The middle layer, also known as the middle layer, refers to theStratopauseTo 85 kmatmosphere。Internal causes of this layerozoneLow content, at the same time, can benitrogen、oxygenEqual to the sun directly absorbedShortwave radiationMost of them have been absorbed by the upper atmosphere, so the vertical decline rate of temperature is very large,convectionStrong sports.[1]
The middle layer is also called the middle layer.sincestratosphereFrom the top to 85 kmatmosphere。
Internal causes of this layerozoneThe content is low, and can be affected by nitrogenoxygenEqual to the sun directly absorbedShortwave radiationMost of them have been absorbed by the upper atmosphere, so the vertical decline rate of temperature is large, and the convection movement is strong.Middle layer topThe temperature nearby is about 190 degrees Kelvin;Air molecules absorb the sunUltraviolet radiationIt can be ionized later, which is customarily calledthe ionosphereD layer;Sometimes in high latitude, summer and duskNoctilucent cloudsappear.
background knowledge
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The earth's atmosphere can be divided into several layers according to its basic characteristics, but there are different layering methods according to different characteristics.From the surface of the earth upward, the air becomes thinner with the increase of height.The upper boundary of the atmosphere can extend to an altitude of 2000~3000 km.In the vertical direction, there are obvious differences in the physical properties of the atmosphere.
According to the vertical distribution of air temperatureAtmospheric disturbanceThe atmosphere is generally divided into five tropospherestratosphere、Middle layer、ThermosphereAnd outer layer (also calledExosphereOr escape layer).The atmospheric area close to the ground and with the most significant convective movement is the troposphere, and the upper boundary of the troposphere is calledTropopause, about 17 to 18 kilometers high in the equatorial region, and about 8 kilometers high in the polar region;The atmosphere from the tropopause to about 50 kilometers is called the stratosphere, and the atmosphere in the stratosphere is mostlyHorizontal movementThe convection is very weak, and the ozone layer is located in this area;The middle layer, also known as the middle layer, is fromStratopauseTo an atmospheric area of about 80 km;The thermosphere isMiddle layer topTo 300-500kmatmosphere；Thermosphere roofThe upper atmosphere is called outer atmosphere.
fromStratopauseIt is an intermediate layer at an altitude of 85 km.Its main features:
(1) The temperature decreases rapidly with the increase of height, and the temperature at the top of the mesosphere drops to - 83 ℃~- 113 ℃.Because the ozone content in this layer is very small, it cannot absorb a lot of solar ultraviolet rays, and the short wave radiation absorbed by nitrogen and oxygen energy is mostly absorbed by the upper atmosphere, so the temperature decreases with the increase of height.
(2) There is a strong convective movement, also known as the upper troposphere or the upper troposphere.This is because the upper part of the atmosphere is cold and the lower part is warm, resulting in convection of air.However, due to the thin air in this layer, the convection movement of air cannot be compared with that in the troposphere.
Vertical temperature distribution
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Compared with thestratosphereThe temperature will increase with height, and the temperature in the mesosphere and troposphere will decrease proportionally with height.At the bottom of the middle layer, high concentrationozoneIt will attract ultraviolet rays and make the average temperature hover around - 2.5 ℃, even up to 0 ℃.However, as the altitude increases, the ozone concentration will decrease, so the average temperature at the top of the mesosphere will drop to - 92.5 ℃.Therefore, usually near the top of the middle layerAtmospheric vertical structureThe part with the lowest temperature inside.Since the average temperature decline rate of the mesosphere is smaller than that of the troposphere, although a few convective activities occur, they are relatively stable and rarely occurHigh barometric pressure、Low atmospheric pressurePhenomenon.Also because of theAtmospheric densityVery low, so the thermal structure of this layer is mainly composed ofoxygenMolecules absorb the sun's ultraviolet rays and then heat the atmosphere, andcarbon dioxideEmit infrared and cool the balance between the two to determine.
Convective movement
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The temperature of the mesosphere will be lower in summer than in winter.This is because in winter, the atmosphereGravity waveCrushing transports westward momentum in this layer, just like exerting westward drag force.In order to balance this drag force, the atmosphere must move toward the pole to get the eastwardCoriolis force。This meridional movement from the summer polar region to the winter polar region caused the atmospheric rise in the summer polar region,Adiabatic expansionCooling;In winter, the atmosphere of the polar region sinks,Adiabatic compressionHeat.This onecirculationThe influence on temperature is more thansolar radiationAs a result, the temperature at the top of the mesosphere is the coldest in the direct sunlight summer polar region, and the hottest in the sunless winter polar region.Therefore, the temperature of the mesopause in summer can be as low as - 100 ℃.At such low temperature, likeNoctilucent cloudsIt is also possible to observe such special thin clouds.The atoms and molecules contained in the atmosphere above the top of the mesosphere are affected by the ultraviolet rays of the sunionization, addedfree electron。The layer where the atmosphere is ionized is calledthe ionosphere, and the bottom layerLevel DIt is located near the top of the middle layer, that is, 50 to 90 kilometers above the groundelectron densityIn a state of many.
pressure
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The middle layer will not be highLow atmospheric pressure。But because the middle tierAtmospheric densityIt is very small, so it looks likePlanetary waveSuch long-period fluctuations will be transmitted from the bottom with a large amplitude.According to such wave phenomenon, mechanical instability will be formed in places with extremely large amplitude.Moreover, this fluctuation phenomenon also affects theAtmospheric cycleMake a great impact.
Radio wave propagation
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In the middle layer, the temperature decreases with the rise of height.The middle layer overlaps the lower part of the ionosphere.In the space 50~800 kilometers from the ground, thin air molecules form ions under strong sunlight.The ionosphere is like a mirror, reflecting back the radio waves sent by the radio station to the ground, so that we can receive the broadcast.
Middle layer phenomenon
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There are many interesting phenomena in the atmosphere. The different charms of each layer, such as the noctilucent clouds in the middle layer, the abnormal weather in summer and winter... In addition to the troposphere and stratosphere, the middle layer, warm layer and outer layer far away from us are also inseparable from our life.
Detecting instrument
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Rayleigh scattering lidar can detect the vertical distribution of atmospheric temperature within the range of 22-60 km.
Rayleigh scattering lidar is suitable for detecting the temperature distribution in the lower mesosphere.The main principles are as follows: the atmospheric echo of the lower atmosphere in the middle layer is mainly molecular Rayleigh scattering signal, ignoring the scattering signal of aerosol particles;Assuming that the atmospheric density at a certain altitude is known, the atmospheric density profile can be obtained;combinationIdeal gas equation of stateAnd the atmospheric static equation to obtain the atmospheric temperature.[2]
