Heavy rain warnings in 12 provinces across the country! An article to understand the "small steel cannon" in the meteorological system - severe convective weather

There is a group of people on the basketball court who look ordinary, short and a little fat. Their layup during warm-up is not noticeable, but once the scoring starts, their moves are fast and fierce. They dribble skillfully and break through boldly. They lower their center of gravity and tighten their core, increase the strength of their jumping legs, wrap their arms around the ball, and score layups in one go. They are not ambiguous when they meet big opponents. They have muscles under their round bodies. They hurt people when they fight. They cut into the inside line with a change of direction. They come and go without a trace. They are called the fat version of Iverson - the little steel cannon on the court. Players with this kind of technical style are also common in basketball games in the meteorological system. We call this faction "strong convection".

If you have never encountered "severe convection" on the court, you must have experienced severe convective weather in life, including strong winds that suddenly blow without any warning, thunderstorms that come quickly after a thunderclap, and hail that crackles on the roof glass. These are known as the "three brothers of severe convection". Any one of them is extremely destructive, and they often travel in teams.

Severe convective weather—which two currents are correct?

In the atmosphere around us, convection can occur between cold and warm, and there is also convection between the upper and lower layers. Energy is exchanged constantly, and corresponding changes occur in temperature, humidity, etc. Strong convection "takes advantage of" the unstable stratification characteristics of the upper cold layer and the lower warm layer in the atmospheric structure.

It is spring now. With the change of the direct point of the sun, the solar radiation energy incident on my country is increasing. The change brought about is that the ground temperature rises rapidly, which in turn makes the temperature of the low-altitude atmosphere rise. The warm and humid air flow originally transported from the south to the north is superimposed on it, further strengthening the temperature and humidity of the low-altitude atmosphere, and a low-altitude warm and humid "flow" is formed. On the other hand, the high-altitude atmosphere is also unambiguous, gathering from the northwest to the south. Their characteristics are "cold + dry", so that an atmospheric stratification structure with one up and one down, one cold and one hot is formed. More importantly, this atmospheric structure is not stable.

When the terrain is undulating, warm air is lifted or cold air accelerates southward, the cold and warm air currents may "meet and shake hands". At this time, the two layers of atmosphere that were originally moving horizontally will form a vertical movement in the up and down directions. The warm air rushes upward with rich water vapor. As the altitude increases, the temperature continues to drop, and the water vapor condenses into water droplets. The water droplets turn downward due to the influence of gravity, but in the process of descent they may encounter strengthening updrafts. The water droplets are carried up again and form larger droplets with the surrounding small droplets. This cycle is repeated several times, and the water droplets become larger and heavier. At this time, the updrafts below can no longer support them, and heavy rain suddenly falls amid rolling thunder.

A powerful and powerful "small steel cannon"

Remember the basketball court cannon we mentioned at the beginning? It is somewhat similar to the characteristics of severe convective weather. It is often sunny and cloudy in a short time, accompanied by lightning and thunder in the thunderstorm clouds, and heavy rain falls, just like a fake move to break through the layup.

For example, the severe convective weather process that occurred in the Sichuan Basin on April 11 this year was caused by the cold air from the Qinghai-Tibet Plateau moving southward to form a plateau trough, which met with the warm and humid air flow from the southwest. Coupled with the large amount of energy accumulated over Chongqing, it was like pouring cold water on a hot pot, which easily triggered severe convective weather in an instant.

This is how severe convective weather occurred around Chongqing. On the evening of the 11th, hail and strong winds appeared in Chongqing. The radar map showed that the gusts in Tongliang District were close to 30m/s. Coupled with the narrow channel effect formed by the terrain and buildings, the ground gusts were further strengthened, which eventually caused huge losses to the local area. The radar echo map of Yibin, Sichuan on the evening of the 11th was "purple red". The air flow moved strongly under the drag of rain, and the strong wind brought hail with it. Anyue, under the jurisdiction of Ziyang, Sichuan, had a level 13 thunderstorm and gale, and a heavy rain of 113.9 mm; the extreme precipitation reached 7.3 mm in 1 minute, and the precipitation in 10 minutes reached an astonishing 52.5 mm, which means that a heavy rain fell in 10 minutes.

Strong energy and fierce force often mean a small range and short duration. The impact range of severe convective weather is generally on the scale of a few kilometers to one or two hundred kilometers, and the duration is mostly one hour to more than ten hours, and the shorter is only a few minutes.

Understanding is the basis, prevention is the key

Weather activity is an inevitable process of nature. Humans currently do not have the ability to prevent it from happening. However, by understanding the formation process of severe convective weather, we can grasp its activity characteristics and the impacts it brings, and then we can find ways to prevent it.

As the general public, we should raise awareness of severe convective weather and enhance our ability to receive relevant warning and forecast information. For example, in the past, we mainly learned about the temperature and precipitation in our area when it comes to weather forecasts. In the season when severe convection is frequent, we can’t just listen to “whether it will rain or whether it will be hot.” ​​The key is the warning information. We should pay attention to the (color) level of the warning signal, the warning time, and the recommended risk avoidance measures. We can’t ignore the information received from the relevant departments. That would be a joke with our lives. In addition to the weather forecast on TV, the official forecast information also includes the severe convective weather forecast of the Central Meteorological Observatory, which will forecast the areas where severe convection may occur, the process prediction, the intensity of the activity, and secondary disasters. You can check it directly on the official website of the Central Meteorological Observatory.

In addition, young friends can obtain monitoring data through the Internet, new media and other means. For example, the most efficient one to reflect changes in precipitation is the "radar echo map", which is a monitoring product that intuitively displays the intensity of precipitation over a region. It calculates the real-time precipitation amount by actively emitting radar waves and collecting their reflected echoes. As the echo map is dynamically refreshed, the movement speed and direction of the precipitation belt can also be seen. This has great guiding significance for people's activities, travel, disaster reduction and avoidance during severe convective weather.

In addition, there is another "sky-watching artifact" for the common people, which is the satellite cloud map of the Fengyun satellite. The Fengyun-2 and Fengyun-4 satellite families can monitor my country 24 hours a day, 365 days a year. Meteorological elements such as wind, clouds, rain and fog can be seen intuitively. The Fengyun-4B satellite, which was the latest to join the observation fleet, has the highest time resolution of minutes, and can even distinguish the fine dynamic changes of rain belts and water vapor clouds.

Although the little cannon on the court is powerful, he is also afraid of those who are taller, stronger and faster than him. As for severe convective weather, with the three-dimensional observation of satellites, radars and ground stations, coupled with automated data transmission and fast processing capabilities, complete channels and networks can send forecast and warning information to the public as soon as possible, allowing early warning and early action to help people minimize the impact of severe convective weather.