PAR units

[jagoosw]

Hi all,

I think we need to clarify the units for PAR. LOBSTER (and other BGC models) seem to use W/m $^2$ while e.g. the kelp model use einsteim/m $^2$ /day.

Since PAR is defined as an integral between 400 and 700nm (by MODIS at least) then we can take the very rough approximaiton at the central wavelength for putting it into the BGC models, but I don't know if this is the best solution.

At the moment we're implicitly assuming W/m $^2$ and converting for the kelp model:

OceanBioME.jl/src/Models/Individuals/SLatissima.jl

Line 536 in 70ff47f

PAR = _interpolate(auxiliary_fields.PAR, ξ, η, ζ, Int(i+1), Int(j+1), Int(k+1)) * day / (3.99e-10 * 545e12) # W / m² / s to einstein / m² / day

(This is, as far as I can tell, also being done wrong). I'm not exactly sure when this got added in but we need to a) agree on units for the defaults, and b) agree how to convert for the different models.

I think the above should read:

...* day / (3.99e-10 * (299792458 / 550e-9))

(the second factor is ~545e12 so we've lost a factor somewhere in the past)

[syou83syou83]

Hi Jago,
I am not sure if I understand this point here. Isn't 299792458 / 550e-9 equivalent to 545e12? I derived this 545e12 from https://en.wikipedia.org/wiki/Einstein_(unit) 1 einstein = 1 mol × NA h f = 1 mol × 6.02214076×1023 mol−1 × 6.62607015×10−34 J s × f = 3.9903127128934321×10−10 J s × f,
and 0.43J=1.191018 quanta according to paper: Optical modeling of the upper ocean in relation to its biogenous matter content Page 10751.

Si

[jagoosw]

Oh yeah, sorry my mistake!

I do think we should agree a standard unit for light. Maybe PAR in Einsteins and light intensity (or something else) in W/m^2.

[jagoosw]

We do watts/m^2