Wang Li-Chiao, Dao Thi Lan, Yu Jia-Yuh
Department of Atmospheric Sciences, National Central University, Taoyuan, Taiwan.
School of Geography, Earth and Atmospheric Sciences and ARC Centre of Excellence for Climate Extremes, The University of Melbourne, Melbourne, VIC, Australia.
Sci Rep. 2022 Sep 16;12(1):15595. doi: 10.1038/s41598-022-19874-2.
This study explores the dynamics of the equatorial Pacific upwelling annual cycle under global warming using the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations. Through a linear-weighted theory developed recently, the theoretical upwelling annual cycles under global warming helped reasonably characterize the patterns of the original upwelling annual cycles simulated in CMIP5 models; however, an apparent weakening in magnitude as compared to that during the present stage was observed. To verify the above, we divided 90-year outputs in the CMIP5 future projections into three 30-year windows and set side by side. The long-term evolution of the upwelling annual cycle reconfirmed an overall weakening tendency in the entire equatorial Pacific. Moreover, the weakening of the Ekman upwelling could most likely be attributed to the meridional surface wind stress divergence, while the gradually smoothing inclination in the overall equatorial thermocline depth was responsible for the weakening of the wave upwelling. The weakening of the wave upwelling in the east and the Ekman upwelling in the west jointly contributed to the gradual weakening of the equatorial Pacific upwelling annual cycle. The above projected changes are robust among the 19 chosen CMIP5 models. Equatorial upwelling largely influences the sea surface temperature, associated atmosphere-ocean interactions, and convection and precipitation in tropical areas; hence, a continuous weakening of the upwelling annual cycle over the equatorial Pacific Ocean could likely affect the major climate phenomena variability with strong seasonal-locking characteristics by modifying the background strength at their peak phases in the future. The theoretical results can provide us the equatorial upwelling annual cycle patterns based on the Ekman and wave dynamics, which would be a strong tool for our investigations on the climate variability under global warming.
本研究利用耦合模式比较计划第五阶段（CMIP5）模拟，探讨全球变暖下赤道太平洋上升流年循环的动态变化。通过最近发展的线性加权理论，全球变暖下的理论上升流年循环有助于合理表征CMIP5模型中模拟的原始上升流年循环模式；然而，与当前阶段相比，幅度明显减弱。为验证上述情况，我们将CMIP5未来预测中的90年输出划分为三个30年窗口并并列设置。上升流年循环的长期演变再次证实了整个赤道太平洋存在总体减弱趋势。此外，埃克曼上升流的减弱很可能归因于经向表面风应力散度，而赤道热比容层深度总体上逐渐变平的倾斜度则导致了波动上升流的减弱。东部波动上升流和西部埃克曼上升流的减弱共同导致了赤道太平洋上升流年循环的逐渐减弱。上述预测变化在所选的19个CMIP5模型中是稳健的。赤道上升流在很大程度上影响海表温度、相关的海气相互作用以及热带地区的对流和降水；因此，赤道太平洋上升流年循环的持续减弱可能会通过改变未来主要气候现象峰值阶段的背景强度，影响具有强烈季节锁定特征的主要气候现象的变率。理论结果可以为我们提供基于埃克曼和波动动力学的赤道上升流年循环模式，这将是我们研究全球变暖下气候变率的有力工具。
