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<p>The evolution of the MJO characteristics and structures is investigated through composite analysis of MJO events during boreal winter that formed over the Indian Ocean and successfully propagated into the Maritime Continent. The phase relationship between the MJO low-level zonal wind and convection shows distinct variations during eastward propagation of MJO, and it is closely linked to the strength of the MJO’s zonal-vertical circulations. During the initial stage of the MJO over the western Indian Ocean, only the Front Walker Cell (FWC) is observed, characterized by strong low-level easterlies ahead of the MJO convection envelope. As the MJO propagates into the Maritime Continent, both the FWC and the Back Reversed Walker Circulation (BRWC) show comparable strength and zonal scale, with the MJO convection located between the low-level easterly and westerly anomalies. Once the MJO enters the Pacific Ocean, the BRWC dominates, with low-level westerlies prevailing over the MJO convection. The strength of the MJO critically depends on the moist air from the east, whereas its convection is suppressed by the cooler, drier air from the west. Both zonal and meridional moisture advection moisten the low-level troposphere ahead of the MJO convection during the initial stage over the Indian Ocean. Meridional moisture advection becomes the dominant moistening mechanism as it propagate into the Maritime Continent. Throughout its life cycle, the MJO meridional wind acting on the background moisture gradient is the dominant contributor to moistening the low-level troposphere ahead of the MJO convection.</p>

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Evolution of MJO structures during eastward propagation

  • 期刊论文

  • 发表日期：

    2025年9月27日

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  • Yuqing Long,
  • Jian Ling,
  • Chongyin Li,
  • Guiwan Chen,
  • Guanshun Zhang,
  • Qun Tian,
  • Lina Huang,
  • Yu Zhu

摘要

The evolution of the MJO characteristics and structures is investigated through composite analysis of MJO events during boreal winter that formed over the Indian Ocean and successfully propagated into the Maritime Continent. The phase relationship between the MJO low-level zonal wind and convection shows distinct variations during eastward propagation of MJO, and it is closely linked to the strength of the MJO’s zonal-vertical circulations. During the initial stage of the MJO over the western Indian Ocean, only the Front Walker Cell (FWC) is observed, characterized by strong low-level easterlies ahead of the MJO convection envelope. As the MJO propagates into the Maritime Continent, both the FWC and the Back Reversed Walker Circulation (BRWC) show comparable strength and zonal scale, with the MJO convection located between the low-level easterly and westerly anomalies. Once the MJO enters the Pacific Ocean, the BRWC dominates, with low-level westerlies prevailing over the MJO convection. The strength of the MJO critically depends on the moist air from the east, whereas its convection is suppressed by the cooler, drier air from the west. Both zonal and meridional moisture advection moisten the low-level troposphere ahead of the MJO convection during the initial stage over the Indian Ocean. Meridional moisture advection becomes the dominant moistening mechanism as it propagate into the Maritime Continent. Throughout its life cycle, the MJO meridional wind acting on the background moisture gradient is the dominant contributor to moistening the low-level troposphere ahead of the MJO convection.