Lately, it's raining almost every day, as if it's raining almost half the time this summer, or it's cloudy, accumulating rain. Now that it is autumn, the rain is not uncommon, and it is often night and day.
Rain
To say that Shandong alone may still lack representation, look at the capital Beijing. Beijing's rainfall this year is quite abundant: the average precipitation in June-August reached 627.4mm, of which July, when precipitation was the most concentrated, reached 400.4mm. What is this concept? If you take the July data alone, it should be the highest value in the same period of history in the 70 years, and if you take the data of the three months from June to August, it is also the highest value in the past two decades. Therefore, some people on the Internet jokingly called this year's Beijing "Little Jiangnan".
Gangnam Rain Lane
In ancient times, when encountering this situation, it was often interpreted as "celestial anomaly". This view deeply influenced the rulers of feudal society, as well as the common people, and this influence continued until the villages and villages after liberation. I remember when I was a child, when I encountered a great drought year, the small-footed old ladies in the village organized themselves in groups to pray for rain together, and they gave this kind of activity a particularly era-sensitive high-level name: "Dangsha".
Ever since there was a weather forecast, people began to know: O! It turns out that the rain can be predicted in advance! This mysterious-looking "praying for rain" has gradually disappeared. But seriously, why it rains, do you really know?
Simply put, rain is the process of water vapor in the air rising into small water droplets, small water droplets continue to converge, hugging each other, when the weight exceeds the maximum weight that the air can carry, it will form rainfall.
Terrain rain
As far as the cause is concerned, if the water vapor is lifted into rain by cold air, it is called frontal rain, if it is lifted into rain because of the terrain, if it is raised into rain due to strong sunlight radiation, it is called convective rain, and if it is rotated by a typhoon at sea, it is called typhoon rain.
The torrential rains that occurred in Zhengzhou this year are topographic rains. China's northeast and north China belong to the typical temperate monsoon climate, and the summer is affected by the subtropical high-pressure air flow from the western Pacific Ocean, and the temperature is high and rainy. That's why even if there is wind in the summer, it is a wet and hot southeast wind. In recent years, affected by global warming, summer winds from the Pacific Ocean have strengthened year by year, and the monsoon boundary has shifted significantly northward. This has brought abundant rain to North China, and even at the junction of North China and Northwest China, the rain is increasing year by year. In June and July this year, the warm and humid air flow from the Pacific Ocean happened to encounter Typhoon "Fireworks", and this enhanced version of the warm and humid air flow came all the way to the foot of the Taihang Mountains during the northward movement, and was forced to rise to form heavy rainfall.
Topography of Zhengzhou
To the northwest of Zhengzhou is the Taihang Mountains, which have an average elevation of more than 1,200 meters, while zhengzhou has an average altitude of just over 100 meters. The difference in altitude is very different, it is easy to form terrain rain, and this time the warm and humid air flow is a strengthened version. According to statistics, from 8 p.m. on July 17 to 8 p.m. on July 20, the rainfall in Zhengzhou reached 617.1mm, which is equivalent to the average annual rainfall in Zhengzhou in these three days. It rained in three days a year. The heaviest rainy period created a record of 201.9mm per hour, according to this rough estimate, it is equivalent to pouring 103 West Lake water into Zhengzhou City in one hour!
After the rainstorm
In this way, the theoretical one atmospheric cycle becomes two. Of course, an atmospheric circulation is also formed between the subtropical high pressure at 30 degrees north latitude and the very low pressure at 60 degrees north latitude due to the difference in air pressure.
Fortunately, after the founding of the People's Republic of China, the banks of the Yellow River have been strengthened one after another. Rainfall can be a disaster, but the Yellow River will never flood.
Rainfall has two necessary conditions: temperature difference and water vapor. The temperature difference promotes the circulation of the atmosphere; the amount of water vapor in the atmosphere directly determines the amount of rainfall. So, how does the temperature difference cause a global atmospheric circulation? This is an interesting question, and finding the answer to this question is a process of exploration that tests the imagination of space.
Temperatures are far from as simple as you might think, such as high altitudes in the mountains, closer to the sun, and in theory it seems that it should be warmer, but the truth is just the opposite. Mount Kilimanjaro, Africa's highest peak near the equator, is 5,892 meters above sea level, but the temperature at the summit is nearly 30 degrees Celsius lower than at the foot of the mountain. The equator is hot, but it does not prevent the snow from being on top of Kilimanjaro.
Mount Kilimanjaro is covered in snow
This is related to solar radiation, the heat generated by solar radiation is absorbed by the ground, and the ground then radiates the heat into the air, so we feel the temperature. Briefly speaking, the heat source of the surface temperature is mainly ground thermal radiation, not direct radiation from the sun, and the mountain top is naturally lower than the foot of the mountain because it is far from the ground, the air is thin, and it is weakened by the influence of ground radiation.
The airflow above ignores an important factor: the rotation of the Earth. Due to the bias force of the Earth's autobiography, the warm air at the high altitude of the equator will gradually shift to the right during the process of flowing northward, and eventually parallel to the parallel line near 30 degrees north latitude and no longer go north, at the same time, along the way, due to the gradual decrease in temperature, the air gradually sinks, forming a subtropical high pressure on the surface; the cold air on the surface of the Arctic will shift in the process of flowing southward, and finally parallel to the latitude near 60 degrees north latitude will no longer go south, at the same time, along the way, because the temperature gradually rises, the air gradually rises. A subpolar low pressure is formed on the surface.
Three loops of circulation
Due to the difference in specific heat capacity between land and ocean, the atmospheric circulation in reality is much more complex than the situation analyzed above. With these preparations, it is much easier to understand the rain in North China. North China is located between the subtropical high pressure and the subpolar low pressure, and the summer is affected by the monsoon from the western Pacific Ocean, hot and rainy, coupled with the influence of typhoons, the rain is particularly strong!