ends with "beginning of winter" or "light snow". In fact, in the dead of winter after light snow, we should not only do a good job in field management of overwintering crops such as wheat and rape, but also do a good job in cold protection and warmth preservation of perennial subtropical fruit trees.

Xue Rui heralds a good year, and first frost returns to sunny days. The snowfall after the light snow festival is timely snow, commonly known as Xue Rui. Xue Rui is not only good for grain harvest, but also good for human health. Because snow water contains a quarter less heavy water than ordinary water, drinking snow water for a long time can strengthen the body and prolong life.

Major Snow

65438+ Every year, around February 7th, when the sun reaches 255 degrees, it is a solar term of heavy snow. "Heavy snow" means that it snows more and more in solar terms than "light snow" and the temperature is lower. The twenty-four solar terms say, "At this time, the snow is abundant."

In the heavy snow season, snowfall began to appear in the Yellow River basin, and the snowfall also increased significantly. The average temperature in the northeast and northwest has been below-10℃, and the northern land has put on winter clothes. Generally, the first snow in the Yangtze River basin will not be seen frequently until after the heavy snow festival. In June this year165438+1October 2 1 day, there was heavy snow in Beijing, with an average snowfall of 7 mm and the lowest temperature of -8℃. The snow did not melt for several days in a row, which was rare in the same period in Beijing in the 1990s.

"It snowed this year, and there will be a good harvest next year." Snowfall in winter is very beneficial to agricultural production, making grain production a bumper harvest. Because the thermal conductivity of snow is only 1% of that of soil, snow covers the ground, so cold air outside is not easy to penetrate into the soil, and heat in the soil is not easy to escape, just like covering a quilt, so snow covers the farmland. First, it can keep the temperature around the ground and crops from falling very low because of the cold wave, creating a good environment for winter crops to overwinter; Second, the temperature of snowflakes is below freezing point, which can freeze the pests that harm crops; Thirdly, snow is like a natural reservoir. When it melts, it can increase soil moisture and is beneficial to crop growth. Fourthly, the content of nitrogen compounds in snow water is five times that of ordinary rain water, which can play a role in fertilizing fields.

In the heavy snow season, the frequency of fog in the Yangtze River Delta is relatively high, and Shanghai is the month with the most fog in a year. Fog has a great influence on traffic, power supply and human health. Therefore, we should always care about the weather forecast, pay attention to the weather changes, and do a good job of prevention before the fog comes to avoid the fog disaster.

Winter solstice

On February 22nd, 65438+ year, when the sun reached 270 degrees of the yellow meridian, the solar term was the winter solstice. The book "Seventy-two Days of the Month" says: "The last hidden qi is extreme at this point." "Winter solstice" is one of the solar terms reflecting seasonal changes.

On the solstice of winter, the sun shines directly on the Tropic of Capricorn, which is the place with the shortest day and the longest night in the northern hemisphere. The higher the latitude, the shorter the day and the longer the night. In the Arctic Circle, it is night all day. After the winter solstice, the direct sunlight point began to move to the northern hemisphere, so the days in the northern hemisphere gradually became longer and the nights became shorter. The southern hemisphere is the opposite.

As the saying goes, "But it's not cold in winter on the solstice", which makes sense. On the solstice of winter, although the sunshine time in the northern hemisphere is the shortest and the solar radiation energy is the least, the heat accumulated on the ground has not been consumed in the summer half year, so the temperature at this time is not the lowest. After the winter solstice, although the sunshine in the northern hemisphere gradually increased, the heat absorbed by the ground was still less than the heat lost, making ends meet, and the temperature continued to drop for some time. After about a month, the heat absorbed by the ground and the heat lost gradually balanced. Therefore, our people call the day after the winter solstice "nine cold days" and compile Ninety-nine Winter Poems to describe the climate change after the winter solstice: "1929 does not shoot; Walking on the ice in 3949; 5969, look at the willows by the river; Seven or nine rivers open; Eighty-nine geese are coming; 99 plus 19, plowing cattle everywhere. "

Song of Nine Nine-Nine takes the solstice of winter as the first day of nine-nine, and then describes the change and phenological phenomenon of the weather from cold to coldest and then gradually warming on the first day of 998 1 year. As can be seen from the Jiujiu songs, 3949 is the coldest period, so there is a folk saying of "3999 cold" or "3999 cold". According to the climate in Shanghai, the coldest period is in the first half of June, 5438+10, which is basically consistent with the Song Dynasty in 1999.