Why is the temperature so low at high altitude?

Different heights have different temperatures. According to the survey, the higher the altitude, the lower the temperature. Why is this happening? Why is the temperature in the sky lower than that on the ground? I believe many friends don't quite understand the reasons. Let me give you a detailed introduction.

Why is the temperature so low at high altitude?

The first law of thermodynamics is often used to study atmospheric phenomena. Usually, a part of air with the same temperature and pressure is taken as the research object, which is called an air mass with a diameter of several kilometers. Because the air mass is very large, the heat exchange between the edge part and the outside world has no obvious influence on the whole air mass, that is, Q=0 in the formula (1), so the increase or decrease of the internal energy of the air mass is only equal to the work done by or to the outside world:

δU = W

The sun warms the earth, and the ground raises the temperature and lowers the density of the air mass below, thus rising. When the air mass expands, it pushes the surrounding air to do work, so the internal energy is reduced and the temperature is lowered. Therefore, the higher the place, the lower the temperature of the air. For dry air, the temperature drops 1 0℃ for every increase of1km.

When the plane flies at an altitude of 10,000 meters, the temperature outside the cabin is often below -50℃. Because of the air-conditioning equipment on board, the cabin is always warm as spring. But at this time, the function of air conditioning is not to heat the air, but to cool it down. The air pressure at high altitude is lower than that in the cabin. In order to get fresh air in the engine room, air compressor must be used to press the air outside the engine room. In this process, the air compressor does work on the gas, so that the internal energy of the gas increases and the temperature rises. If you don't use air conditioning, the temperature in the cabin may reach above 50℃!

Expansion: a factor affecting climate

Solar radiation factor, underlying surface factor, atmospheric circulation factor and human activity factor. Solar radiation factor is the basic power source of climate. Such factors include: latitude factors, etc. Underlying surface factors play a very important role in climate formation. These factors include ocean currents, ground vegetation, topography and geology.

The atmospheric circulation factor itself is an integral part of climate, which has a direct impact on the formation of climate in a certain place. The main factors are: the average state of air mass, the average state of air flow and so on.

The influence of geographical factors on climate formation is manifested in the shape of the earth, the movement of the earth, the distribution of land and sea, topography, airflow and ocean currents, etc., and the influence of geographical factors on climate formation can be mainly attributed to radiation factors in the final analysis.

Latitude factors, the shape and movement of the earth

Different geographical latitudes receive different heat, resulting in different climates; Generally, the higher the latitude, the lower the temperature; The equatorial region has the most precipitation, and the precipitation near the poles is the least. Near the tropic of cancer, there is more precipitation on the east coast of the mainland, and less precipitation on the west coast and inland.

Solar radiation is the heat source of the ground and the atmosphere, and the difference of ground heat budget is an important reason for the formation of climate. Solar radiation is mainly influenced by latitude, earth rotation, revolution, land and sea distribution and topography. For the whole earth, the balance of ground heat is almost zero, but for different regions, the heat received by the ground is different, which will have an impact on the formation of climate. At the same time, the ground continuously exchanges heat with the atmosphere after receiving heat, and each component in the heat balance process also has an important influence on climate formation.

atmospheric circulation

Including atmospheric circulation and weather system, the factors affecting climate are temperature, rainfall, air pressure and wind.

ocean current

The effects of ocean currents on climate are mainly humidity and heat.

Warm current plays a role in warming and humidifying the climate in coastal areas. For example, the formation of maritime climate in western Europe directly benefits from the warm and humid North Atlantic ocean current.

The cold current plays a role in cooling and dehumidifying the climate in coastal areas. For example, the cold current on the west coast of the mainland (southern hemisphere) played a certain role in the formation of desert environment on the west coast of Australia and the Pacific coast of Peru.

Land-sea distribution

Because the ocean and the mainland have different thermodynamic characteristics, such as volumetric heat capacity and thermal conductivity, they are significantly different, so the climate between them is very different. Comparatively speaking, the daily range of the mainland and annual range are larger than the ocean. Temperature annual range is an important indicator to distinguish continental climate from maritime climate. Moreover, the mainland is a heat source in summer and the ocean is a heat source in winter. Heat source is beneficial to the formation and strengthening of low-pressure system, and cold source is beneficial to the formation and strengthening of high-pressure system. The distribution of land and sea divides the planetary wind belt into several high and low pressure activity centers, which has a direct and important impact on the formation of the world monsoon climate. For example, the most typical monsoon climate in eastern and southern Asia is a good example.

topography

It plays an important role in the formation of local climate. For example, the sunny slope effect and shady slope effect, windward slope and leeward slope effect in mountain climate. Generally speaking, the terrain mainly blocks and lifts the airflow. There is more precipitation on windward slope and less precipitation on leeward slope in mountainous area. The influence of topography on climate formation is high altitude, less clouds, enhanced direct solar radiation, reduced scattered radiation, lower temperature and lower humidity. Different landforms have different effects on climate, and the plateau has obvious effects on climate.

Human activities

By changing the ground conditions, the climate in some areas will be affected. For example, artificial afforestation can improve the climate in some areas, and arbitrary logging will worsen the local climate. In addition, human activities will also form a heat island effect. Global warming is caused by human activities.