Abstract
The global carbon cycle research requires precise and sufficient observations of the column-averaged dry-air mole fraction of CO 2 (XCO 2 ) in addition to conventional surface mole fraction observations. In addition, assessing the consistency of multi-satellite data are crucial for joint utilization to better infer information about CO 2 sources and sinks. In this work, we evaluate the consistency of long-term XCO 2 retrievals from the Greenhouse Gases Observing Satellite (GOSAT), Orbiting Carbon Observatory 2 (OCO-2) in comparison with Total Carbon Column Observing Network (TCCON) and the 3D model of CO 2 mole fractions data from CarbonTracker 2017 (CT2017). We create a consistent joint dataset and compare it with the long-term model data to assess their abilities to characterize the carbon cycle climate. The results show that, although slight increasing differences are found between the GOSAT and TCCON XCO 2 in the northern temperate latitudes, the GOSAT and OCO-2 XCO 2 retrievals agree well in general, with a mean bias ± standard deviation of differences of 0.21 ± 1.3 ppm. The differences are almost within ±2 ppm and are independent of time, indicating that they are well calibrated. The differences between OCO-2 and CT2017 XCO 2 are much larger than those between GOSAT and CT XCO 2 , which can be attributed to the significantly different spatial representatives of OCO-2 and the CT-transport model 5 (TM5). The time series of the combined OCO-2/GOSAT dataset and the modeled XCO 2 agree well, and both can characterize significantly increasing atmospheric CO 2 under the impact of a large El Niño during 2015 and 2016. The trend calculated from the dataset using the seasonal Kendall (S-K) method indicates that atmospheric CO 2 is increasing by 2–2.6 ppm per year.
Highlights
The atmospheric carbon dioxide (CO2 ) concentration has increased by 40% since pre-industrial times, which has mainly been caused by emissions from fossil fuels and land use changes [1]
The results show that, slight increasing differences are found between the Gases Observing Satellite (GOSAT) and Total Carbon Column Observing Network (TCCON) XCO2 in the northern temperate latitudes, the GOSAT and Orbiting Carbon Observatory 2 (OCO-2) XCO2 retrievals agree well in general, with a mean bias ± standard deviation of differences of 0.21 ± 1.3 ppm
Our objective is to explore the potential of XCO2 retrievals from GOSAT and OCO-2 to be jointly used for CO2 surface flux inversion analysis
Summary
The atmospheric carbon dioxide (CO2 ) concentration has increased by 40% since pre-industrial times, which has mainly been caused by emissions from fossil fuels and land use changes [1]. Only less than half of the anthropogenic CO2 emissions has remained airborne and has become the main driver of climate change, and the remainder is currently being absorbed by the oceans and taken up by the terrestrial biosphere [1,2]. These processes are far from well understood. There are two common approaches to estimating CO2 sources and sinks on land: bottom-up and top-down methods. Both methods have limitations, and large uncertainties still exist
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