Reasons for the formation of mountain valley wind

The formation of mountain valley wind is due to the thermal difference between the valley and the nearby air, which leads to the daytime wind blowing from the valley to the hillside. What's this wind called? Gu Feng; At night, the wind blows from the hillside to the valley? Mountain wind? . Mountain breeze and valley breeze are always called mountain breeze. Let me give you a detailed introduction to the related knowledge of mountain valley wind.

The formation principle of mountain-valley wind is similar to that of land-sea wind.

During the day, the hillside receives more sunlight and heat from the sun and becomes a small one. Heating stove? The air warms more; Above the valley, the air at the same height is far from the ground and the temperature is less. So the warm air on the hillside keeps rising, flowing from the hillside to the upper valley, and the air at the bottom of the valley supplements the mountain along the hillside, thus forming a thermal cycle between the hillside and the valley. The lower wind blows from the bottom of the valley to the hillside, which is called the valley wind.

At night, the air on the hillside is affected by the radiation cooling of the hillside. Heating stove? Became? Cooler? , the air is cooler; Above the valley, the air at the same height is far from the ground, and the temperature drops less. So the cold air on the hillside flows into the valley along the hillside because of its high density, and the air at the bottom of the valley rises due to convergence, flowing from the top of the mountain to the top of the mountain, forming a thermal circulation opposite to that during the day. The low-level wind blows from the hillside to the valley, which is called mountain wind (see Figure 5-42).

The average speed of the valley wind is about 2~4 meters per second, and sometimes it can reach 7~ 10 meters per second. When Gu Feng passed the mountain pass, the wind speed increased. The wind speed of mountain wind is smaller than that of valley wind, but in the canyon, the wind is stronger, which sometimes damages the crops in the valley. Generally, the thickness of the valley wind is about 500~ 1000 meters above the valley bottom, and this thickness increases with the increase of gas layer instability. Therefore, the tensile thickness in the afternoon is the largest in a day. The thickness of mountain wind is relatively thin, usually only about 300 meters.

On sunny days, the wind from the valley sends warm air to the mountain, which raises the temperature on the mountain and promotes the germination, flowering, fruiting and early maturity of plants, crops and fruit trees on the hillside. Winter can reduce the chill. The valley wind brings water vapor to the top of the valley, which increases the air humidity in the mountains and reduces the air humidity in the valley. This phenomenon is especially obvious at noon.

If there is enough water vapor in the air, the summer breeze will often condense clouds and cause rainfall, which is very beneficial to the growth of trees and crops in mountainous areas; At night, the mountain wind brings the water vapor from the mountain to the valley, so the air humidity in the mountain decreases and the air humidity in the valley increases. In the growing season, mountain breeze can reduce the temperature, which is very beneficial to the accumulation of nutrients in plants and the growth and expansion of root and tuber plants.

Mountain breeze can also transport fresh air to urban areas and factories, and take away the smoke and chemicals floating in the air, which is conducive to improving and protecting the environment. The construction and layout of the factory should consider the regular change of wind direction. The wind direction changes regularly and the wind force is relatively stable, so it can be used as a power resource to study and utilize, give play to its advantages, control its disadvantages and serve the socialist construction.

It is worth noting that, in addition to mountainous areas, the wind similar to the valley wind can also appear on the plateau and basin edge of China: the wind direction and wind speed have obvious daily changes. The mountain-valley wind on the edge of the Qinghai-Tibet Plateau, especially in the area adjacent to the Sichuan Basin, has a great influence on the weather on the edge of the Qinghai-Tibet Plateau. In the case of sufficient water vapor, the white clouds condense over the hillside and cause rainfall at the edge of the basin at night.

The causes of land-sea wind The horizontal range of land-sea wind can reach tens of kilometers, the vertical height can reach 1 ~ 2 kilometers, and the cycle is one day and night. During the day, the earth's surface is heated by solar radiation. Because the heat capacity of land soil is much less than that of sea water, the temperature on land is much faster than that on the ocean, so the temperature on land is obviously higher than that on the nearby ocean. The air column on land is heated and expanded, resulting in different distributions of air temperature and air pressure. Under the action of horizontal pressure gradient force, the air above it flows from land to sea, then sinks to low altitude, then flows from sea surface to land, and rises again, thus forming low-level sea breeze and sea breeze circulation on vertical section. The sea breeze blows from morning to night every day, and the wind is strongest in the afternoon.

After sunset, the land cools faster than the ocean; At night, when the sea water temperature is higher than the land temperature, there will be a thermal circulation opposite to that during the day, resulting in the formation of low-level land wind and land wind circulation on the vertical section.

During the day, the temperature difference between land and sea is greater than at night, so the sea breeze is greater than the land breeze. If the sea breeze is forced to rise along the hillside, it often produces clouds. In larger lakes, lake-land wind similar to sea-land wind circulation can also be generated at the junction of lake and land. Sea breeze and lake breeze have the effect of cooling off summer heat for coastal residents. On the big island, the sea breeze gathers on the island during the day and the land breeze diverges from the island at night. So the island is rainy during the day and sunny at night. For example, in Hainan Island, China, the biggest precipitation intensity in a day appears at the strongest moment when the sea breeze gathers in the afternoon.

If you live by the sea for a period of time, you will have such an experience: on sunny days, there are often winds blowing from the sea; At night, the wind blows from land to sea.

This kind of wind with regular circulation is the land-sea wind in meteorology. During the day, the land is warmed by solar radiation, and the air above the surface quickly heats up and rises upward. Because of its thermal characteristics, the temperature above the sea surface is relatively cold, and the cold air sinks and flows to the hot land surface near the ground to supplement the vacancy caused by the rise of hot air there, forming a sea breeze;

At night, the land cools quickly, the ocean warms, and the near-surface airflow blows from the land to the ocean, which is called land wind, that is, land-sea wind. The sea-land wind is only affected by the temperature difference of one day, with weak energy, weak wind and small range. Generally only 20-50 kilometers deep into the land, also known as coastal wind, is most obvious in calm wind weather. Sea breeze has a good effect on restraining the heat at noon and regulating the climate. China/KLOC-Shanghai, with a population of more than 0/000 million, benefits from the cool breeze of land and sea.

The function of mountain breeze is to send warm air to the mountain in sunny days, so as to raise the temperature on the mountain and promote the plants, crops and fruit trees in hillside areas to germinate, blossom, bear fruit and mature early. Winter can reduce the chill. The valley wind brings water vapor to the top of the valley, which increases the air humidity in the mountains and reduces the air humidity in the valley. This phenomenon is especially obvious at noon. If there is enough water vapor in the air, the summer breeze will often condense clouds and cause rainfall, which is very beneficial to the growth of trees and crops in mountainous areas; At night, the mountain wind brings the water vapor from the mountain to the valley, so the air humidity in the mountain decreases and the air humidity in the valley increases. In the growing season, mountain breeze can reduce the temperature, which is very beneficial to the accumulation of nutrients in plants and the growth and expansion of root and tuber plants.

Mountain breeze can also transport fresh air to urban areas and factories, and take away the smoke and chemicals floating in the air, which is conducive to improving and protecting the environment. The construction and layout of the factory should consider the regular change of wind direction. The wind direction changes regularly and the wind force is relatively stable, so it can be used as a power resource for research and utilization.

It is worth noting that, in addition to mountainous areas, the wind similar to the valley wind can also appear on the plateau and basin edge of China: the wind direction and wind speed have obvious daily changes. The mountain-valley wind on the edge of the Qinghai-Tibet Plateau, especially in the area adjacent to the Sichuan Basin, has a great influence on the weather on the edge of the Qinghai-Tibet Plateau. In the case of sufficient water vapor, the white clouds condense over the hillside and cause rainfall at the edge of the basin at night.

The wind is strong at the top of the mountain, and it rains heavily on the windward slope in the mountainous area. During the day, the wind blows from the valley to the top of the mountain, which is called the valley wind. The night wind blows from the top of the mountain to the valley, which is called mountain wind. The valley wind is strong, but the mountain wind is weak. Valley wind usually appears 2 ~ 3 hours after sunrise, and the wind speed increases with the increase of temperature, reaches the maximum in the afternoon, and then decreases with the decrease of temperature. 1 ~ 2 hours before sunset, the valley wind subsided and the mountain wind took its place. This cycle makes the top of the mountain windy day and night, and it is windy all year round. Especially in summer, the valley wind and mountain wind are more and more obvious.

In summer, the southeast monsoon brings a lot of humid air, and its flow direction is perpendicular to the direction of mountains. The airflow is blocked by the mountain and forced to rise, which makes the water vapor contained cool and condense, and forms rainfall on the windward slope. Tall mountain peaks in the west and north of Beijing, such as natural barriers, on the one hand, are beneficial to the rainfall topography, causing heavy rain and heavy rain to fall on windward slopes, on the other hand, they block the airflow movement, prolong the rainfall time and increase the rainfall intensity.

Due to the influence of height, topography and slope direction, there are great differences in meteorological factors such as solar radiation, rainfall and temperature in mountainous areas. In particular, altitude has become the dominant factor of climatic conditions in mountainous areas. Every time the average altitude rises by 100 m, the temperature drops by 0.5℃ ~ 0.6℃, the weather and frost-free period in Yinjiang River decrease by 5 ~ 6 days, and the accumulated temperature decreases by 159℃, resulting in different climatic conditions and agricultural production environment in the same mountain range.