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Radiation balance at TOA/TOM

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alcide.zhao@...
Radiation balance at TOA/TOM

Hi all,

Just thought it would be useful to people who may by any chance work with radiation balance at the TOA using CESM1.The current CAM master field has diagnostics for net SW radiaiton flux at TOA (FSNTOA), upelling radiaiton SW flux at TOA (FSUTOA), net SW radiaiton flux at Top of the Model (FSNT), upwelling LW radiaiton flux at the top of the model (FLUT), net LW radiaiton flux at the top of the model (FLNT),

From the other discusision (https://bb.cgd.ucar.edu/toa-vs-top-model),  The Totop of the Model (TOM) in CAM is 3.64mb so it is not TOA.

1.  You should not use FLUT to approximate TOA outgoing longwave radiation (OLR), athough a lot of people have done this already.

2. If you are calculating TOA radiation imbalance, you should consider FSNT - FLNT (boht at TOM) instead of FSNTOA - FLNT, since the latter will give you around 4 w/m2 of imbalance due to the reason that they are in two different layers. I think this should be carefully resolved to have better radiation diagnostics to represnet both LW and SW radiaiton at TOA.

3. FLNT is not equal to FLUT (a net difference of around 1.5 W/m2 in an equilibrium model simulaiton), which means that there is longwave radiation coming into the atmosphere from the layer 3hPa-TOA. I do not know how the radiation code handlewith this, but please, if anyone, can explain it?

4. About FSUTOA, please take CAUTION with this diagnostics if you are working with radiation balance.

 

Please feel free to comment on this should anything be inapproprite! discussions is widely open!

Cheers, Alcide

heavens

Dear Alcide,

I am trying to track down some issues I've run into while modifying RRTMG for a Faint Young Sun scenario. 

As I understand how the variables work, SOLIN=FSNT+FSUTOA, or at least very close to it. So I'm probably doing something wrong if FSNT+FSUTOA is significantly smaller (22% or so) than SOLIN?

Thanks,

Nick

 

alcide.zhao@...

Dear Nick,

 

I am not sure with solar radiation (SOLIN), but again, FSNT and FSUTOA are at two different layers. I think you should expect SOLIN=FSNTOA+ FSUTOA.

However, 22% is really large.

Cheers, Alcide

heavens

Dear Alcide,

 

After a bit of work, I determined where the 22% loss was taking place because of some hard-coded insolation information in RRTMG. Indeed, SOLIN=FSNTOA+FSUTOA. 

 

Thanks,

 

Nick

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