Intraseasonal Variability’s Attribution Analysis Of Arctic Oscilation

Based on the NCEP-NCAR reanalysis of daily dataset for30-years, possible mechanisms of AO are discussed, and detailed investigation is conducted of relationship between AO and tropical oscillations. Therefore conclusions are drawn as follows:Studies shows that in tropical regions the variation of atmospheric angular momentum budget is in phase with the variation of mountain torque, and the distribution of atmospheric angular momentum balance shows north-south dipole structure with AO tendency changes on timescale of30-60days. At low latitudes, atmospheric angular momentum balance and the AO index change showed a significant negative correlation,and at high latitudes, atmospheric angular momentum showed a positive correlation with the AO tendency changes. Dynamics analysises show the Himalayas ranges mainly influence AO in comparison with the Rockies ranges.In the period of high(low) indices, the quasi-steady planetary waves triggered by the Himalayas ranges influences subtropical westerly, and the subtropical westerly weaken (strengthen),and high-latitude westerly strengthen(weaken), so AO strengthen (weaken),and the polar vortex in the stratosphere strengthen(weaken).The strong(weak) center of polar vortex tends to Northeast Asia.Investigation shows that zonal atmospheric angular momentum is out of phase with AO indices tendency on timescale of30-60days. Statistical analysis and dynamic diagnosis of the five regions of tropical oceans shows that negative correlation gradually weakened from the west to the east, and the area of negative correlation also decreases, but the area of positive correlation gradually Expands to the north. The negative correlation is completely replaced by the weak positive correlation near the date line in the Pacific region..In the period of high (low) indices, E-P flux and its divergence center of the tropical regions have a better effect on zonal wind anomaly center in the tropical regions of the Northern Hemisphere, and it can better explain the phenomenon of zonal wind anomalies in the regions; But E-P flux and its divergence can not accurately explain the phenomenon of the zonal wind anomalies in the tropical regions of the southern Hemisphere.