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<p>The western North Pacific (WNP) monsoon trough (MT) plays a crucial role in regulating large-scale circulation and tropical cyclone (TC) activity, yet its width as a fundamental structural metric has received limited attention. The present study investigates the interannual variability of MT width over the WNP during the period 1979–2022 and its associated impacts. It is shown that the climatological mean MT width is approximately 12.8°, with pronounced interannual variability that is highly correlated with El Niño–Southern Oscillation (ENSO)-related MT location. However, substantial width differences occur even at similar MT positions. When the MT is displaced eastward, a wide MT is accompanied by a weaker, northward-positioned subtropical high and central Pacific (CP) SST warming. The anomalous Walker circulation in response to the CP SST warming drives an enhanced convection over the northeastern flank of the MT, which in turn induces anomalous low-level cyclonic circulation to the north of the MT through a Gill-type Rossby wave response. These changes favor a northward shift of TC genesis and increase the occurrence of northward-recurving TCs. In contrast, during narrow MT years, a southward-displaced subtropical high and weak Walker circulation anomalies suppress convection over the northeastern flank of the MT, weakening cyclonic circulation to the north and shifting TC genesis southward. When the MT is displaced westward, circulation anomalies associated with the width variation are confined within the MT rather than extending northward. A wide MT enhances cyclonic circulation and convection within the trough, increasing the proportion of TCs that form within the MT and then move northwestward along the trough, whereas a narrow MT exhibits weaker cyclonic circulation and convection, limiting TC formation. Overall, this study demonstrates that the MT width plays a key role in modulating WNP circulation and TC activity, providing new insights into MT variability and its climatic implications, with practical relevance for TC risk assessment.</p>

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Interannual variability of the monsoon trough width over the western North Pacific and its relationship to tropical cyclone activity

  • 期刊论文

  • 发表日期：

    2026年7月2日

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  • Ruyue Xue,
  • Liang Wu,
  • Shangfeng Chen,
  • Xi Cao,
  • Tao Feng,
  • Peishan Chen

摘要

The western North Pacific (WNP) monsoon trough (MT) plays a crucial role in regulating large-scale circulation and tropical cyclone (TC) activity, yet its width as a fundamental structural metric has received limited attention. The present study investigates the interannual variability of MT width over the WNP during the period 1979–2022 and its associated impacts. It is shown that the climatological mean MT width is approximately 12.8°, with pronounced interannual variability that is highly correlated with El Niño–Southern Oscillation (ENSO)-related MT location. However, substantial width differences occur even at similar MT positions. When the MT is displaced eastward, a wide MT is accompanied by a weaker, northward-positioned subtropical high and central Pacific (CP) SST warming. The anomalous Walker circulation in response to the CP SST warming drives an enhanced convection over the northeastern flank of the MT, which in turn induces anomalous low-level cyclonic circulation to the north of the MT through a Gill-type Rossby wave response. These changes favor a northward shift of TC genesis and increase the occurrence of northward-recurving TCs. In contrast, during narrow MT years, a southward-displaced subtropical high and weak Walker circulation anomalies suppress convection over the northeastern flank of the MT, weakening cyclonic circulation to the north and shifting TC genesis southward. When the MT is displaced westward, circulation anomalies associated with the width variation are confined within the MT rather than extending northward. A wide MT enhances cyclonic circulation and convection within the trough, increasing the proportion of TCs that form within the MT and then move northwestward along the trough, whereas a narrow MT exhibits weaker cyclonic circulation and convection, limiting TC formation. Overall, this study demonstrates that the MT width plays a key role in modulating WNP circulation and TC activity, providing new insights into MT variability and its climatic implications, with practical relevance for TC risk assessment.