Description of wind
Wind is a moving airflow and a vector. People generally describe it with three parameters: wind direction, wind speed, and wind level, as follows:
(1) Wind direction. In daily life, people are always accustomed to calling the direction the wind blows as wind direction. If the wind is blowing from the south, it is called the south wind; if the wind is blowing from the north, it is called the north wind; if the wind is blowing from the northeast, it is called the northeast wind. In scientific surveys, the wind direction on land usually adopts 16 directions, and the wind direction on sea surface adopts 32 directions. For example, on land, the direction of true north is defined as 0°, along the clockwise direction, every 22.5° is an azimuth; on the sea surface, the true north direction is also specified as 0°, along the clockwise direction, every 11.25° is an azimuth. The frequency of occurrence of various wind directions is usually represented by a wind rose diagram. In polar coordinates, the frequency of occurrence of various wind directions in 16 or 32 directions in a certain year or a certain month is marked. Because it is shaped like a rose, it is called a “wind direction rose diagram”.
(2) Wind speed. Wind speed specifically refers to the air flow speed corresponding to the wind, that is, the distance that air moves in the horizontal direction per unit time. Commonly used units are m/s or km/h. In specific practice, there are many instruments specifically used to measure wind speed, the common ones are heat-dissipating anemometers, rotary anemometers, acoustic anemometers, etc. Because the wind is unstable, the wind speed often changes. Therefore, wind speed can be divided into instantaneous wind speed and average wind speed. Generally, people call the frequency of wind speed as the percentage of the number of hours that the same wind speed occurs within a certain period of time to the total number of measurement hours. At the same time, the difference between the maximum wind speed and the minimum wind speed within the limited time for obtaining the average wind speed is called the wind speed variation.
(3) Wind level. The wind level is based on various phenomena caused by the influence of wind on the ground or sea surface objects, and the magnitude of the wind is estimated according to the intensity level of the wind. At present, the commonly used wind classification in the world is 0-12 (in 1946, the World Meteorological Organization once changed the wind scale from 13 to 18, but in practice, 0-12 is still used).
Distribution of Earth’s Wind Energy Resources
The wind that contains energy is a kind of energy that can be used, and it is a renewable process energy. Since wind is caused by solar thermal radiation, wind energy is also a form of solar energy. Studies have shown that about 2% of the solar energy reaching the earth is converted into wind energy, but the total amount is still considerable. Some experts estimate that the wind energy on the earth is about 100 times the current total energy consumption in the world, which is equivalent to the energy contained in 1.08 trillion tons of standard coal.
The World Meteorological Organization has conducted a systematic study on the total global wind power (that is, the wind energy obtained per unit time). The result is that the total power of wind energy stored in the global atmosphere is about 1014MW, of which about 3.5×109MW of wind energy can be exploited. Wind energy resources are not only extremely rich, but also distributed in almost all regions and countries. However, due to the influence of seasons, geography, climate and other factors, the distribution of wind energy resources around the world is uneven. The land surface of the earth is about 1.07×108km2, and the area 10m above the ground (average wind speed higher than 5m/s) accounts for about 27%.