The wind of weather

Wind is one of the environmental factors of agricultural production. Moderate wind speed plays an important role in improving farmland environmental conditions. The increase of wind speed accelerates or strengthens the surface heat exchange, evapotranspiration of farmland and the transportation of carbon dioxide and oxygen in the air. Wind can spread plant pollen and seeds and help plants pollinate and reproduce. Wind energy is widely distributed and inexhaustible. Monsoon prevails in China, which is beneficial to the growth of crops. Inner Mongolia Plateau, Northeast Plain, Southeast Coast and Inland Mountainous Area are rich in wind energy resources, which can be used as energy sources.

Wind will also have a negative impact on agriculture. It can spread pathogens and plant diseases. High-altitude wind is a meteorological condition for the long-distance migration of pests such as armyworm, rice planthopper, rice leaf roller and locust. Strong wind causes mechanical wear of leaves, lodging of crops, broken trees, falling flowers and fruits, which affects the yield. Strong winds can also lead to soil erosion and sand dune movement, and destroy farmland. Blindly reclaiming wasteland in arid areas, wind will lead to land desertification. Strong winds and snowstorms in pastoral areas will disperse herds and aggravate freezing damage. Some special properties of local winds often cause wind disasters. Tidal wind with high salinity, scorching wind with high temperature and low temperature, and dry-hot wind blowing from the sea have seriously affected the flowering and fruiting of fruit trees and the filling of cereal crops. In order to prevent wind damage, wind-resistant varieties with dwarfing, lodging resistance and friction resistance are usually cultivated. It is more effective to build windbreaks and set up windbreaks. The kinetic energy formed by airflow is wind energy. Wind energy is a conversion form of solar energy.

The radiation of the sun causes uneven heating of the earth's surface, uneven distribution of atmospheric pressure, and the air moves along the horizontal direction to form wind. The formation of wind is the result of air flow. The formation of wind energy utilization is mainly to convert the kinetic energy of atmospheric movement into other forms of energy. In the equatorial and low latitudes, the solar altitude angle is large, the sunshine time is long, the solar radiation intensity is strong, the ground and atmosphere receive more heat and the temperature is high; At high latitudes, the solar altitude angle is small, the sunshine time is short, the heat received by the ground and the atmosphere is less, and the temperature is low. This temperature difference between high latitude and low latitude forms a north-south pressure gradient, which makes the air move horizontally and the wind blows along the direction of the horizontal pressure gradient, that is, the vertical and isobars blow from high pressure to low pressure. The earth is spinning, and the force that deflects the horizontal movement of air is called geostrophic deflection force, which deflects the airflow in the northern hemisphere to the right and the airflow in the southern hemisphere to the right, so the atmospheric movement of the earth is not only affected by the pressure gradient force, but also by geostrophic deflection. The real motion of the atmosphere is the result of the comprehensive influence of these two forces.

In fact, the sea surface wind is not only dominated by these two forces, but also influenced by the ocean and topography to a great extent. Mountain passes and straits can change the direction of airflow and increase the wind speed, while hills and mountains rub against each other and reduce the wind speed, while isolated peaks increase the wind speed because of their high altitude. Therefore, the temporal and spatial distribution of wind direction and wind speed is more complicated.

In winter, the mainland is colder than the ocean, and the pressure on the mainland is higher than the ocean. The wind blows from the mainland to the sea. In summer, on the other hand, the mainland is hotter than the ocean, and the wind blows inland from the ocean. This seasonal wind is called monsoon. The so-called land-sea breeze is that during the day, the air flow on the mainland is heated and expanded, rises to high altitude and flows to the ocean, and then cools and sinks over the ocean. The air flow near the surface of the ocean blows to the mainland to compensate for the rising air flow from the mainland. The low-level wind blows from the ocean to the mainland, which is called sea breeze. At night (winter), on the other hand, the low-level wind blows from the mainland to the ocean, which is called land wind. In mountainous areas, due to thermal reasons, it blows from the valley to the plain or hillside during the day and from the plain or hillside at night. The former is called valley wind and the latter is called mountain wind. This is because the hillside heats up quickly during the day, and the temperature is higher than the air temperature at the same height above the valley. The warm air on the hillside flows from the hillside to the valley, and the air in the valley supplements the air lost along the hillside. At this time, the wind blowing from the valley to the hillside is called valley wind. At night, the hillside is cooled by radiation, which is faster than the air at the same height. Cold air flows into the valley along the hillside, which is called mountain wind. When solar radiation can pass through the earth's atmosphere, the energy absorbed by the atmosphere is about 2 * 10 16W, and a small part of it is converted into kinetic energy of air. Because the tropics absorb more solar radiation energy than the polar regions, it produces atmospheric pressure difference, which leads to air flow and produces "wind". As for local areas, such as mountains and deep valleys, during the day, the air at the top of the mountains is heated by sunlight and replaced by cold air in the deep valleys, so the wind blows from the deep valleys to the mountains; At night, the air on the mountain dissipates quickly, so the wind blows from the mountain to the deep valley. For another example, in coastal areas, due to the temperature difference between land and ocean during the day, sea breeze blows to land; On the contrary, the land wind blows to the sea at night. Wind speed refers to the horizontal distance of air flow per unit time. According to the phenomenon caused by the wind to the ground objects, the wind is divided into 13 grades, which are called wind grades. Record with a number of 0 ~ 12.

wind scale

Wind grade and symbol name Wind speed (m) * surface wave height (m) wind.

0 no wind, 0.0-0.2 smoke, straight up, calm 0.0.

1 soft wind 0.3- 1.5 smoke indicates that the wind direction is at the peak of microwave 0. 1 and there is no water drop.

2 breeze 1.6-3.3 Feel the wind, and the small wave crest will not be broken by 0.2.

3 breeze 3.4-5.4 standard propagation wavelet peak rupture 0.6

4 breeze 5.5-7.9 blows dust, small waves, foam peak 1.0.

5 Strong breeze 8.0- 10.7 Waves and foam peaks in swaying young trees 2.0

6 strong wind 10.8- 13.8 wire sound waves to water droplets 3.0

7 gale 13.9- 17. 1 difficulty in walking, peak breaking, foam strips 4.0

8 strong wind 17.2-20.7 damaged branches, wave 5.5.

9-level gale 20.8-24.4 Small damaged houses wave crest rollback 7.0

10 gale 24.5-28.4 uprooting trees, waves rolling and roaring 9.0

1 1 Storm 28.5-32.6 was generally damaged, and the peaks were all in water droplets 1 1.5.

12 typhoon 32.7- destructive waves +04.0

Note: The wind speed listed in this table refers to the wind speed value at10m above the flat ground. Gust: When the flow speed of air is up and down, the wind will be up and down, and there will be waves of feeling when blowing on people. It's called a gust.

Cyclone: It is a cyclone when the air flies in the air with dust to form a vortex.

Foehn: When the air crosses the ridge, it is easy to produce dry and hot wind on the leeward side, which is called Foehn.

Tornado: A tornado is a circular column of air that rotates violently. From a distance, it looks like an elephant's nose that keeps swinging or a python hanging in the air.