Inquiry Regarding Possible Sign Issue in NEP Data for CMIP6 Simulation

[krwlng]

I recently downloaded your CMIP6 data from the ESGF and have been analyzing the net ecosystem productivity (NEP) data from the historical, hist-piNTCF, ssp370, and ssp370-lowNTCF experiments（like:CMIP6.ScenarioMIP.NCAR.CESM2-WACCM.ssp370.r3i1p1f1.Emon.nep.gn）.
However, after comparing the NEP patterns in these simulations with other models and FLUXCOM data, I noticed that there may be an issue with the sign of the data. The patterns seem to be inverted when compared to other sources. I wanted to reach out to seek your insight on whether this could indeed be a sign error or if there is another explanation for the discrepancy.

I would greatly appreciate your help and any clarification you can provide.

Thank you for your time, and I look forward to your response.
View attachment 5982

 

[oleson]

Our NEE variable is positive for a source of carbon (positive upward), while the CMIP6 variable nep looks like it is supposed to be positive for a sink of carbon (positive downward). So maybe we should have reported -NEE for submission to CMIP6.

 

[krwlng]

Thank you for your answer.