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    Revisiting the Possible Links between the Quasi-Biennial Oscillation and the Indian Summer Monsoon Using NCEP R-2 and CMAP Fields

    Source: Journal of Climate:;2007:;volume( 020 ):;issue: 005::page 773
    Author:
    Claud, Chantal
    ,
    Terray, Pascal
    DOI: 10.1175/JCLI4034.1
    Publisher: American Meteorological Society
    Abstract: In the past the stratospheric quasi-biennial oscillation (QBO) has sometimes been proposed to explain the tendency for the Indian summer monsoon (ISM) to alternate between strong and weak years. In this study, NCEP Reanalysis-2 (R-2) and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) fields are statistically analyzed to assess the relationship between equatorial zonal winds in the stratosphere and ISM. In a first step, it is shown that zonal winds at 15 hPa during the preceding winter (January?February) are the best stratospheric predictor of the summer rainfall over the Indian subcontinent as a whole. This relationship mainly holds for August and September, or the late ISM. Surprisingly, the QBO pattern is not significantly associated with the rainfall variability during June?July or the early ISM. CMAP and NCEP R-2 fields corroborate these findings and show that westerly QBO years are associated with a deepening of the monsoon trough over the Gangetic plains and decreased convective activity in the eastern equatorial Indian region. However, further statistical analysis shows that the QBO?ISM link is complex since a westerly QBO phase at 15 hPa in boreal winter leads to a weaker monsoon surface circulation with, in particular, a weakening of the Somali jet at the beginning of the monsoon, but a much stronger circulation in September. At that time, the Tibetan high is reinforced, the tropical easterly jet at 200 hPa is stronger over India, and the local reversed Hadley circulation is also strengthened north of the equator. The mechanisms by which the QBO may affect ISM have been explored through, in particular, correlations between stratospheric winds and tropopause temperature and pressure fields. The results provide support for an out-of-phase behavior of convective activity between the Indian subcontinent and the equatorial Indian Ocean induced by the QBO phase, especially during the late ISM. During a westerly QBO phase, convective activity is, in September, enhanced over India, which brings higher precipitation, compared to the east phase. This work also suggests that the winter QBO at 15 hPa could have some skill in foreshadowing the late ISM.
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      Revisiting the Possible Links between the Quasi-Biennial Oscillation and the Indian Summer Monsoon Using NCEP R-2 and CMAP Fields

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    contributor authorClaud, Chantal
    contributor authorTerray, Pascal
    date accessioned2017-06-09T17:02:51Z
    date available2017-06-09T17:02:51Z
    date copyright2007/03/01
    date issued2007
    identifier issn0894-8755
    identifier otherams-78497.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4221172
    description abstractIn the past the stratospheric quasi-biennial oscillation (QBO) has sometimes been proposed to explain the tendency for the Indian summer monsoon (ISM) to alternate between strong and weak years. In this study, NCEP Reanalysis-2 (R-2) and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) fields are statistically analyzed to assess the relationship between equatorial zonal winds in the stratosphere and ISM. In a first step, it is shown that zonal winds at 15 hPa during the preceding winter (January?February) are the best stratospheric predictor of the summer rainfall over the Indian subcontinent as a whole. This relationship mainly holds for August and September, or the late ISM. Surprisingly, the QBO pattern is not significantly associated with the rainfall variability during June?July or the early ISM. CMAP and NCEP R-2 fields corroborate these findings and show that westerly QBO years are associated with a deepening of the monsoon trough over the Gangetic plains and decreased convective activity in the eastern equatorial Indian region. However, further statistical analysis shows that the QBO?ISM link is complex since a westerly QBO phase at 15 hPa in boreal winter leads to a weaker monsoon surface circulation with, in particular, a weakening of the Somali jet at the beginning of the monsoon, but a much stronger circulation in September. At that time, the Tibetan high is reinforced, the tropical easterly jet at 200 hPa is stronger over India, and the local reversed Hadley circulation is also strengthened north of the equator. The mechanisms by which the QBO may affect ISM have been explored through, in particular, correlations between stratospheric winds and tropopause temperature and pressure fields. The results provide support for an out-of-phase behavior of convective activity between the Indian subcontinent and the equatorial Indian Ocean induced by the QBO phase, especially during the late ISM. During a westerly QBO phase, convective activity is, in September, enhanced over India, which brings higher precipitation, compared to the east phase. This work also suggests that the winter QBO at 15 hPa could have some skill in foreshadowing the late ISM.
    publisherAmerican Meteorological Society
    titleRevisiting the Possible Links between the Quasi-Biennial Oscillation and the Indian Summer Monsoon Using NCEP R-2 and CMAP Fields
    typeJournal Paper
    journal volume20
    journal issue5
    journal titleJournal of Climate
    identifier doi10.1175/JCLI4034.1
    journal fristpage773
    journal lastpage787
    treeJournal of Climate:;2007:;volume( 020 ):;issue: 005
    contenttypeFulltext
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