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Questions on solar radiation flux division.

CST1996

Shutao Cao
Member
Dear everyone,
I run CICE model standalone. And as far as I know, the incident solar radiation is divided into four components:
they are visible direct, visible diffuse, near infrared direct and near infrared diffuse respectively. And they are divided
by four variables in the fortran code named frcvdr, frcvdf, frcidr and frcidf. Correspondingly, the broadband albedo can
be weighted by four albedo components using four weighting coefficients named awtvdr, awtvdf, awtidr and awtidf in
the code. To the best knowledge of me, the coefficients which divide the incident solar radiation flux should be consistent with
the corresponding albedo weighting coefficients. For example, the visible-direct band fraction in total incident solar
radiation flux(named frcvdr in the code) should be equal to the visible-direct albedo weighting coefficient(named awtvdr in the code).
However, the fact is that they are not equal in the code. In the Fortran code, the incident solar radiation fraction coefficients
are defined in "ice_forcing.F90" file where frcvdr=0.28, frcvdf=0.24, frcidr=0.31 and frcidf=0.17, while the albedo weighting
coeffcients are defined in "icepack_parameters.F90" where awtvdr=0.00318, awtvdf=0.63282, awtidr=0.00182 and awtidf=0.36218.
Is this a bug of the code? Furthermore, in my opinion, the coefficients should change dynamically depending on the atmosphere
conditions instead of be constants.
I hope what I said didn't make you confused. And look forward to your reply.

Sincerely,
Cao
 

dbailey

CSEG and Liaisons
Staff member
The issue is that with the atmospheric forcing, there is only one band. So, these weights are loosely constrained from observations. Note that the frc values are to distribute the single band of incoming shortwave into four bands. The awt values are simply diagnostic to create a broadband albedo value for the history and are also loosely based on observations. These do not necessarily have to be the same. I would recommend saving the four albedo components and you can create your own broadband value.
 

CST1996

Shutao Cao
Member
The issue is that with the atmospheric forcing, there is only one band. So, these weights are loosely constrained from observations. Note that the frc values are to distribute the single band of incoming shortwave into four bands. The awt values are simply diagnostic to create a broadband albedo value for the history and are also loosely based on observations. These do not necessarily have to be the same. I would recommend saving the four albedo components and you can create your own broadband value.
Thanks for your reply.
But from the perspective of energy conservation, the awt values should be the same as frc valuse.
We ca
 

CST1996

Shutao Cao
Member
The issue is that with the atmospheric forcing, there is only one band. So, these weights are loosely constrained from observations. Note that the frc values are to distribute the single band of incoming shortwave into four bands. The awt values are simply diagnostic to create a broadband albedo value for the history and are also loosely based on observations. These do not necessarily have to be the same. I would recommend saving the four albedo components and you can create your own broadband value.
Thanks for your reply.
But from the perspective of energy conservation, the awt values should be the same as frc valuse.
Now I try to prove it.
Assume the downward shortwave radiation flux is SWDN, the upward is SWUP, the total albedo is α.
As we know, the upward shortwave radiation flux is equal regardless it is calculated in the form of
components or total amount. Thats is:
View attachment 1693
So We can conclude the wt values is the same as frc values.
I don’t know whether there is a problem with the above derivation process.
If so, please give me the reason.
Kindly,
Cao
 

CST1996

Shutao Cao
Member
The issue is that with the atmospheric forcing, there is only one band. So, these weights are loosely constrained from observations. Note that the frc values are to distribute the single band of incoming shortwave into four bands. The awt values are simply diagnostic to create a broadband albedo value for the history and are also loosely based on observations. These do not necessarily have to be the same. I would recommend saving the four albedo components and you can create your own broadband value.
Furthermore, in Ebert and Curry, 1993(doi: 10.1029/93JC00656), the author partition the solar spectrum into four intervals and they
mention that the integrated surface albedo is the sum of the spectral albedo weighted by the relative solar flux in each wavelength region.
 

dbailey

CSEG and Liaisons
Staff member
Again, the awt values are simply for diagnostic purposes and you can do whatever you want here.
 
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