Characteristics of autumn wind solar terms
The work "Twenty-four solar terms" says: "See the vernal equinox in mid-August ...". "Spring and Autumn Stories Yin and Yang in and out" said: "The autumn equinox, Yin and Yang are also half-phase, so it is cold and summer day and night." In ancient China, the autumnal equinox was divided into three periods: "When thunder comes, the sound will stop;" Second, wait for scorpion blank households; Wait for the water to dry. "The ancients thought it thundered because the sun be the spirit is strong, and the yin began to fill after the autumnal equinox, so it didn't thunder.
According to the lunar calendar, "beginning of autumn" is the beginning of autumn and ends with "the first frost", and the "vernal equinox" is just half of the 90-day journey from beginning of autumn to the first frost. At the autumnal equinox, the Yangtze River basin and its vast northern area have entered autumn, and the daily average temperature has dropped below 22℃. The cold air mass in the north began to have some influence. In most areas, the rainy season has just ended, with a cool breeze blowing gently, the sky is high and the clouds are light in Wan Liqing, the air is crisp in autumn, the sweet-scented osmanthus is fragrant, the crab is fat and the chrysanthemum is yellow, and the autumn equinox is a beautiful and pleasant season. It is also an important solar term in agricultural production. After the autumnal equinox, the direct point of the sun moved to the southern hemisphere, and the northern hemisphere got less and less solar radiation, while the ground lost more heat and the temperature dropped significantly.
Agricultural proverbs say: "An autumn rain is a cold", "The white dew is divided into autumn nights, and one night is cold". "In August, the wild goose gate opens, and the foot of the wild goose is frosty." It is not surprising that frost appears in the autumn equinox in a year when the temperature in Northeast China drops early. On the day of the autumnal equinox, the sun is located at the longitude of the yellow meridian 180 degrees, and the sunlight is almost direct to the equator, and the length of day and night in most parts of the world is almost the same. At this time, the waiting temperature in the southern region has generally dropped below 22℃, and it has entered a cool autumn. "An autumn rain and a cold". The cold air from the south meets the warm and humid air that gradually decays, resulting in repeated rainfall and the temperature dropping again and again. In the northern part of the northwest plateau, the daily minimum temperature has dropped below 0℃, and you can already see the magnificent snow scene flying all over the sky and the earth wrapped in silver.
Since the autumnal equinox, the climate has two main characteristics:
(1) The position of direct sunlight continues to move from the equator to the southern hemisphere, and the daytime in the northern hemisphere is shorter than that at night, until the winter solstice reaches the shortest daytime.
(2) The temperature difference between day and night gradually increases. The temperature drops day by day, getting colder every day, and gradually entering the late autumn season. The situation in the southern hemisphere is just the opposite.