Spatial distributions of XCO2 seasonal cycle amplitude and phase over northern high latitude regions

• Main Authors: Jacobs, Nicole, Simpson, William R., Graham, Kelly A., Holmes, Christopher, Hase, Frank, Blumenstock, Thomas, Tu, Qiansi, Frey, Matthias, Dubey, Manvendra K., Parker, Harrison A., Wunch, Debra, Kivi, Rigel, Heikkinen, Pauli, Nothold, Justus, Petri, Christof, Warneke, Thorsten
• Format: Text
• Language: English
• Published: 2021
• Subjects: Tundra
• Online Access: https://doi.org/10.5194/acp-2021-185; https://acp.copernicus.org/preprints/acp-2021-185/

Satellite-based observations of atmospheric carbon dioxide (CO 2 ) provide measurements in remote regions, such as the biologically sensitive but under sampled northern high latitudes, and are progressing toward true global data coverage. Recent improvements in satellite retrievals of total column-averaged dry air mole fractions of CO 2 ( X CO 2 ) from the NASA Orbiting Carbon Observatory 2 (OCO-2) have allowed for unprecedented data coverage of northern high latitude regions, while maintaining acceptable accuracy and consistency relative to ground-based observations, and finally providing sufficient data in spring and autumn for analysis of the satellite-observed X CO 2 seasonal cycles across a majority of terrestrial northern high latitude regions. Here, we present an analysis of X CO 2 seasonal cycles calculated from OCO-2 data for temperate, boreal, and tundra regions, subdivided into 5° latitude by 20° longitude zones. We quantify the seasonal cycle amplitudes (SCA) and the annual half drawdown day (HDD). OCO-2 SCA is in good agreement with ground-based observations at five high latitude sites and OCO-2 SCA show very close agreement with SCA calculated for model estimates of X CO 2 from the Copernicus Atmospheric Monitoring Services (CAMS) global inversion-optimized greenhouse gas flux model v19r1. Model estimates of X CO 2 from the GEOS-Chem CO 2 simulation version 12.7.2 with underlying biospheric fluxes from CarbonTracker2019 yield SCA of larger magnitude and spread over a larger range than those from CAMS and OCO-2; however, GEOS-Chem SCA still exhibit a very similar spatial distribution across northern high latitude regions to that from CAMS and OCO-2. Zones in the Asian Boreal Forest were found to have exceptionally large SCA and early HDD, and both OCO-2 data and model estimates yield a distinct longitudinal gradient of increasing SCA from west to east across the Eurasian continent. Longitudinal gradients in both SCA and HDD are at least as pronounced as meridional gradients (with respect to latitude), suggesting an essential role for global atmospheric transport patterns in defining X CO 2 seasonality. GEOS-Chem surface contact tracers show that the largest X CO 2 SCA occurs in areas with the greatest contact with land surfaces, integrated over 15–30 days. The correlation of X CO 2 SCA with these land contact tracers are stronger than the correlation of X CO 2 SCA with the SCA of CO 2 fluxes within each 5° latitude by 20° longitude zone. This indicates that accumulation of terrestrial CO 2 flux during atmospheric transport is a major driver of regional variations in X CO 2 SCA.