Theta-e question

[Angie Norris]

Hey guys,
I've got a question about theta-e (well, actually a bunch of questions, but one in particular). Is theta-e related to the evaporation of soil moisture?
This is for a report I'm writing for school, so any references are most appreciated, and just be advised if you've got a particularly helpful answer, you will be cited in my references!!
Thanks bunches!!!

 

[Glen Romine]

In short, yes, in as much as the evaporation of water from the soil increases the mixing ratio of water vapor, and larger values of water vapor boost the value of equivalent potential temp (the energy associated with the evaporation of the water in the soil goes into heating the air parcel when it is condensed again).

If you are looking for a citation, you could go with the AMS Glossary. They have a fancy version of equivalent potential temp:

http://amsglossary.allenpress.com/g...quivalent+potential+temperature&submit=Search


Simpler good approximations can also be found many places on the web, so you may want to try google.

 

[Angie Norris]

Glen, thanks very much! That's what I was thinking, but wasn't real sure my brain was going in the right direction. Paper writing will commence tonight

 

[David Wolfson]

I have a question about the answer, because I've understood it differently. I had the understanding that the evaporative process in itself only replaces sensible heat with latent heat, and that Theta-e being a sum of both would be unchanged.

Now my understanding is that growing crops and other dark green vegetation absorb significantly more solar heat than lighter dry grass or soil -- 20% or so, I think. Might that be a source for raising Theta-e due to evapotranspiration?

 

[Glen Romine]

I have a question about the answer, because I've understood it differently. I had the understanding that the evaporative process in itself only replaces sensible heat with latent heat, and that Theta-e being a sum of both would be unchanged.

David,

Your question differs from Angie's. She asked if theta_e was changed by adding moisture (from the soil). All else equal, the answer is still yes. Of course, in nature, all else is not equal, and the factors controlling energy exchange and balance are far more complex. The soil type, fraction of water content, overlying air humidity, turbulent transport, etc..., onto which you can add far more complexity with vegetation and ground cover effects. So, if you have a fixed ground flux, you could either have the energy going into latent or sensible heating, with no net difference, but if the ground flux is variable based on factors such as those noted above, then the problem is not so simple.

Glen