Soil temperature adjustment

[lkugler]

Hi all,
it seems that real.exe is adjusting the soil temperature ("ST") from the met_em-files by some temperature gradient due to the height difference between the source/driving grid terrain and the WRF grid terrain.

Can anyone confirm this? I did not find it in the documentation.

Regards,
Lukas

 

[kwerner]

Hi,

Yes, I can confirm that this is the case, and is done intentionally. The reason is that there are times when the difference in height between the first-guess topography and the model topography can be large enough that the temperature can be too high/low, which can lead to unrealistic values later in the simulation. If you're interested in taking a look at the code, you can find it in share/module_soil_pre.F. If you search for '0065' you'll see this done for each land surface scheme, based on the standard lapse rate. For instance:

st_input(i,k,j) = st_input(i,k,j) - 0.0065 * ( ter(i,j) - toposoil(i,j) )

If you wanted to NOT do this, it would likely be okay to set the lapse rate to 0 here, but you'll want to make sure to look at the code closely, and to do some simple testing to verify that changing it will not cause other issues.