Characteristics and mechanisms of decadal to centennial megadrought events over the eastern Asia during the Holocene
Abstract
The spatio-temporal characteristics and mechanisms of the decadal to centennial scale megadrought events over the eastern Asia have been investigated through a group of climate modeling and comparisons between reconstruction and simulations. The results show that internal climate variability within the coupled climate system plays an essential role in triggering megadroughts, while different external forcings may contribute to persistence and modify the anomaly patterns of megadroughts.
On decadal scale, the simulated megadroughts have comparable magnitudes and durations with those derived from reconstructed proxy data, although the megadroughts are not temporally synchronous. In all experiments, the megadroughts exhibit similar spatial structures corresponding to a weakening of the East Asia summer monsoon (EASM) and a strengthening of the East Asia winter monsoon (EAWM). Then the influences of volcanic eruptions on decadal megadrought events were investigated in details, as an example of the external forcings. Composite analyses showed that, on decadal scale, the volcanic eruptions induce a negative PDO-like pattern, which does not favor the occurrence of decadal megadroughts. The mechanisms of Ming Dynasty megadrought, which has crucial influences on Chinese history, were investigated through a group of sensitivity experiments as a case study. On centennial scale, two major Holocene cold/drought events, 8.2 ka BP event and 4.2 ka BP event, are compared through a group of transient simulations. The differences of the spatial patterns of global temperature and precipitation changes, as well as corresponding large-scale circulation patterns during the 8.2ka BP and 4.2ka BP events are discussed. For the physical mechanisms, the 8.2ka BP event was brought about by an outburst flood from pro-glacial Lake Agassiz, while, the mechanism behind the 4.2ka BP event is still unclear. Based on model simulations under different external forcing, we hypothesized that 4.2ka BP event may be generated by combination of a steady decline in SSTs across the North Atlantic and a reduction in the AMOC over the past 5000 years driven by long-term changes in insolation, and multi-century scale fluctuations in SSTs and AMOC strength superimposed on this decline.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGC14A..01N
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSES;
- 1616 Climate variability;
- GLOBAL CHANGE;
- 1620 Climate dynamics;
- GLOBAL CHANGE