Australian hot and dry extremes induced by weakenings of the stratospheric polar vortex
Australian hot and dry extremes induced by weakenings of the stratospheric polar vortex
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DOI：
10.1038/s41561-019-0456-x
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发表时间：
2019-11-01
影响因子：
18.3
通讯作者：
Arblaster, Julie M.
中科院分区：
文献类型：
--
作者：
Lim, Eun-Pa;Hendon, Harry H.;Arblaster, Julie M.
在温暖季节发生极端炎热和干燥的情况会对人类健康、能源和水供应、农业和野火产生重大影响。人们已经知道，澳大利亚的极端炎热和极端干燥与厄尔尼诺现象的发生和对流层环流的其他变化有关。在这里，我们确定了一个额外的驱动因素：平流层南极极地涡旋的变率。基于对过去40年观测数据的统计分析，我们发现平流层极地涡旋的减弱和变暖（在南春期间偶尔发生）大大增加了从南春到初夏在亚热带东部澳大利亚发生极端炎热和干燥以及相关的有利于火灾的天气的机会。这些澳大利亚极端气候的促进是由于减弱的极地涡旋与对流层水平的向下耦合，在对流层中，它与南环模的低指数极性、中纬度西风急流的赤道移动以及亚热带的下沉和变暖有关。由于极地涡旋变化的长时间尺度，在涡旋减弱的几年里，澳大利亚东部夏初极端炎热和干燥以及野火风险的可能性增加，可以提前一个季节预测。
The occurrence of extreme hot and dry conditions in warm seasons can have large impacts on human health, energy and water supplies, agriculture and wildfires. Australian hot and dry extremes have been known to be associated with the occurrence of El Nino and other variations of tropospheric circulation. Here we identify an additional driver: variability of the stratospheric Antarctic polar vortex. On the basis of statistical analyses using observational data covering the past 40 yr, we show that weakenings and warmings of the stratospheric polar vortex, which episodically occur during austral spring, substantially increase the chances of hot and dry extremes and of associated fire-conducive weather across subtropical eastern Australia from austral spring to early summer. The promotion of these Australian climate extremes results from the downward coupling of the weakened polar vortex to tropospheric levels, where it is linked to the low-index polarity of the Southern Annular Mode, an equatorward shift of the mid-latitude westerly jet stream and subsidence and warming in the subtropics. Because of the long timescale of the polar vortex variations, the enhanced likelihood of early-summertime hot and dry extremes and wildfire risks across eastern Australia may be predictable a season in advance during years of vortex weakenings.