Cold vortex events over Northeast China associated with the Yakutsk-Okhotsk blocking.

ABSTRACT Northeast China cold vortex ( NCCV) circulation associated with a blocking-type circulation over the Yakutsk/Okhotsk ( YO) region brings persistent cool weather over Northeast China from May to mid-June and often causes a considerable reduction of local crop production. This study investigated the dynamic features of the YO-NCCV event on intraseasonal time scale and its relation with climate background circulation through analyzing two typical cases of YO-NCCV events. The first event (E1, from 25 May to 4 June, 2008) selected in this study was a long-lived (12 days) case, while the second event (E2, 16-18 May, 1972) was a short-lived one (only 3 days). Though two typical YO-NCCV events both developed from the southeastward movement of the polar high potential vorticity ( PV) air, they showed different life cycle features. In the E1, the formation of the NCCV circulation was associated with the poleward intrusion of two low- PV tongues over the Kamchatka Peninsula and the Ural Mountains. The low-frequency Rossby waves propagating from the Scandinavia Peninsula along the westerly to Northeast China mainly contributed to the maintenance of the NCCV circulation. In contrast, for the E2, the low- PV tongue over the Ural Mountains was absent and the PV field over Eurasian continent exhibited a synoptic wave feature. The transient eddy feedback forcing ( TEFF) anomalies contributed greatly to the formation and development of the YO-NCCV circulation. From the climatic view, the circulation anomalies associated with the E1 may be regarded as an intensive development of the climatological mean eddy field on the intraseasonal time scale. Results also show that the YO-NCCV event, among the four main types of NCCV event, was most closely related to the negative phase of western Pacific (WP) pattern. [ABSTRACT FROM AUTHOR]