Which days are generally the hottest in summer?

The hottest weather is summer! "Three volts" refers to the first, middle and last volts, which is about the period 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 still longer than the nights. The ground still absorbs more heat than it emit, and the temperature near the ground is getting higher day by 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. Later, the heat absorbed by the ground begins to be less than the heat emitted by the ground, and the temperature slowly drops. Therefore, the hottest time of the year usually occurs during the "three days" of the summer solstice.

The Great Heat is the hottest solar term of the year. The ancient book "Explanation of the Twenty-Four Solar Terms" says: "The Great Heat is the extremely hot season." This is enough to illustrate how hot this solar term is. The reason why the "Great Heat" period is extremely hot is because since the beginning of summer, the ground has absorbed more heat from the sun during the day than is emitted at night. The heat has continued to accumulate. During the Great Heat period, the accumulated heat has reached its peak. So Great Summer is the hottest.

Tou Fu and Er Fu span the Great Heat and are generally the hottest days of the year. Although autumn has begun during the Three Fu period, the weather is still hot, so it is also known as the "Autumn Tiger". Because the first, second and third volt days are very hot, so it is called "hot in the third volt".

In fact, the main factor affecting air temperature is solar radiation intensity. Solar heat cannot directly increase the temperature. Various gases in the air directly absorb only about 14% of the heat energy from sunlight, while about 43% of the heat energy is absorbed by the ground. After the ground absorbs solar radiation heat, it is then conducted to the air through radiation, convection, turbulence, etc. The result of this upward transport of heat is the main reason for the increase in temperature. Therefore, the increase in ground temperature is mainly the result of absorbing solar radiation energy.

This explanation is a bit obscure. To put it simply, the sun shines on the ground and heats the ground. The heat absorbed by the ground is then released to heat the air. The temperature of the air is mainly obtained indirectly from the ground. Although at noon in summer, the sun's rays hit the ground most directly, and the ground and air receive strong heat, the heat emitted 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 emitted by the ground equals the heat supplied by the sun. It all takes time, so the hottest time in summer is not at noon, but at two or three o'clock in the afternoon.

End Heat

The end heat solar term falls on August 23 or 24 every year. According to the "Collection of the Seventy-Two Hours of the Moon Order", it is said: "The place is gone, and the qi has stopped here." It means that the hot summer is about to pass. Although the average daily temperature in the vast areas east and south of Beijing, Taiyuan, Xi'an, Chengdu and Guiyang in my country and the Tarim Basin in Xinjiang is still above 22 degrees Celsius before and after the summer heat, it is summer, but the cold air moves southward several times at this time. increased, and the temperature dropped gradually.

After the extreme heat, the daily temperature range increases in most areas of our country. The warm days and cool nights are very beneficial to the production and accumulation of dry matter in crops. The crops mature faster. There is a folk saying of "the heat field lasts overnight" Change" theory. The early to mid-season rice in the Huanghuai region and along the Yangtze River is ripe for harvest, and continuous rain at this time is the main unfavorable weather. For single-season late rice that is in the stage of young panicle differentiation, abundant rain is very important. In case of drought, timely irrigation is required, otherwise it will lead to small ears and high empty shell rate.

In addition, top-dressing fertilizer should be applied to make the grains plump, but the top-dressing time should not be too late to prevent late ripening. The double-cropping late rice in the south will soon have round stalks around the end of the heat, so the fields should be roasted at the right time. Cotton in most cotton areas begins to form bolls and flocculate. At this time, the temperature is generally still high, and rain and lack of sunshine will lead to a large number of rotten bolls. While fine pruning, pushing plants into ridges, and removing old leaves to improve ventilation and light transmission conditions, timely spraying of Bordeaux mixture can also have a better effect on preventing or reducing boll rot. Before and after the heat, the spring potato tubers swell, the summer potatoes begin to form potatoes, and the summer corn heads and blooms, all of which require sufficient water supply. At this time, drought has a serious impact on the yield. From this point of view, it is not an exaggeration to say that "the rain in summer is like gold".

After the end of summer, the rainy season is coming to an end in most parts of my country, except for South China and Southwest China, and precipitation is gradually decreasing. In particular, North China, Northeast China and Northwest China must urgently store water and conserve moisture to prevent drought during the autumn planting period and delay the sowing period of winter crops.