Solar radiation, Jerlov water types and plankton feedback

[pduarte]

Hi
As I understand, the routine lmd_swfrac.F computes the fraction of solar radiation flux that reaches some specific depth based on the Jerlov water type and an exponential decay function for two wave length bands. In the routine pre_step3D.F the variable srflx is multiplied by the mentioned fraction to compute the amount of solar radiation that reaches different depths.
One the other hand, the variable srflx is used in most (if not all) of the biogeochemical models, to calculate the amount of PAR available at each depth. In this case, light is attenuated as a function of chlorophyll concentration and not a fixed Jerlov water type.
Therefore, I see here some inconsistency between the calculation of underwater light intensity in pre_step3D.F and that of PAR light at depth in the biogeochemical subroutines. I understand that the former is not focused on PAR but I wonder if it would be more consistent to compute the attenuation of the short wave band in lmd_swfrac.F as a function of chlorophyll, similarly to what is done in the biogeochemical subroutines. This would bring more consistency and also would provide a feedback from phytoplankton to physics. Also, it would be similar to what is done in the bulk_flux.F subroutine that calculates light absorbance in the ice as a function of ice algae.
I appreciate any feedback about this or I am afraid I misunderstood something in the code.

Regards

[kate]

Yes, this is a shortcoming in the distributed code. Raphael Dussin has spent a good bit of time working on light limitation as a function of BGC water properties, but it hasn't been been released yet. This is for work with the COBALT BGC model from GFDL. You would have to ask Enrique Curchitser about availability of this branch.

[kfennel]

Bronwyn Cahill had also implemented this a few years ago. Here is a link to her 2008 article: http://onlinelibrary.wiley.com/doi/10.1 ... 33595/full

[pduarte]

Hi, thanks very much for the prompt replies.

[pduarte]

Hi
I wonder if anyone may indicate literature supporting the 9 Jerlov Water types included in ROMS (types I, IA, IB, II, III, 1, 3, 5 and 7). I did not find anything about the last type. Moreover, the classidications I found were based on attenuation at a specific wave lenght and not at two bands as implemented in ROMS.

Cheers

Pedro