2014年夏季长江流域持续性低温的大尺度环流异常

采用中国地面站气温逐日观测资料、NOAA全球逐日海表温度资料，及NCEP/NCAR的全球日均再分析资料，研究了2014年持续性低温的三维结构及大尺度环流异常。结果表明，2014年的低温异常，除了在陆地上区域性地出现在长江流域，还以大尺度带状的形式、从陆地延伸到海洋上。这种带状异常不只出现在近地面，在大气各层（925～500 hPa）都能看到。分析指出，大气中的这个低温带主要由高纬大气环流异常造成。在位势高度场上，最重要的异常出现在高纬60°N，有呈带状的位势高度正距平，它引导（距平意义上的）偏北气流从正北和东北偏东方向侵入，在其南侧形成一带状的偏低温区。大气各层均呈现出这种在高纬有位势高度正距平、相应地在稍南的低纬（40°N）有位势高度负距平、两者之间为低温区的分布特征。从低层往上，这种配置型式整体表现出由南往北的倾斜，其垂直剖面表现为距平意义上的、大尺度、类似于锋面的倾斜结构。文中用简单的概念模型对此进行理解，认为这种结构是由大气动力异常和热力异常相互影响、共同作用而形成的。

The large-scale anomalous circulation responsible for the persistent low temperature over the Yangtze River Basin in summer 2014

Despite the high temperatures associated with the warming climate, there are also occurrences of low temperatures.A persistent low temperature in summer 2014 is typical of recent years.The three-dimensional structure of the low temperature and anomaly in large-scale circulation is investigated using station observations of temperature over China, NOAA observations of sea surface temperature, and NCEP/NCAR reanalysis data.It has been shown that the low temperature anomalies in the near-surface layer are not only regionally located in the Yangtze River Basin, but can extend to the ocean in a large-scale belt pattern.The abnormality belt is not only visible near the surface, but also at all atmospheric levels (925-500 hPa).Based on the analysis, the low temperature in the atmosphere is largely due to anomalous systems at high latitudes.In the geopotential height field, the belt-like positive anomalies at 60°N may induce the inflow of colder-than-normal air in its southern region from the north or northeast.At all levels, the geopotential height shows positive anomalies.Accordingly, there are negative geopotential anomalies at low latitudes (40°N).A region of low temperatures lies between them, and all levels exhibit this distribution pattern.There is an overall tilt in these systems from the near surface to the upper levels, resulting in a large-scale front-like vertical cross-section, which a simple conceptual model can explain.The vertical structure may be maintained by the interaction between the dynamics and thermodynamics in the atmosphere.