Relationship between IOD/ENSO and Planetary Wave Patterns in the Southern Hemisphere

The tropical climate variabilities, such as Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO), are accompanied with changes in tropical deep convection which can influence the Southern hemisphere (SH) atmospheric circulation. Here, we examine September-November (SON) 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 anomalies of sea level pressure, and meridional wind and geopotential height at 300 hPa and to compute the correlation with IOD and ENSO at each latitude. The results show that IOD and ENSO are positively correlated with zonal wave number 1 (ZWN1) PSD but negatively correlated with ZWN2 and ZWN3 PSDs of the meridional wind and geopotential height at 300 hPa in the SH mid-latitude. Considering the climatological wave patterns of them, the negative (positive) phase of these events strengthens (weakens) the ZWN3 pattern considerably, allowing more (less) active meridional exchange of momentum. Unlike ENSO events which can create a rather north-south wave transfer, IOD does the east-west transfer. In addition, the relationship between IOD and ZWN3 has become tighter in recent years which is not seen in that with ENSO. Interestingly, ZWN2 PSD is increased by both extremely positive and negative IOD and ENSO events (exceeding 1 standard deviation). The IOD and ENSO events also modify the sea level pressure patterns and meridional surface winds, modulating the sea-ice extent in the Southern Ocean.The extremely positive IOD event in 2019 left a similar footprint to the mid-latitude planetary wave patterns except for an unusual increase in ZWN2 PSD. This study suggests clear teleconnection patterns between the tropical climate variabilities and extratropics.