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Auteur Serge Janicot |
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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 descripteurs IGN] analyse diachronique
[Termes descripteurs IGN] changement climatique
[Termes descripteurs IGN] convection
[Termes descripteurs IGN] données météorologiques
[Termes descripteurs IGN] pluie
[Termes descripteurs IGN] Sahara, désert du
[Termes descripteurs IGN] Sahel
[Termes descripteurs IGN] température
[Termes descripteurs 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 descripteurs IGN] Afrique occidentale
[Termes descripteurs IGN] données GPS
[Termes descripteurs IGN] données météorologiques
[Termes descripteurs IGN] Mali
[Termes descripteurs IGN] mousson
[Termes descripteurs 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 : Multiscale analysis of precipitable water vapor over Africa from GPS data and ECMWF analyses Type de document : Article/Communication Auteurs : Olivier Bock Année de publication : 2007 Projets : 1-Pas de projet / Article en page(s) : 6 p. Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes descripteurs IGN] Afrique (géographie physique)
[Termes descripteurs IGN] analyse multiéchelle
[Termes descripteurs IGN] données GPS
[Termes descripteurs IGN] données météorologiques
[Termes descripteurs IGN] précipitation
[Termes descripteurs IGN] vapeur d'eauRésumé : (auteur) This is the first climatological analysis of precipitable water vapor (PWV) from GPS data over Africa. The data reveal significant modulations and variability in PWV over a broad range of temporal scales. GPS PWV estimates are compared to ECMWF reanalysis ERA40. Both datasets show good agreement at the larger scales (seasonal cycle and inter‐annual variability), driven by large scale moisture transport. At intra‐seasonal (15–40 days) and synoptic (3–10 days) scales, strong PWV modulations are observed from GPS, consistently with ECMWF analysis. They are shown to be correlated with convection and the passage of equatorial waves and African Easterly waves. The high‐frequency GPS observations also reveal a significant diurnal cycle in PWV, which magnitude and spectral content depends strongly on geographic location and shows a seasonal modulation. The diurnal cycle of PWV is poorly represented in ERA40 reflecting weaknesses in the water cycle of global circulation models at this timescale. Numéro de notice : A2007-682 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2006GL028039 date de publication en ligne : 09/05/2007 En ligne : https://doi.org/10.1029/2006GL028039 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95742
in Geophysical research letters > vol 34 n° 9 (16 May 2007) . - 6 p.[article]
