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    The Representation of Atmospheric Blocking and the Associated Low-Frequency Variability in Two Seasonal Prediction Systems

    Source: Journal of Climate:;2014:;volume( 027 ):;issue: 024::page 9082
    Author:
    Athanasiadis, Panos J.
    ,
    Bellucci, Alessio
    ,
    Hermanson, Leon
    ,
    Scaife, Adam A.
    ,
    MacLachlan, Craig
    ,
    Arribas, Alberto
    ,
    Materia, Stefano
    ,
    Borrelli, Andrea
    ,
    Gualdi, Silvio
    DOI: 10.1175/JCLI-D-14-00291.1
    Publisher: American Meteorological Society
    Abstract: rimarily as a response to boundary forcings, certain components of the atmospheric intraseasonal variability are potentially predictable. Particularly referring to the extratropics, the current generation of seasonal forecasting systems is making advancements in predicting these components by realistically initializing many components of the climate system, using higher resolution and utilizing large ensemble sizes.The operational seasonal prediction system of the Met Office (UKMO) and the corresponding system of the Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC) are analyzed in terms of their representation of different aspects of extratropical low-frequency variability. The UKMO system achieves unprecedented high scores in predicting the winter mean phase of the North Atlantic Oscillation (NAO; correlation 0.62) and the Pacific?North American pattern (PNA; correlation 0.82). The CMCC system, despite its smaller ensemble size and coarser resolution, also exhibits significant skill (0.42 for NAO, 0.51 for PNA). Low-frequency variability is underrepresented in both models, particularly in the eastern North Atlantic. Consequently, their intrinsic variability patterns (sectoral EOFs) are somewhat different from the observed patterns.Regarding the representation of wintertime Northern Hemisphere blocking, after bias correction both systems exhibit a realistic climatology of blocking frequency. In this assessment, instantaneous blocking and large-scale persistent blocking events are identified using daily geopotential height fields at 500 hPa. The blocking signature on the circulation and the dependence of blocking frequency on the NAO are also quite realistic for both systems. Finally, the Met Office system exhibits significant skill in predicting the winter mean frequency of blocking that relates to the NAO.
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      The Representation of Atmospheric Blocking and the Associated Low-Frequency Variability in Two Seasonal Prediction Systems

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    contributor authorAthanasiadis, Panos J.
    contributor authorBellucci, Alessio
    contributor authorHermanson, Leon
    contributor authorScaife, Adam A.
    contributor authorMacLachlan, Craig
    contributor authorArribas, Alberto
    contributor authorMateria, Stefano
    contributor authorBorrelli, Andrea
    contributor authorGualdi, Silvio
    date accessioned2017-06-09T17:10:30Z
    date available2017-06-09T17:10:30Z
    date copyright2014/12/01
    date issued2014
    identifier issn0894-8755
    identifier otherams-80576.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4223483
    description abstractrimarily as a response to boundary forcings, certain components of the atmospheric intraseasonal variability are potentially predictable. Particularly referring to the extratropics, the current generation of seasonal forecasting systems is making advancements in predicting these components by realistically initializing many components of the climate system, using higher resolution and utilizing large ensemble sizes.The operational seasonal prediction system of the Met Office (UKMO) and the corresponding system of the Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC) are analyzed in terms of their representation of different aspects of extratropical low-frequency variability. The UKMO system achieves unprecedented high scores in predicting the winter mean phase of the North Atlantic Oscillation (NAO; correlation 0.62) and the Pacific?North American pattern (PNA; correlation 0.82). The CMCC system, despite its smaller ensemble size and coarser resolution, also exhibits significant skill (0.42 for NAO, 0.51 for PNA). Low-frequency variability is underrepresented in both models, particularly in the eastern North Atlantic. Consequently, their intrinsic variability patterns (sectoral EOFs) are somewhat different from the observed patterns.Regarding the representation of wintertime Northern Hemisphere blocking, after bias correction both systems exhibit a realistic climatology of blocking frequency. In this assessment, instantaneous blocking and large-scale persistent blocking events are identified using daily geopotential height fields at 500 hPa. The blocking signature on the circulation and the dependence of blocking frequency on the NAO are also quite realistic for both systems. Finally, the Met Office system exhibits significant skill in predicting the winter mean frequency of blocking that relates to the NAO.
    publisherAmerican Meteorological Society
    titleThe Representation of Atmospheric Blocking and the Associated Low-Frequency Variability in Two Seasonal Prediction Systems
    typeJournal Paper
    journal volume27
    journal issue24
    journal titleJournal of Climate
    identifier doi10.1175/JCLI-D-14-00291.1
    journal fristpage9082
    journal lastpage9100
    treeJournal of Climate:;2014:;volume( 027 ):;issue: 024
    contenttypeFulltext
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