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用小波多尺度分析和回归等方法研究了近60年新疆降水记录的波动与趋势特征, 结果发现21世纪头十年降水亦然保持增加趋势, 但春、夏降水已呈弱的非线性下降趋势, 秋、冬季节降水增加趋势明显. 这可能与气候暖化的季节不均匀性有关. 年降水量的振荡与北大西洋涛动(NAO)关系密切, 二者约80%的方差都集中在年际尺度和多年代尺度成分两个带上, 年际变化之间呈显著负相关关系. NAO的多年代尺度成分位相超前降水10年左右, 而大西洋海温的多年代尺度涛动与之相差5年, 后者与降水的关联更为密切. "极差"分析表明, 对应于NAO的极端正或负位相事件, 下游的降水和水汽环境明显不同. 在NAO极端负位相年, 中亚和新疆降水都明显增加, 来自欧洲南部的水汽输送和中纬度瞬变涡动水汽输送均偏强, 中亚大气可降水量上升, 冷空气路径偏西, 瞬变天气系统易得到西南水汽输送带的配合, 水汽辐合增强, 有利于新疆和中亚的降水. 反之, 西风带水汽输送偏弱, 天气过程偏少, 降水量偏小, 易发生干旱. 因此, NAO的异常是新疆和中亚降水年际波动的主要原因之一.This paper focuses on the mechanism of the trend and oscillation in precipitation records in northwestern China over the past 60 years. The results from regression and orthogonal wavelet decomposition show a clearly ascending in annual precipitation since 2000, which is contributed mostly by significant increase in autumn and winter precipitations, while almost no trend can be identified in spring and summer time, which shows a weak descending in non-linear form. This may be in connection with different warming rates in seasons. There is a significant anti-correlation between the precipitation and the North Atlantic oscillation (NAO) on the inter-annual scale. About 80% of their variances concentrate on inter-annual and multi-decadal scales. The multi-decadal components of NAO index have a phase leading about 10 years to corresponding precipitation, about 4-5 years leg for AMO. Hence, NAO index can be used as an indicator for inter-decadal change of the precipitation. Other results from combination-difference analysis show that the NAO in extreme negative phase could lead to the precipitation increase in central Asia and northwestern China, owing to increase in eastward water-vapor transport from south Europe to Northwestern China, which causes an increase in column water vapor content in the above areas, and meanwhile the transient eddy activity becomes intensified in the areas or north with a further south route moving from Europe, Central Asia throughout northwestern China. On the contrary, a dry climate might appear in the areas when meet extreme positive phase of NAO. Thus, NAO's oscillation is one of the most important mechanisms for inter-annual change in precipitation of northwestern China.
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Keywords:
- northwestern China precipitation/
- North Atlantic oscillation/
- water-vapor transport/
- transient eddy activity
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