Question about the variable SOLIN(solar radiation)

[pybl]

Hello,

I use WACCM 6 --compset BWma1850 --res f19_g17 for my simulation.

I noticed if I take the global and annual mean of the output variable 'SOLIN' (a variable in the MASTER FIELD list) which represents solar radiation, it is not a constant over time (in year):

In source code, we can find SOLIN depends on cosine of solar zenith angle.

However, we know if the orbital configuration is fixed, and solar radiation on the top of model must be fixed for each year.

Please point out if I misunderstood anything about SOLIN.

Thanks a lot!

 

[mmills]

Hello,

I use WACCM 6 --compset BWma1850 --res f19_g17 for my simulation.

I noticed if I take the global and annual mean of the output variable 'SOLIN' (a variable in the MASTER FIELD list) which represents solar radiation, it is not a constant over time (in year):
View attachment 2489
In source code, we can find SOLIN depends on cosine of solar zenith angle.
View attachment 2488
However, we know if the orbital configuration is fixed, and solar radiation on the top of model must be fixed for each year.

Please point out if I misunderstood anything about SOLIN.

Thanks a lot!

First, because you are running WACCM6, the radiation code is RRTMG, not CAMRT, so you need to look at this code:

physics/rrtmg/radsw.F90

which has a similar definition, but based on summing spectral irradiances over wavelength bands:

! Define solar incident radiation
do i = 1, Nday
solin(i) = sum(sfac(:)*solar_band_irrad(:)) * eccf * coszrs(i)
end do

Here Nday is the number of daylight columns, and solin is the incident solar flux at the top of the atmosphere for each column.

This behavior is different from WACCM4, in which SOLIN was a constant value representing the reference total solar irradiance (TSI) over several solar cycles in the 19th Century. The WACCM4 SOLIN output was not useful.

I am attaching plots showing the global mean and zonal mean variation in SOLIN from our FV2x1 BWma1850 piControl run for CMIP6.

I attribute the fact that you are seeing variation in the annual mean to the fact that you are doing runs with high orbital eccentricity. Is that the case?

 

[pybl]

First, because you are running WACCM6, the radiation code is RRTMG, not CAMRT, so you need to look at this code:

physics/rrtmg/radsw.F90

which has a similar definition, but based on summing spectral irradiances over wavelength bands:

! Define solar incident radiation
do i = 1, Nday
solin(i) = sum(sfac(:)*solar_band_irrad(:)) * eccf * coszrs(i)
end do

Here Nday is the number of daylight columns, and solin is the incident solar flux at the top of the atmosphere for each column.

This behavior is different from WACCM4, in which SOLIN was a constant value representing the reference total solar irradiance (TSI) over several solar cycles in the 19th Century. The WACCM4 SOLIN output was not useful.

I am attaching plots showing the global mean and zonal mean variation in SOLIN from our FV2x1 BWma1850 piControl run for CMIP6.

I attribute the fact that you are seeing variation in the annual mean to the fact that you are doing runs with high orbital eccentricity. Is that the case?

Thanks for the reply!

Yes, I am doing runs with higher orbital eccentricity. The solar radiation should be a variable of time if I plot the monthly mean, but how does SOLIN change its value interannually when the orbit is fixed?

ps: I checked array size =12 months for each year when I calculate the annual mean of SOLIN.

 

[xc-wang]

Hello,

I have encountered a similar issue while using WACCM6 simulations, specifically with the SOLIN variable. It does not exhibit a consistent pattern and shows interannual variability. I wrote my problem here (link: Irregular Fluctuations in Monthly Mean SOLIN Variable in CESM2.1.1 Simulation) . I would like to know if you have found a solution to this problem and what could be the possible reasons behind it. I have not made any modifications to the radiation settings and have used the default parameters.