Tropical Pacific intensifies June extreme rainfall over Southwestern United States/Northwestern Mexico
Tropical Pacific intensifies June extreme rainfall over Southwestern United States/Northwestern Mexico
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热带太平洋地区美国西南部/墨西哥西北部六月极端降雨加剧
DOI：
10.1007/s00382-020-05291-6
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发表时间：
2020
期刊：
影响因子：
4.6
通讯作者：
Zhang, Honghai
中科院分区：
文献类型：
--
作者：
Zhang, Honghai
美国西南部/墨西哥西北部(SWUNWM)的极端降水主要在雨季进行研究，而对旱季极端降水的研究很少或很少，尽管极端降水对维持植被和生态系统至关重要。在这里，我们检查了6月份SWUNWM的前1%的降雨量，这是平均最干燥的月份，并用50公里分辨率的全球气候模式评估它是如何受到海洋的影响的。比较有没有海洋的数千年的模拟，我们发现海洋并没有改变与6月极端降雨相关的大气环流的模式和大小，但显著地增强了降雨强度。这种加强归因于主要由热带太平洋的海表面温度(SST)增强的大气水分含量的较大可变性。两种模拟方法在与6月极端降水相关的大气环流和时间特征上的相似之处表明，大气内在过程和大气-陆地耦合对极端降雨动力学的控制占主导地位。这些模拟结果表明，SWUNWM上6月极端降水发生的可预测性受到大气内在动力和大气-陆地耦合的限制，而对其强度的可靠预测可能需要对SST变率进行忠实的模拟，特别是在热带太平洋。
Extreme rainfall over Southwestern United States/Northwestern Mexico (SWUNWM) has been mostly investigated during wet seasons, while no or little attention has been paid to extreme rainfall during dry seasons despite its vital importance for sustaining vegetation and ecosystems. Here we examine the top 1% rainfall over SWUNWM in June, the driest month on average, and assess how it is affected by the ocean with a 50 km-resolution global climate model. Comparing millennia-long simulations with and without the ocean, we find that the ocean does not change the pattern and magnitude of atmospheric circulation associated with June extreme rainfall, but significantly enhances rainfall intensity. This intensification is attributed to a larger variability of atmospheric moisture content enhanced mainly by the sea surface temperature (SST) in the tropical Pacific. The similarities in the atmospheric circulation associated with, and the temporal characteristics of, June extreme rainfall between the two simulations point to a dominant control of extreme rainfall dynamics by atmospheric intrinsic processes and atmosphere-land coupling. These modeling results imply that the predictability of occurrence of June extreme rainfall over SWUNWM is limited by atmospheric intrinsic dynamics and atmosphere-land coupling, while reliable predictions of its intensity likely require a faithful simulation of SST variability, especially in the tropical Pacific.
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