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Auteur Olivier Bock
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Senior researcher - HDR defense in 2012 - Responsable for Geodesy and atmosphere research area
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Consistency and representativeness of integrated water vapour from ground-based GPS observations and ERA-Interim reanalysis / Olivier Bock in Atmospheric chemistry and physics, vol 19 n° 14 (July 2019)
[article]
Titre : Consistency and representativeness of integrated water vapour from ground-based GPS observations and ERA-Interim reanalysis Type de document : Article/Communication Auteurs : Olivier Bock , Auteur ; Ana-Claudia Bernardes Parracho , Auteur Année de publication : 2019 Projets : GNSS4SWEC / Article en page(s) : 17 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] analyse comparative
[Termes IGN] analyse diachronique
[Termes IGN] données GPS
[Termes IGN] erreur
[Termes IGN] humidité de l'air
[Termes IGN] interpolation spatiale
[Termes IGN] retard troposphérique zénithal
[Termes IGN] teneur intégrée en vapeur d'eau
[Termes IGN] variation diurne
[Termes IGN] variation saisonnièreRésumé : (auteur) This study examines the consistency and representativeness differences of daily integrated water vapour (IWV) data from ERA-Interim reanalysis and GPS observations at 120 global sites over a 16-year period (1995–2010). Various comparison statistics are analysed as a function of geographic, topographic, and climatic features. A small (±1 kg m−2) bias is found in the reanalysis across latitudes (moist in northern and southern midlatitudes and dry in the tropics). The standard deviation of daily IWV differences is generally below 2 kg m−2 but peaks in the northern and southern storm-track regions. In general, the larger IWV differences are explained by increased representativeness errors, when GPS observations capture some small-scale variability that is not resolved by the reanalysis. A representativeness error statistic is proposed which measures the spatiotemporal variability in the vicinity of the GPS sites, based on reanalysis data at the four surrounding grid points. It allows to predict the standard deviation of daily IWV differences with a correlation of 0.73. In general, representativeness differences can be reduced by temporal averaging and spatial interpolation from the four surrounding grid points. A small number of outlying cases (15 sites) which do not follow the general tendencies are further examined. It is found that their special topographic and climatic features strongly enhance the representativeness errors (e.g. steep topography, coastlines, and strong seasonal cycle in monsoon regions). Discarding these sites significantly improves the global ERA-Interim and GPS comparison results. The selection of sites a priori, based on the representativeness error statistic, is able to detect 11 out of the 15 sites and improve the comparison results by 20 % to 30 %. Numéro de notice : A2019-615 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Autre URL associée : vers HAL Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.5194/acp-19-9453-2019 Date de publication en ligne : 24/07/2019 En ligne : https://hal.science/hal-02277609v1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95311
in Atmospheric chemistry and physics > vol 19 n° 14 (July 2019) . - 17 p.[article]Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa / Samuel Nahmani in Atmospheric chemistry and physics, vol 19 n° 14 (July 2019)
[article]
Titre : Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa Type de document : Article/Communication Auteurs : Samuel Nahmani , Auteur ; Olivier Bock , Auteur ; Françoise Guichard, Auteur Année de publication : 2019 Projets : VEGAN / Bock, Olivier, TOSCA / Bock, Olivier Article en page(s) : pp 9541 - 9561 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] Afrique occidentale
[Termes IGN] analyse de sensibilité
[Termes IGN] bande C
[Termes IGN] convection
[Termes IGN] données GPS
[Termes IGN] GAMIT
[Termes IGN] GIPSY-OASIS
[Termes IGN] gradient de troposphère
[Termes IGN] meso échelle
[Termes IGN] modèle atmosphérique
[Termes IGN] Niger
[Termes IGN] propagation troposphérique
[Termes IGN] résidu
[Termes IGN] retard troposphérique zénithal
[Termes IGN] signal GPSRésumé : (Auteur) This study analyzes the characteristics of GPS tropospheric estimates (zenith wet delays – ZWDs, gradients, and post-fit phase residuals) during the passage of mesoscale convective systems (MCSs) and evaluates their sensitivity to the research-level GPS data processing strategy implemented. Here, we focus on MCS events observed during the monsoon season of West Africa. This region is particularly well suited for the study of these events due to the high frequency of MCS occurrences in the contrasting climatic environments between the Guinean coast and the Sahel. This contrast is well sampled with data generated by six African Monsoon Multidisciplinary Analysis (AMMA) GPS stations. Tropospheric estimates for a 3-year period (2006–2008), processed with both the GAMIT and GIPSY-OASIS software packages, were analyzed and intercompared. First, the case of a MCS that passed over Niamey, Niger, on 11 August 2006 demonstrates a strong impact of the MCS on GPS estimates and post-fit residuals when the GPS signals propagate through the convective cells as detected on reflectivity maps from the MIT C-band Doppler radar. The estimates are also capable of detecting changes in the structure and dynamics of the MCS. However, the sensitivity is different depending on the tropospheric modeling approach adopted in the software. With GIPSY-OASIS, the high temporal sampling (5 min) of ZWDs and gradients is well suited for detecting the small-scale, short-lived, convective cells, while the post-fit residuals remain quite small. With GAMIT, the lower temporal sampling of the estimated parameters (hourly for ZWDs and daily for gradients) is not sufficient to capture the rapid delay variations associated with the passage of the MCS, but the post-fit phase residuals clearly reflect the presence of a strong refractivity anomaly. The results are generalized with a composite analysis of 414 MCS events observed over the 3-year period at the six GPS stations with the GIPSY-OASIS estimates. A systematic peak is found in the ZWDs coincident with the cold pool crossing time associated with the MCSs. The tropospheric gradients reflect the path of the MCS propagation (generally from east to west). This study concludes that ZWDs, gradients, and post-fit phase residuals provide relevant and complementary information on MCSs passing over or in the vicinity of a GPS station. Numéro de notice : A2019-572 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.5194/acp-19-9541-2019 Date de publication en ligne : 29/07/2019 En ligne : https://doi.org/10.5194/acp-19-9541-2019 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94444
in Atmospheric chemistry and physics > vol 19 n° 14 (July 2019) . - pp 9541 - 9561[article]The AROME-WMED reanalyses of the first special observation period of the Hydrological cycle in the Mediterranean experiment (HyMeX) / Nadia Fourrié in Geoscientific Model Development, vol 12 n° 7 (July 2019)
[article]
Titre : The AROME-WMED reanalyses of the first special observation period of the Hydrological cycle in the Mediterranean experiment (HyMeX) Type de document : Article/Communication Auteurs : Nadia Fourrié, Auteur ; Mathieu Nuret, Auteur ; Pierre Brousseau, Auteur ; Olivier Caumont, Auteur ; Alexis Doerenbecher, Auteur ; Eric Wattrelot, Auteur ; Patrick Moll, Auteur ; Hervé Bénichou, Auteur ; Dominique Puech, Auteur ; Olivier Bock , Auteur ; Pierre Bosser , Auteur ; et al., Auteur Année de publication : 2019 Projets : HyMeX / Richard, Evelyne Article en page(s) : pp 2657 - 2678 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] analyse de données
[Termes IGN] données localisées
[Termes IGN] données météorologiques
[Termes IGN] Méditerranée, mer
[Termes IGN] modèle de simulationRésumé : (auteur) The AROME-WMED (western Mediterranean) model is a dedicated version of the mesoscale Numerical Weather Prediction AROME-France model that ran in real time during the first special observation period of HyMeX. Two reanalyses were performed after the campaign. This paper depicts the main differences between the real-time version and the benefits brought by both HyMeX reanalyses. The second reanalysis is found to be closer to observations than the previous AROME-WMED analyses. Numéro de notice : A2019-630 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.5194/gmd-12-2657-2019 Date de publication en ligne : 08/07/2019 En ligne : https://dx.doi.org/10.5194/gmd-12-2657-2019 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95330
in Geoscientific Model Development > vol 12 n° 7 (July 2019) . - pp 2657 - 2678[article]Impact of humidity biases on light precipitation occurrence: observations versus simulations / Sophie Bastin in Atmospheric chemistry and physics, vol 19 n° 3 (February 2019)
[article]
Titre : Impact of humidity biases on light precipitation occurrence: observations versus simulations Type de document : Article/Communication Auteurs : Sophie Bastin, Auteur ; Philippe Drobinski, Auteur ; Marjolaine Chiriaco, Auteur ; Olivier Bock , Auteur ; Romain Roehrig, Auteur ; Clemente Gallardo, Auteur ; Dario Conte, Auteur ; Marta Domínguez Alonso, Auteur ; Laurent Li, Auteur ; Piero Lionello, Auteur ; Ana-Claudia Bernardes Parracho , Auteur Année de publication : 2019 Projets : HyMeX / Richard, Evelyne Article en page(s) : pp 1471 - 1490 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] bassin méditerranéen
[Termes IGN] données GPS
[Termes IGN] données météorologiques
[Termes IGN] erreur systématique
[Termes IGN] précipitation
[Termes IGN] température de l'air
[Termes IGN] teneur intégrée en vapeur d'eauRésumé : (auteur) This work uses a network of GPS stations over Europe from which a homogenized integrated water vapor (IWV) dataset has been retrieved, completed with colocated temperature and precipitation measurements over specific stations to (i) estimate the biases of six regional climate models over Europe in terms of humidity; (ii) understand their origins; and (iii) finally assess the impact of these biases on the frequency of occurrence of precipitation. The evaluated simulations have been performed in the framework of HYMEX/Med-CORDEX programs and cover the Mediterranean area and part of Europe at horizontal resolutions of 50 to 12 km.
The analysis shows that models tend to overestimate the low values of IWV and the use of the nudging technique reduces the differences between GPS and simulated IWV. Results suggest that physics of models mostly explain the mean biases, while dynamics affects the variability. The land surface–atmosphere exchanges affect the estimation of IWV over most part of Europe, especially in summer. The limitations of the models to represent these processes explain part of their biases in IWV. However, models correctly simulate the dependance between IWV and temperature, and specifically the deviation that this relationship experiences regarding the Clausius–Clapeyron law after a critical value of temperature (Tbreak). The high spatial variability of Tbreak indicates that it has a strong dependence on local processes which drive the local humidity sources. This explains why the maximum values of IWV are not necessarily observed over warmer areas, which are often dry areas.
Finally, it is shown over the SIRTA observatory (near Paris) that the frequency of occurrence of light precipitation is strongly conditioned by the biases in IWV and by the precision of the models to reproduce the distribution of IWV as a function of the temperature. The results of the models indicate that a similar dependence occurs in other areas of Europe, especially where precipitation has a predominantly convective character. According to the observations, for each range of temperature, there is a critical value of IWV from which precipitation starts to increase. The critical values and the probability of exceeding them are simulated with a bias that depends on the model. Those models, which generally present light precipitation too often, show lower critical values and higher probability of exceeding them.Numéro de notice : A2019-277 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.5194/acp-19-1471-2019 Date de publication en ligne : 04/02/2019 En ligne : https://doi.org/10.5194/acp-19-1471-2019 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95383
in Atmospheric chemistry and physics > vol 19 n° 3 (February 2019) . - pp 1471 - 1490[article]Global IWV trends and variability in atmospheric reanalyses and GPS observations / Ana-Claudia Bernardes Parracho in Atmospheric chemistry and physics, vol 18 n° 22 ([01/11/2018])
[article]
Titre : Global IWV trends and variability in atmospheric reanalyses and GPS observations Type de document : Article/Communication Auteurs : Ana-Claudia Bernardes Parracho , Auteur ; Olivier Bock , Auteur ; Sophie Bastin, Auteur Année de publication : 2018 Projets : REMEMBER / Drobinski, Philippe Article en page(s) : pp 16213 - 16237 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique (géographie physique)
[Termes IGN] analyse diachronique
[Termes IGN] Antarctique
[Termes IGN] circulation atmosphérique
[Termes IGN] données GPS
[Termes IGN] données météorologiques
[Termes IGN] erreur systématique
[Termes IGN] hémisphère Sud
[Termes IGN] humidité de l'air
[Termes IGN] température de surface
[Termes IGN] teneur intégrée en vapeur d'eau
[Termes IGN] variabilitéRésumé : (auteur) This study investigates the means, variability, and trends in integrated water vapour (IWV) from two modern reanalyses (ERA-Interim and MERRA-2) from 1980 to 2016 and ground-based GPS data from 1995 to 2010. It is found that the mean distributions and inter-annual variability in IWV in the reanalyses and GPS are consistent, even in regions of strong gradients. ERA-Interim is shown to exhibit a slight moist bias in the extra-tropics and a slight dry bias in the tropics (both on the order of 0.5 to 1 kg m−2) compared to GPS. ERA-Interim is also generally drier than MERRA-2 over the ocean and within the tropics. Differences in variability and trends are pointed out at a few GPS sites. These differences can be due to representativeness errors (for sites located in coastal regions and regions of complex topography), gaps and inhomogeneities in the GPS series (due to equipment changes), or potential inhomogeneities in the reanalyses (due to changes in the observing system). Trends in IWV and surface temperature in ERA-Interim and MERRA-2 are shown to be consistent, with positive IWV trends generally correlated with surface warming, but MERRA-2 presents a more general global moistening trend compared to ERA-Interim. Inconsistent trends are found between the two reanalyses over Antarctica and most of the Southern Hemisphere, and over central and northern Africa. The uncertainty in current reanalyses remains quite high in these regions, where few in situ observations are available, and the spread between models is generally important. Inter-annual and decadal variations in IWV are also shown to be strongly linked with variations in the atmospheric circulation, especially in arid regions, such as northern Africa and Western Australia, which add uncertainty in the trend estimates, especially over the shorter period. In these regions, the Clausius–Clapeyron scaling ratio is found not to be a good humidity proxy for inter-annual variability and decadal trends. Numéro de notice : A2018-667 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.5194/acp-18-16213-2018 Date de publication en ligne : 15/11/2018 En ligne : http://dx.doi.org/10.5194/acp-18-16213-2018 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94260
in Atmospheric chemistry and physics > vol 18 n° 22 [01/11/2018] . - pp 16213 - 16237[article]Does long-term GPS in the Western Alps finally confirm earthquake mechanisms? / Andrea Walpersdorf in Tectonics, vol 37 n° 10 (October 2018)PermalinkMulti‐scale observations of atmospheric moisture variability in relation to heavy precipitating systems in the northwestern Mediterranean during HyMeX IOP12 / Samiro Khodayar in Quarterly Journal of the Royal Meteorological Society, vol 144 n° 717 (October 2018 Part B)PermalinkComparison of total water vapour content in the Arctic derived from GNSS, AIRS, MODIS and SCIAMACHY / Dunya Alraddawi in Atmospheric measurement techniques, vol 11 n° 5 (May 2018)PermalinkAll-sky search for long-duration gravitational wave transients in the first Advanced LIGO observing run / B.P. Abbott in Classical and Quantum Gravity, vol 35 n° 6 (March 2018)PermalinkReduction of ZTD outliers through improved GNSS data processing and screening strategies [Interactive discussion] / Katarzyna Stępniak in Atmospheric measurement techniques, vol 11 n° 3 (March 2018)PermalinkBilan de l’Action COST ES1206 - GNSS4SWEC (Advanced Global Navigation Satellite Systems tropospheric products for monitoring severe weather events and climate) / Olivier Bock (2018)PermalinkPrecipitable water vapour content from ESR/SKYNET sun–sky radiometers : validation against GNSS/GPS and AERONET over three different sites in Europe / Monica Campanelli in Atmospheric measurement techniques, vol 11 n° 1 (January 2018)PermalinkEnhanced MODIS atmospheric total water vapour content trends in response to Arctic amplification / Dunya Alraddawi in Atmosphere, vol 8 n° 12 (December 2017)PermalinkStudy and mitigation of calibration factor instabilities in a water vapor Raman lidar / Leslie David in Atmospheric measurement techniques, vol 10 n° 7 (July 2017)PermalinkFrequency of extreme Sahelian storms tripled since 1982 in satellite observations / Christopher M. Taylor in Nature letters, vol 544 n° 7651 (27 April 2017)PermalinkGPS - Zenith Total Delay assimilation in different resolution simulations of a heavy precipitation event over southern France / Alberto Caldas-Álvarez in Advances in Science and Research, vol 14 (2017)PermalinkHomogeneizing GPS integrated water vapour time series: methodology and benchmarking the algorithms on synthetic datasets / Roeland Van Malderen (2017)PermalinkStudy of trends and variability of atmospheric water vapour with climate models and observations from global GNSS network / Ana-Claudia Bernardes Parracho (2017)PermalinkReview of the state of the art and future prospects of the ground-based GNSS meteorology in Europe / Guergana Guerova in Atmospheric measurement techniques, vol 9 n° 11 (November 2016)PermalinkDiagnostic study of a high‐precipitation event in the Western Mediterranean: adequacy of current operational networks / Samiro Khodayar in Quarterly Journal of the Royal Meteorological Society, vol 142 n° S1 (August 2016)PermalinkA high-quality reprocessed ground-based GPS dataset for atmospheric process studies, radiosonde and model evaluation, and reanalysis of HyMeX Special Observing Period / Olivier Bock in Quarterly Journal of the Royal Meteorological Society, vol 142 n° S1 (August 2016)PermalinkA multi-instrument and multi-model assessment of atmospheric moisture variability over the Western Mediterranean during HyMeX / Patrick Chazette in Quarterly Journal of the Royal Meteorological Society, vol 142 n° S1 (August 2016)PermalinkOffshore deep convection initiation and maintenance during the HyMeX IOP 16a heavy precipitation event / F. Duffourg in Quarterly Journal of the Royal Meteorological Society, vol 142 n° S1 (August 2016)PermalinkA seamless weather–climate multi‐model intercomparison on the representation of a high impact weather event in the western Mediterranean: HyMeX IOP12 / Samiro Khodayar in Quarterly Journal of the Royal Meteorological Society, vol 142 n° S1 (August 2016)PermalinkThe variability of water vapour and pre-convective conditions over the mountainous island of Corsica / Bianca Adler in Quarterly Journal of the Royal Meteorological Society, vol 142 n° S1 (August 2016)Permalink