平流层极涡振荡与ENSO热带海温异常的时空联系

Temporal and spatial connections of the stratospheric polar vortex oscillation to the ENSO tropical SST anomalies

中文关键词:  极涡振荡， 年际异常， ENSO热带海温， 时空联系

英文关键词:Polar vortex oscillation, Inter annual trend, ENSO tropical SST, Temporal and spatial connection

中文摘要:

      利用一个在等熵位涡坐标下建立的平流层极涡振荡(Polar Vortex Oscillation)指数，以及NCEP/NCAR再分析资料和NOAA –OISST -V2逐周海温资料，研究了月尺度以上热带海温异常与平流层极涡振荡的时间和空间联系，通过相关、回归以及合成分析发现，两者的显著联系主要发生在3—5年的年际时间尺度上，表现为ENSO型海温异常与极涡振荡年际趋势之间的时空关联。首先，两者的关系并不表现在同期相关上，而是当ENSO海温异常超前极涡振荡年际异常9—11个月时，两者具有最大的负相关关系。当前期热带海温偏暖（冷）时，9—11个月后极涡振荡的年际趋势为负（正）的异常，即极涡偏弱（强）或负（正）振荡事件为主。统计合成结果进一步证实，前期热带ENSO海温暖事件背景下，后期极涡振荡负事件的发生比正事件更多，强度更强，持续时间也更长，反之亦然；另外，前期热带ENSO暖海温背景下，极涡正、负振荡事件的发生均更频繁。研究连接热带ENSO海温异常与平流层极涡振荡的过程发现，热带海温异常不仅可在热带地区引起大气温度的异常响应，〖JP3〗而且可以引发从平流层热带到极区的一系列温度异常同时向下和向极区的传播过程，并与9—11个月以后发生在极区的极涡振荡异常相联系。表明与热带海温异常相联系的极涡振荡年际异常，可能存在与季节尺度极涡振荡中类似的全球质量环流的异常变化。

英文摘要:

      Using the polar vortex oscillation (PVO) index established in an isentropic Po tential Vorticity coordinate and based on the NCEP/NCAR reanalysis data and the weekly NOAA -OISST-V2 SST data, the temporal and spatial connections of the stratospheric PVO to the ENSO tropical SST over monthly timescale are investigated through the correlation, regression and composite analyses. It is found that the significant connections exist mainly at the inter annual timescale of about 3-5 year, representing the relationships between the inter annual PVO trend and the ENSO SST anomalies. Firstly, the temporal connections between the two phenomena are not contemporary as expected, but rather that the maximum negative correlation occurs when the ENSO tropical SST anomalies lead the PVO for 9-11 months. Warmer (colder) ENSO SST anomalies tend to be followed by a negative (positive) inter annual trend of PVO, or a weaker (stronger) polar vortex. The composite and statistical results further verify that there tend to be more and stronger negative PVO events followed in the case of a warmer ENSO SST event occurred in the previous period, and vice versa. The warmer ENSO SST may also favor a higher frequency of PVO events than colder SST regardless of positive or negative PVO events. Further, it is found that, following the significant responses in the tropical troposphere and stratosphere to the warmer ENSO SST, there exist a seies of simultaneous poleward and downward propagations of temperature anomalies from the tropics to the polar region, which are coincidently related with the PVO anomalies 9-11 months later. This may suggest that, as in the intra seasonal variations of the PVO, the inter annual variation of PVO associated with leading ENSO SST anomalies might also be accompanied with the inter annual variations of the global mass circulation. This linkage of the tropical SST to the extra tropical PVO trend implies basically new opportunities for the extended climate prediction.