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Evaluation of OCO‐2 X CO 2 Variability at Local and Synoptic Scales using Lidar and In Situ Observations from the ACT‐America Campaigns
Author(s) -
Bell Emily,
O'Dell Christopher W.,
Davis Kenneth J.,
Campbell Joel,
Browell Edward,
Scott Denning A.,
Dobler Jeremy,
Erxleben Wayne,
Fan TaiFang,
Kooi Susan,
Lin Bing,
Pal Sandip,
Weir Brad
Publication year - 2020
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2019jd031400
Subject(s) - lidar , environmental science , latitude , remote sensing , observatory , middle latitudes , atmospheric sciences , sky , atmospheric sounding , depth sounding , ranging , meteorology , climatology , geology , geodesy , geography , physics , cartography , astrophysics
With nearly 1 million observations of column‐mean carbon dioxide concentration (XCO 2) per day, the Orbiting Carbon Observatory 2 (OCO‐2) presents exciting possibilities for monitoring the global carbon cycle, including the detection of subcontinental column CO 2 variations. While the OCO‐2 data set has been shown to achieve target precision and accuracy on a single‐sounding level, the validation of XCO 2spatial gradients on subcontinental scales remains challenging. In this work, we investigate the use of an integrated path differential absorption (IPDA) lidar for evaluation of OCO‐2 observations via NASA's Atmospheric Carbon and Transport (ACT)‐America project. The project has completed eight clear‐sky underflights of OCO‐2 with the Multifunctional Fiber Laser Lidar (MFLL)—along with a suite of in situ instruments—giving a precisely colocated, high‐resolution validation data set spanning nearly 3,800 km across four seasons. We explore the challenges and opportunities involved in comparing the MFLL and OCO‐2 XCO 2data sets and evaluate their agreement on synoptic and local scales. We find that OCO‐2 synoptic‐scale gradients generally agree with those derived from the lidar, typically to ±0.1 ppm per degree latitude for gradients ranging in strength from 0 to 1 ppm per degree latitude. CO 2 reanalysis products also typically agree to ±0.25 ppm per degree when compared with an in situ‐informed CO 2 “curtain.” Real XCO 2features at local scales, however, remain challenging to observe and validate from space, with correlation coefficients typically below 0.35 between OCO‐2 and the MFLL. Even so, ACT‐America data have helped investigate interesting local XCO 2patterns and identify systematic spurious cloud‐related features in the OCO‐2 data set.