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The mid-Pliocene (g1/43 Ma) is one of the most recent warm periods with high CO2 concentrations in the atmosphere and resulting high temperatures, and it is often cited as an analog for near-term future climate change. Here, we apply a moisture budget analysis to investigate the response of the large-scale hydrological cycle at low latitudes within a 13-model ensemble from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The results show that increased atmospheric moisture content within the mid-Pliocene ensemble (due to the thermodynamic effect) results in wetter conditions over the deep tropics, i.e., the Pacific intertropical convergence zone (ITCZ) and the Maritime Continent, and drier conditions over the subtropics. Note that the dynamic effect plays a more important role than the thermodynamic effect in regional precipitation minus evaporation (PmE) changes (i.e., northward ITCZ shift and wetter northern Indian Ocean). The thermodynamic effect is offset to some extent by a dynamic effect involving a northward shift of the Hadley circulation that dries the deep tropics and moistens the subtropics in the Northern Hemisphere (i.e., the subtropical Pacific). From the perspective of Earth's energy budget, the enhanced southward cross-equatorial atmospheric transport (0.22 PW), induced by the hemispheric asymmetries of the atmospheric energy, favors an approximately 1g? northward shift of the ITCZ. The shift of the ITCZ reorganizes atmospheric circulation, favoring a northward shift of the Hadley circulation. In addition, the Walker circulation consistently shifts westward within PlioMIP2 models, leading to wetter conditions over the northern Indian Ocean. The PlioMIP2 ensemble highlights that an imbalance of interhemispheric atmospheric energy during the mid-Pliocene could have led to changes in the dynamic effect, offsetting the thermodynamic effect and, hence, altering mid-Pliocene hydroclimate.
Bibliographical noteFunding Information:
Financial support. This research has been supported by the Swedish Research Council (Vetenskapsrådet; grant nos. 2013-06476 and 2017-04232).
Acknowledgements. Zixuan Han acknowledges financial support from the National Natural Science Foundation of China (grant no. 42130610), the Fundamental Research Funds for the Central Universities (grant no. B210201009), and the National Key R&D Program of China (grant no. 2017YFC1502303). Jianbo Cheng acknowledges financial support from the National Natural Science Foundation of China (grant no. 42005012) and the Natural Science Foundation of Jiangsu Province (grant no. BK20201058). Qin Wen acknowledges financial support from the National Natural Science Foundation of China (grant no. 42106016) and a project funded by the China Postdoctoral Science Foundation (grant no. 2021M691623). The EC-Earth3 model simulations and the data analysis were performed using the ECMWF computing and archive facilities and the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC), which is partially funded by the Swedish Research Council through grant agreement no. 2018-05973. Charles J. R. Williams acknowledges financial support from the UK Natural Environment Research Council within the framework of the SWEET (Super-Warm Early Eocene Temperatures) project (grant no. NE/P01903X/1). Natalie J. Burls acknowledges support from the National Science Foundation (NSF; grant nos. AGS-1844380 and OCN-2002448) and the Alfred P. Sloan Foundation (as a research fellow). Ran Feng acknowledges sponsorship from the U.S. National Science Foundation (grant nos. 1903650 and 1814029). The contributions of Bette L. Otto-Bliesner, Esther C. Brady, and Nan Rosenbloom are based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the NSF under cooperative agreement no. 1852977. The CESM project is primarily supported by the National Science Foundation (NSF). Computing and data storage resources for the CESM and CCSM4 simulations, including the Cheyenne supercomputer (https://doi.org/10.5065/D6RX99HX), were provided by the Computational and Information Systems Laboratory (CISL) at NCAR. Xiangyu Li acknowledges financial support from the National Natural Science Foundation of China (NSFC, grant no. 42005042) and the China Scholarship Council (grant no. 201804910023). The NorESM simulations benefitted from resources provided by UNINETT Sigma2 – the national infrastructure for high-performance computing and data storage in Norway. The work by Anna S. von der Heydt and Michiel L. J. Baatsen was carried out in the framework of the Netherlands Earth System Science Centre (NESSC) program, which is financially supported by the Ministry of Education, Culture and Science (OCW grant no. 024.002.001). Simulations with CCSM4-Utrecht were performed at the SURFsara Dutch national computing facilities and were sponsored by NWO-EW (Netherlands Organisation for Scientific Research, Exact Sciences; project nos. 17189 and 2020.022). Christian Stepanek and Gerrit Lohmann acknowledge computational resources from the Computing and Data Centre of the Alfred Wegener Institute, Helmholtz-Zentrum für Polar-und Meeres-forschung. Christian Stepanek and Gerrit Lohmann also acknowledge funding from the Helmholtz Climate Initiative REKLIM and the Alfred Wegener Institute’s “Changing Earth-Sustaining our Future” research program. The PRISM4 reconstruction and boundary conditions used in PlioMIP2 were funded by the U.S. Geological Survey Climate and Land Use Change Research and Development Program. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government.
© 2021 Zixuan Han et al.