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    Role of the West African Westerly Jet in Sahel Rainfall Variations

    Source: Journal of Climate:;2011:;volume( 025 ):;issue: 008::page 2880
    Author:
    Pu, Bing
    ,
    Cook, Kerry H.
    DOI: 10.1175/JCLI-D-11-00394.1
    Publisher: American Meteorological Society
    Abstract: he West African westerly jet is a low-level feature of the summer climatology that transports moisture from the eastern Atlantic onto the African continent at 8°?11°N. This study examines the relationship between the jet and Sahel precipitation variability in August, when both the jet and rainfall reach their seasonal maxima.Variations of the West African westerly jet are significantly positively correlated with precipitation variations over the Sahel on both interannual and decadal time scales. Three periods are identified (1958?71, 1972?87, and 1988?2009), corresponding to times with a wet Sahel?strong jet, dry Sahel?weak jet, and relatively wet Sahel?strong jet. In wet (dry) periods, enhanced (decreased) westerly moisture fluxes associated with a strong (weak) jet increase (decrease) the low-level moisture content over the Sahel, decreasing (enhancing) the stability of the atmosphere. This association between the jet and Sahel rainfall is also found in case studies of 1964, 1984, 1999, and 2007.The southerly moisture flux associated with the West African monsoon has less pronounced decadal variability than the westerly moisture flux of the West African westerly jet and weaker correlations with Sahel rainfall. When the monsoon flow is weak, for example, 1999 and 2007, the Sahel may still experience positive precipitation anomalies in association with strong westerly moisture transport by the jet.The West African westerly jet is also important for stabilizing the regional vorticity balance by introducing strong relative vorticity gradients. Northward flow advects low relative vorticity south of the jet to balance positive vorticity tendencies generated by midtropospheric condensation.
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      Role of the West African Westerly Jet in Sahel Rainfall Variations

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    contributor authorPu, Bing
    contributor authorCook, Kerry H.
    date accessioned2017-06-09T17:04:55Z
    date available2017-06-09T17:04:55Z
    date copyright2012/04/01
    date issued2011
    identifier issn0894-8755
    identifier otherams-79091.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4221832
    description abstracthe West African westerly jet is a low-level feature of the summer climatology that transports moisture from the eastern Atlantic onto the African continent at 8°?11°N. This study examines the relationship between the jet and Sahel precipitation variability in August, when both the jet and rainfall reach their seasonal maxima.Variations of the West African westerly jet are significantly positively correlated with precipitation variations over the Sahel on both interannual and decadal time scales. Three periods are identified (1958?71, 1972?87, and 1988?2009), corresponding to times with a wet Sahel?strong jet, dry Sahel?weak jet, and relatively wet Sahel?strong jet. In wet (dry) periods, enhanced (decreased) westerly moisture fluxes associated with a strong (weak) jet increase (decrease) the low-level moisture content over the Sahel, decreasing (enhancing) the stability of the atmosphere. This association between the jet and Sahel rainfall is also found in case studies of 1964, 1984, 1999, and 2007.The southerly moisture flux associated with the West African monsoon has less pronounced decadal variability than the westerly moisture flux of the West African westerly jet and weaker correlations with Sahel rainfall. When the monsoon flow is weak, for example, 1999 and 2007, the Sahel may still experience positive precipitation anomalies in association with strong westerly moisture transport by the jet.The West African westerly jet is also important for stabilizing the regional vorticity balance by introducing strong relative vorticity gradients. Northward flow advects low relative vorticity south of the jet to balance positive vorticity tendencies generated by midtropospheric condensation.
    publisherAmerican Meteorological Society
    titleRole of the West African Westerly Jet in Sahel Rainfall Variations
    typeJournal Paper
    journal volume25
    journal issue8
    journal titleJournal of Climate
    identifier doi10.1175/JCLI-D-11-00394.1
    journal fristpage2880
    journal lastpage2896
    treeJournal of Climate:;2011:;volume( 025 ):;issue: 008
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
    نرم افزار کتابخانه دیجیتال "دی اسپیس" فارسی شده توسط یابش برای کتابخانه های ایرانی | تماس با یابش
    yabeshDSpacePersian