The 24-hour rainstorm warning accuracy rate in my country can reach 89%, but forecasting is still a world-class problem
Misunderstandings behind the weather forecast
Some people say that there is no season that pays more attention to weather forecasts than summer. Thunder and lightning, heavy rains, high temperatures, typhoons, and corresponding urban high temperatures, waterlogging, mountain mudslides, floods and other disasters have been staged countless times in this season.
Statistics from the National Early Warning Information Release Center show that summer is the season with more natural disasters in the year. In the past 4 years, the national summer early warning accounted for 46% of the annual early warning, the most frequent early warning, entering June to August, the most common It is thunder and lightning, heavy rain, high temperature warning. Whether these early warning information is accurate and whether it can reach every public is the question and expectation of the meteorological department.
An interesting phenomenon is that every time a heavy rain or high temperature is forecasted, there always seem to be different voices. Some say, "The weather forecast is getting more accurate. If it rains, it will really rain", while some say, "And again I was deceived, why did the torrential rain be delayed?" "Why did the torrential rain turn into patters of light rain?"
Behind these controversies, are there differences in people’s cognition and subjective feelings, how accurate is the objective weather forecast, and what is the level of my country’s weather forecast? This reporter interviewed relevant experts.
The objective forecast is inaccurate or the subjective feeling difference
On August 12, all of Beijing was waiting for the arrival of a heavy rain. The day before, the Central Meteorological Observatory forecasted that the Beijing-Tianjin-Hebei region would usher in the strongest rainfall since the flood season the next day.
However, it wasn't until around noon on August 12 that scattered rains appeared in some areas of Beijing. There was a hot discussion on the Internet. Some ridiculed that "The Dragon King needs a nucleic acid test in Beijing, and the heavy rain is still on the way", while some complained that "I was fooled by the weather forecast, and I really shouldn't cancel the scheduled appointment for the heavy rain."
In the eyes of meteorological experts, there is a misunderstanding behind this hot discussion, that is, when forecasting this heavy rain, the meteorological department has made it clear that the main rainfall period is noon to night, but some people may not pay attention to this.
Early that morning, Hu Xiao, the chief meteorological analyst of China Weather Network, also responded to this: Heavy rain is on the way-as can be seen from the radar chart, heavy rain is gradually northward affecting Beijing.
The Central Meteorological Observatory and the Beijing Meteorological Bureau also respectively gave further weather forecasts: this round of rainfall is the most violent from 18:00 to 22:00, with heavy rains and local heavy rains, which will end tomorrow morning.
In fact, people do have certain differences in their subjective feelings about the weather. Hu Xiao took heavy rain as an example. Generally speaking, the magnitude of heavy rain and heavy rain in meteorology refers to the accumulated rainfall, that is, the rainfall in 24 hours a day. Precipitation with precipitation greater than 25 mm in 24 hours is called heavy rain; precipitation with precipitation greater than or equal to 50 mm in 24 hours is called heavy rain.
"When this amount is reached, it is called torrential rain, but everyone feels differently, because there is a difference between the short-term heavy rainfall and the cumulative rainfall level." Hu Xiao said that when a short-term heavy rainfall occurs, it may take a few minutes. The internal rain is heavy, but the accumulated rainfall may not reach a very large level, or even a heavy rainfall level, which is not called a heavy rain.
Correspondingly, sometimes heavy rain or heavy rain, the rain is relatively gentle, the accumulated rainfall is large, but the public does not feel deeply, and some people may even think that they have encountered "fake heavy rain."
Not only heavy rain, but sometimes people also have a certain degree of "misunderstanding" regarding high temperatures.
Every summer, I sometimes hear similar questions: On a hot day, I feel that the surface temperature can spread eggs, why is the weather forecast only 30°C? Why is the temperature you feel when you walk on the street is obviously higher than the actual temperature announced by the meteorological department?
To answer these questions, we must start with the "twin" pair of body temperature and forecast temperature. The forecast temperature refers to the temperature of the air in the louver at a height of 1.5 meters. Studies have shown that the temperature difference between the ground and a place at a height of two meters can exceed 10°C from noon to noon in summer. This results in a difference between the somatosensory temperature and the forecast temperature. difference.
More importantly, the body temperature is not only affected by the forecast temperature, but also affected by factors such as humidity, wind speed and radiation. Experts from the China Meteorological Administration took wind speed as an example. A certain wind speed will make people feel the air moving, and the heat emitted by the body will be blown away from the body surface. Even if the temperature is high, it will feel relatively dry.
From this perspective, the "predicted temperature" is just one of the four factors that affect the somatosensory temperature. The public judges their personal feelings solely on the basis of the forecast temperature, which will lead to "scientific misunderstandings."
Why extreme precipitation forecasting is a global scientific problem
In interviews with reporters, many meteorological experts repeatedly mentioned that although the public has misunderstood the weather forecast, it must be admitted that there is still room for improvement in the accuracy of the weather forecast. Among them, rainstorm forecast is a world-class problem.
Some people say that the next rain is like pouring a basin of water from the sky on the ground. The forecaster can predict the approximate amount of water, and can also predict which ground will be wetted by water, but the water will not fall evenly on the ground. In some places, the wet area is large, and in some places, the water falls less. You must predict the ground It is very difficult to determine how wet each point is.
Lan Yu, deputy director of the Strong Weather Forecast Center of the Central Meteorological Observatory, said that as far as heavy rain is concerned, it is the result of different time scales and different spatial scales affecting the interaction of the system. It is not within a certain space and time range. It is difficult to draw correct forecast conclusions through comprehensive and comprehensive analysis with data.
He took the conventional high-altitude observation system as an example. At present, the observation data and information related to heavy rain provided by the system are mainly for the weather scale, and the small and medium-scale observations that directly cause heavy rain are insufficient or even scarce.
"This is like fishing with a net. If the mesh is too large, the small-scale weather system will inevitably become a fish that slips through the net." Lan Yu said, so the term "local" often appears in heavy rain forecasts, precisely because the current The forecasting ability of the city can only predict the possible range of local strong weather in advance, but cannot predict the exact location of its occurrence in advance.
Lan Yu said that from the perspective of the whole world, the accuracy of rainstorm forecasts has not been high, which is a worldwide problem.
Chen Tao, the chief forecaster of the Central Meteorological Observatory, also said that the weather is unpredictable and various types of weather have different "predictability". Extreme precipitation forecasting is a scientific problem facing the world. The accuracy of heavy rain forecasting in my country is currently at the same level as that of the world's powerful countries. The Meteorological Department will continue rolling updates based on weather trends and issue forecasts and warnings in a timely manner.
The rolling forecast he mentioned, as the name suggests, is the constantly updated weather forecast. Fu Gueran, a senior researcher at the Central Meteorological Observatory, said that the weather forecasters use numerical forecasts as the basis, and then comprehensively use various information analysis, and finally reach a forecast conclusion.
This does not mean that the forecaster can "report it casually" a day or two before, and then update it all before the onset of severe weather. The focus of rolling forecasts includes those small and medium-scale disaster weather. These weather systems are "small boats are good for turning around" and "face change coefficients" are high. It is difficult to accurately grasp the development trend in advance.
Fu Jiaolan therefore reminded that the public should pay more attention to the rolling forecast, that is, the constantly updated weather forecast. Because the atmospheric circulation situation is adjusted every day and the weather system is constantly changing, forecasters need to use the latest observational data and numerical model conclusions to produce forecast products, then make corrections, and finally give "weather forecast updated at this moment" .
How far is it from "Ten Reports and Ten Standards"
So, what is the current level of weather forecasting in my country? Fu Jiaolan said that with the continuous advancement of forecasting technology, the accuracy and timeliness of forecasting are constantly improving. Basically, the area and intensity of heavy rainfall can be predicted more accurately about 3 days in advance. The current 24-hour rainstorm warning accuracy rate in my country can reach 89%.
According to her, the temporal and spatial resolution of the numerical model currently used in my country is getting higher and higher, and the forecast of the fine distribution characteristics of the time and space of heavy rainfall is becoming more and more accurate. At the same time, the precision spatial resolution of the refined intelligent grid precipitation forecast developed by the Central Station can reach a resolution of 5 kilometers, and the time interval is hour by hour. At the same time, it can be updated according to the actual situation to continuously improve the accuracy of the precipitation forecast.
Numerical model, a term that is both unfamiliar and familiar. At the beginning of this year, 85-year-old Zeng Qingcun won the 2019 National Highest Science and Technology Award. An important contribution of everyone is in the field of numerical weather prediction. He pioneered the "semi-implicit difference method" and successfully realized the original equation numerical weather prediction, which became a milestone in the development of numerical weather prediction.
Numerical weather forecasting is also regarded by the World Meteorological Organization as one of the greatest technological and social advancements in the 20th century. Nature praises the development of numerical weather forecasting as a quiet revolution. “Global weather forecasting can be combined with the simulation of the human brain. The evolution of the early universe is comparable".
Zeng Qingcun once said in an interview with a reporter from China Youth Daily and China Youth Daily that today’s meteorological monitoring has changed from simply “site monitoring” to global monitoring including remote sensing of meteorological satellites, and meteorological forecasts have also evolved from empirical forecasts to numerical values. Weather forecast.
According to him, the effectiveness of international weather forecasts has increased from 1-3 days in the early days to 5-7 days. The current 3-day forecast can reach 70% to 80% accuracy on a global scale. If it is a certain area, such as the 3-day forecast in South China, the accuracy can be higher than 80%.
Among them, the improvement effect of typhoon forecast is the most obvious.
According to experts from the Central Meteorological Observatory, in recent years, the difference between the 24-hour forecast landing point and the actual landing point of multiple typhoons is about 50 kilometers, and the typhoon radius is 1,000 kilometers. Looking at the relative value, 50 kilometers is already a small margin of error.
Ma Xuequan, chief forecaster of the Central Meteorological Observatory, said that numerical weather forecasting is "the country's most important tool." The GRAPES global numerical forecasting system, which my country has vigorously developed in recent years, has performed better and better in the competition on the same platform. In 2017, the China Meteorological Administration was officially recognized as the World Meteorological Center by the World Meteorological Organization and became one of the 9 world meteorological centers in the world. The self-developed GRAPES numerical forecast system is the most important factor.
According to him, compared with 1998, the scientific and technological support of my country's comprehensive meteorological observation, numerical forecasting and forecasting platform has undergone earth-shaking changes. On the basis of numerical weather prediction, forecasters then make judgments based on their own experience and make corrections to form forecast and early warning information obtained by the public.
Zeng Qingcun is still very calm in the face of these advances. He said that it is unlikely that the weather forecast will reach "9 in ten" or even "10 in ten". "The weather is accidental. It is not in artificial laboratories, nor is it Being controlled by man, there will always be deviations in forecasts."
This is the reality that mankind must face: fearing the power of nature, but also exerting subjective initiative to deal with "unpredictable circumstances."
China Youth Daily · China Youth Daily reporter Qiu Chenhui Source: China Youth Daily