4
$\begingroup$

When trying to calculate the adiabatic lapse rate of moist air based on known values of basic thermodynamic properties of the constituents (ice, water, vapor,...) I came to the following question:

Lapse rate of moist air is less as compared to dry air because of the latent head released during condensation of water-vapor.

Now, below 0°C there is no liquid phase in equilibrium, therefore instead of the latent heat of evaporation $L_{ev}$ of liquid I used the value for sublimation $L_{sub}$. However, of course $L_{sub} > L_{ev}$, so according to my calculations the lapse rate must have a discontinuity at 0°C (see graph, where the dotted line is the dry lapse rate).

This discontinuity is not in accordance with observation - so where is my fault? What happens in rising air that this effect is not visible? enter image description here

Improve this question
$\endgroup$
2
  • 5
    $\begingroup$ The fallacy is: Water becomes ice below 0°C. In the atmosphere water will often be "supercooled". It might be worth checking the "Bergeron-Findeisen process". A nice resource is: Physics and Dynamics of Clouds and Precipitation by Pao K. Wang. $\endgroup$
    – Joscha Fregin
    Apr 28 at 21:41
  • 3
    $\begingroup$ @JoschaFregin Classic home experiment - take a bottle of distilled water and keep it in the fridge. It never freezes even below 0 degrees. The same is observed in the clouds $\endgroup$
    – user1066
    Apr 29 at 14:12

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.