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ZHANG

current knowledge on the earth's climate and its variation is mainly constructed on data collected during the modern instrumental era, which is generally shorter than 150 years. Numerical models are indispensable tools to extend the study period back to the past. In this thesis, we used a global coupled climate system model FGOALS_gl, to reproduce the climate evolution during the last millennium.

In comparison with data from both paleo-reconstruction and instrumental measurements, the model simulation presents a very good performance for the surface air temperature. Changes of surface air temperature are mainly in the Northern Hemisphere for the natural-forcing-dominant period, and they are significant in the two hemispheres for the anthropogenic-forcing-dominant period. Clouds play an important role in modulating the external perturbation.

The North Atlantic Oscillation experiences a broadband frequency during the last millennium. Concerning the spatial structure of the NAO, it is found that the NAO is highly correlated with the changes in the tropical Pacific in the natural forcing period, whereas the changes in the 20th century are more pronounced at mid and high latitudes. The enhancement of interdecadal variability in the 20th century is responsible for the differences. We suspect that the NAO variability may be disturbed by solar irradiance forcings in the natural forcing period and by anthropogenic forcings in the modern epoch.

Changes in the NAO have great climate consequences. The climate impacts of the NAO on the Atlantic Meridional Overturning circulation and the East Asian Winter Monsoon are also examined.
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