How to change semi-major axis or mean solar flux

[pybl]

Hello,

I am trying to adjust the mean flux received from the Sun on Earth, there are two methods I am thinking of.

The first one is to increase or decrease the semi-major axis 'a' which essentially changes the flux;

For the second one, I could scale up/down the total luminosity of the Sun knowing that we can redefine the spectrum in the user_nl_cam/user_nl_cpl namelists.

Does anyone know if it is possible to change the semi-major axis 'a' in the model, any hint is appreciated.

Thanks in advance.

 

[pybl]

Hello,

I just read in the driver name lists, that there are no variables that I can change for the semi-major axis.
But, there is a way to define or scale up or down the total solar luminosity by giving a solar spectrum in the user_nl_cam.

Any hints on how to adjust TSI (total solar irradiance) in the simulations?

Thanks!

 

[brianpm]

The easiest way is to modify the file that defines the (spectral resolved) irradiance. Here is a thread where that is discussed: how to change incoming shortwave radiation

You other method would also work, but I don’t think we have a semi-major axis parameter, so you’d probably have to adjust the eccentricity of the orbit (which would change semi major and semi minor axes).

 

[pybl]

Thanks for your reply.

I have found it easier to change the solar profile in atm_in in the run directory.

Also, from my experiment, changing eccentricity would only affect the semi-minor axis.

 

[brianpm]

For reproducibility and avoiding mistakes if you need to rebuild or re-run, I would strongly advise not to modify things in the run directory. Use the user_nl_* namelists in the case directory, and keep your modified file somewhere convenient.

I just took a look, and you are right that changing the eccentricity is not going to control the TSI very well. The Earth-Sun distance is controlled by a scaling factor called `eccf`. That factor is a function of the eccentricity, mvelpp (moving vernal equinox longitude plus pi), and lamb (longitude of perihelion). So by changing these parameters, I think the orbital shape could be controlled, but it is more complicated than one might think at first.

Leaving the orbit alone but changing the TSI in the file seems like the right way to go.