Choice of pressure in the CLMU building energy model

[cathyxinchangli]

Brief summary of bug

In the CLMU building energy model (BEM), standard pressure is assumed when calculating indoor air density. It may be more realistic and accurate to assume bottom layer of atmosphere pressure, which is used by CLMU to calculate canyon air properties, since indoor and outdoor pressure differences are usually small.

General bug information

CTSM version you are using: ctsm5.2.001

Does this bug cause significantly incorrect results in the model's science? Not much (see below for details)

Details of bug

I changed the pressure used in the air density calculation in BEM from standard pressure to bottom layer of atmosphere pressure of the corresponding grid cell, and compared results from land-only simulations of the year 2000 before and after the change. The change leads to a small reduction in urban 2m air temperature (up to -0.08 K) and a small increase in urban 2m relative humidity (up to 0.25%) in places of higher altitude. This is likely due to a reduction in urban air-conditioning energy flux (up to -0.9 W/m^2 of urban area) and urban heating energy flux (up to -3 W/m^2 of urban area) caused by reduced indoor air density in those areas. Plots are available here:
bugfix_pressure_4vars_diff_global_2000mean_urbanarea.pdf

Important details of your setup / configuration so we can reproduce the bug

The code change was done in this commit on my CTSM fork.

Below are details of the simulations I ran to produce the results above:

• compset: 2000_DATM%GSWP3v1_CLM51%SP_SICE_SOCN_MOSART_CISM2%NOEVOLVE_SWAV
• resolution: f09_g17
• machine: Derecho

[samsrabin]

Bugfix and urban, so should be allowed now that we're in the chill.

[olyson]

Thanks for this @cathyxinchangli . Do you have time to create a branch off of CTSM main and issue a PR? If not, I'm happy to do it.

[cathyxinchangli]

Hi @olyson! I'd be happy to, but it seems my account doesn't have the authorization to do that. However, I can create a PR from the branch on my forked repository. Would that be okay? Or if I am allowed to be given the authorization then I can create a branch then!

[olyson]

Yes, sorry for the confusion, I just meant that your CTSM fork should be updated to the latest, you have ctsm5.2.001, and the latest tag is ctsm5.2.028.

[cathyxinchangli]

I see! Sure, I just synced the branch to the CTSM main. I will create a pull request now!

[cathyxinchangli]

PR #2758 is up now! @olyson