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Climate Dynamics

, Volume 48, Issue 3–4, pp 987–997 | Cite as

Relative roles of differential SST warming, uniform SST warming and land surface warming in determining the Walker circulation changes under global warming

  • Lei Zhang
  • Tim Li
Article

Abstract

Most of CMIP5 models projected a weakened Walker circulation in tropical Pacific, but what causes such change is still an open question. By conducting idealized numerical simulations separating the effects of the spatially uniform sea surface temperature (SST) warming, extra land surface warming and differential SST warming, we demonstrate that the weakening of the Walker circulation is attributed to the western North Pacific (WNP) monsoon and South America land effects. The effect of the uniform SST warming is through so-called “richest-get-richer” mechanism. In response to a uniform surface warming, the WNP monsoon is enhanced by competing moisture with other large-scale convective branches. The strengthened WNP monsoon further induces surface westerlies in the equatorial western-central Pacific, weakening the Walker circulation. The increase of the greenhouse gases leads to a larger land surface warming than ocean surface. As a result, a greater thermal contrast occurs between American Continent and equatorial Pacific. The so-induced zonal pressure gradient anomaly forces low-level westerly anomalies over the equatorial eastern Pacific and weakens the Walker circulation. The differential SST warming also plays a role in driving low-level westerly anomalies over tropical Pacific. But such an effect involves a positive air-sea feedback that amplifies the weakening of both east–west SST gradient and Pacific trade winds.

Keywords

Global warming The Walker circulation Uniform SST warming and extra land warming 

Notes

Acknowledgments

This work was supported by China National 973 project 2015CB453200, NRL grant N00173-13-1-G902, ONR grant N00014-16-12260 and the International Pacific Research Center that is sponsored by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). All the datasets from CMIP5 models can be accessed through ESGF data portals (http://pcmdi-cmip.llnl.gov/cmip5/availability.html). This is SOEST contribution number 9611, IPRC contribution number 1185, and ESMC contribution number 101.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.IPRC and Department of Atmospheric SciencesUniversity of HawaiiHonoluluUSA
  2. 2.International Laboratory on Climate and Environment Change and Key Laboratory of Meteorological Disaster of Ministry of EducationNanjing University of Information Science and TechnologyNanjingChina

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