Regional expression of interglacial climates in Eastern Asia during the last 800000 years
(2022)
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- Authors
- Supervisors
- Yin, Qiuzhen
- Abstract
- Understanding interglacial climate diversity and intra-interglacial variability can help assess the sensitivity of the Earth system to different forcings during warm periods. This study examines the individual and combined effects of astronomical parameters (obliquity, precession, and eccentricity), Greenhouse gases concentrations and ice sheets as well as internal feedback mechanisms on the East Asian climate during the last nine interglacials. It has been achieved through simulations with an atmosphere-ocean coupled general circulation model HadCM3 using two different approaches. The first approach is to use a Gaussian emulator that was developed based on 61 well-designed HadCM3 experiments, which allows quantifying the sensitivity of the East Asian precipitation and temperature to orbital parameters, CO2 and ice volume during the past 800 ka. The second is to perform two groups of snapshot experiments covering the entire period of each interglacial and by a time step of 2-ka, which leads to 468 experiments in total. Results based on the emulator approach show that in the East Asian summer monsoon domain north of 25° N, the variation of the summer precipitation is dominated by precession, leading to strong 23-ka cycles. However, in the southern part, ice sheets play a more important role than insolation, generating the 100-ka cycles, by influencing the latitude of the Intertropical Convergence Zone and the Hadley cell. Obliquity and CO2 have little effect on the summer precipitation as compared to precession and ice sheets. To study the detailed mechanisms and internal feedbacks involved in the impact of astronomical forcing, GHG and ice sheets on the East Asian climate, MIS-5 is presented as an example. Results show that during MIS-5, astronomical and GHG forcings both have positive effects on the summer temperature and precipitation. Within the range of its variability during MIS-5, CO2 can cause a similar degree of warming effect but much a lower degree of humidifying effect as compared with insolation. Insolation and GHG affect the precipitation by dynamic and thermodynamic processes, respectively. The influence of ice sheets on temperature and precipitation is much less than insolation and varies in regions and in time. The summer temperature in northern China and precipitation in southern China are more sensitive to ice sheets, respectively. When the background insolation is higher, precipitation variation caused by ice volume is small. Changing the location, height and area of ice sheets can make a difference in precipitation, and the differences mainly act by changing the vertical dynamic components. Finally, the nine interglacials are studied and compared with each other. The general impacts of astronomical forcing, CO2 and ice sheets on the regional climate in East Asia are similar between the interglacials but have different intensities. The vertical dynamic component is the primary contributor to the boreal summer precipitation change in the East Asian summer monsoon domain, and the vertical thermodynamic component is the secondary one. Horizontal meridional dynamic and zonal thermodynamic components also have positive effects on the JJA precipitation. All the four key components are significantly correlated with precession. The results of the interglacial snapshot simulations show that insolation plays a dominant role in the East Asian summer monsoon during interglacials, and ice sheets just modulate the magnitude of the East Asian summer monsoon's response to insolation. At 20°N-30°N, ice sheets reinforce summer precipitation regardless insolation when their volume is below a threshold. At 30°N-35°N, ice sheets reinforce summer precipitation regardless their volume when insolation is below a threshold. The comparison of the nine interglacials show that their intensity and internal variability have strong regional diversity in East Asia. The evaluation of the HadCM3 results show that the emulated and simulated climate show similarly in most regions of East Asia. The inconsistency may be related to the internal feedback and regional sensitivity of precipitation in East Asia to the shapes of ice sheets. The inconsistency in the data-model comparison may result from the uncertainties in both the proxy records and model simulations.
- Affiliations
Citations
Lyu, A. (2022). Regional expression of interglacial climates in Eastern Asia during the last 800000 years. https://hdl.handle.net/2078.5/103403