On the westward shift of tropical Pacific climate variability since 2000
A profound westward shift in atmosphere–ocean variability in the tropical Pacific is observed when 2000–2017 is compared to 1979–1999. This westward displacement is associated with changes in oceanic Kelvin wave activity along the equator, especially a remarkable reduction in the eastern Pacific (175°–145°W). This coincides with a weakening of low-level westerly winds in this region, and a westward shift of low-level easterly winds in the central and eastern tropical Pacific, as well as decreased variability of vertical entrainment, vertical diffusion in the ocean mixed-layer in the eastern Pacific. The observed enhancement of the zonal contrast of the mean state across the tropical Pacific seems to be associated with the westward shift of climate variability along the equator. This systematically westward shift of the atmosphere–ocean variability in the tropical Pacific alters the impact of the tropical Pacific on extra-tropical climate.
KeywordsWestward shift of tropical Pacific variability Oceanic Kelvin wave activity Zonal gradient of SST
The authors appreciate the constructive comments and insightful suggestions from reviewers. The procedure of the heat budget calculation used in this work was developed by Dr. Boyin Huang and is maintained by Dr. C. Wen. Prof. Li was supported by National Natural Science Foundation of China (41775040 and 41475039) and National Key Basic Research and Development Project of China (2015CB953601). The scientific results and conclusions, as well as any view or opinions expressed herein, are those of the authors and do not necessarily reflect the views of NWS, NOAA, or the Department of Commerce.
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