青藏高原积雪时空变化特征及其环流背景研究

发布时间：2019-04-11 13:00

【摘要】：积雪是冰冻圈的重要组成部分,因其高反照率、低导热率的特性,能够显著改变下垫面的特性,对气候系统中的能量平衡和水量循环有着深远的影响。青藏高原积雪不仅是气候变化的敏感指示器,还能显著影响区域乃至全球的气候和水文条件。因此,在气候变暖的背景下,加强对青藏高原积雪时空变化的研究,深入探讨高原积雪变化的原因机理,具有重要的理论和现实意义。本文基于MODIS 8日合成积雪产品和ERA-Interim再分析资料,采用气候统计诊断方法,研究了 2002-2014年青藏高原积雪的时空变化特征,并探讨了高原冬季积雪年际变化主模态与大尺度环流异常的关系,结果表明:高原积雪分布空间差异明显,主要集中分布在高原东部、西部和南部边缘的高海拔山区,而高原内部的低海拔腹地则鲜有积雪分布。高原东部的巴颜喀拉山和东南部的念青唐古拉山是积雪的大值区也是高原积雪年际变化的大值区。高原西部的喀喇昆仑山及其周边地区为积雪大值区也是稳定积雪区。高原积雪主要集中在冬季和春季,高原平均积雪覆盖率年内变化曲线呈多峰型的分布特征,10月下旬至次年3月下旬,高原平均积雪覆盖率较高,年际波动也较大,是高原积雪较为活跃的时段。高原积雪年际变化总体呈微弱的下降趋势,而高原东部唐古拉山和西南部喜马拉雅山沿线的积雪呈增长的年际变化趋势。高原冬季积雪经验正交函数(EOF)分解的第一模态EOF1在空间上表现为东-西反位相的变化特征,其时间系数PC1以年际波动为主,与高原整体冬季积雪覆盖率(SCF)年际变化的时间序列相一致。高原冬季积雪东-西反位相的年际变化特征与北极涛动(AO)具有密切的联系。高原积雪PC1回归的北半球赤道外位势高度场表现为AO正位相,AO指数(AOI)回归的SCF场则与冬季积雪EOF1空间分布相一致,高原冬季积雪PC1与AOI显著正相关。AO影响高原冬季积雪年际变化的可能机制是:AO正位相时,欧洲东部大槽东移且向南加深,乌拉尔山附近的高压脊加强东移至贝加尔湖附近,使得东亚大槽相对减弱,冬季风减弱,同时南支槽加深东移,西太平洋副高加强西伸,有利于来自南海和西北太平洋的暖湿气流抬升进入高原,与加深的南支槽配合,高原东部自近地面至平流层底层都表现为强烈的相对上升运动,造成高原东部多雪的环流背景,高原西部则受干燥下沉的西风气流控制,不利于降雪产生,同时,高原中西部地面气温异常偏高,不利于积雪的维持,致使高原西部积雪减少;AO负位相时情况相反,冬季风增强使得西伯利亚冷空气易于从西北部入侵高原,与来自阿拉伯海和孟加拉湾的暖湿气流在高原西部交汇,有利于降雪产生,高原东部则受来自西北的干燥下沉气流控制,不易发生降雪,导致高原积雪东部偏少,西部偏多。
[Abstract]:Snow cover is an important part of the freezing circle. Because of its characteristics of high albedo and low thermal conductivity, it can significantly change the characteristics of the underlying surface, and has a far-reaching impact on the energy balance and water cycle in the climate system. Snow cover in Qinghai-Xizang Plateau is not only a sensitive indicator of climate change, but also can significantly affect regional and even global climate and hydrological conditions. Therefore, under the background of climate warming, it is of great theoretical and practical significance to strengthen the research on the spatio-temporal variation of snow cover in the Qinghai-Tibet Plateau and to explore the causes and mechanisms of the snow change in the plateau. Based on the MODIS 8-day synthetic snow product and ERA-Interim reanalysis data, the temporal and spatial characteristics of snow cover over the Qinghai-Xizang Plateau from 2002 to 2014 are studied by using the climatic statistical diagnosis method. The relationship between the interannual variation of snow cover in winter and the large-scale circulation anomaly is discussed. The results show that the spatial difference of snow cover distribution in the plateau is obvious, mainly distributed in the high altitude mountain areas of the eastern, western and southern edge of the plateau. On the other hand, the low altitude hinterland of the plateau has little snow distribution. The Banyankala mountain in the eastern part of the plateau and the Nianqingtang Gula mountain in the southeast of the plateau are the large areas of snow cover and the interannual variation of snow cover in the plateau. The Karakoram Mountain and its surrounding areas in the western part of the plateau are snow-covered areas and stable snow-covered areas. The snow cover over the plateau is mainly concentrated in winter and spring, and the annual variation curve of the average snow cover over the plateau is a multi-peak pattern. From late October to late March of the following year, the average snow cover of the plateau is high and the annual fluctuation is also large. Is the plateau snow is more active period. The interannual variation of snow cover in the plateau generally shows a weak downward trend, while the snow cover along the Tanggula Mountains in the eastern part of the plateau and along the Himalayas in the southwest of the plateau shows an increasing interannual trend. The first mode EOF1 of the empirical orthogonal function (EOF) decomposition of snow cover in the plateau is characterized by the change of the east-west phase in space, and the time coefficient PC1 is dominated by the inter-annual fluctuation. It is consistent with the time series of the interannual variation of snow cover (SCF) in winter over the plateau. The interannual variations of the East-West inversion of snow cover in winter over the plateau are closely related to the Arctic Oscillation (AO). The height field of the equatorial potential in the Northern Hemisphere of the PC1 regression of snow cover over the plateau is AO positive phase, while the SCF field of the AO index (AOI) regression is consistent with the spatial distribution of the snow EOF1 in winter. There is a significant positive correlation between PC1 and AOI in winter snow cover over the plateau. The possible mechanism of AO effect on the interannual variation of snow cover in the plateau in winter is as follows: when the AO phase is positive, the great trough in eastern Europe moves eastward and deepens southward, and the high pressure ridge near Ural Mountain moves eastward to the vicinity of Lake Baikal. As a result, the East Asian trough is relatively weakened, and the winter monsoon weakens. At the same time, the southern branch channel deepens eastward and the western Pacific subtropical high is strengthened westward, which is conducive to the warm and wet air flow coming from the South China Sea and the northwest Pacific Ocean rising to the plateau and coordinating with the deepening southern branch trough. The eastern part of the plateau shows a strong relative upward movement from near the surface to the bottom of the stratosphere, resulting in a snowy circulation background in the eastern part of the plateau, while the western part of the plateau is controlled by dry and sinking westerly airflow, which is not conducive to snowfall, and at the same time, The surface temperature of the central and western plateau is unusually high, which is not conducive to the maintenance of snow, resulting in the reduction of snow cover in the western part of the In contrast to the negative phase of AO, the enhancement of the winter monsoon makes it easier for Siberian cold air to invade the plateau from the northwest and meet warm and wet airflow from the Arabian Sea and Bay of Bengal in the western part of the plateau, which is conducive to snow production. The eastern part of the plateau is controlled by dry downdraft from the northwest, which is not easy to cause snowfall, resulting in less snow in the eastern part of the plateau and more snow in the western part of the plateau.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P426.635;P434

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