对流层北极极涡强度和形态的年代际变化及其季节性特征

Seasonality and Interdecadal Variation of the Tropospheric Arctic Polar Vortex Intensity and Spatial Pattern

摘要: 基于1960~2020年的NCEP/NCAR再分析资料中500 hPa月平均位势高度场数据，结合500 hPa描述北极极涡边界的特征等值线，本文定义并计算了对流层描述北极极涡物理特征的范围指数、强度指数和综合指数，并在此基础上分析了1960~2020年对流层北极极涡的季节变化以及年际年代际变化特征，初步探究了全球变暖背景下北极极涡的强度和形态变化新特征及其与北极放大的关系。结果表明：1) 北极极涡的范围和强度具有一致的季节变化特征，夏季7月份极涡范围最小，强度最弱，极涡边界特征等值线(5560 gpm)呈四波结构；冬季1月份极涡范围最大，强度最强，极涡特征等值线呈现三波结构。2) 北极极涡的综合指数与强度指数具有高度一致的年际年代际变化特征，除夏季外，其他季节二者之间的相关达0.99以上。北极极涡的变化主要体现在极涡强度的年代际减弱，年代际转折时间发生在1995年前后，秋季的年代际减弱最显著。3) 北极极涡的空间形态也发生了显著的年代际变化，特别是在春季绕极非对称的北极极涡中心在后一年代时段分裂成东西半球的欧亚和北美两个中心。

Abstract: Based on the 500 hPa monthly reanalysis data during 1960~2020 from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), combined with the characteristic contour line of 500 hPa describing the boundary of the Arctic polar vortex, this paper defines and calculates the polar vortex extent index, intensity index and comprehensive index describing the physical characteristics of the Arctic polar vortex. On this basis, the seasonal variation, interannual and interdecadal variation characteristics of the tropospheric Arctic polar vortex during 1960~2020 are analyzed, and the new characteristics of the intensity and spatial pattern changes of the polar vortex under the background of global warming and its relationship with the Arctic Amplification are preliminarily explored. The results show that: 1) the extent and intensity of the polar vortex have the same seasonal variation characteristics. The extent is the smallest and the intensity is the weakest in July, and the characteristic contour of the polar vortex boundary (5560 gpm) shows a four-wave structure in summer. The extent is the largest and the intensity is the strongest in January, and the characteristic contour of the polar vortex presents a three-wave structure in winter. 2) The composite index and intensity index of polar vortex have highly consistent interdecadal variation characteristics, and the correlation coefficient between them is more than 0.99 in other seasons except summer. The variation of the polar vortex is mainly reflected by the interdecadal weakening of the polar vortex intensity. The turning year occurs around 1995, and the interdecadal weakening is most significant in autumn. 3) The spatial pattern of the polar vortex also has significant interdecadal changes, especially in spring, the center of the polar vortex which is asymmetrical around the pole splits into two centers located in the eastern and western hemispheres of Eurasia and North America during the later decades.