<p>In addition to the answer by @Kaberett lapse rate explains the height variation of the tropopause quite well.   Lapse rate is a property of gravity and the ideal gas law and it has to be adjusted for circulation and condensation and the top-down heating from the sun, which is a small effect given a mostly transparent atmosphere.   Lapse rate isn't perfect, but it's still good for an approximation.</p>

<p><a href="https://en.wikipedia.org/wiki/Lapse_rate#Convection_and_adiabatic_expansion" rel="nofollow noreferrer">Wikipedia summary</a></p>

<p>Shorter, <a href="https://www.britannica.com/science/adiabatic-lapse-rate" rel="nofollow noreferrer">Britannica summary</a></p>

<p>From the Britannica summary:   </p>

<blockquote>
  <p>The lapse rate of nonrising air—commonly referred to as the normal, or
  environmental, lapse rate—is highly variable, being affected by
  radiation, convection, and condensation; it averages about 6.5 °C per
  kilometre (18.8 °F per mile) in the lower atmosphere (troposphere).</p>
</blockquote>

<p>If we take that averaged 6.5°C per km, that explains pretty close to the surface temperature variation on the Earth at sea level.  (Antarctica, being mostly more than a mile in elevation, you need to adjust the temperature -6.5°C per km in altitude for surface temperature).   The troposphere being an average of 8 km higher at the equator, corresponds to 52°c variation using that -6.5 degree estimate, or about 32 degrees (equator) to minus 20 (pole), which is very much in the ballpark.</p>

<p>Also, as noted in the Wikipedia article</p>

<blockquote>
  <p>the dry adiabatic lapse rate is a constant 9.8 °C/km (5.38 °F per
  1,000 ft, 3 °C/1,000 ft), the moist adiabatic lapse rate varies
  strongly with temperature. A typical value is around 5 °C/km</p>
</blockquote>

<p>Moist air has a lower lapse rate, which explains why the troposphere is highest over warm equatorial Pacific and why it peaks over monsoons. - see <a href="http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html" rel="nofollow noreferrer">this article</a>. </p>

<p>It's the surface temperature and water vapor.  That's the gist of it.  The rotation of the Earth can't account for a troposphere that's twice as high over the equator.  The rotation of the Earth (and if we want to get silly, also the Moon's atmospheric tidal bulges) both affect the troposphere some, but they are minor players.</p>

<p>Earth's atmosphere shouldn't bulge much more than it's body, about <a href="https://en.wikipedia.org/wiki/Equatorial_bulge#Other_celestial_bodies" rel="nofollow noreferrer">1 part in 298</a>, even if you multiply that by 4, and I think that's too aggressive a mathematical approach, but even so, that would be less than 1 part in 70 of atmospheric expansion over the equator due to the spin of the Earth.  That's very far from the doubling that temperature explains.  </p>

CC BY-SA 4.0
2017-10-25T05:53:21.560Z
2019-04-18T11:22:04.177Z
2019-04-18T11:22:04.177Z
userLTK
<p>To start with a definition, the tropopause is the boundary between troposphere and stratosphere; within the troposphere temperature decreases with increase in altitude (the temperature profile is dominated by radiative heat from the Earth's surface), whereas in the stratosphere temperature increases with altitude (the temperature profile is dominated by solar radiation).</p>

<p>Increases in troposphere temperature are associated with increase in tropopause height. Factors in play include the amount of water vapour being evaporated from equatorial seas; <a href="http://onlinelibrary.wiley.com/doi/10.1029/JD090iD03p05629/full">interannual variations in tropopause height can result from both local and large-scale driving forces</a>. The tropopause responds to the average temperature of the entire underlying layer: this is higher at the equator and lower at the poles.</p>

CC BY-SA 3.0
2017-10-24T13:09:26.197Z
Wow, this is wrong and it got accepted. Thermal expansion around a few Kelvin cannot account for a increase of the Tropopause by a factor of two. Do the math, it's the centrifugal force.
AtmosphericPrisonEscape
CC BY-SA 3.0
2017-10-24T15:56:13.030Z
@AtmosphericPrisonEscape it is thermal expansion. Use the hydrostatic equation over a layer with an average temperature, and you will find that it does explain MOST of the variability. There are some other influences, but the hydrostatic equation is sufficient on a large scale.
BarocliniCplusplus
CC BY-SA 3.0
2017-10-24T16:24:20.863Z
@Baro: Exactly. It gives you $H \sim T$ and T doesn't vary by a factor of 2. So it's NOT the temperature.
AtmosphericPrisonEscape
CC BY-SA 3.0
2017-10-25T05:14:31.523Z
This answer is correct, not wrong.   This really should get cleared up cause we don't want two conflicting answers to a question (unless the question is genuinely unresolved).   See this article here:   http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html   It says the highest Tropopause is over warm oceans and monsoons (water-vapor clearly plays a role).   It also indicates that Temperature is a key factor.  The tropopause rises and falls based on the seasons over the same location.
userLTK
CC BY-SA 3.0
2014-05-01T13:49:09.800Z
2014-05-01T13:49:09.800Z
kaberett
<p>Fundamentals of atmospheric modeling show that the height of the tropopause depends on the location, notably the latitude, and that the troposphere is roughly 8km higher at the equator than the poles depending on the time of year.</p>

<p>First guess was that the temperature of the would impact its density (for example, here's the data for <a href="https://www.wolframalpha.com/input/?i=air%20density%20at%20-50%C2%B0%20c" rel="noreferrer">-50°</a> and <a href="https://www.wolframalpha.com/input/?i=air%20density%20at%2050%C2%B0%20c" rel="noreferrer">50° c</a>) - though this does not appear to show the cause of why is the troposphere 8km higher at the equator than the poles.</p>

<p><strong>Why is the troposphere 8km higher at the equator than the poles?</strong></p>

<p><img src="https://i.sstatic.net/XTu3M.gif" alt="enter image description here"></p>

CC BY-SA 3.0
2014-05-01T06:22:59.863Z
A significant part (but not all) of the answer to this question will be the same as the answers at [Why is earth not a sphere?](http://earthscience.stackexchange.com/questions/108)
naught101
CC BY-SA 3.0
2014-05-01T13:23:06.103Z
It depends not only on location, but also on season and even on the weather.  Might write down an answer if I find the time, unless somebody else does first.
gerrit
CC BY-SA 3.0
2014-05-01T13:50:03.250Z
I'm pretty certain the Coriolis force has nothing to do with tropopause height? Will edit my answer below when I'm in the same place as my lecture notes on this.
kaberett
CC BY-SA 3.0
2016-11-24T04:27:41.587Z
It is due to centrifugal force being greatest above the equator.
Douglas Cotton
CC BY-SA 3.0
2017-10-25T05:07:03.600Z
It is NOT due to the centrifugal force being greatest at the equator, though that adds 1, maybe 2%.    It has to do with temperature.   Warmer temperature =  higher troposphere.    More heat creates a greater vertical region of convection.  The tropopause is at the relative equilibrium of temperature where it stops falling and begins to rise.
userLTK
<troposphere><equator><poles>
Why is the troposphere 8km higher at the equator than the poles?
blunders
# Why is the troposphere 8km higher at the equator than the poles?

(Asked by: username_0 on 2014-05-01)

Fundamentals of atmospheric modeling show that the height of the tropopause depends on the location, notably the latitude, and that the troposphere is roughly 8km higher at the equator than the poles depending on the time of year.

First guess was that the temperature of the would impact its density (for example, here's the data for [-50°](https://www.wolframalpha.com/input/?i=air%20density%20at%20-50%C2%B0%20c) and [50° c](https://www.wolframalpha.com/input/?i=air%20density%20at%2050%C2%B0%20c)) - though this does not appear to show the cause of why is the troposphere 8km higher at the equator than the poles.

**Why is the troposphere 8km higher at the equator than the poles?**

![enter image description here](https://i.sstatic.net/XTu3M.gif)

**Tags:** troposphere, equator, poles

> **Comments:**
> **username_1**: A significant part (but not all) of the answer to this question will be the same as the answers at [Why is earth not a sphere?](http://earthscience.stackexchange.com/questions/108)  
> **username_2**: It depends not only on location, but also on season and even on the weather.  Might write down an answer if I find the time, unless somebody else does first.  
> **username_3**: I'm pretty certain the Coriolis force has nothing to do with tropopause height? Will edit my answer below when I'm in the same place as my lecture notes on this.  
> **username_4**: It is due to centrifugal force being greatest above the equator.  
> **username_5**: It is NOT due to the centrifugal force being greatest at the equator, though that adds 1, maybe 2%.    It has to do with temperature.   Warmer temperature =  higher troposphere.    More heat creates a greater vertical region of convection.  The tropopause is at the relative equilibrium of temperature where it stops falling and begins to rise.  

---

## 2 answers

### Answer by username_3 on 2014-05-01. Score: 7 | Accepted answer

To start with a definition, the tropopause is the boundary between troposphere and stratosphere; within the troposphere temperature decreases with increase in altitude (the temperature profile is dominated by radiative heat from the Earth's surface), whereas in the stratosphere temperature increases with altitude (the temperature profile is dominated by solar radiation).

Increases in troposphere temperature are associated with increase in tropopause height. Factors in play include the amount of water vapour being evaporated from equatorial seas; [interannual variations in tropopause height can result from both local and large-scale driving forces](http://onlinelibrary.wiley.com/doi/10.1029/JD090iD03p05629/full). The tropopause responds to the average temperature of the entire underlying layer: this is higher at the equator and lower at the poles.

> **Comments:**
> **username_6**: Wow, this is wrong and it got accepted. Thermal expansion around a few Kelvin cannot account for a increase of the Tropopause by a factor of two. Do the math, it's the centrifugal force.  
> **username_7**: @username_6 it is thermal expansion. Use the hydrostatic equation over a layer with an average temperature, and you will find that it does explain MOST of the variability. There are some other influences, but the hydrostatic equation is sufficient on a large scale.  
> **username_6**: @Baro: Exactly. It gives you $H \sim T$ and T doesn't vary by a factor of 2. So it's NOT the temperature.  
> **username_5**: This answer is correct, not wrong.   This really should get cleared up cause we don't want two conflicting answers to a question (unless the question is genuinely unresolved).   See this article here:   http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html   It says the highest Tropopause is over warm oceans and monsoons (water-vapor clearly plays a role).   It also indicates that Temperature is a key factor.  The tropopause rises and falls based on the seasons over the same location.  

---

### Answer by username_5 on 2017-10-25. Score: 0

In addition to the answer by @username_3 lapse rate explains the height variation of the tropopause quite well. Lapse rate is a property of gravity and the ideal gas law and it has to be adjusted for circulation and condensation and the top-down heating from the sun, which is a small effect given a mostly transparent atmosphere. Lapse rate isn't perfect, but it's still good for an approximation.

[Wikipedia summary](https://en.wikipedia.org/wiki/Lapse_rate#Convection_and_adiabatic_expansion)

Shorter, [Britannica summary](https://www.britannica.com/science/adiabatic-lapse-rate)

From the Britannica summary:

> The lapse rate of nonrising air—commonly referred to as the normal, or
> environmental, lapse rate—is highly variable, being affected by
> radiation, convection, and condensation; it averages about 6.5 °C per
> kilometre (18.8 °F per mile) in the lower atmosphere (troposphere).

If we take that averaged 6.5°C per km, that explains pretty close to the surface temperature variation on the Earth at sea level. (Antarctica, being mostly more than a mile in elevation, you need to adjust the temperature -6.5°C per km in altitude for surface temperature). The troposphere being an average of 8 km higher at the equator, corresponds to 52°c variation using that -6.5 degree estimate, or about 32 degrees (equator) to minus 20 (pole), which is very much in the ballpark.

Also, as noted in the Wikipedia article

> the dry adiabatic lapse rate is a constant 9.8 °C/km (5.38 °F per
> 1,000 ft, 3 °C/1,000 ft), the moist adiabatic lapse rate varies
> strongly with temperature. A typical value is around 5 °C/km

Moist air has a lower lapse rate, which explains why the troposphere is highest over warm equatorial Pacific and why it peaks over monsoons. - see [this article](http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html).

It's the surface temperature and water vapor. That's the gist of it. The rotation of the Earth can't account for a troposphere that's twice as high over the equator. The rotation of the Earth (and if we want to get silly, also the Moon's atmospheric tidal bulges) both affect the troposphere some, but they are minor players.

Earth's atmosphere shouldn't bulge much more than it's body, about [1 part in 298](https://en.wikipedia.org/wiki/Equatorial_bulge#Other_celestial_bodies), even if you multiply that by 4, and I think that's too aggressive a mathematical approach, but even so, that would be less than 1 part in 70 of atmospheric expansion over the equator due to the spin of the Earth. That's very far from the doubling that temperature explains.


---

