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Climate of the Past An interactive open-access journal of the European Geosciences Union
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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Oct 2018

Research article | 11 Oct 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Physical processes of cooling and megadrought in 4.2 ka BP event: results from TraCE-21ka simulations

Mi Yan1,2, Jian Liu1,2, and Liang Ning1,2,3 Mi Yan et al.
  • 1Key Laboratory of Virtual Geographic Environment, Ministry of Education; State key Laboratory of Geographical Environment Evolution, Jiangsu Provincial Cultivation Base; School of Geographical Science, Nanjing Normal University, Nanjing, 210023, China
  • 2Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing, 210023, China
  • 3Climate System Research Center, Department of Geosciences, University of Massachusetts, Amherst, 01003, USA

Abstract. It is widely believed that multidecadal to centennial cooling and drought occurred from 4500BP to 3900BP, known as the 4.2kaBP event that triggered the collapse of many cultures. However, whether this event was a global event or a regional event and what caused this event remain unclear. In this study, we investigated the spatiotemporal characteristics, the possible causes and the related physical processes of the event using a set of long-term climate simulations, including one all-forcing experiment and four single-forcing experiments. The results derived from the all-forcing experiment show that this event occurred over most parts of the Northern Hemisphere (NH), indicating that this event could have been a hemispheric event. The cooler NH and warmer Southern Hemisphere (SH) illustrate that this event could be related to the slowdown of the Atlantic Meridional Overturning Circulation (AMOC). The comparison between the all-forcing experiment and the single-forcing experiments indicates that this event was likely caused by internal variability. A positive North Atlantic Oscillation (NAO)-like pattern in the atmosphere (low troposphere) triggered a negative Atlantic Multidecadal Oscillation (AMO)-like pattern in the ocean, which then triggered a Circumglobal Teleconnection (CGT)-like wave train pattern in the atmosphere (high troposphere). The positive NAO-like pattern and the CGT-like pattern are the direct physical processes that led to the NH cooling and megadrought. The AMO-like pattern plays a bridge role in maintaining this barotropic structure in the atmosphere at a multidecadal-centennial time scale. Our work provides a global image and dynamic background to help better understand the 4.2kaBP event.

Mi Yan et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Mi Yan et al.
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