## 2 Materials and Methods
### OCO-2 SIF Data and Flux Tower Data
\begin{table}
\begin{tabular}{l l c c c c c} \hline \hline
**Site ID** & **Type** & **Lon (\({}^{\circ}\))** & **Lat (\({}^{\circ}\))** & **Year** & **Max (LC)** & **PIs** \\ \hline CA-SCC & ENF & \(-121.30\) & 61.31 & 2014–2016 & 55 & [PERSON] \\ CA-TP1 & ENF & \(-80.56\) & 42.66 & 2014–2017 & 75 & M. [PERSON] \\ CA-TP3 & ENF & \(-80.35\) & 42.71 & 2014–2017 & 73 & [PERSON] \\ CA-TP4 & ENF & \(-80.36\) & 42.71 & 2014–2017 & 73 & [PERSON] \\ CA-TPD & DBF & \(-80.56\) & 42.64 & 2014–2015 & 73 & [PERSON] \\ US-EML & OSH & \(-149.25\) & 63.88 & 2014–2018 & 46 & [PERSON] \\ US-KFS & GRA & \(-95.20\) & 39.06 & 2014–2017 & 58 & [PERSON] \\ US-KLS & GRA & \(-97.59\) & 38.77 & 2014–2017 & 59 & [PERSON] \\ US-Los & WET & \(-89.98\) & 46.08 & 2014–2019 & 87 & [PERSON] \\ US-PFa & MFs & \(-90.27\) & 45.95 & 2014–2019 & 83 & [PERSON] \\ US-PHM & WET & \(-70.83\) & 42.74 & 2014–2018 & 47 & [PERSON] \\ US-Ro2 & CRO & \(-93.09\) & 44.73 & 2014–2016 & 63 & [PERSON] \\ US-Ro4 & GRA & \(-93.07\) & 44.68 & 2014–2019 & 73 & [PERSON] \\ US-Syv & MF & \(-89.35\) & 46.24 & 2014–2018 & 89 & [PERSON] \\ US-Tw1 & WET Weltands & \(-121.65\) & 38.11 & 2014–2018 & 52 & [PERSON] \\ US-Tw3 & CRO & \(-121.65\) & 38.12 & 2014–2018 & 52 & [PERSON] \\ US-Tw4 & CRO Wetlands & \(-121.64\) & 38.10 & 2014–2017 & 53 & [PERSON] \\ US-Twt & CRO & \(-121.65\) & 38.11 & 2014–2017 & 51 & [PERSON] \\ US-UMd & DBF & \(-84.70\) & 45.56 & 2014–2019 & 44 & [PERSON] \\ US-WCr & DBF & \(-90.08\) & 45.81 & 2014–2018 & 78 & [PERSON] \\ US-ALQ & WET & \(-89.61\) & 46.03 & 2015–2019 & 86 & [PERSON] \\ US-GLE & ENF & \(-106.24\) & 41.37 & 2014–2018 & 71 & [PERSON] \\ US-RIs & CSH & \(-116.74\) & 43.14 & 2014–2018 & 88 & [PERSON] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Site descriptions of the flux towers, including the site ID, vegetation type, longitude, latitude, year the data was used, maximum land cover (Max(LC)), and flux tower principal investigators (PIs) of each flux tower (ENF: evergreen needleleaf forests, DBF: deciduous broadleaf forests, OSH: open shrulands, GRA: grasslands, CSH: closed shrulands, MF: mixed forests, WET: permeland wetlands, CRO: croplands). Figure 1: Locations and attributes of selected eddy covariance (EC) sites. The five-pointed star indicates the location of the study area, and the base map was created in Arcgis using MCD12Q1 data. transforming original measurements from individual sensors to ecologically or micro-meteorologically meaningful quantities. The EC data analysis procedure includes quality marks, filtering criteria, and gap-filling. These methods can reduce the bias and generate high-quality and standardized datasets. Among them, missing data are reported using -9999 as the replacing value. The L2 Flux data obtained from AmeriFlux include the net ecosystem exchange (NEE), total ecosystem respiration (Re), photosynthetically available radiation (PAR), wind speed, heat, water vapor, and temperature (T), with a time resolution of half an hour or an hour [33; 34]. The NEE measurements are routinely partitioned into GPP and ecosystem respiration using a high-time partitioning method [35]. NEE is considered to be the primary source of observed interannual variability in atmospheric accumulation of carbon dioxide. Reis a process of oxidative decomposition of vegetation. For vegetation, NEE is governed by GPP and Re [36]. In this study, we used the flux tower GPP data spanning from 2014 to 2018 (Table 2). There are eight biome types around the 23 flux towers: mixed forest (two sites), permanent wetlands (five sites), evergreen needleleaf forests (five sites), croplands (three sites), deciduous broadleaf forests (three sites), grasslands (three sites), open shrublands (one site), and closed shrublands (one site). For US-GLE and US-RIs, we used the night-time partitioning method to process the original GPP products [37]. The daytime ecosystem respiration \(\mathrm{Re}_{\mathrm{day}}\) was deduced from the relationship between Renight (equal to NEE exchange of the net ecosystem at night) and temperature.