# If heat rises, why is it cold in the mountains? **URL:** \ **Category:** Factual Questions\ **Created:** [May 30, 2012, 2:02pm UTC](https://boards.straightdope.com/t/if-heat-rises-why-is-it-cold-in-the-mountains/623542 "2012-05-30T14:02:27Z")\ **Posts on this page:** 7\ **Page:** 3
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [May 31, 2012, 3:50pm UTC](https://boards.straightdope.com/t/if-heat-rises-why-is-it-cold-in-the-mountains/623542/41 "2012-05-31T15:50:58Z")
> **[Solar irradiance](https://en.wikipedia.org/wiki/Insolation)** > > Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. > Solar irradiance is measured in watts per square metre (W/m2) in SI units. > Solar irradiance is often integrated over a given time period in order to report the radiant energy emitted into the surrounding environment (joule per square metre, J/m2) during that time period. This integrated solar irradiance is called ... The top of the atmosphere receives 1366 W/m2. On sunlight’s way down, the atmosphere reduces this to 1000 W/m2 at Earth’s surface. So: 2.7 times as much energy delivered to the surface, which transfers it to the air by conduction, and I don’t think conduction goes further than a few meters, VS 1 unit of energy spread over 1,000,000 meters. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [May 31, 2012, 4:01pm UTC](https://boards.straightdope.com/t/if-heat-rises-why-is-it-cold-in-the-mountains/623542/42 "2012-05-31T16:01:43Z")
> **[Diurnal air temperature variation](https://en.wikipedia.org/wiki/Diurnal_temperature_variation)** > > In meteorology, diurnal temperature variation is the variation between a high air temperature and a low temperature that occurs during the same day. > Temperature lag, also known as thermal inertia, is an important factor in diurnal temperature variation. Peak daily temperature generally occurs after noon, as air keeps absorbing net heat for some period of time after noon. Similarly minimum daily temperature generally occurs substantially after midnight, indeed occurring during early morning in ... “As solar energy strikes the earth’s surface each morning, a shallow (1–3 cm) layer of air directly above the ground is heated by conduction. Heat exchange between this shallow layer of warm air and the cooler air above is very inefficient. On a warm summer’s day, for example, air temperatures may vary by 30°F from just above the ground to waist level.” ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [May 31, 2012, 4:43pm UTC](https://boards.straightdope.com/t/if-heat-rises-why-is-it-cold-in-the-mountains/623542/43 "2012-05-31T16:43:30Z")
> [@AaronX](#): > > The same reason it’s colder in winter. Sunlight falling on the ground at angle heats less than falling perpendicularly. This would be true if we were talking about locations at two different latitudes (e.g. the north pole versus the equator), but Lhasa and SA are at the same latitude, and so both receive the _same_ insolation: for both places, the sun follows the same path through the sky, and the ground receives the sun’s radiation at the same angle. The question remains unanswered: why is Lhasa cooler than San Antonio? ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [May 31, 2012, 5:18pm UTC](https://boards.straightdope.com/t/if-heat-rises-why-is-it-cold-in-the-mountains/623542/44 "2012-05-31T17:18:17Z")
No, at higher altitudes, the rays strike the side of the mountain, at an angle. You could say the top of the mountain is flat, but that’s negligible compared to the area of the sides. Just search for “temperature inversion” and see for yourself. Air is heated by the ground. That’s why air near the ground is warmest. [http://www.wrh.noaa.gov/slc/climate/TemperatureInversions.php](http://www.wrh.noaa.gov/slc/climate/TemperatureInversions.php) ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [May 31, 2012, 5:36pm UTC](https://boards.straightdope.com/t/if-heat-rises-why-is-it-cold-in-the-mountains/623542/45 "2012-05-31T17:36:00Z")
> [@Machine\_Elf](#): > > clearly this is not perpetual motion. Well, duh. You split my paragraph in two and answered the second half out of context. > [@](#): > > The question remains unanswered: why is Lhasa cooler than San Antonio? Less insulting atmosphere will make Lhasa cooler. Your example doesn’t distinguish between those two causes. > [@Fubaya](#): > > I don’t understand the part about the vacuum tube. If there’s nothing inside it, it won’t warm up or cool down, how are you taking advantage of the high and low temperature difference? If the bottom is warmer than the top, there will be energy flowing from the bottom to the top via radiation. That could be tapped into to do work. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [May 31, 2012, 5:57pm UTC](https://boards.straightdope.com/t/if-heat-rises-why-is-it-cold-in-the-mountains/623542/46 "2012-05-31T17:57:09Z")
> [@ZenBeam](#): > > Well, duh. You split my paragraph in two and answered the second half out of context. We agree that a perfectly insulated column of quiescent air will equilibrate to a single temperature. Do you agree that a perfectly insulated column of air that is forced to circulate vertically will develop a temperature gradient due to adiabatic heating/cooling, and that a heat engine operating on the difference in temperatures between two different altitudes can be made to produce mechanical work without violating the laws of thermodynamics? ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [May 31, 2012, 10:13pm UTC](https://boards.straightdope.com/t/if-heat-rises-why-is-it-cold-in-the-mountains/623542/47 "2012-05-31T22:13:50Z")
> [@Machine\_Elf](#): > > We agree that a perfectly insulated column of quiescent air will equilibrate to a single temperature. > > Do you agree that a perfectly insulated column of air that is forced to circulate vertically will develop a temperature gradient due to adiabatic heating/cooling I’ll accept that. Do you agree that the atmosphere will act as an insulator, causing a temperature gradient even in the absence of vertical circulation, or adding to the gradient when there is vertical circulation? > [@](#): > > , and that a heat engine operating on the difference in temperatures between two different altitudes can be made to produce mechanical work without violating the laws of thermodynamics? Of course. I have no idea why you keep bringing this up. I never said or implied otherwise. [Previous page](https://boards.straightdope.com/t/if-heat-rises-why-is-it-cold-in-the-mountains/623542.md?page=2)