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See detailTen years of atmospheric methane from ground-based NDACC FTIR observations
Bader, Whitney ULg; Bovy, Benoît ULg; Conway, S. et al

in Atmospheric Chemistry & Physics Discussions (2016), 2016

Changes of atmospheric methane (CH4) since 2005 have been evaluated using Fourier Transform Infrared (FTIR) solar observations performed at ten ground-based sites, all members of the Network for Detection ... [more ▼]

Changes of atmospheric methane (CH4) since 2005 have been evaluated using Fourier Transform Infrared (FTIR) solar observations performed at ten ground-based sites, all members of the Network for Detection of Atmospheric Composition Change (NDACC). From this, we find an increase of atmospheric methane total columns that amounts to 0.31 ± 0.03 % year-1 (2-sigma level of uncertainty) for the 2005–2014 period. Comparisons with in situ methane measurements at both local and global scales show good agreement. We used the GEOS-Chem Chemical Transport Model tagged simulation that accounts for the contribution of each emission source and one sink in the total methane, simulated over the 2005–2012 time period and based on emissions inventories and transport. After regridding according to NDACC vertical layering using a conservative regridding scheme and smoothing by convolving with respective FTIR seasonal averaging kernels, the GEOS-Chem simulation shows an increase of atmospheric methane of 0.35 ± 0.03 % year-1 between 2005 and 2012, which is in agreement with NDACC measurements over the same time period (0.30 ± 0.04 % year-1, averaged over ten stations). Analysis of the GEOS-Chem tagged simulation allows us to quantify the contribution of each tracer to the global methane change since 2005. We find that natural sources such as wetlands and biomass burning contribute to the inter-annual variability of methane. However, anthropogenic emissions such as coal mining, and gas and oil transport and exploration, which are mainly emitted in the Northern Hemisphere and act as secondary contributors to the global budget of methane, have played a major role in the increase of atmospheric methane observed since 2005. Based on the GEOS-Chem tagged simulation, we discuss possible cause(s) for the increase of methane since 2005, which is still unexplained. [less ▲]

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See detailRemote sensing of the atmospheric composition in the infrared spectral region within the Network for the Detection of Atmospheric Composition Change (NDACC) and the Total Carbon Column Observing Network (TCCON)
Notholt, J; Blumenstock, T; Deutscher, N et al

Conference (2015, May 12)

Remote sensing has been established as a powerful tool in atmospheric research. Throughout the last decades satellite and ground-based remote sensing instruments and methods have been developed to sample ... [more ▼]

Remote sensing has been established as a powerful tool in atmospheric research. Throughout the last decades satellite and ground-based remote sensing instruments and methods have been developed to sample the atmosphere from the microwave to the UV/Vis. The international ground based networks NDACC-IR and TCCON are based on solar absorption spectrometry in the infrared. Both networks consist of more than 30 observations sites around the globe, from the high Arctic through mid-latitudes and the tropics to the southern hemisphere and Antarctica. NDACC concentrates on stratospheric observations in relation to ozone chemistry, in many instances, information on the vertical distribution of the target species is determined. Measured trace gases include O3, HCl, HF, HNO3, ClONO2 and many others. In addition, the tropospheric composition is studied by measuring anthropogenic and biogenic species including HCN, OCS, H2O, CO, CH2O, C2H6, and C2H2. The aim of TCCON is to acquire accurate and precise column-averaged abundances of CO2, CH4, N2O, i.e. atmospheric trace gases which have a very small natural variability. TCCON measurements are linked to WMO calibration scales by comparisons with co-incident in situ profiles measured from aircraft or balloon. Results from both networks have been used in many studies in relation to stratospheric ozone chemistry, air-pollution, and with regard to the carbon-cycle. Long-term series are necessary for trend analysis, gaining insight into annual and longer term variability and placing into context shorter term process studies. Due to the similar observation geometry, the ground-based observations are optimally suitable for satellite and model validation and form an essential part of many satellite projects. They also play an important role in the validation of the Copernicus Atmospheric Monitoring Service. In our contribution we will give an overview on the current status of both networks, ongoing efforts to improve network coverage, precision and accuracy, and several examples of scientific highlights. [less ▲]

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See detailTrends of ozone total columns and vertical distribution from FTIR observations at eight NDACC stations around the globe
Vigouroux, C; Blumenstock, T; Coffey, M et al

in Atmospheric Chemistry and Physics (2015), 15

Ground-based Fourier transform infrared (FTIR) measurements of solar absorption spectra can provide ozone total columns with a precision of 2 % but also independent partial column amounts in about four ... [more ▼]

Ground-based Fourier transform infrared (FTIR) measurements of solar absorption spectra can provide ozone total columns with a precision of 2 % but also independent partial column amounts in about four vertical layers, one in the troposphere and three in the stratosphere up to about 45 km, with a precision of 5–6 %. We use eight of the Network for the Detection of Atmospheric Composition Change (NDACC) stations having a long-term time series of FTIR ozone measurements to study the total and vertical ozone trends and variability, namely, Ny-Ålesund (79ºN), Thule (77ºN), Kiruna (68ºN), Harestua (60ºN), Jungfraujoch (47ºN), Izaña (28ºN), Wollongong (34ºS) and Lauder (45ºS). The length of the FTIR time series varies by station but is typically from about 1995 to present. We applied to the monthly means of the ozone total and four partial columns a stepwise multiple regression model including the following proxies: solar cycle, quasi-biennial oscillation (QBO), El Niño–Southern Oscillation (ENSO), Arctic and Antarctic Oscillation (AO/AAO), tropopause pressure (TP), equivalent latitude (EL), Eliassen–Palm flux (EPF), and volume of polar stratospheric clouds (VPSC). At the Arctic stations, the trends are found mostly negative in the troposphere and lower stratosphere, very mixed in the middle stratosphere, positive in the upper stratosphere due to a large increase in the 1995–2003 period, and non-significant when considering the total columns. The trends for mid-latitude and subtropical stations are all non-significant, except at Lauder in the troposphere and upper stratosphere and at Wollongong for the total columns and the lower and middle stratospheric columns where they are found positive. At Jungfraujoch, the upper stratospheric trend is close to significance (+0.9 ± 1.0 %/decade). Therefore, some signs of the onset of ozone mid-latitude recovery are observed only in the Southern Hemisphere, while a few more years seem to be needed to observe it at the northern mid-latitude station. [less ▲]

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See detailValidation of IASI FORLI carbon monoxide retrievals using FTIR data from NDACC
Kerzenmacher, T; Dils, B; Kumps, N et al

in Atmospheric Measurement Techniques (2012), 5

Carbon monoxide (CO) is retrieved daily and globally from space-borne IASI radiance spectra using the Fast Optimal Retrievals on Layers for IASI (FORLI) software developed at the Université Libre de ... [more ▼]

Carbon monoxide (CO) is retrieved daily and globally from space-borne IASI radiance spectra using the Fast Optimal Retrievals on Layers for IASI (FORLI) software developed at the Université Libre de Bruxelles (ULB). The IASI CO total column product for 2008 from the most recent FORLI retrieval version (20100815) is evaluated using correlative CO profile products retrieved from groundbased solar absorption Fourier transform infrared (FTIR) observations at the following FTIR spectrometer sites from the Network for the Detection of Atmospheric Composition Change (NDACC): Ny-Alesund, Kiruna, Bremen, Jungfraujoch, Izana and Wollongong. In order to have good statistics for the comparisons, we included all IASI data from the same day, within a 100 km radius around the ground-based stations. The individual ground-based data were adjusted to the lowest altitude of the co-located IASI CO profiles. To account for the different vertical resolutions and sensitivities of the ground-based and satellite measurements, the averaging kernels associated with the various retrieved products have been used to properly smooth coincident data products. It has been found that the IASI CO total column products compare well on average with the co-located ground-based FTIR total columns at the selected NDACC sites and that there is no significant bias for the mean values at all stations. [less ▲]

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See detailProcess-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopologues: 1. Comparison between models and observations
Risi, C; Noone, D; Worden, J et al

in Journal of Geophysical Research (2012), 117(D5), 05303

N2 - The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in ... [more ▼]

N2 - The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in atmospheric general circulation models (GCMs). We analyze a large number of isotopic data sets (four satellite, sixteen ground-based remote-sensing, five surface in situ and three aircraft data sets) that are sensitive to different altitudes throughout the free troposphere. Despite significant differences between data sets, we identify some observed HDO/H2O characteristics that are robust across data sets and that can be used to evaluate models. We evaluate the isotopic GCM LMDZ, accounting for the effects of spatiotemporal sampling and instrument sensitivity. We find that LMDZ reproduces the spatial patterns in the lower and mid troposphere remarkably well. However, it underestimates the amplitude of seasonal variations in isotopic composition at all levels in the subtropics and in midlatitudes, and this bias is consistent across all data sets. LMDZ also underestimates the observed meridional isotopic gradient and the contrast between dry and convective tropical regions compared to satellite data sets. Comparison with six other isotope-enabled GCMs from the SWING2 project shows that biases exhibited by LMDZ are common to all models. The SWING2 GCMs show a very large spread in isotopic behavior that is not obviously related to that of humidity, suggesting water vapor isotopic measurements could be used to expose model shortcomings. In a companion paper, the isotopic differences between models are interpreted in terms of biases in the representation of processes controlling humidity. [less ▲]

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