冬季蒙古反气旋和伊朗反气旋的年代际变化特征

Interdecadal Variations of Wintertime Anticyclonic Activity in the Mongolian Plateau and Iranian Plateau

根据NCEP/NCAR再分析资料,采用客观判定和追踪方法,研究了1948~2013年欧亚地区冬季温带反气旋的年代际气候变化的活动特征。结果发现,反气旋的高频分布区也是反气旋气候变化最大的区域,其中蒙古高原和伊朗高原的反气旋最活跃。反气旋的频数和强度既有长期趋势也有年代际变化。蒙古高原和伊朗高原的反气旋频数具有明显的年代际变化特征。反气旋频数具有2~6年和16~30年周期,且具有变频特征。EOF分解发现蒙古高原和伊朗高原的反气旋频数分布均在较高纬度和较低纬度地区呈现显著相反的偶子极态分布形式。蒙古高原的反气旋强度的变化基本可以体现欧亚大陆反气旋强度的变化。反气旋分布和强度的年代际变化可以用对流层低层经向温度梯度表示的斜压锋的位置和强度的年代际变化来解释,但斜压锋对欧亚反气旋的影响具有区域性。蒙古高原的反气旋在1960~1975年50°N以北较多,1990~2005年50°N以南较多的偶极子态变化与80°~120°E区域的斜压锋纬度位置自55°N南移到45°N有密切关系,30°~80°E区域的斜压锋纬度位置变化不能单独解释伊朗高原反气旋偶极子态年代际变化。自21世纪00年代中期斜压锋偏强对反气旋强度偏强有重要影响。

The NCEP/NCAR（National Centers for Environmental Prediction/National Center for Atmospheric Research） reanalysis data from 1948 to 2013 is employed to investigate wintertime anticyclone activity and its decadal variability over Eurasia using an improved objective anticyclone detection and tracking algorithm. The results reveal that the highfrequency distribution areas of the anticyclones are also areas of large climatic change of the anticyclones, especially in the Mongolian Plateau and Iranian Plateau, where the anticyclone activity is the most active. Therefore, both the decadal variability and long term trends are important features of climate change for extratropical anticyclones in Eurasia. The frequencies of the anticyclones in the Mongolian Plateau and the Iranian Plateau show obvious interdecadal variations. The occurrence frequency of the anticyclones shows significant periods of 2–6 years and 16–30 years in Eurasia, while the period often varies with time. The leading EOF（empirical orthogonal function） modes of the anticyclones in the Mongolian Plateau and Iranian Plateau for the 1948–2013 periods show a significant dipole-like distribution. The anticyclone activity has decreased in lower latitudes but increased in higher latitudes. The change in the intensity of anticyclones in the Mongolian Plateau can reflect the change in the intensity of the anticyclones over the Eurasian continent. The interdecadal variability of the movement of the distribution center of the anticyclones and their intensity in Eurasia can be explained by interdecadal variations of the position and intensity of the baroclinic front, which is mainly dominated by meridional temperature gradient in the lower troposphere. The influence of the baroclinic front on anticyclones in Eurasian is a regional phenomenon. The extratropical anticyclone changes in the Mongolian Plateau show a dipole-like structure with increases to the north of 50°N during 1960–1975 and to the south of 50°N during 1990–2005, which is associated with the southward shift of the baroclinic front from 55°N to 45°N within 80°–120°E of the region. However, the decadal latitudinal change in the baroclinic front within 30°–80°E cannot fully explain the dipole-like structure of changes in anticyclones over the Iranian Plateau. Since the middle 2000 s, the intensified Eurasian anticyclones are caused by the intensified baroclinic front.