Units for input forcing fields?

[mangelesg]

Hello,

Im trying to figure which units the input fields should have.

In the MARBL documentation it says Dust Flux should be in g/cm^2/s , however the file containing the inputs (call_compute_subroutines.20190718.nc), shows Dust Flux in kg/m^2/s.

Which are the correct units?

Thanks,

Angeles

[mnlevy1981]

Sorry for the confusion -- the netCDF file is in kg/m^2/s because we eventually want MARBL's internal computations to be done with units of meters, kilograms, and seconds rather than centimeters, grams, and seconds (see #41). Currently, the stand-alone driver applies a conversion factor for many of the forcing fields, and for dust flux the conversion factor is 0.1.

[mangelesg]

Thanks for the fast reply!

[mangelesg]

Hello,

Do you know if the units system used in MARBL is the same as used in the Biogeochemical Elemental Cycling model (BEC)?

Thanks!

Angeles

[mnlevy1981]

Hi @angeles2013 -- sorry for the delay in responding. MARBL was developed out of BEC in POP2, and in that case we have left the units the same. If you are looking at BEC as ported to a different model, though, it's possible that the units were modified to match the base units in that other model (though I suspect it would be easier to just convert the inputs and outputs)

[mangelesg]

@mnlevy1981 thanks for the information!

[mangelesg]

The NO3 variable is on units of micromol/Liter, however the NOx flux is on units of nmol/cm2/sec (after using the scale_factor 7.1429e+06).

When the flux NOx is added to NO3, wouldn't be necessary another conversion to match their units?

Also, NOx is per area, while NO3 is per volume. Is the flux multiplied by the water column height?

[mnlevy1981]

The NOx flux is the nitrogen deposition flux and it is added to the surface tracer flux being returned to MARBL (see line 407 of marbl_surface_flux_mod.F90). The units work out, even though it doesn't look like it at first blush:

Note that the NO3 units, mmol / m^3, are equivalent to nmol / cm^3 because 1 mmol = 1e6 nmol and also 1 m^3 = 1e6 cm^3 so the 1e6 terms cancel. For the surface fluxes, we multiply the tracer units by velocity (which has units cm / s) so nmol / cm^2 / s are the proper units for the surface flux of NO3.

[mangelesg]

Thank you, but when is the surface tracer flux added to the total tracer?

[mnlevy1981]

MARBL doesn't add the surface tracer flux to the total tracer at all, it expects the GCM to know how to do that as part of the vertical mixing routine.

[mangelesg]

That helps a lot, thank you