The tropopause is a deep convective barrier layer, which is characterized by a sharp decrease in the vertical decline rate of temperature. It hinders the vertical development of cumulonimbus cloud tops and the vertical exchange of aerosols and water vapor.
The tropopause is an obvious transition layer between the troposphere and the stratosphere. It was discovered at the same time with the stratosphere at the end of the 19th century and the beginning of the 20th century. The discovery of the tropopause aroused great research interest of scholars.The position, intensity and variation of the ozone top and tropopause are closely related.In recent years, the research level of stratopause has been increasing, but many problems need to be further studied.
Chinese name
Tropopause
Foreign name
tropopause
Category
Tropical and very low tropopause
Physical essence
Discontinuities
Main features
The vertical decline rate of temperature decreases sharply
From different perspectives, tropopause has different definitions, such as thermal tropopause (temperature decline rate), dynamic tropopause (potential vorticity), chemical composition tropopause, coldest point tropopause (tropical), etc[1]。
1957WMOThe tropopause is defined as follows[2]: The lowest altitude above 500 hPa isobaric surface where the temperature decline rate is as low as 2 ℃/km or below, and the average temperature decline rate at this altitude and in the gas layer 2 km above it does not exceed 2 ℃/km, which is commonly referred to as the "thermodynamic" definition of tropopause.Above the tropopause determined by this definition, if the average temperature decline rate between any altitude and all altitudes 1 km above it exceeds 3 ℃/km, the "second tropopause" shall be determined according to the above criteria.The tropopause is either within or above the 1 km layer[3]。Another thermodynamic definition of tropopause is often used, that is, CPT (Cold Point Tropopause), which is defined as the stratification height corresponding to the lowest temperature point on the vertical temperature profile[4]。In addition, the tropopause has a dynamic definition based on potential vorticity.
The tropospheric atmosphere is wet but lack of ozone, and the stratosphere is dry and rich in ozone. Therefore, Bathan et al. put forward the concept of ozone tropopause in 1996.However, no matter which definition, its physical essence is the same, and the tropopause is regarded asDiscontinuities。The thermodynamic tropopause is a discontinuity of temperature gradient, the dynamic tropopause is a discontinuity of zero order potential vorticity, and the ozone tropopause is a discontinuity of vertical gradient of ozone mixing ratio.The thermodynamic definition of tropopause is commonly used[5]。
classification
According to the vertical profile distribution of temperature, the tropopause height can be divided into tropical tropopause and polar tropopause. According to statistics, the polar tropopause is generally below 150 hPa, and the tropical tropopause is generally 150 hPa or above.The thickness of the tropopause is about several hundred meters to 1 - 2 km, and the maximum thickness can reach 4 - 5 km.Hess calculated the average value based on the observation data of 80 ° W during 1942-1945, and pointed out that there is a dual structure of the tropopause: high in the south and low in the north.The high and low tropopause will overlap locally over the latitude area where strong stable west (jet) appears in the upper troposphere.Hess calls the high tropopause the tropical tropopause (the second tropopause) and the low tropopause the polar tropopause (the first tropopause).The area between these two types of tropopause is called the tropopause fracture area.
Two types of tropopause are also used in the global atmospheric model: polar tropopause and tropical tropopause.The cold and high tropical tropopause appears between the equatorial and subtropical latitudes, and its height gradually decreases with the increase of latitude.The tropical tropopause and the polar tropopause can be found at different altitudes in the 30 ° - 45 ° latitude zone, and they overlap each other. The height difference between the two types of tropopause in this zone is 4-5 km[5]。
Tropopause fracture
The area between the first tropopause and the second tropopause is called the tropopause fracture area.The tropopause fracture is alwaysUpper air jetorHigh air frontUnder the weather background.It can be considered that the tropopause often breaks in the strong subtropical jet stream, because there is a large temperature difference between the interacting air masses.However, some studies have pointed out that tropopause fractures can be observed not only in the subtropical jet stream, but also in mid latitude regions and even over the Arctic[5]。
Relationship with ozone
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For a long time,Atmospheric ozoneThe relationship with tropopause height has received special attention.Goody's early research in 1949 found that,carbon dioxide、steam、ozoneIt has an important impact on the formation of the tropopause, so the conclusion that the stratospheric temperature will rise when the ground temperature decreases is put forward.Because ozone affects the sunultraviolet raysIt has a strong absorption capacity, and ozone is mainly concentrated in the lower stratosphere. The concentration of ozone will directly affect the ultraviolet intensity reaching the lower troposphere, thus affecting the temperature of the stratosphere and troposphere, and further affecting the structural changes of the transition layer between them - the tropopause.Therefore, there is a very close relationship between tropopause and ozone.Manabe et al. used ozone absorption to explain the thermal state of the lower stratosphere and the upper troposphere, and believed that the main factors for the cooling of the lower stratosphere wereLong wave radiationThe main factor of warming is that ozone affects the atmosphere and the earthinfrared radiationAbsorption of.The low temperature in the tropical stratosphere and the high temperature in the "warm layer" above 40 km can be explained by the distribution of radiation and the absorption characteristics of ozone to radiation.Steinbrecht et al. analyzed the sounding and ozone profile data of Hohenpeissenberg station in southern Germany, and found that when the total amount of ozone is low (high), the tropopause height in this area is high (low), and has increased by about 150 ± 70 m since the late 1960s.Chakrabarty et alNew Delhi32 years (1965 - 1996) andTrivandrum(Thrivan drum) 26 year (1965 - 1991) tropopause sounding data analyzed the variation trend of tropical tropopause height and tropopause temperature, and found that the tropopause height (temperature) over the two regions has an upward (downward) trend in recent decadesstratosphereOzone reduction related[5]。
Subtropical zoneThere are also two types of ozone tops in the region, and there are also fractures between the two types of ozone tops, which correspond to the tropical tropopause and the polar tropopause respectively.Reiter studied the ozone infiltration from stratosphere to troposphere and the role of tropopause in this process.Li Guohui et al. used a two-dimensional model to simulate and study the impact of tropopause changes on the distribution of ozone in the upper troposphere (lower stratosphere). The results showed that the seasonal changes of tropopause had a significant impact on the distribution of ozone in the upper troposphere (lower stratosphere), and the local change of ozone could exceed 10%.Angel pointed out that the quasi biennial cycle change of tropopause height is quite consistent with the change of ozone content: the minimum value of total ozone content is consistent with the maximum height in the two-year range of tropopause height, and vice versa.Randel et alSounding balloonAnd near equatorial ozone data from satellite observations, it is found that there is a large annual ozone cycle over the tropical tropopause[5]。
becauseQinghai Tibet PlateauThe special distribution of ozone over the Tibetan Plateau makes the impact of ozone on the tropopause more special.There is an abnormal low value of atmospheric ozone in the plateau, which is closely related to the plateau thermodynamic process, and the change of total atmospheric ozone is closely related to the tropopause height.Bian JianchunThrough the total ozone data provided by TOMS and ground-based observation, etc., it was found that a large area of extremely low ozone values appeared over the plateau from December 14 to 17, 2003.Zhou XiujiThe fact that the Qinghai Tibet Plateau has a low value center of total atmospheric ozone in summer has been found by et al.Li Peng studied the relationship between ozone and tropopause over the Tibetan Plateau, and concluded that the southern part of the Tibetan Plateau is a closed low value area of total ozone, while the northern part of the Tibetan Plateau is a low value disturbance.The Northern Hemisphere is divided into the Qinghai Tibet Plateau region, the same latitude region and other regions of the same latitude for research. It is found that there is a large difference between the tropopause over the Qinghai Tibet Plateau and other regions of the same latitude. It is also found that the Qinghai Tibet Plateau is the region with the lowest tropopause pressure in the world.Zou et al. pointed out that in the Tibetan Plateau, the height of the maximum atmospheric ozone loss is near the tropopause.Zhou et al. analyzed the possible role of ozone reduction over the plateau in the temperature change of the plateau stratosphere, and proposed that the reduction of the total amount of ozone over the plateau would reduce the absorption of solar ultraviolet radiation in the plateau stratosphere, while the radiation entering the lower troposphere would increase, which would lead to the cooling of the lower stratosphere over the plateau and the warming of the troposphere.Stratospheric cooling and tropospheric warming make tropopause structure change.In addition, the intensity of convective activity has a very important impact on the tropopause[5]。
Among the many factors that affect the change of tropopause height, although it is still impossible to quantitatively determine the contribution of each factor to the change of tropopause height, Santer et al., using radiosonde data and NCEP/NCAR reanalysis data, proved that the global tropopause height has increased by several hundred meters in the past 20 years (1979 - 1999), and used complex atmospheric models to assesssulfateaerosol, solar radiation changes, volcanic aerosolsgreenhouse gasesIt is found that the warming of the troposphere caused by greenhouse gases and the cooling of the stratosphere caused by ozone are the main reasons for the rise of the troposphere[5]。
Research prospect
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In recent years, many foreign scholars have turned their attention to the tropopausedynamicsResearch, they combined tropopause with potential vorticity andwaveConnect.This indicates that the research level of tropopause is improving day by day.
There are still many problems in the study of tropopause, such as the fine structure near tropopause, near tropopause and lower stratosphereGravity waveCharacteristics, statistical characteristics of convection near the tropopause, etc. With the increasingly in-depth study of the tropopause and the use of models to simulate the impact of changes in the tropopause on climate, these issues need to be further studied.
In addition, although the relationship between tropopause height or temperature and volcanoes has been studied, the specific relationship still needs to be further studied[5]。
