东北冷涡低频活动特征及背景环流

研究了1965-2007年夏季(5-8月)东北冷涡活动的时空分布特征和同期背景环流型.东北冷涡活动区域5月主要是45°N以北,6月向南扩展到40°N以南,然后逐月向北收缩.夏季,随着东亚急流的逐渐减弱和北进,东北冷涡天数逐渐增加,6月6日前后达到峰值,但入梅后冷涡频数有所减少.随着梅雨期结束,冷涡频数进一步降低.强冷涡事件集中于入梅之前,中等和弱强度的事件主要发生在梅雨期和出梅之后.在入梅之前和出梅之后,东北冷涡频数呈现准2 a振荡特征.夏季东北冷涡频数在1965-2007年具有增加趋势,其中,梅雨期的增加趋势尤为明显.东北冷涡的形态根据其上游高压脊的位置可分为4种:叶尼塞河型、贝加尔湖型、乌拉尔-雅库斯克型和鄂霍次克海-北冰洋型.西太平洋遥相关(WP)型为东北冷涡活动的同期背景环流型,东北冷涡在其负位相易于生成.此外,5-6月东北冷涡活动与太平洋/北美(PNA)型、8月东北冷涡活动与北大西洋涛动(NAO)密切联系.

Low frequency characteristics of northeast China cold vortex and its background circulation pattern

In this study, the spatial-temporal distribution of the northeast China cold vortex (NCCV) in summer and the concurrent background teleconnection pattern have been investigated using a long-term data (1965-2007). The spatial extent of the NCCV activity is extended southward to the south of 40°N in June, while it is constrained to the north of 45°N in May. From July to August, it is gradually shrunk back to the north. Starting from May 1, the number of the NCCV days gradually increases as the East Asian Jet gradually weakens and moves northwards, and it reaches the peak about June 6. However, it begins to decrease when the meiyu period begins, and further decreases after the period. The strong NCCV events tend to happen in the pre meiyu period, while the weak and moderate events occur in the meiyu and post meiyu period. The NCCV activities show a quasi-biennial oscillation feature in the pre-meiyu and post-meiyu period. During years of 1965-2007, an increasing trend is found for the number of the NCCV days in summer, particularly during the meiyu period. Based on the position of the upstream ridge, the NCCV-related circulations can be classified into four types, namely, the Yenisei-type, the Baikal-type, the Ural/Yakutsk-type and the Okhotsk/Arctic-type. The western Pacific (WP) pattern is the primary background teleconnection pattern for the NCCV activity, with its negative phase being favorable for the NCCV formation. In addition, the NCCV activity is associated with the Pacific/North American (PNA) pattern in May and June and with the North Atlantic Oscillation (NAO) in August.