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<p>Extreme winter weather in North America is strongly influenced by atmospheric intraseasonal oscillations (ISOs), yet the dominant modes of intraseasonal variability in this region remain insufficiently documented. Using upper-level meridional winds from the ERA5 reanalysis dataset, this study identifies two leading ISO modes: a quasi-biweekly mode (10–22&#xa0;days) and a quasi-monthly mode (23–50&#xa0;days). Both modes share an equivalent barotropic vertical structure and are sustained primarily by baroclinic energy conversion, but they differ markedly in spatial structure, propagation, and climatic impacts. The quasi-biweekly mode manifests as a circumglobal wave train with zonal wave number 6, propagating eastward along the subtropical Asian jet in the Eastern Hemisphere and following a great circle-like pathway in the Western Hemisphere. It produces eastward-propagating precipitation and surface air temperature anomalies across North America. By contrast, the quasi-monthly mode is confined to the Western Hemisphere and exhibits a quasi-stationary Pacific-North America (PNA)-like wave train pattern, originated from westward-propagating precipitation anomalies over the western tropical Pacific. It induces a dipole pattern of precipitation and temperature anomalies between western and eastern North America. Distinguishing between these two modes provides new insights into sources of subseasonal predictability for extreme weather in North America.</p>

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Quasi-biweekly and quasi-monthly intraseasonal oscillations in North American winter atmospheric circulation

  • 期刊论文

  • 发表日期：

    2025年11月20日

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  • Yifeng Cheng,
  • Lu Wang,
  • Xuan Zhou,
  • Lijuan Wang

摘要

Extreme winter weather in North America is strongly influenced by atmospheric intraseasonal oscillations (ISOs), yet the dominant modes of intraseasonal variability in this region remain insufficiently documented. Using upper-level meridional winds from the ERA5 reanalysis dataset, this study identifies two leading ISO modes: a quasi-biweekly mode (10–22 days) and a quasi-monthly mode (23–50 days). Both modes share an equivalent barotropic vertical structure and are sustained primarily by baroclinic energy conversion, but they differ markedly in spatial structure, propagation, and climatic impacts. The quasi-biweekly mode manifests as a circumglobal wave train with zonal wave number 6, propagating eastward along the subtropical Asian jet in the Eastern Hemisphere and following a great circle-like pathway in the Western Hemisphere. It produces eastward-propagating precipitation and surface air temperature anomalies across North America. By contrast, the quasi-monthly mode is confined to the Western Hemisphere and exhibits a quasi-stationary Pacific-North America (PNA)-like wave train pattern, originated from westward-propagating precipitation anomalies over the western tropical Pacific. It induces a dipole pattern of precipitation and temperature anomalies between western and eastern North America. Distinguishing between these two modes provides new insights into sources of subseasonal predictability for extreme weather in North America.