Near Real Time Data Processing In ICOS RI

This paper describes the implementation of (near) real-time (NRT) data processing in the recently launched European environmental research infrastructure ICOS. NRT applications include handling of raw sensor data (including safe storage and quality control), processing and evaluation of greenhouse gas mixing ratios and exchange fluxes, and the provision of data to the RI’s user communities

Technical note: The CAMS greenhouse gas reanalysis from 2003 to 2020

The Copernicus Atmosphere Monitoring Service (CAMS) has recently produced a greenhouse gas reanalysis (version egg4) that covers almost 2 decades from 2003 to 2020 and which will be extended in the future. This reanalysis dataset includes carbon dioxide (CO2) and methane (CH4). The reanalysis procedure combines model data with satellite data into a globally complete and consistent dataset using the European Centre for Medium-Range Weather Forecasts' Integrated Forecasting System (IFS). This dataset has been carefully evaluated against independent observations to ensure validity and to point out deficiencies to the user. The greenhouse gas reanalysis can be used to examine the impact of atmospheric greenhouse gas concentrations on climate change (such as global and regional climate radiative forcing), assess intercontinental transport, and serve as boundary conditions for regional simulations, among other applications and scientific uses. The caveats associated with changes in assimilated observations and fixed underlying emissions are highlighted, as is their impact on the estimation of trends and annual growth rates of these long-lived greenhouse gases.</p

The effect of inhomogeneities in the lower atmosphere on coordinates determined from GPS measurements

International audienceWe analyze the effect of small-scale refractivity inhomogeneities, associated with the water vapor field in the lower troposphere, on GPS station height determination. Numerical simulations of GPS signals have been performed in several model atmospheres and inverted using a continuous satellite distribution approach and Bernese GPS software. Results show cm-level errors in station heights, when ZTD parameters are estimated with standard mapping functions. The errors are due to mismodeling of the refractivity distribution in the troposphere. A means to calibrate properly humidity inhomogeneities is to sense the wet path delay with a water vapor radiometer (WVR) or a lidar. Numerical simulations based on radiosoundings show that wet path delay retrieved with WVRs can exhibit up to ∼10 mm biases, due to temperature inversions and high humidity contents. Lidars show higher accuracy, even when only the water vapor concentration is measured (neglecting the effect of temperature inversions). In order to achieve the highest accuracy from GPS, we propose to combine a Raman lidar data for external wet path delay calibration and estimate the remaining path delays during GPS data analysis. Since the latter is quasi-homogeneous, once the highly inhomogeneous humidity component is removed, this should indeed improve the positioning accuracy. Numerical weather prediction (NWP) models might also be used to replace standard mapping functions, especially to estimate the hydrostatic path delay component

Automatic processing of atmospheric CO₂ and CH₄ mole fractions at the ICOS Atmosphere Thematic Centre

The Integrated Carbon Observation System Atmosphere Thematic Centre (ICOS ATC) automatically processes atmospheric greenhouse gases mole fractions of data coming from sites of the ICOS network. Daily transferred raw data files are automatically processed and archived. Data are stored in the ICOS atmospheric database, the backbone of the system, which has been developed with an emphasis on the traceability of the data processing. Many data products, updated daily, explore the data through different angles to support the quality control of the dataset performed by the principal operators in charge of the instruments. The automatic processing includes calibration and water vapor corrections as described in the paper. The mole fractions calculated in near-real time (NRT) are automatically revaluated as soon as a new instrument calibration is processed or when the station supervisors perform quality control. By analyzing data from 11 sites, we determined that the average calibration corrections are equal to 1.7 ± 0.3 µmol mol−1 for CO2 and 2.8 ± 3 nmol mol−1 for CH4. These biases are important to correct to avoid artificial gradients between stations that could lead to error in flux estimates when using atmospheric inversion techniques. We also calculated that the average drift between two successive calibrations separated by 15 days amounts to ±0.05 µmol mol−1 and ±0.7 nmol mol−1 for CO2 and CH4, respectively. Outliers are generally due to errors in the instrument configuration and can be readily detected thanks to the data products provided by the ATC. Several developments are still ongoing to improve the processing, including automated spike detection and calculation of time-varying uncertainties

Raman lidar for external GPS path delay calibration devoted to high accuracy height determination

International audienc

Study of external path delay correction techniques for high accuracy height determination with GPS

International audienceFor specific applications such as permanent GPS network calibration and national leveling network surveying, a vertical accuracy of ∼1 mm for observing durations of a few hours to a few days at maximum in 10–100-km baselines would be required. To achieve a 1-mm accuracy in height determinations with differential-GPS measurements, path delay must be corrected with an accuracy of ∼0.3 mm. This level of accuracy is not achievable with standard GPS data analysis procedures. External correction from a water vapor remote sensing technique is therefore necessary. Microwave radiometers, which have been most extensively used for this purpose, solar spectrometers, DIAL and Raman lidars are considered in this paper. The principle and performance of these techniques is reviewed in the context of wet path delay retrieving. Namely, we evaluate the errors arising during the conversion of raw measurements to wet path delay, using retrieval coefficients or standard profiles. It is shown that changes in temperature profiles can produce errors of up to 1 cm in wet path delay with microwave radiometers. Similarly, mismodeled temperature profiles can produce errors of 2–3 mm in wet path delay with DIAL and Raman lidars. Raman lidar offers the possibility to retrieve the temperature profile from total air density. Assuming that absolute concentrations of water vapor and dry gases can be retrieved, the accuracy would be unbiased. In addition, Raman lidar would also allow for the correction of hydrostatic path delay without requiring the use of mapping functions. This might reduce the residual errors due to horizontal pressure and temperature gradients. This technique will therefore be investigated in more details in a future study

GPS water vapor project associated to the ESCOMPTE programme: description and first results of the field experiment

International audienc

GPS water vapor project associated to the ESCOMPTE programme: description and first results of the field experiment

International audienc

Variation of CO₂ mole fraction in the lower free troposphere, in the boundary layer and at the surface

Eight years of occasional flask air sampling and 3 years of frequent in situ measurements of carbon dioxide (CO₂) vertical profiles on board of a small aircraft, over a tall tower greenhouse gases monitoring site in Hungary are used for the analysis of the variations of vertical profile of CO₂ mole fraction. Using the airborne vertical profiles and the measurements along the 115 m tall tower it is shown that the measurements at the top of the tower estimate the mean boundary layer CO₂ mole fraction during the mid-afternoon fairly well, with an underestimation of 0.27–0.85 μmol mol⁻¹ in summer, and an overestimation of 0.66–1.83 μmol mol⁻¹ in winter. The seasonal cycle of CO₂ mole fraction is damped with elevation. While the amplitude of the seasonal cycle is 28.5 μmol mol⁻¹ at 10 m above the ground, it is only 10.7 μmol mol⁻¹ in the layer of 2500–3000 m corresponding to the lower free atmosphere above the well-mixed boundary layer. The maximum mole fraction in the layer of 2500–3000 m can be observed around 25 March on average, two weeks ahead of that of the marine boundary layer reference (GLOBALVIEW). By contrast, close to the ground, the maximum CO₂ mole fraction is observed late December, early January. The specific seasonal behavior is attributed to the climatology of vertical mixing of the atmosphere in the Carpathian Basin

GPS water vapor project associated to the ESCOMPTE programme: description and first results of the field experiment

International audienc