中国东北及邻近地区夏半年极端暖事件的时空和环流特征分析

夏半年（5—10月）是我国东北农作物生长的关键期，但偏高的气温尤其是大范围极端偏暖事件会对农业生产造成不良影响。基于强度、范围和持续时间等指标，对1980—2019年夏半年发生在我国东北及其邻近地区的16个极端暖事件进行分析。结果表明，东北及邻近地区的极端暖事件的强度和频率呈明显增加的趋势，夏初（5—6月）和秋初（9—10月）发生的暖事件频次较多。地面极端增暖事件发生时，东北区域的西北侧大陆地面低压异常和东侧西北太平洋海上高压异常导致东北地区出现异常偏南风及暖平流；对流层至平流层呈现出准正压的结构，最大位势高度异常中心多出现在250 hPa附近，其下方的正温度异常（暖气柱）会延伸到地面，有利于地面异常增温。暖事件发生时，地面增暖区位于对流层上层急流入口区的左侧，利于下沉气流出现。上述大气温压场扰动结构和环流特征通过影响短波辐射和绝热增温过程，共同导致地面极端暖事件的发生。在预报意义上，有90%以上的东北极端暖事件可以在250 hPa上至少提前10天追踪到位势高度的扰动信号。 

SPATIO-TEMPORAL AND CIRCULATION FEATURES OF EXTREME WARM EVENTS DURING SUMMER HALF YEAR IN NORTHEAST CHINA AND ADJACENT AREA

The summer half year (May-October) is a critical period for the growth of crops in Northeast China. The extreme warm events can greatly affect the growth of crops and their harvest. In this paper, an integrated criterion involving intensity, coverage and duration are used to study the 16 extreme warm events in Northeast China and its adjacent area during the summer half years from 1980 to 2019. Results show the intensity and frequency of warm events in these areas increase significantly with the majority occurring in early summer (May-June) and early autumn (September-October). During extreme warm events, the anomalous surface continental low-pressure system and marine high-pressure system, which are respectively located on the western and eastern sides of the study area, result in anomalous southerlies and warm advection in the focus area. Positive geopotential height (GPH) anomalies extend from troposphere to stratosphere with a quasi-barotropic feature, which peaks at around 250 hPa. The anomalous warm column under the height anomalies can reach the surface. Northeast China is located to the left of the entrance region of the upper-level jet stream in the upper troposphere, which is favorable for the sinking motion and associated heating. These circulation features cause the extreme warm events by affecting the shortwave radiation and adiabatic heating. The anomalous GPH signal at 250 hPa can be tracked 10 days in advance for more than 90% events.