Column-averaged CO₂ concentrations in the subarctic from GOSAT retrievals and NIES transport model simulations

Author links open overlay panelD.A. Belikov ^{a b e}, A. Bril ^b, S. Maksyutov ^b, S. Oshchepkov ^b, T. Saeki ^{b 1}, H. Takagi ^b, Y. Yoshida ^b, A. Ganshin ^c, R. Zhuravlev ^c, S. Aoki ^d, T. Yokota ^b

The distribution of atmospheric carbon dioxide (CO₂) in the subarctic was investigated using the National Institute for Environmental Studies (NIES) three-dimensional transport model (TM) and retrievals from the Greenhouse gases Observing SATellite (GOSAT). Column-averaged dry air mole fractions of subarctic atmospheric CO₂ (XCO₂) from the NIES TM for four flux combinations were analyzed. Two flux datasets were optimized using only surface observations and two others were optimized using both surface and GOSAT Level 2 data. Two inverse modeling approaches using GOSAT data were compared. In the basic approach adopted in the GOSAT Level 4 product, the GOSAT observations are aggregated into monthly means over 5° ×ばつ 5° grids. In the alternative method, the model–observation misfit is estimated for each observation separately. The XCO₂ values simulated with optimized fluxes were validated against Total Carbon Column Observing Network (TCCON) ground-based high-resolution Fourier Transform Spectrometer (FTS) measurements. Optimized fluxes were applied to study XCO₂ seasonal variability over the period 2009–2010 in the Arctic and subarctic regions. The impact on CO₂ levels of emissions from enhancement of biospheric respiration induced by the high temperature and strong wildfires occurring in the summer of 2010 was analyzed. Use of GOSAT data has a substantial impact on estimates of the level of CO₂ interanual variability.