北半球平流层极涡崩溃早晚的环流特征及其对5月南亚降水的影响

Inter-annual variation of the Northern Hemisphere stratospheric polar vortex breakdown and its impact on the precipitation over the South Asia in May

本文采用1979—2014年NCEP/NCAR月平均再分析资料、CMAP和GPCP月平均降水资料,分析了北半球平流层极涡崩溃早晚的环流特征及其与南亚降水的关系。结果表明,北半球平流层极涡崩溃时间存在明显的年际变化特征。极涡崩溃偏早(偏晚)年,自3月开始异常信号从平流层向下传播,之后的4月,从平流层到对流层高层极区温度异常偏高(偏低),极涡异常偏弱(偏强),极夜急流异常偏弱(偏强)。结果还表明,5月南亚降水异常与平流层极涡崩溃时间的早晚存在显著相关,5月南亚降水异常与平流层极涡崩溃早晚年平流层异常信号的下传有关。当平流层极涡崩溃偏晚年,4月平流层极区表现为位势高度异常偏低,而中纬度则位势高度场异常偏高,并伴随位势高度异常场的向下传播,5月该位势高度异常场下传至阿拉伯海北部大陆上空对流层顶,形成有利于降水的环流场,导致南亚降水偏多。反之,则相反。

Based on NCEP/NCAR monthly mean reanalysis, CMAP and GPCP monthly mean pre- cipitation datasets over the period of 1979--2014, the inter-annual characteristics of the stratospheric po- lar vortex breakdown and its relationship with the precipitation over the South Asia in May were studied. Results show that the Northern Hemisphere stratospheric polar vortex breakdown is characterized by inter- annual variations. In addition, as the stratospheric polar vortex breaks down early （late） , abnormal signals propagate downward from the stratosphere in March and reaches upper troposphere in April, with high （low） temperature, weak（strong） polar vortex, weak（strong） polar jet above the upper troposphere. It is also found that inter-annual variations of the stratospheric polar vortex breakdown are closely related tothe precipitation anomalies over the South Asia in May. As the stratospheric polar vortex breaks down late, in the stratosphere, the negative geopotential height anomalies dominate over the Arctic region while the positive geopotential height anomalies over the middle latitudes in April. These positive geopotential height anomalies over the middle latitudes propagate downward and even reach the upper troposphere above the North Arabian Sea in May, which act to form a favorable condition for precipitation over the South Asia, and vice versa.