中文摘要：

比较了南北半球春季平流层极涡的崩溃过程以及涡动在此崩溃过程中的作用。极涡的崩溃时间以平流层极夜急流核区最后一次西风转换为东风的时间来确定。结果表明南北半球平流层极涡的崩溃过程有着共同的特点,涡动和非绝热加热过程都对极涡的崩溃起着重要的作用,在极涡崩溃前平流层行星尺度波动活动明显,极涡崩溃以后,这种波动活动便迅速减弱。其中从对流层上传的行星波决定着极涡的具体崩溃时间。两个半球的差别主要表现在南半球极涡崩溃过程一般始于平流层高层,然后逐渐下传,而北半球这种下传不是很明显。其次,北半球平流层极涡崩溃偏晚年,极涡的减弱有两次过程,第一次为快速变化过程,第二次变化比较缓慢,而南半球平流层极涡崩溃无论早晚年只有一次减弱过程。长期的变化趋势分析表明南北半球平流层极涡的崩溃时间逐渐推迟,特别是20世纪90年代中后期以来,这种推迟更加明显。进一步的研究还发现,伴随着平流层极涡的崩溃过程平流层和对流层存在强烈的动力耦合,南北半球极涡迅速减弱前,各自半球的环状模指数也由负指数增加为正指数,表明低层环流对于平流层极涡的崩溃起到重要的作用;同时极涡不同强度所对应的低层环状模指数也不同,这可能与不同强度平流层极涡对于上传的行星波的反射有关。

英文摘要：

The breakup of the stratospheric polar vortex and the role of eddy activities during the breaking are investigated with focus on the differences between the southern and northern hemispheres. The time when the polar vortex breaks up is determined by the date when the winter westerly at the core of polar night jet turns to summer easterly. Results obtained show that dynamical and diabatic heating both play an important role in the breakup of stratospheric polar vortex in the two hemispheres. Strong activities of planetary waves are observed in both stratosphere and troposphere before the breakup; thereafter, the eddy activities decline quickly. It is pointed out that the upward planetary waves determine the exact time of breaking. The two hemispheres show several differences. First, the breaking of polar vortex begins from the upper stratosphere and then propagates downward in the Southern Hemisphere （SH） ; however, the seasonal downward propagation is not evident in the Northern Hemisphere （NH）. Second, composite of zonal wind at the core of polar jet shows that the Nil late breaking years have two periods of westerly weakening while the early breaking years have only one. The first weakening in the NH late breaking years is a quick process while the second is a slow one. For the SH, there is only one weakening of the westerly regardless of the time of breaking. The long-term trend indicates that the breaking time of the stratospheric polar vortex has been postponed in both hemispheres, especially since the middle 1990s. It is also pointed out in this study that the evolution of the stratospheric polar vortex breaking is associated with strong bi-directional dynamical coupling of the stratosphere and the troposphere in both hemispheres. On one hand, the annular mode increases from negative value to positive value before the breaking in corresponding hemisphere, indicating that the circulation pattern change at the lower levels heralds the breaking at upper levels; on the other hand, the phase and the