Effects Of ENSO And IOD On Winter And Spring Droughts In The Southern Hemisphere Of Australia

Based on observational and reanalysis datasets from 1979 to 2020,the effects of El Nino-Southern Oscillation(ENSO)and Indian Ocean Dipole(IOD)on austral winter and spring precipitation over Australia and their physical mechanisms are explored.The main conclusions are as follows:(1)Australian austral winter and spring precipitation anomalies are significantly related to ENSO.ENSO mainly affects precipitation in eastern and northeastern Australia.When El Nino develops,it will stimulate the PSA wave train to the southern hemisphere.It will cooperate with the ground circulation in eastern and northeastern Australia to form a strong sinking movement.At the same time,the cold SST anomaly in the eastern Australia causes water vapor dry and cold in eastern Australia.This leds to negative precipitation anomalies in the eastern and northeastern regions,which is more likely to cause drought.The impacts of ENSO on Australia are diverse in consideration of ENSO flavor.The EP El Nino event has little impact on Australian precipitation,while the CP El Nino event has a great impact on Australian precipitation.(2)Precipitation in austral winter and spring in Australia also presents a good negative correlation with the IOD mode.IOD mainly affects the southern region.During positive IOD developing phase,a quasi-barotropic Rossby wave train starting from eastern Indian Ocean,the low-level circulation field are configured to form a relatively deep sinking motion over Australia.At the same time,there appears negative SST anomaly in the southeast region.The local circulation field keeps warm wet moisture from being transported to southern Australia.Therefore,the southern region exhibits negative precipitation deficit and drought.(3)In addition to the intensity,the zonal location of the CP El Nino event SST anomaly center is also closely related to Australian precipitation.The more westward the zonal location of the SST anomaly center of the CP El Nino event,the more likely it is to cause Australian drought.At the same time,the greater the intensity of the positive IOD event,the greater the impact on Australian precipitation.When the two situations occur simultaneously,this effect is magnified.We use the AM2.1 model and the extreme drought in 2019 to verify this conclusion.