new 5-bands light penetration scheme
Taking UV into account in NEMO's light scheme.
The RGB and IR parts remain unchanged. This scheme is called 5BD for 5 bands, with the 5 bands being UV-R-G-B-IR covering the entire spectrum from 0.2 micrometers to 4 micrometers.
This scheme can be activated in the namelist using the ln_qsr_5bd flag. In addition to the existing parameter rn_abs, which corresponds to the fraction of infrared light, the parameter rn_par has been added to determine the fraction of PAR (Photosynthetically Active Radiation). The fraction of UV is therefore determined as 1 - rn_abs - rn_par.
The absorption coefficients used in the UV part of the spectrum are derived from the paper by Morel and Maritorena (2001) for the wavelength lambda=0.350 micrometers. These values have been added as a fifth column in the subroutine trc_oce_rgb, which is recalled trc_oce_tab for clarity (similar to all the other variables including rgb in their names in trc_oce.F90 and traqsr.F90). The routine trc_oce_rgb_read.F90 is no longer used; thus, it has been deleted to clean up the code.
Regarding its implementation, since UV radiation penetrates significantly into the water column, it is considered in all calculation blocks similar to the blue light.
With such a scheme, one can expect a lower temperature input in the surface layers but a stronger input around 50 meters depth (see the attached plot of T established using ORCA025 simulations).