The role of OCO-3 XCO<sub>2</sub> retrievals in estimating global terrestrial net ecosystem exchanges
<p>Satellite-based column-averaged dry-air CO<span class="inline-formula"><sub>2</sub></span> mole fraction (XCO<span class="inline-formula"><sub>2</sub></span>) retrievals are frequently used to improve the estimates of terre...
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| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/867/2025/acp-25-867-2025.pdf |
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| Summary: | <p>Satellite-based column-averaged dry-air CO<span class="inline-formula"><sub>2</sub></span> mole fraction (XCO<span class="inline-formula"><sub>2</sub></span>) retrievals are frequently used to improve the estimates of terrestrial net ecosystem exchanges (NEEs). The Orbiting Carbon Observatory 3 (OCO-3) satellite, launched in May 2019, was designed to address important questions about the distribution of carbon fluxes on Earth, but its role in estimating global terrestrial NEE remains unclear. Here, using the Global Carbon Assimilation System, version 2, we investigate the impact of OCO-3 XCO<span class="inline-formula"><sub>2</sub></span> on the estimation of global NEE by assimilating the OCO-3 XCO<span class="inline-formula"><sub>2</sub></span> retrievals alone and in combination with the OCO-2 XCO<span class="inline-formula"><sub>2</sub></span> retrievals. The results show that when only the OCO-3 XCO<span class="inline-formula"><sub>2</sub></span> is assimilated (Exp_OCO3), the estimated global land sink is significantly lower than that from the OCO-2 experiment (Exp_OCO2). The estimate from the joint assimilation of OCO-3 and OCO-2 (Exp_OCO3&2) is comparable on a global scale to that of Exp_OCO2. However, there are significant regional differences. Compared to the observed global annual CO<span class="inline-formula"><sub>2</sub></span> growth rate, Exp_OCO3 has the largest bias and Exp_OCO3&2 shows the best performance. Furthermore, validation with independent CO<span class="inline-formula"><sub>2</sub></span> observations shows that the biases of Exp_OCO3 are significantly larger than those of Exp_OCO2 and Exp_OCO3&2 at middle and high latitudes. The reasons for the poor performance of assimilating OCO-3 XCO<span class="inline-formula"><sub>2</sub></span> alone include the lack of observations beyond 52° S and 52° N, the large fluctuations in the number of data, and the varied observation time. Our study indicates that assimilating OCO-3 XCO<span class="inline-formula"><sub>2</sub></span> retrievals alone leads to an underestimation of land sinks at high latitudes and that a joint assimilation of OCO-2 XCO<span class="inline-formula"><sub>2</sub></span> and the OCO-3 XCO<span class="inline-formula"><sub>2</sub></span> retrievals observed in the afternoon is required for a better estimation of global terrestrial NEE.</p> |
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| ISSN: | 1680-7316 1680-7324 |