Why is the high temperature in summer hotter than the solstice in summer?

"Three volts" refers to the first, middle and last three volts, that is, from mid-July to mid-August. After the summer solstice, although the days are getting shorter and the nights are getting longer, the days are longer than the nights in a day. Every day, the ground absorbs more heat than it emits, and the temperature near the ground is getting higher every day. During the "three volts" period, the heat absorbed by the ground is almost less than the heat emitted, and the weather is the hottest. After that, the heat absorbed by the ground began to be less than the heat emitted by the ground, and the temperature gradually decreased. Therefore, the hottest time of the year generally appears in the "dog days" from the summer solstice.

The summer solar term is the hottest solar term in a year. The ancient book "Twenty-four solar terms" said: "It is extremely hot in the summer." This is enough to explain the fiery degree of this solar term. The reason why it is extremely hot during the "Great Summer" is that since the beginning of summer, the heat absorbed from the ground sun during the day is more than that emitted at night, and the heat keeps accumulating. During summer, accumulated heat reaches its peak, so summer is the hottest.

Fu Tou, Er Fu, crosses the high temperature in summer, which is usually the hottest day of the year; Although it is already beginning of autumn in dog days, it is still very hot, so it is also called "autumn tiger". Because the first, second and third days are very hot, it is called "third day fever".

In fact, the main factor affecting the temperature is the intensity of solar radiation, and the light and heat of the sun can not directly raise the temperature. The heat energy directly absorbed by various gases in the air is only about 14%, while about 43% of the heat energy is absorbed by the ground. After the ground absorbs solar radiation heat, it is conducted into the air through radiation, convection, turbulence and other forms. The result of this upward heat transfer is the main reason for the temperature increase. Therefore, the increase of ground temperature is mainly the result of absorbing solar radiation energy.

This explanation is somewhat obscure. Simply put, the sun shines on the ground, making it hot, and the heat absorbed by the ground is released, making the air dry. The temperature of air is mainly obtained indirectly from the ground. Although at noon in summer, the sun shines on the ground closest to direct light, and both the ground and the air are strongly heated, the heat released by the ground is less than the heat provided by the sun, so this is not the hottest time. After noon, the ground temperature can continue to rise until the heat released by the ground is equal to the heat provided by the sun, and the ground temperature can rise to the highest; The temperature rise near the ground must be obtained from the heat released from the ground, which takes time, so the hottest time in summer is not at noon, but at two or three o'clock in the afternoon.

The heat is over

The annual summer solar term is August 23rd or 24th. According to the "Twenty-four Solar Terms", "If you go, you will go, and the department will stop here."

oh "This means that the hot summer is coming to an end. Although the average daily temperature in Beijing, Taiwan, Taiyuan, Xi, Chengdu, the vast areas to the east and south of Guiyang, and the Tarim Basin in Xinjiang are still above 22 degrees Celsius, it is in summer, but at this time, the cold air going south is increasing and the temperature is gradually decreasing.

After the summer heat, the daily temperature difference in most parts of China has increased. The conditions of warm day and cool night are very beneficial to the production and accumulation of dry matter of crops, and the crops mature quickly. There is a folk proverb called "changing fields overnight in hot summer". The early and mid-season rice in Huanghuai area and south of the Yangtze River is ripe for harvesting, and the continuous rain at this time is the main unfavorable weather. For single-season late rice, it is in the stage of young panicle differentiation, and abundant rainfall is very important. In case of drought, it should be irrigated in time, otherwise it will lead to small panicle and high empty shell rate.

In addition, the topdressing of ear fertilizer should make the grain full, but the topdressing time should not be too late, so as not to cause greed for green and late maturity. Double-cropping late rice in the south is about to round around the heat, so it should be baked in time. In most cotton areas, cotton began to vomit, when the temperature was generally high, and rainy days led to a large number of rotten bells. At the same time of fine pruning, pushing plants and ridging, picking old leaves, improving ventilation and light transmission conditions, and spraying Bordeaux mixture in time also have a good effect of preventing or alleviating bell rot. Around summer, sweet potato tubers swell in spring, sweet potato begins to bear tubers in summer, and summer corn heads and blossoms, all of which need sufficient water supply. At this time, the drought seriously affected the yield. From this point of view, it is no exaggeration to say that "summer rain is like gold".

After the summer, except for South China and Southwest China, the rainy season is coming to an end in most parts of China, and the precipitation is gradually decreasing. Especially in North China, Northeast China and Northwest China, we must pay close attention to water storage and moisture conservation, prevent autumn sowing drought and postpone the sowing date of winter crops.