Variation Characteristics Of The Northern Hemisphere Stratospheric Polar Vortex Breakdown And Its Impact On The Climate Over The Asia In Spring

Based on the multiple reanalysis datasets, the climatic circulation characteristics and their differences between the early and later years of the stratospheric polar vortex breakdown are studied. The relationship between the occurrence of stratospheric polar vortex breakdown and Asian climate is also explored.The main conclusions are as follows:(1)Long term mean occurrence date of Northern Hemisphere stratospheric polar vortex breakdown is April 20th while the breakdown datesfor earlier years and later years of stratospheric polar vortex breakdown are March 30th and May 10th,respectively. In addition,stratospheric polar vortex breakdown is characterized by inter-annual variations, together with a marked late breakdown trend.(2)Atmospheric circulation evolution (zonal winds and geopotential height anomalies) experiences an anti-phase temporal evolution for the early and late breakdown years of the stratospheric polar vortex.As the stratospheric polar vortex breaks down in early years,zonal wind anomaly changes intensely with the stratospheric warming, and vice versa. Atmospheric circulation evolution (zonal winds,geopotential height and temperature) experiences an anti-phase temporal evolution for the early and late breakdown years of the stratospheric polar vortexIn addition, zonal windanomalies and geopotential height anomalies reverse their signs in March and reach their maximum in February and April,together with a marked downward propagation breakdown trend.(3) Statistical results shows that that inter-annual variations of the stratospheric polar vortex breakdown are closely related to the precipitation anomalies over the south Asia in May,which is related to downward signal from stratosphere.As the stratospheric polar vortex breaks down late, in the stratosphere, negative geopotential height anomalies dominate over the arctic region while 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.(4)It is also found that inter-annual variations of the stratospheric polar vortex breakdown are closely related to the temperature anomalies over the Central Asia in March,which is related to downward signal from stratosphere.As the stratospheric polar vortex breaks down in early years, in the stratosphere, negative geopotential height anomalies over the arctic region strengthen in February and weaken in March while positive geopotential height anomalies over North America and Eurasia in March. These positive geopotential height anomalies propagate downward and even reach the upper troposphere above Eurasia in March, which act to strengthened ridge in favor of the southward propagation of cold air, and vice versa.