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Auteur Serge Janicot |
Documents disponibles écrits par cet auteur (6)
Ajouter le résultat dans votre panier Affiner la recherche Interroger des sources externesFrequency of extreme Sahelian storms tripled since 1982 in satellite observations / Christopher M. Taylor in Nature letters, vol 544 n° 7651 (27 April 2017)
Titre : Frequency of extreme Sahelian storms tripled since 1982 in satellite observations Type de document : Article/Communication Auteurs : Christopher M. Taylor, Auteur ; Danijel Belušić, Auteur ; Françoise Guichard, Auteur ; Douglas J. Parker, Auteur ; Théo Vischel, Auteur ; Olivier Bock Année de publication : 2017 Projets : AMMA & AMMA-2 / Janicot, Serge Article en page(s) : pp 475 - 478 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] analyse diachronique
[Termes IGN] changement climatique
[Termes IGN] convection
[Termes IGN] données météorologiques
[Termes IGN] pluie
[Termes IGN] Sahara, désert du
[Termes IGN] Sahel
[Termes IGN] température
[Termes IGN] tempêteRésumé : (auteur) The hydrological cycle is expected to intensify under global warming, with studies reporting more frequent extreme rain events in many regions of the world, and predicting increases in future flood frequency. Such early, predominantly mid-latitude observations are essential because of shortcomings within climate models in their depiction of convective rainfall. A globally important group of intense storms—mesoscale convective systems (MCSs)—poses a particular challenge, because they organize dynamically on spatial scales that cannot be resolved by conventional climate models. Here, we use 35 years of satellite observations from the West African Sahel to reveal a persistent increase in the frequency of the most intense MCSs. Sahelian storms are some of the most powerful on the planet, and rain gauges in this region have recorded a rise in ‘extreme’ daily rainfall totals. We find that intense MCS frequency is only weakly related to the multidecadal recovery of Sahel annual rainfall, but is highly correlated with global land temperatures. Analysis of trends across Africa reveals that MCS intensification is limited to a narrow band south of the Sahara desert. During this period, wet-season Sahelian temperatures have not risen, ruling out the possibility that rainfall has intensified in response to locally warmer conditions. On the other hand, the meridional temperature gradient spanning the Sahel has increased in recent decades, consistent with anthropogenic forcing driving enhanced Saharan warming. We argue that Saharan warming intensifies convection within Sahelian MCSs through increased wind shear and changes to the Saharan air layer. The meridional gradient is projected to strengthen throughout the twenty-first century, suggesting that the Sahel will experience particularly marked increases in extreme rain. The remarkably rapid intensification of Sahelian MCSs since the 1980s sheds new light on the response of organized tropical convection to global warming, and challenges conventional projections made by general circulation models. Numéro de notice : A2017-859 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1038/nature22069 Date de publication en ligne : 26/04/2017 En ligne : http://doi.org/10.1038/nature22069 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=89838
in Nature letters > vol 544 n° 7651 (27 April 2017) . - pp 475 - 478[article]
Titre : On the late northward propagation of the West African monsoon in summer 2006 in the region of Niger/Mali Type de document : Article/Communication Auteurs : Philippe Drobinski, Auteur ; Sophie Bastin, Auteur ; Serge Janicot, Auteur ; Olivier Bock Année de publication : 2009 Projets : AMMA & AMMA-2 / Janicot, Serge 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] Mali
[Termes IGN] mousson
[Termes IGN] NigerRésumé : (auteur) This paper investigates the fine‐scale dynamical processes at the origin of the late northward migration of the monsoon flow in summer 2006 in the region of Niger and Mali (onset on 3 July 2006 compared to the climatological onset date, 24 June). Compared to a 28‐year climatology, 2006 NCEP‐2 reanalyses show evidence of an anomalous pattern during 10 days between 25 June and 3 July 2006, characterized by the African Easterly Jet (AEJ) blowing from the northeast along a narrow northeast/southwest band located over the Hoggar and Air mountains associated with an unusually strong northeasterly harmattan in the lee of the mountains. Using data collected during the African Monsoon Multidisciplinary Analysis (AMMA) experiment and mesoscale numerical simulations, this study shows evidence of interaction between the AEJ and the orography supported by the reduced gravity shallow water theory which explains the enhancement of the harmattan downstream of the Hoggar and Air mountains in summer 2006. The enhanced harmattan contributes to move southward the intertropical discontinuity (ITD) defined as the interface between the cool moist southwesterly monsoon flow and the warm dry harmattan. Finally, an interaction between the ITD and African Easterly waves contributes to propagate the ITD southward retreat about 1500 km to the west of the Hoggar and Air mountains. Numéro de notice : A2009-594 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2008JD011159 Date de publication en ligne : 13/05/2009 En ligne : https://doi.org/10.1029/2008JD011159 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=96202
in Journal of geophysical research : Atmospheres > vol 114 n° D9 (2009)[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 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]
Titre : Assessment of water budgets computed from NWP models and observational datasets during AMMA-EOP Type de document : Article/Communication Auteurs : Olivier Bock 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
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 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]
