Why is it hotter in summer in the south than in the north?

In fact, sometimes it is hotter in the north than in the south. 、

It is a fact that everyone can understand that the north is colder than the south in winter. However, it seems unreasonable that it is sometimes hotter in the north than in the south in summer. In fact, from the meteorological point of view, it is not surprising that the summer in the north is hotter than that in the south.

Generally speaking, the southern region of low latitude is close to the equator, with almost direct sunlight and strong solar radiation, more heat is thrown into the ground and the temperature is relatively high. In the northern region of high latitude, the sunlight is mostly oblique, the solar radiation is weak, the heat thrown to the ground is less, and the temperature is naturally lower. But when the solar altitude angle is small (morning and evening and winter), as long as the solar altitude angle changes slightly, the solar radiation intensity will change greatly; When the solar altitude angle is large (around noon and in summer), even if the solar altitude angle changes greatly, the solar radiation intensity will not change much. Therefore, in summer, the direct point of the sun moves northward, and the solar altitude angle in the north is relatively large, and the solar radiation in the north is not much weaker than that in the south. At the same time, the summer days in the north are longer than those in the south, and there may be more sunshine hours every day. For example, the average daily sunshine hours in Guangzhou in July are 13.3 hours, and those in Beijing are 14.6 hours. The more sunshine hours, the longer sunshine time, the more solar radiation the ground gets, and the higher the heat, the higher the temperature will naturally rise.

It is particularly noteworthy that there are many paddy fields, rivers and lakes in southern China, and the water evaporation is far more than that in the north; There are many forests, thick vegetation and large transpiration in the south; The south is close to the high-temperature ocean, and the evaporation of seawater is quite amazing. A large amount of water vapor enters the air in the south of China with the south wind. In this way, the air in the south contains a lot of water vapor, which is easy to form clouds and cause rainfall, making the sky often overcast and the weather often rainy, which greatly reduces the actual sunshine hours, and sometimes there is no sunshine for three to five days or even ten days. Even if the weather is fine, a lot of water vapor in the clouds and air will obviously absorb and reflect solar radiation, which will greatly reduce the amount of solar radiation reaching the ground. For example, in July, Guangzhou received 1.855 joules of solar radiation per square centimeter of ground every day, while Beijing received 1.930 joules.

In addition, there are many thunderstorms in summer due to the southern region of low latitude. Rain comes from high altitude and the temperature is very low. Low temperature rain will absorb the heat in the air and the heat on the ground, so that the temperature will drop. Rainfall evaporation, water surface evaporation and plant transpiration will take away a lot of heat on the ground and make the temperature drop again and again. Therefore, in the rainy and vegetated south, the temperature will not rise too high in summer.

Sometimes, the south is located at the northern edge of the subtropical high, controlled by the stationary front, with continuous rain and no sunshine for many days. The north is controlled by the mainland high pressure, the weather is fine, and the burning sunshine follows everyone all day, bringing unacceptable but irresistible heat every minute. If there is more heat, the temperature will naturally increase. One of the main reasons for the high temperature and summer in the north of 1999 is the influence of relatively strong warm and high pressure ridge. It can be seen that in summer in northern China, the ground receives more solar radiation than the south, but the heat lost from the ground is less than that in the south, which will undoubtedly lead to hot and hot weather, and even a strange phenomenon that the north is hotter than the south.

Blocked by the cold air in the north, warm air accumulates in large quantities, and the temperature rises day by day, which looks sultry. However, extremes meet, and once the air explodes south, it will rain and cool down, bringing a chill to people. 1984 On August 6th, the highest temperature in Beijing was 36. 1℃, but on August 8th, there was a torrential rain of 207mm, and there was heavy rain nearby. 1999 In late June, after several days of high temperature in North China, there was a large-scale heavy rainfall from July 2 to 4, and the temperature dropped significantly, and the summer heat was temporarily relieved.