Shortwave radiation balance at the wall missing reflected direct and diffuse radiation reflection from the wall terms.

[joshi994]

TYPE: Bug fix

KEYWORDS: Shortwave radiation balance, reflected radiation, shadowing effect, single-layer urban canopy model (SLUCM), direct and diffuse radiation.

SOURCE: Parag Joshi, Katia Lamer (Brookhaven National Laboratory)

DESCRIPTION OF CHANGES:

Problem:
The single-layer urban canopy model missed a couple of terms that represent the direct and diffuse radiation reaching at a wall reflected from the other wall. It leads to an inaccurate calculation of the shortwave radiation at the walls.

Solution:
Mathematical formulation by Kusaka et. al. (2001) was followed to verify the equations used in the SLUCM module in WRF. The equations are corrected.

More details can be found in this attachment.

LIST OF MODIFIED FILES: module_sf_urban.F

TESTS CONDUCTED:

1. It compiles.
2. It passes the Jenkins tests.

RELEASE NOTE:
This PR corrects the shortwave radiation balance at the wall, particularly the reflected direct and diffuse radiation reaching the wall which leads to underestimation of SW radiation at the wall.

[cenlinhe]

Could you also attach your pdf file (or snapshot) you sent to me that showing the equation and code difference?

[joshi994]

Could you also attach your pdf file (or snapshot) you sent to me that showing the equation and code difference?

@cenlinhe I have attached the document.

[cenlinhe]

@chenghaow @tslin2 @xuelingbo This is the bug we discussed through emails in the last few days, please also review this proposed bug fix to see if it looks good to you when you have time. Thank you! We need multiple approvals from urban model experts.

[weiwangncar]

The regression test results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None

[tslin2]

@chenghaow @tslin2 @xuelingbo This is the bug we discussed through emails in the last few days, please also review this proposed bug fix to see if it looks good to you when you have time. Thank you! We need multiple approvals from urban model experts.

The fix looks good to me, considering longwave included radiation reflection.

[weiwangncar]

@cenlinhe Would this bug fix be ready for 4.6.1 release? The release could be a few weeks away.

[cenlinhe]

yes, I think so. I will review and approve it next week.

[xuelingbo]

@chenghaow @tslin2 @xuelingbo This is the bug we discussed through emails in the last few days, please also review this proposed bug fix to see if it looks good to you when you have time. Thank you! We need multiple approvals from urban model experts.

The fix looks good to me

[weiwangncar]

@cenlinhe Can you review this PR?

[cenlinhe]

This bug fix looks good to me, which includes the missing multireflection shortwave radiation flux at the building wall. The original Kusaka 2001 equation has that term but it is missing in the code implementation.
I approve it.

[cenlinhe]

I approve it.