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<p>The mid-latitude cold vortex (CV) induced heavy rainfall event in North China is a great challenge at subseasonal forecast, due to the short life cycle of CV. Based on the case in July 2017, here we investigate the precursor of downstream Okhotsk blocking high (OKBH) and the western North Pacific subtropical high (WNPSH) in the CV-induced rainfall event. Our results show the CV is originated from 90º to 100ºE, caused by the upstream positive potential vorticity (PV) advection at 200&#xa0;hPa. The WNPSH, featured by 30–90&#xa0;day intraseasonal oscillation (ISO), transports moisture to North China, while OKBH characterized by 10–30&#xa0;day ISO further transports moisture northward and establishes a downstream blocking pattern. Their interaction provides both moisture supply and circulation background for intense CV rainfall. The OKBH leads the developing of CV by approximately 5&#xa0;days, which is observed in 14&#xa0;years during 1991–2020. As a result, its earlier establishment can serve as a precursor signal for the later CV-induced rainfall events in North China.</p>

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Precursor of Okhotsk blocking high in the cold vortex induced rainfall event over North China: a case study in July 2017

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  • 发表日期：

    2025年7月3日

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  • Zhiqi Yan,
  • Wanyi Sun,
  • Congwen Zhu

摘要

The mid-latitude cold vortex (CV) induced heavy rainfall event in North China is a great challenge at subseasonal forecast, due to the short life cycle of CV. Based on the case in July 2017, here we investigate the precursor of downstream Okhotsk blocking high (OKBH) and the western North Pacific subtropical high (WNPSH) in the CV-induced rainfall event. Our results show the CV is originated from 90º to 100ºE, caused by the upstream positive potential vorticity (PV) advection at 200 hPa. The WNPSH, featured by 30–90 day intraseasonal oscillation (ISO), transports moisture to North China, while OKBH characterized by 10–30 day ISO further transports moisture northward and establishes a downstream blocking pattern. Their interaction provides both moisture supply and circulation background for intense CV rainfall. The OKBH leads the developing of CV by approximately 5 days, which is observed in 14 years during 1991–2020. As a result, its earlier establishment can serve as a precursor signal for the later CV-induced rainfall events in North China.