Westward and downward migration of the Western Pacific Warm Pool during recent global surface warming slow-down and its implications

Since the net rate of ocean heat uptake is unabated, the surface warming slowdown (so called hiatus) signature is considered to be due to an internal rearrangement of heat within the ocean. The cooling in the Pacific has been proved to contribute the most to the hiatus, with the largest contribution in tropics. The Western Pacific Warm Pool (WPWP) is the largest warm water mass and is located in the tropical Pacific Ocean. By exploring the temporal and spatial variability of the WPWP size location, and heat content, we provide a new perspective on the temporal and spatial evolution of the WPWP during global warming and the hiatus period. An advanced time-series analysis technique known as Multidimensional Ensemble Empirical Mode Decomposition (MEEMD) is used to study the centroid migration, volume, and heat content of the WPWP. We show the evolution of the warm pool in last three decades and how it interacts with natural and anthropogenic climate forcing mechanisms. The volume of WPWP increased 14%, while its centroid travelled 3.19°to the west and 3.16m downward. The variabilities are more obvious during the hiatus than previous. We find a westward and downward movement of the WPWP during the thirty-year period, while the warm pool heat content anomaly increases. The movement pattern of the WPWP can be well explained by the wWind-driven cCirculation. When wind intensifies, the Ekman pumping rate is enhanced, the slope of the thermocline increases, leading a westward and downward movement of the WPWP, which is consistent with the understanding of heat transferring from the tropical Pacific Ocean to the Indian Ocean and deeper ocean during the hiatus period. While if a weakened Ekman pumping is seen, the opposite process takes place.