Westward Wind Changes over the Tropical and Midlatitude Pacific in the Past Three Decades Driven by the Interbasin Teleconnections

Due to its active role in the atmosphere-ocean interactions and in the global climate variability, the trade wind regime over the Pacific Ocean has been receiving increased attention. Although the intensification of the equatorial trade wind in recent decades has been widely investigated, the meridional extension of this decadal-scale easterly wind anomaly and the associated mechanism remain unclear. In this study, we combine observations, reanalysis datasets, and a hierarchy of climate model simulations to untangle this problem.

Analysis based on multiple measurements and reanalysis datasets consistently show that the intensified easterly wind anomaly is not only confined within the tropics, but also extends to the mid-latitude Pacific, from 40°S to 40°N.

According to the coupled model simulation results, in the tropics, the decadal changes of the trade wind are primarily attributed to the enhanced Walker circulation driven by the inter-basin teleconnection and further the decadal variability over the Atlantic and the Pacific oceans, i.e. the Atlantic Multi-decadal Oscillation and the Pacific Decadal Oscillation. This results agree well with several previous studies.

In the mid-latitudes, on the other hand, the decadal changes of the easterly wind are more attributed to the decadal variability of the sub-tropical highs and Aleutian Low. Model results indicate that, while these decadal wind anomalies significantly contribute to the observed sea surface temperature (SST) changes in both tropical and mid-latitude Pacific, they are not driven by the local Pacific SST changes. Instead, the wind changes are mostly caused by inter-basin teleconnections originated from the tropical Atlantic and Indian Ocean SST variability through the stationary Rossby waves. This finding builds a direct pathway linking the tropical Atlantic and Indian Ocean to the mid-latitude Pacific on decadal timescales. This pathway has a broad implication for understanding air-sea interactions, the atmosphere teleconnections and the sea level changes over the Pacific basin, and may have an important impact on the decadal predictability of the Pacific climate variability, such as Pacific Decadal Oscillation.