Springtime Southern Hemisphere Quasi-Stationary Planetary Wave Activities Associated With ENSO/IOD

The tropical climate variabilities, such as Indian Ocean Dipole (IOD) and El Nino Southern Oscillation (ENSO), are accompanied by changes in the tropical deep convection which can influence the atmospheric circulation in the Southern Hemisphere (SH). To investigate each role of IOD and ENSO in the September-November (SON) circulation, we examine teleconnection patterns associated with IOD and ENSO events using the ERA5 monthly averaged data from 1979 to 2020. Our approach is to calculate the power spectral density (PSD) of the sea level pressure (SLP) and meridional wind and geopotential height at 300 hPa that are decomposed by zonal wave numbers (ZWNs), and to compute their correlations with IOD and ENSO at each latitudinal band. The main results are that IOD (ENSO) is negatively (positively) correlated with PSDs of ZWN2 and ZWN3 (ZWN1) at 300 hPa in the SH middle latitudes. Considering the Rossby wave train, IOD (ENSO) considerably affects the variability of the ZWN3 (ZWN1) pattern, which influences the meridional exchange of momentum. Additionally, the relationship between IOD and ZWN3 has become tighter in recent years, which is not seen in that with ENSO. The IOD and ENSO events also modify the SLP patterns and meridional surface winds, modulating the sea ice extent in the Southern Ocean. During the highly positive 2019 IOD event, the variability of the middle latitudes atmospheric circulation was considerably larger than climatology, suggesting a higher chance of more extreme weather patterns associated with more frequent intense IOD events in the warming climate. The two tropical climate variabilities, Indian Ocean Dipole (IOD) and El Nino Southern Oscillation (ENSO), can change the location and intensity of tropical convection, generate anomalous Rossby wave trains heading to the Southern Hemisphere (SH), and the zonal wave pattern of the middle latitudes' atmospheric circulation and further the Antarctic climate. We analyzed this low-high latitudes teleconnection in the austral spring when IOD and ENSO strongly affect the wave patterns using atmospheric reanalysis data. The results show that ENSO is positively correlated with zonal wave number 1 (ZWN1) activity, but IOD negatively correlates with ZWN2 and ZWN3 activities in the SH middle latitudes. The relationship between IOD and ZWN3 has become tighter in recent years, which is not seen in that with ENSO. The IOD and ENSO events also modify the sea level pressure patterns and meridional surface winds in the Southern Ocean, leaving the ZWN3 features. The surface wind patterns affect the sea ice concentration, but with a difference between IOD and ENSO. Indian Ocean Dipole (IOD)'s Rossby wave train is partially similar to the climatology; a negative IOD enormously increases zonal wavenumber 3IOD (El Nino Southern Oscillation) is negatively (positively) correlated with zonal wavenumber 2 and 3 (1) in austral springThe extremely positive IOD in 2019 exhibited more significant increases and unusual changes in wave patterns