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Large-scale overview of the summer monsoon over West Africa during the AMMA field experiment in 2006 / Serge Janicot in Annales Geophysicae, vol 26 n° 9 (September 2008)
[article]
Titre : Large-scale overview of the summer monsoon over West Africa during the AMMA field experiment in 2006 Type de document : Article/Communication Auteurs : Serge Janicot, Auteur ; Chris Thorncroft, Auteur ; A. Ali, Auteur ; Nicole Asencio, Auteur ; Gérard Berry, Auteur ; Olivier Bock , Auteur ; et al., Auteur Année de publication : 2008 Projets : AMMA & AMMA-2 / Janicot, Serge Article en page(s) : pp 2569 - 2595 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique occidentale
[Termes IGN] circulation atmosphérique
[Termes IGN] moussonRésumé : (auteur) The AMMA (African Monsoon Multidisciplinary Analysis) program is dedicated to providing a better understanding of the West African monsoon and its influence on the physical, chemical and biological environment regionally and globally, as well as relating variability of this monsoon system to issues of health, water resources, food security and demography for West African nations. Within this framework, an intensive field campaign took place during the summer of 2006 to better document specific processes and weather systems at various key stages of this monsoon season. This campaign was embedded within a longer observation period that documented the annual cycle of surface and atmospheric conditions between 2005 and 2007. The present paper provides a large and regional scale overview of the 2006 summer monsoon season, that includes consideration of of the convective activity, mean atmospheric circulation and synoptic/intraseasonal weather systems, oceanic and land surface conditions, continental hydrology, dust concentration and ozone distribution. The 2006 African summer monsoon was a near-normal rainy season except for a large-scale rainfall excess north of 15° N. This monsoon season was also characterized by a 10-day delayed onset compared to climatology, with convection becoming developed only after 10 July. This onset delay impacted the continental hydrology, soil moisture and vegetation dynamics as well as dust emission. More details of some less-well-known atmospheric features in the African monsoon at intraseasonal and synoptic scales are provided in order to promote future research in these areas. Numéro de notice : A2008-599 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.5194/angeo-26-2569-2008 Date de publication en ligne : 01/09/2008 En ligne : https://doi.org/10.5194/angeo-26-2569-2008 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=103433
in Annales Geophysicae > vol 26 n° 9 (September 2008) . - pp 2569 - 2595[article]Assessment of water budgets computed from NWP models and observational datasets during AMMA-EOP / Olivier Bock (2008)
Titre : Assessment of water budgets computed from NWP models and observational datasets during AMMA-EOP Type de document : Article/Communication Auteurs : Olivier Bock , Auteur ; Rémi Meynadier, Auteur ; Françoise Guichard, Auteur ; Pascal Roucou, Auteur ; Aaron Boone, Auteur ; Jean-Luc Redelsperger, Auteur ; Serge Janicot, Auteur Editeur : American meteorological society AMS Année de publication : 2008 Projets : AMMA & AMMA-2 / Janicot, Serge Conférence : CHTM 2008, 28th Conference on Hurricanes and Tropical Meteorology 27/04/2008 02/05/2008 Orlando Floride - Etats-Unis OA Proceedings Importance : 6 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique occidentale
[Termes IGN] données GPS
[Termes IGN] données météorologiques
[Termes IGN] mousson
[Termes IGN] précipitation
[Termes IGN] prévision météorologique
[Termes IGN] vapeur d'eauRésumé : (auteur) Understanding the water cycle in the West African Monsoon (WAM) system is a major objective of AMMA. The water cycle is the result of the interplay of various coupled atmospheric ocean continental surface processes. The identification of the mechanisms involved and the scales at which they operate is approached here through the investigation of water budgets terms (precipitable water vapour PWV, water vapour fluxes WVF, precipitation P, and evapo-transpiration ETP). The present study focuses on the intercomparison of datasets that are currently used for the computation of such water budgets are large scale. Numerical Weather Prediction (NWP) models provide their own complete description of the water cycle but with limitations (especially in P and ETP terms). During the AMMA EOP, many additional observations went into the NWP operational analyses which might thus be of unprecedented quality. We describe here the seasonal cycles (monthly-mean and short-term variability) of PWV, WVF, P and ETP obtained from ECMWF operational analyses, as well as NCEP reanalysis 1 and 2, for years 2005 to 2007. Significant differences are seen between the different analyses, with NCEP reanalysis 1 being of much poorer quality (in term of overall bias, seasonal cycle and spatial structure). Water vapour convergence and budget closure from the different NWP datasets are also examined in several boxes over continental West Africa. There also, significant differences are found for the different analyses. The water budget estimates are also assessed comparing some terms with observational datasets (PWV from GPS, radiosondes, and satellites; P from EPSAT-SG and GPCP; ETP from land and ocean surface models). A combined water budget is computed, using NWP estimates for WVF and observation-based datasets for P and ETP. This is used to investigate the origine of the sources of water (e.g., oceanic versus continental), the significance of water recycling and atmospheric advection of water, and the link between the intra-seasonal variability in the water budget terms and the coupled atmospheric ocean continental surface processes. Numéro de notice : C2008-037 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl DOI : sans En ligne : https://ams.confex.com/ams/pdfpapers/138101.pdf Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=103422 Comparison of ground-based GPS precipitable water vapour to independent observations and NWP model reanalyses over Africa / Olivier Bock in Quarterly Journal of the Royal Meteorological Society, vol 133 n° 629 (Octobre 2007 part B)
[article]
Titre : Comparison of ground-based GPS precipitable water vapour to independent observations and NWP model reanalyses over Africa Type de document : Article/Communication Auteurs : Olivier Bock , Auteur ; Marie-Noëlle Bouin , Auteur ; Andrea Walpersdorf, Auteur ; Jean-Philippe Lafore, Auteur ; Serge Janicot, Auteur ; Françoise Guichard, Auteur ; Anna Agusti-Panareda, Auteur Année de publication : 2007 Article en page(s) : pp 2011 - 2027 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique (géographie physique)
[Termes IGN] analyse comparative
[Termes IGN] cohérence des données
[Termes IGN] mousson
[Termes IGN] vapeur d'eauRésumé : (auteur) This study aims at assessing the consistency between different precipitable water vapour (PWV) datasets over Africa (between 35°N and 10°S). This region is characterized by large spatial and temporal variability of humidity but also by the scarcity of its operational observing network, limiting our knowledge of the hydrological cycle. We intercompare data from observing techniques such as ground-based Global Positioning System (GPS), radiosondes, AERONET sun photometers and SSM/I, as well as reanalyses from European Centre for Medium-Range Weather Forecasts (ERA-40) and National Center for Environmental Prediction (NCEP2). The GPS data, especially, are a new source of PWV observation in this region. PWV estimates from nine ground-based GPS receivers of the international GPS network data are used as a reference dataset to which the others are compared. Good agreement is found between observational techniques, though dry biases of 12–14% are evidenced in radiosonde data at three sites. Reasonable agreement is found between the observational datasets and ERA-40 (NCEP2) reanalyses with maximum bias ⩽9% (14%) and standard deviation ⩽17% (20%). Since GPS data were not assimilated in the ERA-40 and NCEP2 reanalyses, they allow for a fully independent validation of the reanalyses. They highlight limitations in the reanalyses, especially at time-scales from sub-daily to periods of a few days. This work also demonstrates the high potential of GPS PWV estimates over Africa for the analysis of the hydrological cycle, at time-scales ranging between sub-diurnal to seasonal. Such observations can help studying atmospheric processes targeted by the African Monsoon Multidisciplinary Analysis project. Numéro de notice : A2007-690 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1002/qj.185 Date de publication en ligne : 20/09/2007 En ligne : https://doi.org/10.1002/qj.185 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102776
in Quarterly Journal of the Royal Meteorological Society > vol 133 n° 629 (Octobre 2007 part B) . - pp 2011 - 2027[article]Assessment of GPS data for meteorological applications over Africa: Study of error sources and analysis of positioning accuracy / Andrea Walpersdorf in Journal of Atmospheric and Solar-Terrestrial Physics, vol 69 n° 12 (August 2007)
[article]
Titre : Assessment of GPS data for meteorological applications over Africa: Study of error sources and analysis of positioning accuracy Type de document : Article/Communication Auteurs : Andrea Walpersdorf, Auteur ; Marie-Noëlle Bouin , Auteur ; Olivier Bock , Auteur ; Erik Doerflinger, Auteur Année de publication : 2007 Article en page(s) : pp 1312 - 1330 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] Afrique tropicale
[Termes IGN] données météorologiques
[Termes IGN] mousson
[Termes IGN] précision du positionnement
[Termes IGN] retard troposphérique zénithal
[Termes IGN] vapeur d'eauRésumé : (auteur) The aim of this study is to assess the availability and quality of data from the International GNSS Service (IGS) Global Positioning System (GPS) network in Africa, especially for retrieving zenith tropospheric delay (ZTD), from which precipitable water vapour (PWV) can be derived, in view of application to the African Monsoon Multidisciplinary Analysis (AMMA) project. Three major error sources for the GPS data analysis evaluating PWV in Africa are the accuracy of the satellite orbits, the correction for the radio delay induced by the ionosphere and the vertical site displacements due to ocean loading. The first part of this study examines these error sources and the validity of GPS data for meteorological applications in Africa in dedicated analyses spanning the year 2001. These analyses were performed using the IGS precise orbits. Weak degradation of baseline precision with increasing baseline lengths suggests that the average orbital error is not limiting the GPS analysis in Africa. The impact of the ionosphere has been evaluated during a maximum of solar activity in 2001. The loss of L2 data has actually been observed. It amounts to 2% on average for 2001, with maxima of 8% during magnetic storm events. A slight decrease in formal accuracy of ZTD seems to be related to the loss of L2 data at the end of the day. This indicates that scintillation effects are present in the GPS observations but however are not a major limitation. The impact of ocean loading is found to be significant on ZTD estimates (up to ±2 mm in equivalent PWV). The use of a proper ocean loading model eliminates this effect.
The second aspect of this study concerns the IGS analysis quality for the African stations. The accuracy has been assessed through position dispersion between individual solutions and the most recent version of the IGS combined solution IGb00, and residuals from the transformation of the IGS combined solution into the International Terrestrial Reference Frame 2005. The positioning performance of the IGS analysis is consistent with an accuracy in ZTD of ±6 mm (±1 mm in PWV), as requested for meteorological applications such as planned in AMMA.Numéro de notice : A2007-672 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.jastp.2007.04.008 Date de publication en ligne : 08/05/2007 En ligne : https://doi.org/10.1016/j.jastp.2007.04.008 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102771
in Journal of Atmospheric and Solar-Terrestrial Physics > vol 69 n° 12 (August 2007) . - pp 1312 - 1330[article]AMMA, une étude multidisciplinaire de la mousson ouest-africaine / Jean-Luc Redelsperger in La Météorologie, n° 54 ([01/10/2006])
[article]
Titre : AMMA, une étude multidisciplinaire de la mousson ouest-africaine Type de document : Article/Communication Auteurs : Jean-Luc Redelsperger, Auteur ; et al., Auteur Année de publication : 2006 Projets : AMMA & AMMA-2 / Janicot, Serge Article en page(s) : pp 22 - 32 Langues : Français (fre) Descripteur : [Vedettes matières IGN] Atmosphère
[Termes IGN] Afrique occidentale
[Termes IGN] données météorologiques
[Termes IGN] mousson
[Termes IGN] précipitationRésumé : (auteur) Le projet international AMMA, d'initiative française, a pour objectif d'améliorer la connaissance et la compréhension de la mousson d'Afrique de l'ouest et de sa variabilité, de l'échelle journalière à l'échelle interannuelle. Le projet est motivé par la forte variabilité des précipitations associées à ce système de mousson, et par ses conséquences sur la sécurité alimentaire, les ressources en eau et la santé. Numéro de notice : A2005-614 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.4267/2042/20098 En ligne : https://doi.org/10.4267/2042/20098 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=100835
in La Météorologie > n° 54 [01/10/2006] . - pp 22 - 32[article]Estimation of the horizontal velocity of the Socotra eddy and some observations of sea surface thermal features using Insat-1b / M.M. Ali in International Journal of Remote Sensing IJRS, vol 11 n° 1 (January 1990)PermalinkMonsoon flood boundary delineation and damage assessment using space borne imaging radar and Landsat data / M.L. Imhoff in Photogrammetric Engineering & Remote Sensing, PERS, vol 53 n° 4 (april 1987)PermalinkLa répartition des pluies et les régimes pluviométriques au Cameroun / J.B. Suchel (1972)Permalink