Extreme precipitation at Padang, Sumatra triggered by convectively coupled Kelvin waves
Extreme precipitation at Padang, Sumatra triggered by convectively coupled Kelvin waves
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对流耦合开尔文波引发苏门答腊岛巴东极端降水
DOI：
10.1002/qj.4506
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发表时间：
2023
影响因子：
8.9
通讯作者：
Senior N
中科院分区：
文献类型：
--
作者：
Senior N
对流耦合开尔文波（CCKW）是一种热带天气系统，它沿着赤道波导向东传播，以前与印度尼西亚苏门答腊岛90%的洪水事件有关。在这里，通过CCKW影响对流产生极端降水的过程进行了研究，重点放在巴塘，苏门答腊岛西海岸的一个城市。极端降水日在巴塘，定义为日总降水量超过第95个百分位数时，被发现是59%更有可能发生的CCKW的存在。我们发现，CCKWs调制的日周期产生极端降水。这首先是通过提供低水平的水分和会聚来实现的，其作用是将开尔文波耦合到对流。其次，CCKW的作用是将辐合区移向巴塘，使其经历持续整夜的降雨，并在第二天傍晚达到峰值。我们研究了2017年8月21日经过巴塘的CCKW的案例研究，带来了导致西苏门答腊地区洪水的极端降水，记录了137 mm的最大日累积降雨量。该案例研究表明，其传播，结构和降水模式的CCKWs的复合研究非常相似的特点。一套对流允许配置的英国气象局统一模型（MetUM），嵌入在一个参数化的对流全球模型，在预测这个CCKW的性能进行了评估。一般来说，模型的所有配置都能很好地捕捉到这一事件。我们发现，将高分辨率模式域的西部边界从90°E扩展到65°E，可以显著改善预测，因为与低分辨率全球驱动模式相比，高分辨率嵌套模式更准确地捕捉到印度洋上空CCKW的发展。
Convectively coupled Kelvin waves (CCKWs) are tropical weather systems that travel eastward along the equatorial waveguide and have previously been linked to 90% of flooding events in Sumatra, Indonesia. Here, the processes through which CCKWs influence convection to produce extreme precipitation are investigated, with a focus on Padang, a city on the west coast of Sumatra. Extreme precipitation days at Padang, defined as days when the daily total precipitation exceeds the 95th$$ 95\mathrm{th} $$ percentile, are found to be 59% more likely to occur given the presence of a CCKW. We find that CCKWs modulate the diurnal cycle to produce extreme precipitation. This is achieved firstly through providing low‐level moisture and convergence that acts to couple the Kelvin wave to the convection. Secondly, the CCKW acts to displace the convergence zone towards Padang, such that it experiences rainfall that persists throughout the night and peaks the following day in the early evening. We examine the case study of a CCKW that passed over Padang on August 21, 2017, bringing extreme precipitation that led to flooding in the West Sumatra region, recording a maximum daily accumulated rainfall of 137 mm. This case study showed remarkably similar characteristics in its propagation, structure, and precipitation patterns to composite studies of CCKWs. The performance of a suite of convection‐permitting configurations of the UK Met Office Unified Model (MetUM), embedded within a parameterised convection global model, in forecasting this CCKW is evaluated. In general, all configurations of the model capture this event reasonably well. We find that extending the western boundary of the high‐resolution model domain from 90°E to 65°E leads to a significantly improved forecast, as the CCKW development over the Indian Ocean is captured more accurately by the high‐resolution nested model, compared with the lower‐resolution global driving model.
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