Biotic pump: Comments and questions: 7
Main page in English Russian version of current document BIOTIC REGULATION OF THE ENVIRONMENT Welcome to discussion of biotic regulation!

Nature photos News Demography Contacts Hot topic Publications
topical :
: recent
Your questions Biotic regulation
in simple words

Biotic Regulation has moved.
You are on the first web site of Biotic Regulation.
Since February 14, 2008 it is no longer updated.
Welcome to!

Hot topic: Biotic pump of atmospheric moisture



Main publication

Overview of the results

Comments and responses
[you are here]
List [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]




Anonymous (2006): Question on condensation, heat release and the evaporative force.

Can the release of heat during condensation of water vapor and the associated rise of pressure of the heated air counteract the pressure shortage produced by "annihilation" of water vapor molecules?

Besides of the "volume collapse" associated with water vapor condensation, being an exothermic process, there is release of latent heat as sensible heat at those levels. Sensible heat means temperature rise, which will mean expansion of that volume of air. What effect will that release of heat have on the pressure deficit produced by condensation?

In other words, since water vapor condensation is an exothermic process, therefore, expansion from heating (condensation) could counter contraction in the core of the evaporative force, as you describe it. Sure that warming at the condensation level produces buoyancy and thus an upward movement, but, as you discussed the traditional convection consideration in your response to Dr. Dovgaluk, simple expansion of the air would go against the horizontal pressure deficit produced by condensation, right? Could you illuminate me with this apparent paradox?



Gorshkov V.G., Makarieva A.M. (2006): Response to the question on condensation, heat release and evaporative force.

This question, although simple, is quite fundamental in its physics.

Importantly, condensation CANNOT LEAD TO HEATING (i.e. rise of temperature). Condensation can only partially counteract and weaken THE DROP OF TEMPERATURE that initiated condensation.

Imagine that you have a jar with saturated water vapor. How can you condense it? By DECREASING temperature of the jar. Then, during condensation, some heat will be released. But the jar temperature will not rise, it will DROP LESS than it would without condensation. That is why moist adiabatic lapse rate is less than dry adiabatic lapse rate.

Now let us think again from a different angle. Imagine one takes some heat away from that saturated jar, temperature drops, water vapor condenses, heat is released and warms the jar to a temperature higher than the initial one. What will happen? Water vapor will evaporate again, because the temperature has risen. So ultimately you will see no condensation at all. This means that if one does observe condensation, the temperature can do nothing but drop.

But this is not very relevant to the picture of the evaporative force. Here everything is clear. Temperature of the rising air parcels drops, water condenses and produces pressure shortage.


Main page in English Russian version of current document   Modified 5 November 2006.
© 2006 V.G. Gorshkov, A.M. Makarieva