We usually understand the interannual variability (gC/Year) of carbon fluxes (i.e. NEE,GPP) on an interannual scale. The inter-annual variability of carbon fluxes can be expressed by a simple method such as annual values minus multi-year averages (annual anomalies); or it can be decomposed by spectral analyses into components on different time scales, thus extracting the components with a period greater than 1 year as inter-annual variability.

So, I take a daily-resolved carbon flux time series and perform a singularity spectral analysis, and add up all components with periods greater than 1 year (excluding the trend) to get the interannual variability, how does this differ from the simple method mentioned above? Because it is logical that the units of the interannual variation component obtained from spectral decomposition should be (gC/day).