Revise "ensure carbon balance" step for partitioned carbon fluxes

[gremau]

Should we fix or remove the "ensure carbon balance" step for partitioned carbon fluxes?

The UNM_ameriflux_filemaker_TWH script has a step in which the GPP and RE values produced by the partitioning tool are adjusted to balance the carbon budget (GPP - RE = NEE). This step:

1. Recalculates GPP as RE (modeled) - NEE (observed).
2. Sets negative GPP values to zero and adds these to modeled RE.
3. Removes nighttime positive GPP values and reduces RE by the same amount?

I'm pretty sure that this results in a bias. The GPP and RE values provided by the Reichstein partitioner should already be balanced, so subtracting negative GPP and adding it to RE makes both of these fluxes bigger. I'm not sure what the effect of the nighttime removal is yet.

[gremau]

For now I am including GPP, RE, and NEE without this ensure carbon balance step as columns in new Ameriflux files. Fluxes that have been altered have column headers ending with _ecb or _oldecb.

We should look at how these different versions of partitioned fluxes compare.

see commit 8f11c53