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Tropopause

January 10, 2024

The tropopause is the atmospheric boundary that demarcates the troposphere from the stratosphere, which are the lowest two of the five layers of the atmosphere of Earth. The tropopause is a thermodynamic gradient-stratification layer that marks the end of the troposphere, and is approximately 17 kilometres (11 mi) above the equatorial regions, and approximately 9 kilometres (5.6 mi) above the polar regions.

The tropopause extends to high altitudes in the tropical latitudes and extends to low altitudes in the polar latitudes.

Definition edit

 
The atmosphere of planet Earth: The tropopause is between the troposphere and the stratosphere.

Rising from the planetary surface of the Earth, the tropopause is the atmospheric level where the air ceases to become cool with increased altitude and becomes dry, devoid of water vapor. The tropopause is the boundary that demarcates the troposphere below from the stratosphere above, and is part of the atmosphere where there occurs an abrupt change in the environmental lapse rate (ELR) of temperature, from a positive rate (of decrease) in the troposphere to a negative rate in the stratosphere. The tropopause is defined as the lowest level at which the lapse rate decreases to 2°C/km or less, provided that the average lapse-rate, between that level and all other higher levels within 2.0 km does not exceed 2°C/km.[1] The tropopause is a first-order discontinuity surface, in which temperature as a function of height varies continuously through the atmosphere, while the temperature gradient has a discontinuity.[2]

Location edit

The troposphere is the lowest layer of the Earth's atmosphere; it starts at the planetary boundary layer, and is the layer in which most weather phenomena occur. The troposphere contains the boundary layer, and ranges in height from an average of 9 km (5.6 mi; 30,000 ft) at the poles, to 17 km (11 mi; 56,000 ft) at the Equator.[3][4] In the absence of inversions and not considering moisture, the temperature lapse rate for this layer is 6.5 °C per kilometer, on average, according to the U.S. Standard Atmosphere.[5] A measurement of the tropospheric and the stratospheric lapse rates helps identify the location of the tropopause, since temperature increases with height in the stratosphere, and hence the lapse rate becomes negative. The tropopause location coincides with the lowest point at which the lapse rate is less than a prescribed threshold.

Since the tropopause responds to the average temperature of the entire layer that lies underneath it, it is at its maximum levels over the Equator, and reaches minimum heights over the poles. On account of this, the coolest layer in the atmosphere lies at about 17 km over the equator. Due to the variation in starting height, the tropopause extremes are referred to as the equatorial tropopause and the polar tropopause.

Given that the lapse rate is not a conservative quantity when the tropopause is considered for stratosphere-troposphere exchanges studies, there exists an alternative definition named dynamic tropopause.[6] It is formed with the aid of potential vorticity, which is defined as the product of the isentropic density, i.e. the density that is measurable by using potential temperature as the vertical coordinate, and the absolute vorticity, given that this quantity attains quite different values for the troposphere and the stratosphere.[7] Instead of using the vertical temperature gradient as the defining variable, the dynamic tropopause surface is expressed in potential vorticity units (PVU, 1 PVU = 10-6 K m2 kg-1 s-1[8]). Given that the absolute vorticity is positive in the Northern Hemisphere and negative in the Southern Hemisphere, the threshold value should be considered as positive north of the Equator and negative south of it.[9] Theoretically, to define a global tropopause in this way, the two surfaces arising from the positive and negative thresholds need to be matched near the equator using another type of surface such as a constant potential temperature surface. Nevertheless, the dynamic tropopause is useless at equatorial latitudes because the isentropes are almost vertical.[8] For the extratropical tropopause in the Northern Hemisphere the WMO established a value of 1.6 PVU,[8]: 152  but greater values ranging between 2 and 3.5 PVU have been traditionally used.[10]

It is also possible to define the tropopause in terms of chemical composition.[11] For example, the lower stratosphere has much higher ozone concentrations than the upper troposphere, but much lower water vapor concentrations, so an appropriate boundary can be defined.

Tropical Tropopause Layer Cold Trap edit

In 1949 Alan West Brewer proposed that tropospheric air passes through the tropopause into the stratosphere near the equator, then travels through the stratosphere to temperate and polar regions, where it sinks into the troposphere. [12] This is now known as Brewer-Dobson circulation. Because gases primarily enter the stratosphere by passing through the tropopause in the tropics where the tropopause is coldest, water vapor is condensed out of the air that is entering the stratosphere. This ″tropical tropopause layer cold trap″ theory has become widely accepted. [13] This cold trap limits stratospheric water vapor to 3 to 4 parts per million. [14] Researchers at Harvard have suggested that the effects of Global Warming on air circulation patterns will weaken the tropical tropopause layer cold trap. [15]

Water vapor that is able to make it through the cold trap eventually rises to the top of the stratosphere, where it undergoes photodissociation into oxygen and hydrogen or hydroxide ions and hydrogen.[16][17] This hydrogen is then able to escape the atmosphere. Thus, in some sense, the tropical tropopause layer cold trap is what prevents Earth from losing its water to space. James Kasting has predicted that in 1 to 2 billion years, as the Sun increases in luminosity, the temperature of the Earth will rise enough that the cold trap will no longer be effective, and so the Earth will dry out.[18]

Phenomena edit

The tropopause is not a fixed boundary. Vigorous thunderstorms, for example, particularly those of tropical origin, will overshoot into the lower stratosphere and undergo a brief (hour-order or less) low-frequency vertical oscillation.[19] Such oscillation results in a low-frequency atmospheric gravity wave capable of affecting both atmospheric and oceanic currents in the region.[citation needed]

Most commercial aircraft are flown in the lower stratosphere, just above the tropopause, during the cruise phase of their flights; in this region, the clouds and significant weather perturbations characteristic of the troposphere are usually absent.[20]

See also edit

References edit

  1. ^ International Meteorological Vocabulary (2nd ed.). Geneva: Secretariat of the World Meteorological Organization. 1992. p. 636. ISBN 978-92-63-02182-3.
  2. ^ Panchev 1985, p. 129.
  3. ^ Hoinka, K. P. (1999). "Temperature, Humidity, and Wind at the Global Tropopause". Monthly Weather Review. 127 (10): 2248–2265. Bibcode:1999MWRv..127.2248H. doi:10.1175/1520-0493(1999)127<2248:THAWAT>2.0.CO;2.
  4. ^ Gettelman, A.; Salby, M. L.; Sassi, F. (2002). "Distribution and influence of convection in the tropical tropopause region". Journal of Geophysical Research. 107 (D10): ACL 6–1–ACL 6–12. Bibcode:2002JGRD..107.4080G. CiteSeerX 10.1.1.469.189. doi:10.1029/2001JD001048.
  5. ^ Petty 2008, p. 112.
  6. ^ Andrews, Holton & Leovy 1987, p. 371.
  7. ^ Hoskins, B. J.; McIntyre, M. E.; Robertson, A. W. (1985). "On the use and significance of isentropic potential vorticity maps". Quarterly Journal of the Royal Meteorological Society. 111 (470): 877–946. Bibcode:1985QJRMS.111..877H. doi:10.1002/qj.49711147002.
  8. ^ a b c Tuck, A. F.; Browell, E. V.; Danielsen, E. F.; Holton, J. R.; Hoskins, B. J.; Johnson, D. R.; Kley, D.; Krueger, A. J.; Megie, G.; Newell, R. E.; Vaughan, G. (1985). "Strat-trop exchange". Atmospheric Ozone 1985 – WMO Global Ozone Research and Monitoring Project Report No. 16. World Meteorological Organization. 1: 151–240.
  9. ^ Hoinka, Klaus P. (December 1998). "Statistics of the Global Tropopause Pressure". Journal of Climate. American Meteorological Society. 126 (126): 3303–3325. Bibcode:1998MWRv..126.3303H. doi:10.1175/1520-0493(1998)126<3303:SOTGTP>2.0.CO;2.
  10. ^ Zängl, Günther; Hoinka, Klaus P. (15 July 2001). "The Tropopause in the Polar Regions". Journal of Climate. 14 (14): 3117 –&#32, 3139. Bibcode:2001JCli...14.3117Z. doi:10.1175/1520-0442(2001)014<3117:ttitpr>2.0.co;2.
  11. ^ L. L. Pan; W. J. Randel; B. L. Gary; M. J. Mahoney; E. J. Hintsa (2004). "Definitions and sharpness of the extratropical tropopause: A trace gas perspective" (PDF). Journal of Geophysical Research. 109 (D23): D23103. Bibcode:2004JGRD..10923103P. doi:10.1029/2004JD004982. hdl:1912/3670.
  12. ^ Brewer, A. W. (Oct 1949). "Evidence for a world circulation provided by the measurements of helium and water vapor distribution in the stratosphere". Quarterly Journal of the Royal Meteorological Society. 75 (326): 351–363. Bibcode:1949QJRMS..75..351B. doi:10.1002/qj.49707532603.
  13. ^ Hasebe, F.; Inai, Y.; Shiotani, M.; Fujiwara, M.; Vömel, H.; Nishi, N.; Ogino, S.-Y.; Shibata, T.; Iwasaki, S.; Komala, N.; Peter, T.; Oltmans, S. J. (Apr 2013). "Cold trap dehydration in the Tropical Tropopause Layer characterised by SOWER chilled-mirror hygrometer network data in the Tropical Pacific". Atmospheric Chemistry and Physics. 13 (8): 4393–4411. Bibcode:2013ACP....13.4393H. doi:10.5194/acp-13-4393-2013. hdl:20.500.11850/67923.
  14. ^ Catling, David C.; Kasting, James F. (2017). Atmospheric Evolution on Inhabited and Lifeless Worlds. Bibcode:2017aeil.book.....C.
  15. ^ Bourguet, Stephen; Linz, Marianna (2023). "Weakening of the tropical tropopause layer cold trap with global warming". Atmospheric Chemistry and Physics. 23 (13): 7447–7460. Bibcode:2023ACP....23.7447B. doi:10.5194/acp-23-7447-2023. S2CID 259520137.
  16. ^ Lewis, B. R.; Vardavas, I. M.; Carver, J. H. (June 1983). "The aeronomic dissociation of water vapor by solar H Lyman α radiation". Journal of Geophysical Research. 88 (A6): 4935–4940. Bibcode:1983JGR....88.4935L. doi:10.1029/JA088iA06p04935.
  17. ^ Nicolet, Marcel (July 1984). "On the photodissociation of water vapour in the mesosphere". Planetary and Space Science. 32 (7): 871–880. Bibcode:1984P&SS...32..871N. doi:10.1016/0032-0633(84)90011-4.
  18. ^ Caldeira, K; Kasting, J F (December 1992). "The life span of the biosphere revisited". Nature. 360 (6406): 721–23. Bibcode:1992Natur.360..721C. doi:10.1038/360721a0. PMID 11536510. S2CID 4360963.
  19. ^ Shenk, W. E. (1974). "Cloud top height variability of strong convective cells". Journal of Applied Meteorology. 13 (8): 918–922. Bibcode:1974JApMe..13..917S. doi:10.1175/1520-0450(1974)013<0917:cthvos>2.0.co;2.
  20. ^ Petty 2008, p. 21.

Bibliography edit

External links edit

  • The height of the tropopause

January 10, 2024
tropopause, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor, march, 2012, le. This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Tropopause news newspapers books scholar JSTOR March 2012 Learn how and when to remove this template message The tropopause is the atmospheric boundary that demarcates the troposphere from the stratosphere which are the lowest two of the five layers of the atmosphere of Earth The tropopause is a thermodynamic gradient stratification layer that marks the end of the troposphere and is approximately 17 kilometres 11 mi above the equatorial regions and approximately 9 kilometres 5 6 mi above the polar regions The tropopause extends to high altitudes in the tropical latitudes and extends to low altitudes in the polar latitudes Contents 1 Definition 2 Location 3 Tropical Tropopause Layer Cold Trap 4 Phenomena 5 See also 6 References 7 Bibliography 8 External linksDefinition edit nbsp The atmosphere of planet Earth The tropopause is between the troposphere and the stratosphere Rising from the planetary surface of the Earth the tropopause is the atmospheric level where the air ceases to become cool with increased altitude and becomes dry devoid of water vapor The tropopause is the boundary that demarcates the troposphere below from the stratosphere above and is part of the atmosphere where there occurs an abrupt change in the environmental lapse rate ELR of temperature from a positive rate of decrease in the troposphere to a negative rate in the stratosphere The tropopause is defined as the lowest level at which the lapse rate decreases to 2 C km or less provided that the average lapse rate between that level and all other higher levels within 2 0 km does not exceed 2 C km 1 The tropopause is a first order discontinuity surface in which temperature as a function of height varies continuously through the atmosphere while the temperature gradient has a discontinuity 2 Location editThis section may be too technical for most readers to understand Please help improve it to make it understandable to non experts without removing the technical details September 2018 Learn how and when to remove this template message The troposphere is the lowest layer of the Earth s atmosphere it starts at the planetary boundary layer and is the layer in which most weather phenomena occur The troposphere contains the boundary layer and ranges in height from an average of 9 km 5 6 mi 30 000 ft at the poles to 17 km 11 mi 56 000 ft at the Equator 3 4 In the absence of inversions and not considering moisture the temperature lapse rate for this layer is 6 5 C per kilometer on average according to the U S Standard Atmosphere 5 A measurement of the tropospheric and the stratospheric lapse rates helps identify the location of the tropopause since temperature increases with height in the stratosphere and hence the lapse rate becomes negative The tropopause location coincides with the lowest point at which the lapse rate is less than a prescribed threshold Since the tropopause responds to the average temperature of the entire layer that lies underneath it it is at its maximum levels over the Equator and reaches minimum heights over the poles On account of this the coolest layer in the atmosphere lies at about 17 km over the equator Due to the variation in starting height the tropopause extremes are referred to as the equatorial tropopause and the polar tropopause Given that the lapse rate is not a conservative quantity when the tropopause is considered for stratosphere troposphere exchanges studies there exists an alternative definition named dynamic tropopause 6 It is formed with the aid of potential vorticity which is defined as the product of the isentropic density i e the density that is measurable by using potential temperature as the vertical coordinate and the absolute vorticity given that this quantity attains quite different values for the troposphere and the stratosphere 7 Instead of using the vertical temperature gradient as the defining variable the dynamic tropopause surface is expressed in potential vorticity units PVU 1 PVU 10 6 K m2 kg 1 s 1 8 Given that the absolute vorticity is positive in the Northern Hemisphere and negative in the Southern Hemisphere the threshold value should be considered as positive north of the Equator and negative south of it 9 Theoretically to define a global tropopause in this way the two surfaces arising from the positive and negative thresholds need to be matched near the equator using another type of surface such as a constant potential temperature surface Nevertheless the dynamic tropopause is useless at equatorial latitudes because the isentropes are almost vertical 8 For the extratropical tropopause in the Northern Hemisphere the WMO established a value of 1 6 PVU 8 152 but greater values ranging between 2 and 3 5 PVU have been traditionally used 10 It is also possible to define the tropopause in terms of chemical composition 11 For example the lower stratosphere has much higher ozone concentrations than the upper troposphere but much lower water vapor concentrations so an appropriate boundary can be defined Tropical Tropopause Layer Cold Trap editIn 1949 Alan West Brewer proposed that tropospheric air passes through the tropopause into the stratosphere near the equator then travels through the stratosphere to temperate and polar regions where it sinks into the troposphere 12 This is now known as Brewer Dobson circulation Because gases primarily enter the stratosphere by passing through the tropopause in the tropics where the tropopause is coldest water vapor is condensed out of the air that is entering the stratosphere This tropical tropopause layer cold trap theory has become widely accepted 13 This cold trap limits stratospheric water vapor to 3 to 4 parts per million 14 Researchers at Harvard have suggested that the effects of Global Warming on air circulation patterns will weaken the tropical tropopause layer cold trap 15 Water vapor that is able to make it through the cold trap eventually rises to the top of the stratosphere where it undergoes photodissociation into oxygen and hydrogen or hydroxide ions and hydrogen 16 17 This hydrogen is then able to escape the atmosphere Thus in some sense the tropical tropopause layer cold trap is what prevents Earth from losing its water to space James Kasting has predicted that in 1 to 2 billion years as the Sun increases in luminosity the temperature of the Earth will rise enough that the cold trap will no longer be effective and so the Earth will dry out 18 Phenomena editThe tropopause is not a fixed boundary Vigorous thunderstorms for example particularly those of tropical origin will overshoot into the lower stratosphere and undergo a brief hour order or less low frequency vertical oscillation 19 Such oscillation results in a low frequency atmospheric gravity wave capable of affecting both atmospheric and oceanic currents in the region citation needed Most commercial aircraft are flown in the lower stratosphere just above the tropopause during the cruise phase of their flights in this region the clouds and significant weather perturbations characteristic of the troposphere are usually absent 20 See also editJet stream Maximum parcel levelReferences edit International Meteorological Vocabulary 2nd ed Geneva Secretariat of the World Meteorological Organization 1992 p 636 ISBN 978 92 63 02182 3 Panchev 1985 p 129 Hoinka K P 1999 Temperature Humidity and Wind at the Global Tropopause Monthly Weather Review 127 10 2248 2265 Bibcode 1999MWRv 127 2248H doi 10 1175 1520 0493 1999 127 lt 2248 THAWAT gt 2 0 CO 2 Gettelman A Salby M L Sassi F 2002 Distribution and influence of convection in the tropical tropopause region Journal of Geophysical Research 107 D10 ACL 6 1 ACL 6 12 Bibcode 2002JGRD 107 4080G CiteSeerX 10 1 1 469 189 doi 10 1029 2001JD001048 Petty 2008 p 112 Andrews Holton amp Leovy 1987 p 371 Hoskins B J McIntyre M E Robertson A W 1985 On the use and significance of isentropic potential vorticity maps Quarterly Journal of the Royal Meteorological Society 111 470 877 946 Bibcode 1985QJRMS 111 877H doi 10 1002 qj 49711147002 a b c Tuck A F Browell E V Danielsen E F Holton J R Hoskins B J Johnson D R Kley D Krueger A J Megie G Newell R E Vaughan G 1985 Strat trop exchange Atmospheric Ozone 1985 WMO Global Ozone Research and Monitoring Project Report No 16 World Meteorological Organization 1 151 240 Hoinka Klaus P December 1998 Statistics of the Global Tropopause Pressure Journal of Climate American Meteorological Society 126 126 3303 3325 Bibcode 1998MWRv 126 3303H doi 10 1175 1520 0493 1998 126 lt 3303 SOTGTP gt 2 0 CO 2 Zangl Gunther Hoinka Klaus P 15 July 2001 The Tropopause in the Polar Regions Journal of Climate 14 14 3117 amp 32 3139 Bibcode 2001JCli 14 3117Z doi 10 1175 1520 0442 2001 014 lt 3117 ttitpr gt 2 0 co 2 L L Pan W J Randel B L Gary M J Mahoney E J Hintsa 2004 Definitions and sharpness of the extratropical tropopause A trace gas perspective PDF Journal of Geophysical Research 109 D23 D23103 Bibcode 2004JGRD 10923103P doi 10 1029 2004JD004982 hdl 1912 3670 Brewer A W Oct 1949 Evidence for a world circulation provided by the measurements of helium and water vapor distribution in the stratosphere Quarterly Journal of the Royal Meteorological Society 75 326 351 363 Bibcode 1949QJRMS 75 351B doi 10 1002 qj 49707532603 Hasebe F Inai Y Shiotani M Fujiwara M Vomel H Nishi N Ogino S Y Shibata T Iwasaki S Komala N Peter T Oltmans S J Apr 2013 Cold trap dehydration in the Tropical Tropopause Layer characterised by SOWER chilled mirror hygrometer network data in the Tropical Pacific Atmospheric Chemistry and Physics 13 8 4393 4411 Bibcode 2013ACP 13 4393H doi 10 5194 acp 13 4393 2013 hdl 20 500 11850 67923 Catling David C Kasting James F 2017 Atmospheric Evolution on Inhabited and Lifeless Worlds Bibcode 2017aeil book C Bourguet Stephen Linz Marianna 2023 Weakening of the tropical tropopause layer cold trap with global warming Atmospheric Chemistry and Physics 23 13 7447 7460 Bibcode 2023ACP 23 7447B doi 10 5194 acp 23 7447 2023 S2CID 259520137 Lewis B R Vardavas I M Carver J H June 1983 The aeronomic dissociation of water vapor by solar H Lyman a radiation Journal of Geophysical Research 88 A6 4935 4940 Bibcode 1983JGR 88 4935L doi 10 1029 JA088iA06p04935 Nicolet Marcel July 1984 On the photodissociation of water vapour in the mesosphere Planetary and Space Science 32 7 871 880 Bibcode 1984P amp SS 32 871N doi 10 1016 0032 0633 84 90011 4 Caldeira K Kasting J F December 1992 The life span of the biosphere revisited Nature 360 6406 721 23 Bibcode 1992Natur 360 721C doi 10 1038 360721a0 PMID 11536510 S2CID 4360963 Shenk W E 1974 Cloud top height variability of strong convective cells Journal of Applied Meteorology 13 8 918 922 Bibcode 1974JApMe 13 917S doi 10 1175 1520 0450 1974 013 lt 0917 cthvos gt 2 0 co 2 Petty 2008 p 21 Bibliography editAndrews D G Holton J R Leovy C B 1987 R Dmowska Holton J R eds Middle Atmosphere Dynamics Academic Press p 371 ISBN 978 0 12 058576 2 Panchev Stoǐcho 1985 1981 Dynamic meteorology D Reidel Publishing Company ISBN 978 90 277 1744 3 Petty Grant W 2008 A First Course in Atmospheric Thermodynamics Madison WI Sundog Publishing ISBN 978 0 9729033 2 5 External links editThe height of the tropopause Portals nbsp Earth sciences nbsp Weather nbsp Astronomy nbsp Science Retrieved from https en wikipedia org w index php title Tropopause amp oldid 1186783523, wikipedia, wiki, book, books, library,

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