Atlantic Multidecadal Variability modulates the climate impacts of El Nino-Southern Oscillation in Australia

Atlantic Multidecadal Variability (AMV) modulates El Nino-Southern Oscillation (ENSO) dynamics. Here, we explore the effect of warm (AMV+) and cold (AMV-) AMV conditions on the austral summer teleconnection of ENSO to Australia using idealized simulations performed with the NCAR-CESM1 model. AMV+ strengthens the mean and extreme precipitation and temperature responses to El Nino in south-western Australia and weakens the mean precipitation and temperature impacts in north-eastern Australia. The modulation of La Nina impacts by AMV is asymmetric to El Nino, with a weakening of the mean and extreme precipitation and temperature responses in eastern Australia. Decomposing the total difference in ENSO response between AMV phases, we find that the signals are mainly explained by the direct AMV modulation of ENSO and its teleconnections rather than by changes in background climate induced by AMV. The exception is ENSO-driven fire impacts, where there is a significant increase in burned area in south-eastern Australia only when El Nino and AMV+ co-occur. However, modulation of ENSO between AMV+ and AMV- does offset & SIM;37% of the decrease in burned area extent during La Nina summers. The altered surface climate response to ENSO in Australia by AMV is attributed to variations in large-scale atmospheric circulation. Under AMV+, there is increased subsidence over western Australia during El Nino associated with a westward shift of the local Walker circulation. A weakening of the upwelling branch of the local Hadley circulation over north-eastern Australia is responsible for the weakening of La Nina impacts in AMV+, accompanied by a strengthening of subsidence in south central Australia due to a weakening of the local Hadley circulation, amplifying La Nina impacts over this region. The results suggest the potential for AMV to drive multidecadal variability in ENSO impacts over Australia.