Among the process methods treating the penetrative solar radiation available in NEMO are
the "bio-model" light penetration method and the "RGB" light penetration method.

For the calculation of the phytoplankton light limitation as well as the oceanic heating 
rate due to the penetrative solar radiation, both mothods use a polychromatic (3-waveband)
model called "RGB (Red-Green-Blue) model."

It is a simplified version of the 61-waveband model proposed by Morel (1988) 
in which light absorption in the ocean is dependent of the particle concentration 
and is spectrally selective.

The solar radiation in the wavelength range longer than 700 nm is strongly absorbed
and contributes to heating the top few centimeters of the ocean. On the other hand, 
the solar radiation in shorter wavelenghts (400-700nm) propagates to deeper depths and 
contributes to local heating below the surface.

In the "RGB model" implemented in NEMO, visible light is divided into three wavelengths 
blue (400-500 nm), green (500-600 nm) and red (600-700 nm). 

The RGB model reproduces the light penetration profiles quite closely those predicted by 
the full spectral model of Morel (1988) with much better computer efficiency 
(Lengaine et al, 2007; Lengaine et al, 2009).   

In the "bio-model" light penetration method implemented in NEMO, 
the chlorophyll concentration produced by the biological component in the biogeochemical 
PISCES model retroacts on the ocean heat budget by modulating the absorption of light via
a polychromatic model, the RGB model, that is used to calculate the phytoplankton light 
limitation as well as the oceanic heating rate (Lengaigne et al., 2007). No external
chlorophyll data is required in this method.

In contrast, the "RGB" light penetration method in NEMO uses 
the observed monthly satellite chlorophyll field as input chlorophyll data with 
the RGB model to calculate the phytoplankton light limitation as well as the oceanic 
heating rate at the depth up to 400m deep. 

In this method, the chlorophyll concentration is still produced by the biological 
component in the biogeochemical PISCES model but it will not retroacts on the ocean heat 
budget by modulating the absorption of light.

We'll use available observed monthly satellite (SeaWiFs and other satellites) 
chlorophyll field with the "RGB" light penetration method and the results are compared to
the output from experiments with the "bio-model" light penetration method.

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Lengaigne, M., C. Menkes, O. Aumont, T. Gorgues, L. Bopp, J.-M. Andre, and G. Madec, 2007: 
Influence of the oceanic biology on the tropical Pacific climate in a coupled general
circulation model. Clim. Dyn. 28:503-516, doi:10.1007/s00382-006-0200-2.

Lengaigne, M., G. Madec, L. Bopp, C. Menkes, O. Aumont, and P. Cadule, 2009: Bio-physical
feedbacks in the Arctic Ocean using an Earth system model,Geophys. Res. Lett., 36, L21602,
doi:10.1029/2009GL040145.

Morel, A., 1988: Optical modeling of the upper ocean in relation to its biogenous
matter content (Case I waters). J. Geophys. Res., 93(C9), 10,749-10,768.