Exploring the asymmetries of pan-tropical connections from the tropical Indian to the Pacific basin

Abstract

Recent analysis of pan-tropical interactions suggests that post-1980, the tropical Indian Ocean’s (TIO) influence on the tropical Pacific Ocean (TPO) appears to have subdued, while the tropical Atlantic Ocean’s (TAO) influence has become more pronounced. The present study explores whether we can identify and dynamically explain any asymmetries in the pan-tropical connection between the TIO and TPO SSTs in an attempt to explain the recently reported weakening of the TIO influence. To this end, we carry out two idealised atmosphere-only experiments using the ACCESS atmospheric general circulation model where the sign of the decadal TIO SST signal is varied – presenting warm and cool TIO scenarios. We find a relatively strong asymmetric response of TPO precipitation to TIO SST anomalies, where average TPO precipitation shows a strong increase in response to TIO cooling, but a weaker decrease in response to TIO warming. The asymmetry is hypothesized to result from differences in the depth of latent heating over the TIO which ultimately affects the depth of the remote response over the TPO. Asymmetries also occur in the spatial pattern of the changes in precipitation and surface winds. In the fully coupled system, these asymmetries would be expected to also alter the background state on which ENSO develops, providing a further mechanism by which the TIO influence may vary depending on its phase.