Could FSDS be changed?

[SelenaChou]

Dear all,

I have doubt with the output variable "FSDS" in clm2.h0 files. From my perspective, FSDS means the downwelling shortwave raidation land received and FSDS = FSA (absorbed) + FSR (reflected). From biogeophys/BalanceCheckMod.F90, I know that fsa(p) + fsr(p) - (forc_solad(g,1) + forc_solad(g,2) + forc_solai(g,1) + forc_solai(g,2)) should equals 0, which means FSDS = forc_solad + forc_solai. forc_solad and forc_solai are two variables imported from cam component.

I run two parallel cases with the same compset and years, one is the base case and the other is the test case. In test case I modified the albedo and so changed the proportion of FSA and FSR. However, after comparing the FSDS of the two cases, I found the obvious difference. However, it passed the balance check.

Is this reasonable? What are the possible reasons behind this? I need your help. Thanks for all suggestions.

Selena

 

[SelenaChou]

Attach a picture.

 

[SelenaChou]

Update:

Now I think FSDS refers to the part of radiation that can pass through the atmosphere and eventually reach the surface, which means cloud and water vapour will effect FSDS before it reaches surface.

I did a simple test to check if FSDS will be changed. I modified albedo in a simplest way and output the FSDS. As I expected，FSDS is also changed, which proves that it isn't a constant.

If you have more ideas, please share with me. Thanks a lot!

 

[slevis]

I am pretty sure that you described FSDS in the CLM correctly. From what you've shared, I suspect that you are running with active atmosphere. If you ran with datm instead (i.e. active land only), then I would expect FSDS to remain unchanged in response to a change in the surface albedo.

 

[SelenaChou]

I am pretty sure that you described FSDS in the CLM correctly. From what you've shared, I suspect that you are running with active atmosphere. If you ran with datm instead (i.e. active land only), then I would expect FSDS to remain unchanged in response to a change in the surface albedo.

Thanks, slevis! I am running with active atmosphere acturally.