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Top‐down estimates of CO2 fluxes are typically constrained by either surface‐based or space‐based CO2 observations. Both of these measurement types have spatial and temporal gaps in observational coverage that can lead to differences in inferred fluxes. Assimilating both surface‐based and space‐based measurements concurrently in a flux inversion framework improves observational coverage and reduces sampling related artifacts. This study examines the consistency of flux constraints provided by these different observations and the potential to combine them by performing a series of 6‐year (2010–2015) CO2 flux inversions. Flux inversions are performed assimilating surface‐based measurements from the in situ and flask network, measurements from the Total Carbon Column Observing Network (TCCON), and space‐based measurements from the Greenhouse Gases Observing Satellite (GOSAT), or all three data sets combined. Combining the data sets results in more precise flux estimates for subcontinental regions relative to any of the data sets alone. Combining the data sets also improves the accuracy of the posterior fluxes, based on reduced root‐mean‐square differences between posterior flux‐simulated CO2 and aircraft‐based CO2 over midlatitude regions (0.33–0.56 ppm) in comparison to GOSAT (0.37–0.61 ppm), TCCON (0.50–0.68 ppm), or in situ and flask measurements (0.46–0.56 ppm) alone. These results suggest that surface‐based and GOSAT measurements give complementary constraints on CO2 fluxes in the northern extratropics and can be combined in flux inversions to improve constraints on regional fluxes. This stands in contrast with many earlier attempts to combine these data sets and suggests that improvements in the NASA Atmospheric CO2 Observations from Space (ACOS) retrieval algorithm have significantly improved the consistency of space‐based and surface‐based flux constraints. Key Points: Consistent flux constraints are provided by surface in situ and flask, TCCON, and GOSAT measurements of atmospheric CO2Combining data sets improves agreement between modeled and measured aircraft‐based CO2 measurementsImprovements in NASA ACOS retrieval explain improved consistency of space‐based and surface‐based CO2 [ABSTRACT FROM AUTHOR]

Five portable Bruker EM27/SUN FTIR spectrometers have been used for the accurate and precise observation of column averaged abundances of CO2 and CH4 around the megacity Berlin. In the first part of this work (Frey et al., 2015) we have presented the various measures that were undertaken to ensure that the observations are consistent between sites, accurate and precise. Here, we present the recorded time series of XCH4 and XCO2 and demonstrate that the CO2 emissions of Berlin can be clearly identified in the observations. A simple dispersion model is applied which indicates a total strength of the Berlin source of about 0.8 t CO2 s-1. In the Supplement of this work, we provide the measured dataset and auxiliary data. We hope that the model community will exploit this unique dataset for state-of-the art inversion studies of CO2 and CH4 sources in the Berlin area. [ABSTRACT FROM AUTHOR]

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) presents new opportunities for the retrieval of trace gases in the upper troposphere and lower stratosphere. The radiometric calibration of the measured signal is achieved using in-flight measurements of reference blackbody and upward-pointing "deep space" scenes. In this paper, we present techniques developed specifically to calibrate GLORIA data exploiting the instrument's imaging capability. The algorithms discussed here make use of the spatial correlation of parameters across GLORIA's detector pixels in order to mitigate the noise levels and artefacts in the calibration measurements. This is achieved by combining a priori and empirical knowledge about the instrument background radiation with noise-mitigating compression methods, specifically low-pass filtering and principal component analysis. In addition, a new software package for the processing of GLORIA data is introduced which allows us to generate calibrated spectra from raw measurements in a semi-automated data processing chain. [ABSTRACT FROM AUTHOR]

Five portable Bruker EM27/SUN FTIR spectrometers have been used for the accurate and precise observation of column averaged abundances of CO2 and CH4 around the megacity Berlin. In the first part of this work (Frey et al., 2015) we have presented the various measures that were undertaken to ensure that the observations are consistent between sites, accurate and precise. Here, we present the recorded time series of XCH4 and XCO2 and demonstrate that the CO2 emissions of Berlin can be clearly identified in the observations. A simple dispersion model is applied which indicates a total strength of the Berlin source of about 0.8 t CO2 s-1. In the Supplement of this work, we provide the measured dataset and auxiliary data. We hope that the model community will exploit this unique dataset for state-of-the art inversion studies of CO2 and CH4 sources in the Berlin area. [ABSTRACT FROM AUTHOR]

During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO 2 ) exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO 2 seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO 2 gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO 2 cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO 2 due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO 2 transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO 2 uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO 2 anomaly observed in 2018 was compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO 2 anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.