Inter-decadal Change Of Asia–Australia Monsoon System Links To The Onsets Of Two Types Of El Ni(?)o

The Asia–Australia monsoon system,which has an impact on the climate change over Asia and Australia regions and even the world,plays an important role in the global monsoon.This study investigates the inter-decadal changes and interaction of the East Asian winter monsoon(EAWM)and Australian summer monsoon(AuSM)and their link to onsets of different types of El Ni?o by analyzing Japan Meteorological Agency(JMA)sea temperature and salinity data(1950-2010),the National Centers for Environmental Prediction/ National Center for Atmospheric Research(NCEP/NCAR)reanalysis data(1948-2011)and the Hadley Center sea surface temperature(SST)data(1948-2011).The SST change in the western waters of Australia may affect the EAWM via enhanced AuSM can be found in Community Atmospheric Model version 5.3(CAM5.3)which is part of Community Earth System Model(CESM).The results show that significant inter-decadal change in Asia–Australia monsoon system appears around 1990.After 1990,weaker EAWM is related to southerlies anomalous in the eastern Asia and stronger AuSM has the high anomalous in the southern East Asia,which is response to the rossby wave source(RWS).Anomalous divergent winds advect large vorticity northward and result in negative RWS anomalies by crossing the maximum absolute vorticity gradient latitude that is intense during the strong AuSM.Moreover,corresponding to the upper-level convergence over southeastern China,descending motion in the troposphere induces vortex stretching in the upper troposphere and produces a pronounced patch of positive RWS anomalies over southeastern China.The abnormal high that been sustained positive RWS anomalies reduced the tendency of pressure and thus weaken EAWM.We use the CAM5.3 which is part of CESM to prove the mechanization and interaction.We also found that EAWM plays an important role in Eastern-Pacific(EP)El Ni?o and AuSM plays an important role in Central-Pacific(CP)El Ni?o,during the onset period.The EAWM connected to the EP El Ni?o via the equatorial west wind and SST(Bjerknes positive feedback)while AuSM leads to onset of CP El Ni?o because of the high anomalous over the eastern Pacific.This high anomalous,which are stimulated by abnormal circulation over the mid-eastern Pacific and the negative feedback of cloud-sea surface temperature over eastern Pacific,can cause the westerly wind extend to the west of the Mexico sea and thus lead to warm SST anomalous in this region.At last,the relationship between the change of Asia-Australia monsoon system and two types of El Ni?o can explain the increasing CP El Ni?o emergence in the recent years as well as the complexity of the interaction between ENSO and monsoon in different time scales.