The role of intraseasonal variability at mid-high latitudes in regulating Pacific blockings during boreal winter
The role of intraseasonal variability at mid-high latitudes in regulating Pacific blockings during boreal winter
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中高纬度地区季节内变化对调节北半球冬季太平洋阻塞的作用
DOI：
10.1002/joc.5080
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Li Tim
中科院分区：
文献类型：
--
作者：
Yang Shuangyan;Li Tim
利用1979 - 2015年美国国家环境预测中心-能源部的每日再分析数据，研究了太平洋阻塞与北方冬季500 hPa中高纬大气季节内振荡（ISO）之间的关系。在150°E-155°W， 60°-75°N的关键区域上的ISO扰动与太平洋阻塞的协变最大。该关键区域的平均位势高度在统计上具有显著的10-35天的周期性。与太平洋阻塞活动相关的ISO扰动表现出明显的西向传播。扰动开始于约120°W，由季节内波能积累触发。位势趋势诊断表明，关键区域位势高度的时间变化率主要归因于ISO经向流对行星涡度的平流。提出了一种机制，其中西向传播的ISO扰动引起太平洋扇区上空的阻塞。当一个向北的强ISO气流到达关键区域时，它与行星涡度梯度作用，导致负涡度平流。这种负平流倾向于加强局地反气旋涡度和位势高度异常。因此，向西传播的ISO经向气流在诱发太平洋扇区低频阻塞活动中发挥了积极作用。
By using daily National Centers for Environmental Prediction‐Department of Energy reanalysis data from 1979 to 2015, we investigated the connection between Pacific blockings and mid‐high latitude atmospheric intraseasonal oscillation (ISO) at 500 hPa in boreal winter. The ISO perturbation over a key area of 150°E–155°W, 60°–75°N is most co‐variated with Pacific blockings. The averaged geopotential height over this key area exhibits a statistically significant 10–35‐day periodicity. The ISO perturbation associated with the Pacific blocking activity shows pronounced westward propagation. The perturbation initiates at about 120°W, triggered by intraseasonal wave energy accumulation. A geopotential tendency diagnosis reveals that the time change rate of the geopotential height over the key area is primarily attributed to the advection of planetary vorticity by the ISO meridional flow. A mechanism is put forward in which the westward‐propagating ISO perturbations induce a blocking over the Pacific sector. When a strong northward ISO flow arrives in the key area, it acts against the gradient of planetary vorticity, leading to a negative vorticity advection. This negative advection tends to strengthen local anticyclonic vorticity and geopotential height anomalies. Thus, the westward‐propagating ISO meridional flow plays an active role in inducing the low‐frequency blocking activity over the Pacific sector.