The 2019 Southern Hemisphere Stratospheric Polar Vortex Weakening and Its Impacts
The 2019 Southern Hemisphere Stratospheric Polar Vortex Weakening and Its Impacts
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DOI：
10.1175/bams-d-20-0112.1
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发表时间：
2021-06-01
影响因子：
8
通讯作者：
Wang, Guomin
中科院分区：
文献类型：
--
作者：
Lim, Eun-Pa;Hendon, Harry H.;Wang, Guomin
本研究概述了2019年南方春季发生的罕见的南半球平流层变暖的低频（即月度至季节性）演变、动态、可预测性和地表影响。2019年8月下旬至9月中旬，平流层环极西风急流迅速减弱，南极平流层温度急剧上升。涡旋在10hpa的减速与2002年在SH首次观测到的平流层突然变暖一样剧烈，而2019年春季南极平流层中部的平均变暖打破了2002年的记录，幅度接近50%。在这一事件发生之前，在初冬，平流层最上层的SH极夜急流向极地移动，随后在8月，创纪录的强烈行星波1活动从对流层向上传播，极大地削弱了整个平流层深处的极地涡旋。从10月中旬到12月，减弱的涡旋风和升高的气温向下移动到地面，推动了创纪录的南环模（SAM）向负相的强烈摆动。这种创纪录的负SAM似乎是澳大利亚亚热带东部极端炎热和干燥条件的主要驱动因素，这种条件伴随着2019年春末发生的严重野火。最先进的动态季节预报系统早在7月下旬就熟练地预测了2019年春季涡旋的显著减弱和随后的负SAM的发展。
This study offers an overview of the low-frequency (i.e., monthly to seasonal) evolution, dynamics, predictability, and surface impacts of a rare Southern Hemisphere (SH) stratospheric warming that occurred in austral spring 2019. Between late August and mid-September 2019, the stratospheric circumpolar westerly jet weakened rapidly, and Antarctic stratospheric temperatures rose dramatically. The deceleration of the vortex at 10 hPa was as drastic as that of the first-ever-observed major sudden stratospheric warming in the SH during 2002, while the mean Antarctic warming over the course of spring 2019 broke the previous record of 2002 by similar to 50% in the midstratosphere. This event was preceded by a poleward shift of the SH polar night jet in the uppermost stratosphere in early winter, which was then followed by record-strong planetary wave-1 activity propagating upward from the troposphere in August that acted to dramatically weaken the polar vortex throughout the depth of the stratosphere. The weakened vortex winds and elevated temperatures moved downward to the surface from mid-October to December, promoting a record strong swing of the southern annular mode (SAM) to its negative phase. This record-negative SAM appeared to be a primary driver of the extreme hot and dry conditions over subtropical eastern Australia that accompanied the severe wildfires that occurred in late spring 2019. State-of-the-art dynamical seasonal forecast systems skillfully predicted the significant vortex weakening of spring 2019 and subsequent development of negative SAM from as early as late July.