Impact of the Madden-Julian Oscillation on Persistent Heavy Rainfall over Hainan Island in October
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摘要: 本文研究了1979—2019年热带季节内振荡(MJO)对海南岛持续性强降水(PHR)的影响。结果表明,海南岛PHR的降水量和发生频次均以10月最多,且受强MJO的明显调控。当MJO对流位于热带东印度洋-西太平洋(位相3~6)时,海南岛10月持续性强降水偏多;而MJO对流位于热带西印度洋和中太平洋一带(位相7、8、1和2)时,持续性强降水较少。热带东印度洋-西太平洋的MJO对流在海南岛上空引发MJO扰动东风异常,配合其北侧有东北风异常,南侧的南海中北部存在气旋环流异常,与海南岛秋季暴雨的典型环流模态一致,使得低频水汽通量辐合增强,加湿低层大气,有利于海南岛持续性强降水的发生和维持。热带西印度洋和中太平洋一带的MJO对流引发海南岛上空的反气旋环流异常,减弱水汽辐合,不利于低层大气增湿。海洋性大陆附近偏暖的海温以及赤道中东太平洋偏低的海温有助于热带东印度洋-西太平洋MJO对流生成和发展,使得海南岛PHR增强。Abstract: This paper examines the influence of the Madden-Julian Oscillation (MJO) on the characteristics of persistent heavy rainfall (PHR) over Hainan Island for the period of 1979-2019. It is unique that abundant PHR amounts and significant rainfall variability are observed on Hainan Island during October, which are tightly connected with the stronger MJO events. The results show that Hainan Island has more PHR when MJO is in phase 3-6 (i.e., the active convections over the tropical East Indian Ocean-Western Pacific), and less PHR when MJO is in phase 7, 8, 1, and 2 (i.e., the active convections over the tropical West Indian Ocean and the central Pacific). The active MJO convections in phase 3-6 cause the MJO disturbance easterly over Hainan Island, with northeast wind anomalies from the north and a cyclone circulation anomaly over the north-central South China Sea. It is consistent with the typical circulation mode of the autumnal rainstorm on Hainan Island, which enhances the low-frequency water vapor flux convergence and humidifies the lower atmosphere, resulting in more PHR on Hainan Island. The MJO disturbance anticyclonic circulation over Hainan Island could limit convergence of water vapor flux and lower atmospheric moistening, when the MJO active convections are in phase 7, 8, 1, and 2. The warmer SST in the tropical Eastern Indian Ocean-western Pacific and the lower SST in the tropical Eastern Pacific contribute to the local MJO convections in phase 3-6, which could strengthen PHR on Hainan Island.
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Key words:
- Persistent heavy rainfall /
- Madden-Julian Oscillation /
- Hainan Island
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