[Wrf-users] Triggering of Grell Devenyi cumulus in WRF

[Gareth Berry]

Hi Folks,

I've got a very basic but very important question for any folks who are familiar 
with the WRF cumulus parameteriztions.

Basically what I want to know is how is the Grell Devenyi cu scheme 'activated' 
in WRF?

I'm not after the feedback to the model, as this is well documented, what I 
would like to know is what conditions have to be fulfilled for the GD scheme to 
produce convection. I know for the case of other types of cu scheme there are 
requirements for there to be a layer x hPa think of greater than y precent 
relative humidity and with greater than z m/s vertical motion, but I can't find 
any documentation of any thing similar in the documentation.

I've googled until the cows come home and found a few reference that hint there 
is a Arakawa-Schubert type trigger that requires a 'cloud work function' (a 
function of integrated buoyancy) to exceed a critial value. If this is the case 
I would like to find out what the critial value is or how I can find it. 

I've try using the WRF code browser, but it is pretty difficult to follow if 
you're not familiar with the model architecture, plus the links to the search 
function and documentation are down. Based on this I think that the triggering 
itself might also be done using the GD ensemble approach, but I would like to 
make certain.

Any help would be welcome!

Cheers,

Gareth.