Physical processes of cooling and mega-drought during the 4.2 ka BP event: results from TraCE-21ka simulations
<p>It is widely believed that multi-decadal to centennial cooling and drought occurred from 4500 to 3900 BP, known as the 4.2 ka BP event that triggered the collapse of several cultures. However, whether this event was a global event or a regional event and wha...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-02-01
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| Series: | Climate of the Past |
| Online Access: | https://www.clim-past.net/15/265/2019/cp-15-265-2019.pdf |
| Summary: | <p>It is widely believed that multi-decadal to centennial cooling and drought
occurred from 4500 to 3900 BP, known as the 4.2 ka BP event that triggered
the collapse of several cultures. However, whether this event was a global
event or a regional event and what caused this event remains 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 occurs 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 might have been caused by
internal variability, while external forcings such as orbital and greenhouse
gases might have modulation effects. A positive North Atlantic Oscillation
(NAO)-like pattern in the atmosphere (low troposphere) triggered a negative
Atlantic Multi-decadal Oscillation (AMO)-like pattern in the ocean, which then
triggered a circum-global 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
mega-drought. The AMO-like pattern played a “bridge” role in maintaining this
barotropic structure in the atmosphere at a multi-decadal–centennial timescale. Our work provides a global image and dynamic background to help better
understand the 4.2 ka BP event.</p> |
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| ISSN: | 1814-9324 1814-9332 |