Diurnal Cycle and Dipolar Pattern of Precipitation over Borneo during an MJO Event: Lee Convergence and Offshore Propagation
Diurnal Cycle and Dipolar Pattern of Precipitation over Borneo during an MJO Event: Lee Convergence and Offshore Propagation
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MJO 事件期间婆罗洲降水的日循环和偶极模式：Lee 辐合和离岸传播
DOI：
10.1175/jas-d-21-0258.1
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Juan Fang
中科院分区：
文献类型：
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作者：
Yihao Zhou;Shuguang Wang;Juan Fang
在麦登-朱利安涛动（MJO）对流相到来之前，海洋大陆岛屿表面降水异常通常以偶极型的形式引领海洋降水一周。作者使用允许云的建模、观测和再分析数据集，研究了2017年1月至2月北方冬季MJO事件期间婆罗洲上空的这种偶极模式。分析了该MJO事件在局部增长期和衰减期的降水日循环。观测和模拟结果均表明，婆罗洲西南部和东北部的降水异常在生长阶段与MJO偏东有关，而在衰减阶段则相反。由于地势较高，婆罗洲上空低空气流在日尺度上在地形附近分裂。在下午晚些时候和晚上（当地太阳时1700-2000），分裂流诱导的尾流涡和热驱动的海风倾向于在背风面汇聚，都有助于背风辐合和降水，并在午夜达到峰值。随后在午夜和清晨由背风内陆对流发展而来的近海传播，在西婆罗洲的生长阶段向西北传播，在东婆罗洲的衰减阶段向东传播。离岸传播持续到下一个中午，这时海风和岛屿对流开始。近海传播的时间和位置表明它不是一个独立的对流模式。相反，它与MJO调制的岛屿降水的偶极分布有关。
Abstract Surface precipitation anomalies over Maritime Continent islands typically lead oceanic precipitation by a week in the form of dipolar pattern before the arrival of Madden–Julian oscillation (MJO) convective phase. The authors study this dipolar pattern over Borneo during the boreal winter MJO event in January–February 2017 using cloud-permitting modeling, observation, and reanalysis datasets. The diurnal cycles of precipitation are analyzed during the local growing and decaying stages of this MJO event. Both the observation and simulation show positive precipitation anomaly over southwestern Borneo and negative anomaly over northeastern Borneo associated with the MJO easterly in the growing stage, whereas the pattern reverses in the decaying stage. Due to relatively high terrain, the low-level flows over Borneo split near the topography on the diurnal time scale. During the late afternoon and night (1700–2000 local solar time), the splitting-flow-induced wake vortices and thermally driven sea breezes tend to converge at the leeside, both contributing to leeward convergence and precipitation, which peaks at midnight. Subsequent offshore propagation during midnight and early morning develops from the leeward inland convection, and propagates northwestwards in the growing stage over west Borneo, and eastward in the decaying stage over east Borneo. Offshore propagation lasts until the next noon when sea breezes and island convection initiate. The timing and location of the offshore propagation suggest that it is not an independent convective mode. Instead, it is tied to the dipolar distribution of island precipitation modulated by the MJO.