New approach to evaluate satellite-derived XCO.sub.2 over oceans by integrating ship and aircraft observations.

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From: Atmospheric Chemistry and Physics(Vol. 21, Issue 10)
Publisher: Copernicus GmbH
Document Type: Brief article
Length: 406 words

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Abstract :

Satellite observations provide spatially resolved global estimates of column-averaged mixing ratios of CO.sub.2 (XCO.sub.2) over the Earth's surface. The accuracy of these datasets can be validated against reliable standards in some areas, but other areas remain inaccessible. To date, limited reference data over oceans hinder successful uncertainty quantification or bias correction efforts and preclude reliable conclusions about changes in the carbon cycle in some regions. Here, we propose a new approach to analyze and evaluate seasonal, interannual, and latitudinal variations of XCO.sub.2 over oceans by integrating cargo-ship (Ship Of Opportunity - SOOP) and commercial aircraft (Comprehensive Observation Network for Trace gases by Airliner - CONTRAIL) observations with the aid of state-of-the art atmospheric chemistry-transport model calculations. The consistency of the "observation-based column-averaged CO.sub.2 " dataset (obs. XCO.sub.2) with satellite estimates was analyzed over the western Pacific between 2014 and 2017, and its utility as a reference dataset evaluated. Our results demonstrate that the new dataset accurately captures seasonal and interannual variations of CO.sub.2 . Retrievals of XCO.sub.2 over the ocean from GOSAT (Greenhouse Gases Observing Satellite: National Institute for Environmental Studies - NIES v02.75; Atmospheric CO.sub.2 Observation from Space - ACOS v7.3) and OCO-2 (Orbiting Carbon Observatory, v9r) observations show a negative bias of about 1 part per million (ppm) in northern midlatitudes, which was attributed to measurement uncertainties of the satellite observations. The NIES retrieval had higher consistency with obs. XCO.sub.2 at midlatitudes as compared to the other retrievals. At low latitudes, it shows many fewer valid data and high scatter, such that ACOS and OCO-2 appear to provide a better representation of the carbon cycle. At different times, the seasonal cycles of all three retrievals show positive phase shifts of 1 month relative to the observation-based data. The study indicates that even if the retrievals complement each other, remaining uncertainties limit the accurate interpretation of spatiotemporal changes in CO.sub.2 fluxes. A continuous long-term XCO.sub.2 dataset with wide latitudinal coverage based on the new approach has great potential as a robust reference dataset for XCO.sub.2 and can help to better understand changes in the carbon cycle in response to climate change using satellite observations.

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Gale Document Number: GALE|A663442606