Variation in Brewer–Dobson circulation during three sudden stratospheric major warming events in the 2000s

Abstract

As the strongest subseasonal atmospheric variability during boreal winter, three remarkable sudden stratospheric major warming (SSW) events in the 2000s are investigated in terms of the Brewer–Dobson circulation (BDC) response. Our study shows that the changes of cross-isentropic velocity during the SSWs are not only confined to the polar region, but also extend to the whole Northern Hemisphere: enhanced descent in the polar region, as well as enhanced ascent in the tropics. When the acceleration of the deep branch of the BDC descends to the middle stratosphere, its strength rapidly decreases over a period of one to two weeks. The acceleration of the deep branch of the BDC is driven by the enhanced planetary wave activity in the mid-to-high-latitude stratosphere. Different from the rapid response of the deep branch of the BDC, tropical upwelling in the lower stratosphere accelerates up to 20%–40% compared with the climatology, 20–30 days after the onset of the SSWs, and the acceleration lasts for one to three months. The enhancement of tropical upwelling is associated with the large-scale wave-breaking in the subtropics interacting with the midlatitude and tropical Quasi-Biennial Oscillation–related mean flow.

摘要

本文讨论了2000以来三次平流层爆发性增温(SSW)事件对Brewer-Dobson(BD)环流的影响. 结果表明, SSW期间穿越等熵面的垂直运动不只出现在极区, 而是在整个北半球, SSW后极区下沉和热带地区上升都有所增强. 位于平流层中高层的BD深环流上升支在SSW开始前后在中高纬度行星波的拖曳作用下明显增强, 持续时间在10天左右; 不同于BD深环流, 平流层低层的BD浅环流的热带上升支, 在SSW发生后约一个月左右才明显加强, 持续时间在1-3个月, 这是大尺度波在副热带地区的拖曳作用同副热带和赤道纬向风场相互作用的结果. 赤道纬向风的垂直结构(即QBO东西风位相)调节着波动破碎在副热带地区发生的位置.