Coldest upper atmosphere temperature?

It would seem like a simple enough question: what’s the lowest the air temperature has ever gotten in the upper atmosphere? But the cites I’ve been able to search have answers all over the place. All agree that the “mesosphere” and more specifically the “mesopause” region of the upper atmosphere is the coldest- but hard figures are hard to come by. Since this region is only accessible by sounding rockets do we in fact not know for sure?

If by upper atmosophere you mean the thermosphere (the upper low density area of the Earth’s atmosphere that extends up to Low Earth Orbit) then the temperature actually goes up considerably, up to almost 1200 K (over 900 deg C). This is due to the low density of the atmosphere and the composition containing lighter molecular weight constituants which therefore absorb more energy per mass (especially in the high frequency UV wavelengths that are mostly filtered out by the time sunlight gets to the surface) and has a higher temperature per molar composition. Of course, your perception of the atmospheric temperature would be much lower than at ground level because the atmosphere is so thin that there is little convection, and whether you feel warm or cold would largely be governed by whether you are in direct sunlight or shade.

The temperatures at the interface between the thermosphere and mesosphere are lower, getting down to around 200 K (around -75 deg C), but the temperatures at the interface between the troposphere and the stratosphere is nearly as low (around 220 K). Here is an infograph of the atmospheric temperature and major components with regard to altitude.


200 K is well above the record low at Earth’s surface, so I don’t see how that could be correct.


Average vs. extreme, I would expect. The figure of 200 K is probably a long-term average over all times and locations; the corresponding figure for the Earth’s surface would be something like 287 K. I don’t know how much we know about fluctuations of temperature in the upper atmosphere, either with time or with location; but it wouldn’t surprise me if the upper atmosphere gets colder than 200 K from time to time.

The air temperature required for noctilucent cloud formation is often cited in the ballpark of -180 degrees F. Or 155K / ~-120 C. This site mentions temps of -230 F. And this one mentions they can get down to -160 C / -256 F.


Here are examples of the different info I’ve researched.

Preview: I see Gray Ghost has also encountered different cites. Although it may be moot because as one site put it: “Temperatures there only have significance in influencing the mesosphere’s molecular physics and chemistry rather than in any ability to heat objects like spacecraft or even dust”