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See detailThree-dimensional analysis of oceanographic data with the software DIVA
Troupin, Charles ULg; Ouberdous, Mohamed ULg; Rixen, Michel et al

in Geophysical Research Abstracts (2008)

In oceanography, the process of gridding data is frequently used for various purposes, e.g. initialization of hydrodynamic models, or graphical representation of sparse data. DIVA (Data-Interpolating ... [more ▼]

In oceanography, the process of gridding data is frequently used for various purposes, e.g. initialization of hydrodynamic models, or graphical representation of sparse data. DIVA (Data-Interpolating Variational Analysis) is designed to perform such gridding tasks. It has the advantage of taking into account the intrinsic nature of oceanographic data, i.e. uncertainty in in situ measurements and anisotropy due to advection and irregular coastlines and topography. Three-dimensional reconstruction of temperature and salinity fields is achieved by stacking horizontal layers where independent analysis with DIVA are performed. Nevertheless, analysis in regions void of data may result in the presence of static instabilities between two or more consecutive layers. The method implemented in DIVA to remove such kinds of instabilities is the object of the present work. It consists of adding pseudo-data from one layer to the upper adjacent layer in order to create stable stratification in the vicinity of instabilities. Two approaches for assigning values to the pseudo data are tested: the first is called the mixing approach and aims at simulating a mixing process between two layers; the second is called the minimal perturbation, as it strives to minimise the perturbations inthe pseudo-data. A realistic application using temperature and salinity profiles in the North Atlantic is carried out and the results are compared with World Ocean Atlas climatologies. [less ▲]

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See detailRetrievals of C2H2 from high-resolution FTIR solar spectra recorded at the Jungfraujoch station (46.5ºN) and comparison with ACE-FTS observations
Mahieu, Emmanuel ULg; Duchatelet, Pierre ULg; Bernath, P. F. et al

in Geophysical Research Abstracts (2008), 10

Acetylene (C2H2) is among the nonmethane hydrocarbons (NMHCs) accessible to infrared remote sensing technique. As a product of combustion and biomass burning, it is emitted at the Earth’s surface and ... [more ▼]

Acetylene (C2H2) is among the nonmethane hydrocarbons (NMHCs) accessible to infrared remote sensing technique. As a product of combustion and biomass burning, it is emitted at the Earth’s surface and further transported and mixed into the troposphere. Destruction by OH is the main removal process. The average tropospheric lifetime of C2H2 is estimated at about 1 month on the global scale; at mid-latitudes, it varies between 20 days in summer to 160 days in winter. This compound is appropriate to study tropospheric pollution and transport, and is often used in conjunction with other tracers of fires. C2H2 presents exploitable infrared absorption features near 3 and 15 μm, where weak isolated lines of the nu5 and the nu2 + nu4 + nu5 bands are found, respectively. Several of these lines can be used to retrieve abundances of C2H2 from high-resolution groundbased infrared solar spectra. Typical observations recorded at the Jungfraujoch station (46.5ºN, 8.0ºE, 3580m asl, Swiss Alps) by the NDACC (Network for the Detection of Atmospheric Composition Change)-affiliated Bruker instrument have been fitted with the OEM-SFIT-2 (v3.91) algorithm. Various approaches and combination of lines have been tested, seeking for the optimum inversion strategy. The HITRAN-2004 spectroscopic line parameters including the August 2006 updates for water vapor have been adopted in the retrievals. These approaches will be presented and critically compared, with the help of error budget and information content analyses, taking into account the impact of major interferences such as water vapor. The time series of C2H2 tropospheric column abundances above Jungfraujoch will also be presented, including determination of its long-term trend and strong seasonal cycle. The ground-based results will further be compared with zonal mean observations performed by the ACE-FTS space-based instrument since early 2004. [less ▲]

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See detailGround-based CO observations at the Jungfraujoch: Comparison between FTIR and NDIR measurements
Dils, Bart; Mahieu, Emmanuel ULg; Demoulin, Philippe ULg et al

in Geophysical Research Abstracts (2008), 10

Measurements of CO have been performed at the Swiss Alpine Jungfraujoch station (46.5º N, 8.0° E, 3580m a.s.l.) on a regular basis since the mid-1980’s, using Fourier Transform Infrared solar absorption ... [more ▼]

Measurements of CO have been performed at the Swiss Alpine Jungfraujoch station (46.5º N, 8.0° E, 3580m a.s.l.) on a regular basis since the mid-1980’s, using Fourier Transform Infrared solar absorption spectrometry (FTIR), and since 1996 using an in situ Nondispersive Infrared technique (NDIR). While the in situ measurements detect local CO concentrations at the site, the FTIR technique provides integrated measurements along the line-of-sight. Nevertheless, the pressure broadening of the spectral absorption lines recorded at high resolution enables retrieving information on the vertical distribution of CO, mainly in the troposphere, including its concentration near the surface. Considering the inherent capabilities of the two independent measurement techniques, substantial differences between both data sets for surface level CO could potentially arise. Here we present a comparison of both data sets for the 1997 -2004 time period. Both data sets have been analysed by using successive Kolmogorov-Zurbenko filters. It appears that the long-term trend over the given time period is significantly different for both datasets. Possible causes for this difference will be critically discussed. [less ▲]

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See detailRecent evolution of stratospheric inorganic chlorine (Cly) inferred from long-term ground-based FTIR observations of HCl and ClONO2
Mahieu, Emmanuel ULg; Duchatelet, Pierre ULg; Zander, Rodolphe ULg et al

in Geophysical Research Abstracts (2007, May 02), 9

Over the past decades, the increase of the stratospheric inorganic chlorine (Cly) loading has been the major cause for the ozone layer depletion, a matter of particular concern because of its ... [more ▼]

Over the past decades, the increase of the stratospheric inorganic chlorine (Cly) loading has been the major cause for the ozone layer depletion, a matter of particular concern because of its anthropogenic nature. Fortunately, appropriate decisions have been defined and put into force at the international level, leading to regulations adopted within the frame of the Montreal Protocol and its Amendments and Adjustments, and aiming at the suppression of all chlorine-bearing source gas emissions. Since its formalization, the NDSC (Network for Detection of Stratospheric Change, recently renamed NDACC, Network for the Detection of Atmospheric Composition Change) has given high priority to the monitoring of Cly based on solar observations with Fourier transform infrared (FTIR) spectrometers operated at the ground. Within this context, high-resolution solar absorption spectra recorded at Northern and Southern mid-latitudes have been analyzed to retrieve total vertical column abundances of the two main inorganic chlorine species, i.e. HCl and ClONO2. At these latitudes and in the absence of chlorine activation, these two reservoirs account for more than 92% of the total Cly loading. In this contribution, column abundance time series of HCl and ClONO2 for both the Jungfraujoch (46.5°N) and Lauder (45°S) NDACC primary stations will be presented. Comparison of these measurements with the 3-D CTM KASIMA model predictions will be shown and discussed critically, with some focus on the time period following the peak loading. Related trends will be determined and compared to expectations deduced from the most recent emission scenarios. [less ▲]

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See detailRetrievals of HCN from high-resolution FTIR solar spectra recorded at the Jungfraujoch station
Mahieu, Emmanuel ULg; Duchatelet, Pierre ULg; Demoulin, Philippe ULg et al

in Geophysical Research Abstracts (2007, April)

Recent investigations have resulted in the revision of the lifetime of hydrogen cyanide (HCN) from 2.5 years to 2-5 months, more in line with its important and well documented variability in the ... [more ▼]

Recent investigations have resulted in the revision of the lifetime of hydrogen cyanide (HCN) from 2.5 years to 2-5 months, more in line with its important and well documented variability in the troposphere. The main HCN source is believed to be biomass burning, making this species a useful tracer of fires, e.g. the widespread and intense 2004 boreal fires. Oxidation by the OH radical is among the identified sinks, while uptake by oceans has been hypothesized as the dominant sink. As shown by previous investigations, several lines from the nu3 fundamental HCN band at 3 μm can be used to retrieve information on vertical distribution of hydrogen cyanide from high-resolution FTIR solar absorption spectra. The major interfering gas in this region is water vapor. A series of typical observations recorded at the Jungfraujoch station (46.5ºN, 8.0ºE, 3580m asl, Swiss Alps) by the NDACC (Network for the Detection of Atmospheric Composition Change)-affiliated Bruker instrument have been fitted using various approaches to determine the optimum strategy to be used for HCN retrievals at that site, even under very wet conditions. The selected approach is made of 7 windows encompassing 5 HCN lines. The a priori information (HCN vertical distribution and covariance matrix) is based on ACE-FTS measurements performed over northern midlatitudes. The HITRAN-2004 spectroscopic line parameters including the August 2006 updates for water vapor have been adopted in the retrievals performed with the OEM-SFIT-2 (v3.91) algorithm. This contribution will give a full description of the adopted retrieval approach, including error budget and information content analysis. Tropospheric column time series of HCN from 1994 onwards will also be presented and discussed. [less ▲]

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See detailAssessment of Lake Sediment Sensitivity to Earthquakes and Climate Cycles along the North Anatolian Fault,
Boes, Xavier; Avsar, Ulas; King, J et al

in Geophysical Research Abstracts (2007, April), 9

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See detailNew constraints on the Karliova Triple Junction between Arabia, Eurasia and Anatolia.
Hubert, Aurelia ULg; Van Der Woerd, Jerome; King, G. et al

in Geophysical Research Abstracts (2007, April), 9

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See detailPotential of Shallow Lake Systems to Trace Environmental Changes Caused by Earthquakes
Avsar, Ulas; Boes, X; Hubert, Aurelia ULg et al

in Geophysical Research Abstracts (2007, April), 9

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See detailDevelopment of paleoseismic trench logging and dating techniques: a case study on the Central North Anatolian Fault
Fraser, Jeff; Pigati, J.S.; Hubert, Aurelia ULg et al

in Geophysical Research Abstracts (2007, April), 9

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See detailUnderstanding the irregularity of Seismic cycles: A Case study in Turkey-A Marie Curie Excellence Team Project
Hubert, Aurelia ULg; Boes, X; Fraser, J et al

in Geophysical Research Abstracts (2007, April), 9

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See detailControlling factors of gully erosion in the upper part of the Isser river watershed (Algiers, N. Algeria)
Daoudi, M.; Dewitte, Olivier ULg; Gérard, Paul et al

in Geophysical Research Abstracts (2007), 9

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See detailSynthesis of primary impacts of climate change in Belgium, as an onset to the development of an assessment tool for adaptation measures
Dewals, Benjamin ULg; De Sutter, Renaat; De Smet, Lieven et al

in Geophysical Research Abstracts (2007), 9(11217),

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See detailGround-based FTIR measurements at Ile de La Réunion: Observations, error analysis and comparisons with satellite data.
Senten, Cindy; De Mazière, Martine; Hermans, Christian et al

in Geophysical Research Abstracts (2007), 9

Ground-based Fourier-transform infrared (FTIR) spectroscopy is a powerful remote sensing technique to obtain information on the total column abundances and on the vertical distribution of various ... [more ▼]

Ground-based Fourier-transform infrared (FTIR) spectroscopy is a powerful remote sensing technique to obtain information on the total column abundances and on the vertical distribution of various constituents in the atmosphere. Many of these species are essential for the investigation of important atmospheric phenomena, such as the overall greenhouse effect or the stratospheric ozone decrease and recovery. In the frame of the Network for the Detection of Atmospheric Composition Change (NDACC), such observations have been made since many years at several measurement stations for the worldwide long-term monitoring of the atmospheric composition. In this work, we present the results from two short-term FTIR measurement campaigns in 2002 and 2004 at the Ile de La Réunion (21°S, 55°E), a complementary NDACC site in the subtropics, in the Indian Ocean. All spectra were recorded in solar absorption mode. The results discussed here concern the direct greenhouse gases methane (CH4), nitrous oxide (N2O) and ozone (O3), and the indirect greenhouse gases carbon monoxide (CO) and ethane (C2H6), as well as hydrogen cyanide (HCN) and stratospheric hydrogen chloride (HCl), hydrogen fluoride (HF) and nitric acid (HNO3). For the latter species (HCN, HCl, HF and HNO3), we show time series of total column amounts from the surface up to 60 km. For CO, CH4, N2O and O3, it is possible to derive additionally independent information on a few partial columns; these time series are discussed as well. A complete error budget of the retrieval products is given. Temporary mutually correlated enhancements of CO, C2H6and HCN have been observed. They have been traced back to biomass burning events in southern Africa and Madagascar using the FLEXPART model. Comparisons of our retrievals with correlative data from satellite experiments, such as ACE and MOPITT, and with available ozone soundings, show generally good agreements between the different data sets. [less ▲]

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See detailCarbon balance of two Belgian crops
Moureaux, Christine ULg; Debacq, Alain ULg; Vilret, Amélie et al

in Geophysical Research Abstracts (2006), 8(1),

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See detailAdvanced exploitation of ground-based Fourier transform infrared observations for tropospheric studies over Europe: achievements of the UFTIR project
De Mazière, Martine; Vigouroux, Corinne; Blumenstock, Thomas et al

in Geophysical Research Abstracts (2006), 8

Solar absorption measurements using Fourier transform infrared (FTIR) spectrometry carry information about the atmospheric abundances of many constituents, including information about their vertical ... [more ▼]

Solar absorption measurements using Fourier transform infrared (FTIR) spectrometry carry information about the atmospheric abundances of many constituents, including information about their vertical distributions in the troposphere and the stratosphere. Such observations have regularly been made since many years as a contribution to the NDSC (Network for the Detection of Stratospheric Change). They are the only ground-based remote sensing observations available nowadays that carry information about key atmospheric trace species in the free troposphere, among which the most important greenhouse gases. The European UFTIR project (Time series of Upper Free Troposphere observations from a European ground-based FTIR network, http://www.nilu.no/uftir) has focused on maximizing the information content of FTIR long-term monitoring data of some direct and indirect greenhouse gases (CH4, N2O, O3,HCFC-22, and CO and C2H6, respectively). The UFTIR network includes six NDSC stations in Western Europe, covering the polar to subtropical regions. At several stations of the network, the observations span more than a decade. Existing spectral time series have been reanalyzed according to a common optimized retrieval strategy, in order to derive distinct tropospheric and stratospheric abundances of the abovementioned target gases. A bootstrap resampling method has been implemented to evaluate trends of the tropospheric and total burdens of the target gases, including their uncertainties. In parallel, simulations of the target time series have been made with the Oslo CTM2 model: comparisons between the model results and the observations provide valuable information to improve the model, and in particular, to optimize emission estimates that are used as inputs to the model simulations, and to explain the observed trends. The final results of the project will be presented, and ways to proceed will be discussed. [less ▲]

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See detailCan sea ice-specific biogeochemical processes support significant air-ice CO2 fluxes?
Delille, Bruno ULg; Lannuzel, Delphine; Schoemann, Véronique et al

in Geophysical Research Abstracts (2006), 8

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See detailModelling the Ligurian Sea ecosystem by means of a 1D couled physical-biogeochemical model. Improvement of model results using sequential data assimilation
Raick, C.; Soetaert, K.; Grégoire, Marilaure ULg

in Geophysical Research Abstracts (2005), 7

A 1D coupled physical-biogeochemical model has been built to study the pelagic food web of the Ligurian Sea (NW Mediterranean Sea). The physical model is the turbulent closure model (version 1D) developed ... [more ▼]

A 1D coupled physical-biogeochemical model has been built to study the pelagic food web of the Ligurian Sea (NW Mediterranean Sea). The physical model is the turbulent closure model (version 1D) developed at the GHER (University of Liège, Belgium). The ecosystem model contains nineteen state variables describing the carbon and nitrogen cycles of the pelagic food web. Silicate is considered as a potential limiting nutrient of diatoms’ growth. The aggregation model described in Kriest and Evans (2000) is used to evaluate the sinking rate of particulate detritus. The model is forced at the air-sea interface by the METEO France meteorological data. The DYFAMED time series data of year 2000 are used to calibrate and validate the biological model (Raick et al., 2005). By combining the numerical model and the available observations, data assimilation techniques are useful to improve the state estimation of the ocean. A Singular Fixed Extended Kalman filter (Pham et al., 1998) has been implemented in this way. Twin experiments are first performed to choose the suitable experimental protocol, which is then applied to perform real data assimilation experiments using DYFAMED data (Raick et al., submitted). To be coupled in a 3D environment, the ecosystem model is too complex. Our ongoing work is to perform a simplification, by studying simplified structures in comparison with the original ecosystem model. The advantage of deriving a simplified model from the complex one, is that we would be able to identify the most important processes of the Ligurian Sea ecosystem. [less ▲]

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See detailCarbon budget of a sugar beet crop
Moureaux, Christine ULg; Vilret, Amélie; Delvoye, Sébastien et al

in Geophysical Research Abstracts (2005), 7(1),

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