How many days can the weather forecast predict?
Weather forecast is to predict the weather changes in a few days. The traditional weather forecast is based on semi-experience and semi-theory, which is fuzzy and has a large error. The development of science provides a good tool for short-term weather forecast. For example, using Doppler radar to detect clouds within hundreds of kilometers, we can know the structure of thunderstorm clouds, know where water droplets and raindrops are, and know the moving direction of clouds. Satellite cloud pictures bring us a lot of information, which was impossible in the past. Now, the weather forecast in three days is quite accurate. Many people are used to listening to the weather forecast every day and deciding the arrangement of various activities according to the weather conditions. Very important activities even require the meteorological department to give regular, quantitative and fixed-point accurate forecasts.
Climate prediction is medium and long term. For example, it is impossible to predict the weather in April every day in March, but it can be predicted whether the temperature in April is higher or lower than usual; Is the rainfall more or less than usual? Inter-seasonal climate forecast is very important, such as rainfall and snowfall forecast, gale cooling forecast, river flood season forecast, whether there are more or less disastrous weather and so on. It is related to the government's decision-making and the safety of people's lives and property, and requires meteorologists to make accurate and scientific predictions.
The accuracy of weather forecast is getting higher and higher. Experience alone, half experience and half theory is not enough. New scientific methods are needed. With the development of computing technology, meteorology and mathematics are more and more closely linked. Numerical weather forecast is a new scientific method. Based on the study of the physical process of atmospheric change, it uses a high-performance computer to solve a set of equations that control atmospheric movement and "calculate" the changes of rain and snow.
Meteorology studies the whole atmosphere, so it is impossible to do experiments in the laboratory. People feel sunny, rainy, snowy and other weather every day, which occurs in the atmosphere around the earth's surface 10 kilometers where people live. The atmosphere is a fluid, and its motion changes obey six classical mathematical and physical equations, such as the conservation of mass and energy. This is the source of the mathematical model and mathematical physical equation of numerical weather forecast. But there are too many factors that affect the weather, so we have to take them into account, and we have great freedom.
If mathematical models and high-performance computers are the brains of numerical forecasting systems, then various atmospheric observation stations, meteorological radars and meteorological satellites constitute the eyes of numerical forecasting.
In order to improve the accuracy of numerical prediction, a set of dense atmospheric observation network is needed.
We divide the earth's atmosphere into many discontinuous networks, each node is a degree of freedom, and many layers of spheres can be taken vertically. There are a large number of high-altitude meteorological observation stations in the world (there are more than 300 in China), as well as remote sensing observation instruments such as meteorological satellites (including sun-synchronous satellites and geosynchronous satellites). There will soon be more than 3000 observation points on the sea buoy. The data obtained from meteorological observation, on the one hand, is used as the initial field of numerical prediction, on the other hand, it is used to check whether the results calculated by mathematical model are correct.
Many factors on the earth's surface affect the parameters in the mathematical model. For example, is the earth's surface sea or land, forest or grassland or swamp, whether there is ice or snow, and so on.
China is located in the east of Asia, spanning three latitudes: high, middle and low, with complex terrain and frequent meteorological disasters. Improving the ability of severe weather forecasting is a major event related to the national economy and people's livelihood, and it is also the advantage of numerical forecasting. China is one of the few countries in the world that can carry out medium-range numerical weather forecast.