## 4 Discussion
### Possible Impact of LST on Seasonal Variation of XCO\({}_{2}\) on Tropical Land  
Abnormal results are shown over some regions (e.g., CnI, GeA, FsA, and CeB) in the tropical area (30\({}^{\circ}\)N-30\({}^{\circ}\)S), where large XCO\({}_{2}\) SCA can be seen from both GM-XCO\({}_{2}\) and CT-XCO\({}_{2}\), even the former is slightly larger than the latter, and high PCCs exist for NDVI and EVI, as shown in Figure 5. These regions are covered by vegetation, such as grass, forest, and crop mixed with bare land, where the interaction between CO\({}_{2}\) uptake and release from vegetation and soil respiration likely has impact on the seasonal cycle of CO\({}_{2}\). As indicated from previous studies on CO\({}_{2}\) emission from soils, the soil respiration in the tropic and subtropical areas is much larger than high latitudes [(72; 73)] and, therefore, likely has non-negligible impact on the XCO\({}_{2}\) seasonal pattern. LST, a remotely sensed terrestrial parameter, is effective in depicting the land surface temperature distribution at the global scale with long time-series. LST has been used as one of the critical parameters in estimating seasonal soil respiration over forests in the Midwest USA [(74)]. Higher surface temperature is associated with stronger soil and plant respiration rates, but also possibly enhanced photosynthesis [(33)]. However, the net effect of increasing LST in the tropical areas has been shown to result in increasing atmospheric CO\({}_{2}\)[(34)]. In tropical areas, soil and plant respiration contribute a very important part to the seasonal variation of atmospheric CO\({}_{2}\). The tropical carbon storage is very vulnerable to temperature change [(34)]. Therefore, an investigation of the correlation between XCO\({}_{2}\) from satellite observation and LST can  
Figure 10: XCO\({}_{2}\) from GOSAT-ACOS retrievals (black) and CarbonTracker (red) from June 2009 to May 2014 over mid- and high latitude of North Hemisphere. XCO\({}_{2}\) over latitude bands between 50\({}^{\circ}\)–60\({}^{\circ}\)N in (**a**) Eurasia and (**c**) North-America land regions, and between 40\({}^{\circ}\)–50\({}^{\circ}\)N for the same two regions in (**b**,**d**), respectively. indicate the possible impact of LST on the seasonal variation of XCO\({}_{2}\) in the tropical areas, where the carbon storage has been shown to be sensitive to future temperature variabilities [34]. Figure 11 shows the correlation between seasonal XCO\({}_{2}\) and LST variation over the tropical areas. The results interestingly show the seasonal cycle of XCO\({}_{2}\) is highly positive correlated with seasonal variation of LST, which is opposite to the negative correlation with NDVI, as shown in Figure 5a. Especially, over Central Africa and Southern Asia, the PCC is generally larger than 0.70, indicating the possible impact of LST on the seasonal cycle of XCO\({}_{2}\). Additionally, Figure 12 shows the detailed time series of the selected five regions of interest shown in Figure 1. The seasonal variation of XCO\({}_{2}\) is generally consistent with the variation of LST; especially, the variation around peak XCO\({}_{2}\) matches well with the variation around peak LST. Coincident with the maximum LST, terrestrial respiration and weakened photosynthesis could contribute to the maximum XCO\({}_{2}\). As is shown in [PERSON] et al. [75], XCO\({}_{2}\) showed a positive correlation with temperature, and soil respiration and biomass burning may be an important terrestrial carbon source contributing to the CO\({}_{2}\) concentration in India. To further investigate the possible influence from anthropogenic emissions on the SCA anomaly, we found that the fossil fuel emission from bottom-up estimation in CnI [76; 77] (shown in Figure S4) does show a seasonal cycle, which, however, has much less consistency than LST with XCO\({}_{2}\) around the peaks of the XCO\({}_{2}\) cycle.