Simulations Of Climate Changes Over China In LGM And Mid-Holocene

In the process of the earth environment evolution, the phenomena that global climate becomes warm in 20^th Century had happened. A lot of geological researches show climate variations in past several 10 ka. These indicate that under the condition of no anthropogenic disturbance earth climate system practiced magnitude changes. It means that there is the conference for the predication of future climate changes, which can be used to examine the prediction. Moreover, these facts provide basis for exploring the mechanisms of climate changes.Numerical simulation is one of main methods by which palace-climate are explored. The models that are used to simulate palace-climate are developed from early single general circulation model to update atmosphere-ocean-biosphere coupled model. The model simulations are changing from simulating climate equilibrium to transit variation. At present, some issues in LGM and Holocene are paid more attention, which includes: 1. during glacial age and inter-glacial age, there were the climate change on thousand and hundred years scale. What is the mechanism? 2. During glacial age, how were dust transported? How did tundra change? How did they affect the climate? 3. Under the background of global palace-climate and palace-environment changes, how does regional climate response? How does results of low resolution global model compare with geological records, especially precipitation.In order to explore above Issue 3, with a regional model MM5 nested to an atmospheric global climate model CCM3, a series of simulations and sensitivity experiments have been performed to investigate relative Last Glacial Maximum (LGM) and Mid-Holocene (MH) climate response to different mechanisms over China. Some of main results are as follows:·It is one difficult problem that how GCM results compare with geological records. At present, one method by which GCM local and regional precipitations are estimated is statistical downscaling. The statistical model builds relationship between large-scale process and local changes on modern climate with linear mode. However, this method has some shortages, because the relationship between large-scale process and local changes isn't based on physical and dynamical rule, and it may change when climate and environment change. Another method is GCM model nesting regional model, whose merit is that is based on physical and dynamical rules. This thesis adopts this nesting way to investigate climate changes over China in LGM and Mid-Holocene. Comparing with early work, the global and regional models are advanced in this work. Our model results are better than early model results. Our modeled LGM and Mid-Holocene climate change are agreeable with geological records; especially in simulation of precipitation change (GCM results aren't agreeable with geological records). This indicates that GCM model nesting regional model can use to investigate palace-climate and regional climate responses, and this is very good method.·In this thesis, a series of simulations and sensitivity experiments have been performed to investigate in the round the factors that influence China climate in LGM and Mid-Holocene, which involve earth orbit, CO₂, sea-land distribution, vegetation and large-scale circulation background change. Previous modeled works about climate changes over China in LGM and Mid-Holocene mainly paid attention to the influence factors which are focused, such as vegetation change etc, but these aren't all-around.·During the LGM, two large ice sheets in North America and Europe causes a lower than PD sea-level in the extent of globe, and greatly alters the sea-land configuration. We first simulate the climate effect of land-sea distribution change in East Asia. Model results indicate that relative to the present climate, the changes of sea-land distribution in eastern Asia during the LGM result in temperature decrease in winter and increase summer. It has significant impact on the temperature and precipitation in the east coastal region of China. The impact on precipitation in the east coastal region of China is the most significant one, with 25-50% decrease in total precipitation change during the LGM. On the other hand, the changes in land-sea distribution have less influence on the climate of inland and western part of China.·We first suggest that precipitation increases happen in regions where convergences of water vapor enhance, but precipitation mustn't increase though summer monsoon enhances. Generally, it is known that summer monsoon over China enhanced in Mid-Holocene, and the precipitation increased due to enhanced summer monsoon. Some works found that precipitation in some regions decreases in Mid-Holocene, and propounded that summer monsoon appears a time weaken in Mid-Holocene. We think that summer monsoon intensified in Mid-Holocene, but precipitation in some regions may reduce although the summer monsoon enhances. ·In this thesis, comparisons of modeled cloud and satellite cloud data indicate that the model can reproduce main characteristics of middle and high cloud distributions and their season variations under the condition of modern climate. Based on this, we first explore changes of hydrogen cycle components in atmosphere during LGM and Mid-Holocene. The results show that maximum of relative humidity change is more than 15% in Mid-Holocene, which isn't conservative. Water vapor decreases while temperature increases in some region. This further proves that precipitation mustn't increase although summer monsoon enhanced in some regions. In LGM, water vapor decreases while temperature reduces. The relative humidity in summer increases in Western China, which became wet. These indicate that when temperature reduces water vapor decreases, but water vapor mustn't increase as temperature enhances. This is different with results on global scale that relative humidity is conservative.