喜马拉雅山中部过去约300年季风降水变化

MONSOON RAINFALL VARIABILITY IN CENTRAL HIMALAYA MOUNTAINS OVER THE PAST ca. 300 YEARS

重建了 1 70 0年以来喜马拉雅山中部达索普冰芯积累量 ,该积累量直接反映了喜马拉雅山中部季风降水。研究了该积累量的变化规律 ,并分析了其与尼泊尔和印度东北部夏季风降水之间的关系 ,最后讨论了陆海热力差异与该积累量之间的关系。

A 149.2m long ice core was drilled at the accumulation area of Dasuopu glacier (28°23′N, 85°43′E , 7?200m a.s.l.) in the central Himalaya Mountains in 1997. The ice core was analyzed continuously for stable isotopes ( δ 18 O), cations and anions throughout the core. Cycles indicated by δ 18 O, cations and anions were identified and counted as seasonal fluctuations as annual increment from minimum to maximum values. Reconstructed 295 year (1700～1995) annual net accumulation from the core reflects a major precipitation trend for the central Himalaya Mountains. Then the accumulation record is analyzed to reveal variation characteristics and associations to Indian monsoon rainfall using methods of (EOF) and singular spectrum analysis (SSA). EOF analysis show in the EOF1 associations precipitation in Himalaya Mountains and in North West India are positively correlated,and anti correlated with that in all India. In the EOF2 associations precipitation in Himalaya Mountains are positively correlated with northern Indian,and negatively correlated with southern Indian. Based on these associations,we identified distinct climatic regimes in monsoon precipitation with main changes around the year 1930. The period 1850～ 1930 is characterized by more wet years over Himalaya Mountains and by more dry years over central India,while the period 1930～1995 is characterized by more dry years over Himalaya Mountains and by more wet years over central India. The precipitation record indicates in central Himalaya Mountains dry climate occurred in early 18 th , wet condition prevailed between 1830～1930, but the accumulation has decreased to its present value after 1930. However distinct secular trends were not found in the record. For the periods 1955～1995 variability of the accumulation is found to correlate significantly with the thermal contrast between the Tibetan Plateau and the Indian Ocean surface temperature. The thermal contrast correlates more strongly with the accumulation ( r =0.42, sig.=99%) than does either Tibetan Plateau temperature ( r =0.3, sig.=95%) or Indian Ocean surface temperature (0.02).