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    Nonstationary Synchronization of Equatorial QBO with SAO in Observations and a Model

    Source: Journal of the Atmospheric Sciences:;2009:;Volume( 066 ):;issue: 006::page 1654
    Author:
    Kuai, Le
    ,
    Shia, Run-Lie
    ,
    Jiang, Xun
    ,
    Tung, Ka-Kit
    ,
    Yung, Yuk L.
    DOI: 10.1175/2008JAS2857.1
    Publisher: American Meteorological Society
    Abstract: It has often been suggested that the period of the quasi-biennial oscillation (QBO) has a tendency to synchronize with the semiannual oscillation (SAO). Apparently the synchronization is better the higher up the observation extends. Using 45 yr of the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data of the equatorial stratosphere up to the stratopause, the authors confirm that this synchronization is not just a tendency but a robust phenomenon in the upper stratosphere. A QBO period starts when a westerly SAO (w-SAO) descends from the stratopause to 7 hPa and initiates the westerly phase of the QBO (w-QBO) below. It ends when another w-SAO, a few SAO periods later, descends again to 7 hPa to initiate the next w-QBO. The fact that it is the westerly but not the easterly SAO (e-SAO) that initiates the QBO is also explained by the general easterly bias of the angular momentum in the equatorial stratosphere so that the e-SAO does not create a zero-wind line, unlike the w-SAO. The currently observed average QBO period of 28 months, which is not an integer multiple of SAO periods, is a result of intermittent jumps of the QBO period from four SAO to five SAO periods. The same behavior is also found in the Two and a Half Dimensional Interactive Isentropic Research (THINAIR) model. It is found that the nonstationary behavior in both the observation and model is caused not by the 11-yr solar-cycle forcing but by the incompatibility of the QBO?s natural period (determined by its wave forcing) and the ?quantized? period determined by the SAO. The wave forcing parameter for the QBO period in the current climate probably lies between four SAO and five SAO periods. If the wave forcing for the QBO is tuned so that its natural period is compatible with the SAO period above (e.g., at 24 or 30 months), nonstationary behavior disappears.
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      Nonstationary Synchronization of Equatorial QBO with SAO in Observations and a Model

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    contributor authorKuai, Le
    contributor authorShia, Run-Lie
    contributor authorJiang, Xun
    contributor authorTung, Ka-Kit
    contributor authorYung, Yuk L.
    date accessioned2017-06-09T16:23:07Z
    date available2017-06-09T16:23:07Z
    date copyright2009/06/01
    date issued2009
    identifier issn0022-4928
    identifier otherams-66911.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4208299
    description abstractIt has often been suggested that the period of the quasi-biennial oscillation (QBO) has a tendency to synchronize with the semiannual oscillation (SAO). Apparently the synchronization is better the higher up the observation extends. Using 45 yr of the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data of the equatorial stratosphere up to the stratopause, the authors confirm that this synchronization is not just a tendency but a robust phenomenon in the upper stratosphere. A QBO period starts when a westerly SAO (w-SAO) descends from the stratopause to 7 hPa and initiates the westerly phase of the QBO (w-QBO) below. It ends when another w-SAO, a few SAO periods later, descends again to 7 hPa to initiate the next w-QBO. The fact that it is the westerly but not the easterly SAO (e-SAO) that initiates the QBO is also explained by the general easterly bias of the angular momentum in the equatorial stratosphere so that the e-SAO does not create a zero-wind line, unlike the w-SAO. The currently observed average QBO period of 28 months, which is not an integer multiple of SAO periods, is a result of intermittent jumps of the QBO period from four SAO to five SAO periods. The same behavior is also found in the Two and a Half Dimensional Interactive Isentropic Research (THINAIR) model. It is found that the nonstationary behavior in both the observation and model is caused not by the 11-yr solar-cycle forcing but by the incompatibility of the QBO?s natural period (determined by its wave forcing) and the ?quantized? period determined by the SAO. The wave forcing parameter for the QBO period in the current climate probably lies between four SAO and five SAO periods. If the wave forcing for the QBO is tuned so that its natural period is compatible with the SAO period above (e.g., at 24 or 30 months), nonstationary behavior disappears.
    publisherAmerican Meteorological Society
    titleNonstationary Synchronization of Equatorial QBO with SAO in Observations and a Model
    typeJournal Paper
    journal volume66
    journal issue6
    journal titleJournal of the Atmospheric Sciences
    identifier doi10.1175/2008JAS2857.1
    journal fristpage1654
    journal lastpage1664
    treeJournal of the Atmospheric Sciences:;2009:;Volume( 066 ):;issue: 006
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
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