Editing Tropopause (section)

== Alternative definitions ==
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''.<ref>{{Cite book |last=Andrews |first=David G. |title=Middle atmosphere dynamics |last2=Holton |first2=James R. |last3=Leovy |first3=Conway B. |date=1999 |publisher=Acad. Pr |isbn=978-0-12-058576-2 |edition=3. print |series=International geophysics series |location=Orlando, Fla.}}</ref> 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.<ref>{{Cite journal|last1= Hoskins|first1= B. J.|last2= McIntyre|first2= M. E.|author2-link=Michael E. McIntyre|last3= Robertson|first3= A. W.|date= 1985|title= On the use and significance of isentropic potential vorticity maps|journal= [[Quarterly Journal of the Royal Meteorological Society]]|volume= 111|issue= 470|pages= 877–946|bibcode = 1985QJRMS.111..877H |doi = 10.1002/qj.49711147002 }}</ref> Instead of using the vertical temperature gradient as the defining variable, the dynamic tropopause surface is expressed in ''[[potential vorticity unit]]s'' (PVU, 1&nbsp;PVU&nbsp;=&nbsp;10{{sup|-6}}&nbsp;K&nbsp;m{{sup|2}}&nbsp;kg{{sup|-1}}&nbsp;s{{sup|-1}}<ref name=":3">{{Cite web |last=World Meteorological Organization (WMO) |last2=National Aeronautics and Space Administration (NASA) |last3=Administration |first3=Federal Aviation |last4=National Oceanic and Atmospheric Administration (NOAA) |last5=United Nations Environment Programme (UNEP) |last6=Commission |first6=European |last7=Bundesministerium für Forschung und Technologie |title=Atmospheric ozone 1985 – volume I |url=https://library.wmo.int/records/item/60466-atmospheric-ozone-1985-volume-i |archive-url=http://web.archive.org/web/20231128090246/https://library.wmo.int/records/item/60466-atmospheric-ozone-1985-volume-i |archive-date=2023-11-28 |access-date=2025-04-15 |website=library.wmo.int |language=en}}</ref>). 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.<ref>{{Cite journal |last=Hoinka |first=Klaus P. |date=1998 |title=Statistics of the Global Tropopause Pressure |url=http://journals.ametsoc.org/doi/10.1175/1520-0493(1998)1262.0.CO;2 |journal=Monthly Weather Review |language=en |volume=126 |issue=12 |pages=3303–3325 |doi=10.1175/1520-0493(1998)126<3303:SOTGTP>2.0.CO;2 |issn=0027-0644|doi-access=free }}</ref> 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.<ref name=":3" /> For the extratropical tropopause in the [[Northern Hemisphere]] the WMO established a value of 1.6 PVU,<ref name=":3" />{{rp|152}} but greater values ranging between 2 and 3.5 PVU have been traditionally used.<ref>{{Cite journal |last=Zängl |first=Günther |last2=Hoinka |first2=Klaus P. |date=2001 |title=The Tropopause in the Polar Regions |url=http://journals.ametsoc.org/doi/10.1175/1520-0442(2001)0142.0.CO;2 |journal=Journal of Climate |language=en |volume=14 |issue=14 |pages=3117–3139 |doi=10.1175/1520-0442(2001)014<3117:TTITPR>2.0.CO;2 |issn=0894-8755|doi-access=free }}</ref>

It is also possible to define the tropopause in terms of chemical composition.<ref>{{Cite journal |last=Pan |first=L. L. |last2=Randel |first2=W. J. |last3=Gary |first3=B. L. |last4=Mahoney |first4=M. J. |last5=Hintsa |first5=E. J. |date=2004 |title=Definitions and sharpness of the extratropical tropopause: A trace gas perspective |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2004JD004982 |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=109 |issue=D23 |doi=10.1029/2004JD004982 |issn=2156-2202|hdl=1912/3670 |hdl-access=free }}</ref> 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.

Additionally, a stability-based definition can be applied, in which the vertical gradient of potential temperature is used to identify where the chemical composition changes the most. This can be defined as potential temperature gradient tropopause, or PTGT.<ref name=":1">{{Cite journal |last=Tinney |first=Emily N. |last2=Homeyer |first2=Cameron R. |last3=Elizalde |first3=Lexy |last4=Hurst |first4=Dale F. |last5=Thompson |first5=Anne M. |last6=Stauffer |first6=Ryan M. |last7=Vömel |first7=Holger |last8=Selkirk |first8=Henry B. |date=2022 |title=A Modern Approach to a Stability-Based Definition of the Tropopause |url=https://journals.ametsoc.org/view/journals/mwre/150/12/MWR-D-22-0174.1.xml |journal=Monthly Weather Review |volume=150 |issue=12 |pages=3151–3174 |doi=10.1175/MWR-D-22-0174.1 |issn=0027-0644|hdl=11603/26155 |hdl-access=free }}</ref> In order to examine these stability metrics, the relationship between a low-stability troposphere and high-stability troposphere is used to analyze gradients in the transition layer. The composition change of O3 on this vertical gradient is also considered.<ref name=":1" /> This strategy aims to overcome potential failures of more traditional systems with static stability observations.