Understanding a Nonstationary Relationship between PDO and IOBM in the Observations

There exists a low frequency variability of sea surface temperature in the Pacific and Indian Ocean, i.e., Pacific Decadal Oscillation (PDO) and Indian Ocean Basin Mode (IOBM), respectively. These low frequency variabilities not only affect a local marine ecosystem but also affect weather and climate in the globe via atmospheric teleconnections. Also, it is widely known that such variabilities interact with each other. While many previous studies have discussed the interaction between PDO and IOBM, it is lack of understanding their non-stationary relationship. To examine this, we analyzed the observational datasets and pacemaker experiments using the Nanjing University of Information Science and Technology Earth System Model version 3 (NESM.v3). A 31-year running correlation between PDO and IOBM indies shows that there are decades when the PDO and IOBM is significantly positively correlated or not. We found that the PDO structure during each decade is quite different, which subsequently leads to a different response of temperature and precipitation in the globe. By conducting pacemaker experiments, we found that a non-stationary relationship of PDO-IOBM is mainly due to the structural change of PDO between two decades. We also further examined the role of Atlantic ocean on the change in the PDO structure.