drop the 'positive' from rsdoabsorb ?

[jkettleb]

Although rdsoabsorb has unins Wm-2 we don't think its a flux so doesn't have direction.

Do you agree or have we misunderstood?

[martinjuckes]

I think this is a flux of energy into an ocean layer. After discussion with Karl, we have adopted the convention that transfers into the ocean from land or atmosphere should be considered as having a vertical direction and hence requiring a positive attribute.

Looking at this now, I'm not sure that rdso is the correct naming stem for this variable ... as it is not really linked with downwelling radiation directly, .. but I think we have to live with that for now (I've raised an issue for CMIP7 here: https://github.com/cmip6dr/cmip7_forward_look/issues/14 )

[taylor13]

I think what is requested here is the difference in the net SW flux at the base and top of each ocean layer. "absorbtion" in the standard_name makes it clear that we are not talking about the opposite (energy loss from the layer). The absorbed energy is independent of what the convention is governing the SW flux itself, so I agree with @jkettleb that "positive" should be dropped for this variable.

[jkettleb]

Hello Karl @taylor13,

Thanks for finding time to have a quick look at this. I was a little worried in case we had misunderstood this diagnostic. But I think our interpretation is consistent with yours.

Jamie

[martinjuckes]

This is not consistent with usage elsewhere. The use of positive has nothing to do with ambiguity being present of absent in the standard name (e.g. rsds), it is there because the physical quantity being represented could have one of two sign conventions. I'll change if necessary, but I'd like an explanation which is consistent with usage elsewhere.

[taylor13]

rsds is a vertical flux (formally a "flux density") across a single "quasi-horizontal" surface with a positive direction defined as either "up" or "down", whereas rsdoabsorb is a rate of energy flow into a layer (not across a single horizontal surface).

Perhaps some background would be helpful. Although vertical fluxes of energy, substance, and momentum are traditionally saved by modelers, not all of them adopt the same sign convention. The CF standard names recognize this and provide options, for example, for both net_downward_shortwave_flux_in_air and net_upward_shortwave_flux_in_air, which makes the positive direction explicit. In CMIP where we want to facilitate conformance with the specs using CMOR, we provide users with an option to say what their convention is for the positive direction of a flux, and then CMOR looks at the specs and reverses the sign of their data before writing it, relying on the "positive" entry in the table. Thus, all energy fluxes and surface stress invariably are assigned a "positive" value ("up" or "down"). Sometimes the "positive" entry is the only way to deduce the direction of a vertical flux (i.e., when it isn't indicated by the standard_name as in, for example, conductive_heat_flux_at_sea_ice_surface)

For certain vertical fluxes, all or nearly all groups have adopted the same convention for a vertical flux, and the direction is implied by the standard name, so the "positive" indication is not essential and has been omitted (e.g., "precipitation" the flux is invariably considered positive downward)

Reviewing the tables, it appears that a "positive" attribute needs to be defined in the following cases (because direction isn't implied by the standard_name and/or groups may adopt different conventions in practice): EhrPt: rsucsaf, rsucsafbnd, rsucsbnd Emon: fN2O, fNOx, expfe, irrLut, fahLut, fLulccAtmLut SImon: siflcondtop, siflcondbot

And the following should not have "positive" defined: Amon & CFsubhr: fco2antt, fco2fos E3hr: gpp?? Emon: fHarvestToProduct, rsdoabsorb

[matthew-mizielinski]

Should we also drop the positive from evs ("Water Evaporation Flux Where Ice Free Ocean over Sea") in Omon? I think it only makes sense if positive='up' in this case.

[taylor13]

That would be o.k. with me.

[martinjuckes]

For 01.00.21 I'll make these changes: "positive" attribute dropped: gpp, fco2antt, fco2fos, evs, fHarvestToProduct, rsdoabsorb "positive" attribute added: "up": rsucsaf, rsucsafbnd, rsucsbnd, fN2O, fNOx, fLulccAtmLut, fahLut; "down": siflcondtop, siflcondbot, expfe;

For "irrLut" (Irrigation flux including any irrigation for crops, trees, pasture, or urban lawns) I'm not sure what you would want for the "positive" attribute. I assume an irrigation flux will be from the irrigation system onto the land, but I'd imagine it could be pumped from below or gravity fed from above.

[taylor13]

irrLut increases the wetness starting at/near the surface and then diffusing down. Other water fluxes that wet the surface of the earth (usually from the atmosphere) are postive down, so I suggest positive down for irrLutt.

[martinjuckes]

OK .. but I don't think it makes much sense.