Studies On Mid-Holocene Climate Change In Central And East Asia Based On PMIP2 Simulations

Having carefully analyzed the winter North Pacific sea level pressure (SLP) of 6ka and Oka with the method of Empirical Orthogonal Function analyses from the simulated results of Mid-Holocene and Pre-industry from four models in PMIP2 (Paleoclimate Modeling Intercomparison Project), we find all of the four models can simulate the spatial structure of winter North Pacific Oscillation Index compared to the results from NCEP/NCAR data. In order to deeply understand the relationship of the winter North Pacific sea level pressure between 6ka and Oka, changes of SLP at 6ka relative to Oka are analyzed. The simulated results (except MIROC3.2) show that a lower pressure in Aleutian region than in Hawaii region in 6ka, so that the discrepancy of sea level pressure between south and north is greater than Oka and the winter North Pacific Oscillation in 6ka was stronger. We also illustrate that winter North Pacific Oscillation had similar spatial structure in 6ka and Oka as the results from NCEP/NCAR data through Correlation Analysis between North Pacific Oscillation Index and winter North Pacific sea level pressure. Furthermore, we find North Pacific Oscillation had high correlation with winter temperature and precipitation in central arid Asia and eastern monsoon Asia in 6ka by comparing with the results from NCEP/NCAR data, showing that the North Pacific Oscillation is one of the factors that influence the central and eastern Asian climate variability in 6ka.The effect of vegetation in 6ka climate change is analyzed with the results of ECV model. The mid-latitude arid central Asian is climatically dominated by westerly circulation while the monsoon circulation deeply embedded into the inland. Influenced by different atmospheric circulations, the two regions have large differences in large-scale climatic features. At the same time, the flourished vegetation enhanced the response of climate system to the earth's orbital parameters. In order to evaluate the effect of the solar insolation in 6ka climate variability, the anomalies of the results of 6k(oa) minus to Ok(oa) are analyzed. At the same time, the anomalies of the results of 6k(oav) minus 6k(oa) are analyzed to evaluate the vegetation role in 6k climate changes. The results show significant response from vegetation feedback. However, the model has a disadvantage that it always underestimates the range of warming in 6ka, especially the winter Coupled with vegetation, the driving factors of climate change in 6ka and their relationships still need to be further investigate in future studies.