# Estimating the upper limit for cloud formation?

I know that on our planet, the highest clouds reach up to the tropopause, roughly 10km above ground (varying from polar regions to tropics). If we ignore overshooting Cumulonimbus cloud tops and other excotic clouds, that is the cloud top for Earth. Is there a way of deducing this upper cloud top on the back of an envelope?

You might already be guessing it: I am after some kind of universal approximation formula which would reproduce the 45-70km cloud top height of Venus, or 0.6–0.9 bar level for Jupiter, see e.g. Wikipedia on Jupiter's Atmosphere

My metereologist friends could not help me with that one, maybe someone out there can?

The existence of clouds depends on the complex physics of atmospheric transport. In atmospheric layers where a condensible species exists in vapour-pressure-equilibrium, clouds can form. The latter depends on temperature, and large-scale cloud formation influences the radiative properties of an atmosphere, i.e. the temperature.
So in all generality this is a very complex problem.

However it is possible to set limits onto where condensible species can be transported to, by setting a limit on convection. The large-scale transport of material in planetary atmospheres seems to have a hard limit to < 0.1 bars, which is the absolute upper limit for atmospheric convection to happen.
This is because above 0.1 bar a temperature inversion forms as the atmospheric gases become radiatively inefficient, with the exception of Titan, which prohibits convection, according to the Schwarzschild criterion.

The 0.1 limit on temperature inversions is described more in detail in this article (https://www.nature.com/articles/ngeo2020, and their more detailed model description in https://iopscience.iop.org/article/10.1088/0004-637X/757/1/104).

So then, once you have translated pressure coordinates into altitude, via using a planetary structure model, you would have your answer in km above some reference level. Sadly the latter is not an entirely trivial task, and people have worked on planetary structure models for decades now.

As a snarky comment, I would expect your meteorologist contacts couldn't help you with this because they seldom study more than one atmosphere.

• Thanks for the insights and the funny comment on studying only a single atmosphere. My 50 cents to that: Interestingly, ocean and atmosphere have so many state equations in common, if you map salinity and humidity, but oceanographers and metereologists usually do not mingly too much. What I am saying: I am a fan of generalizing things. Dec 10, 2020 at 9:50