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学科主题: 地理学::自然地理学
题名: 青藏高原中部长江源区的冰芯气候环境记录研究
作者: 张拥军
答辩日期: 2009-06-05
导师: 康世昌
专业: 自然地理学
授予单位: 中国科学院研究生院
授予地点: 北京
学位: 博士
关键词: 各拉丹冬冰芯 ;  青藏高原 ;  气候变化 ;  气温 ;  降水 ;  18O ;  积累量 ;  大气环境
索取号: S000023
部门归属: 图书馆
摘要: 本文利用各拉丹冬附近气象台站(五道梁、沱沱河、那曲、班戈)的器测资料和2005年10-11月中美联合考察期间,在各拉丹冬峰北部果曲冰川钻取的74 m冰芯数据,分析了长江源区的气温与降水变化,并利用冰芯中的离子浓度记录恢复了青藏高原中部的大气粉尘变化。主要结论如下所述: 器测资料的分析结果显示,近50年来(1959~2007),长江源区的气温具有显著的增暖趋势。长江源区的年平均气温的气候倾向率为0.35 ℃/10a,累积增温幅度达到1.72 ℃。年平均最高气温的气候倾向率为0.15 ℃/10a,远小于年平均最低气温的气候倾向率(0.58 ℃/10a),这说明长江源区变暖的主要特征是年平均最低气温显著升高。从季节的角度来看,长江源区冬季(1月)增暖的幅度(0.35 ℃/10a)要大于夏季(0.14 ℃/10a),即冬季增暖比夏季显著。同期,长江源区的年降水量具有显著的增长趋势。年降水量的增长率为14.8 mm/10a。年降水日数也呈现出显著的增长趋势,增长率为4.58 d/10a,并通过了显著性检验,但年降水强度却表现出了下降的趋势(未通过显著性检验)。各拉丹冬冰芯中δ18O记录可以作为长江源区气温变化的指标。依据各拉丹冬冰芯δ18O与该区夏季气温的线性关系,恢复了近70a(1935~2004) 来各拉丹冬地区气温的变化历史。1940s气温较低,随后逐渐升高至1950s后期,接着气温降低,至1970s中期达到近70a 来的最低值,1980s仍然处于一个低温期,自1990s以来气温急剧升高并延续到21世纪初。各拉丹冬冰芯记录的气温在1970s以来的增温率在0.5℃/10a,1990s以来,冰芯记录的增温率达到1.1℃/10a,约为1970s以来增温率的2倍,表明近期的增温有加速趋势且高海拔区域对全球变暖的响应更加敏感。各拉丹冬冰芯记录的气温存在着明显的7a周期,与NAO的周期具有一致性,说明该地区的气候变化很可能受到了NAO的影响。此外,本文从季节的角度探讨了各拉丹冬冰芯δ18O记录的变化趋势,发现非季风期的δ18O记录与安多气象站4月的气温记录有很好的相关性,而季风期的δ18O记录与7-9月的安多气温记录相关性较高,这表明各拉丹冬冰芯中非季风期的δ18O记录较好的反映了各拉丹冬地区的春季气温变化,而季风期δ18O记录则主要反映了各拉丹冬地区的夏季气温变化。根据各拉丹冬冰芯恢复的积累量时间序列,过去近70年来各拉丹冬地区降水序列被恢复。结果表明,70年来各拉丹冬冰芯积累量经历了从低积累期到高积累期的转变。各拉丹冬冰芯积累量的变化与临近的班戈气象站降水量变化具有较好的一致性。利用M-K方法,检测出各拉丹冬冰芯记录在1967年发生了一次由低积累量期向高积累量期的突变。对500 hpa流场和高度场差值图的分析表明,在高积累期的1968~2004年西南风要比低积累期的1948~1967北扩约2个纬度,且高积累期的巴尔喀什湖槽比低积累期要显著一些,同时这两个时段经向风差值和水汽输送的差值均为正值。因此,1968年以来南亚季风的北扩,巴尔喀什湖槽的增强,经向风以及水汽输送的增强,是导致该阶段降水量增大的直接原因。各拉丹冬雪坑和冰芯中主要离子的浓度分析表明,雪坑和冰芯中的主要离子皆为陆源。其中,非季风期时雪坑的离子浓度高,这与附近气象台站观测到沙尘天气多发生在冬、春两季的结果相一致。各拉丹冬冰芯中的离子浓度记录了1940~2005年青藏高原中部的大气粉尘变化,即1970s的高值期和1980s的低值期,并且大气中的粉尘载荷与大气环流关系密切。利用NCEP再分析资料,计算了1970s与1980s的经向风与纬向风风速差值场,结果表明:在青藏高原地区,不论是经向风还是纬向风1970s的风速都要比1980s风速大。这也是青藏高原1970s的沙尘天气远高于1980s的动力原因。同时,也说明青藏高原沙尘天气的主导风向为西南风。各拉丹冬冰芯的沙尘记录与全球春季TOMS气溶胶指数(AI)存在显著相关,尤其是北半球35ºN邻近区域。这说明青藏高原中部的大气粉尘气溶胶可被远程传输,同时,这种相关性也说明青藏高原冰芯中的陆源离子变化可以被用来重建青藏高原甚至北半球大气的粉尘记录。
英文摘要: Based on the meteorological data from meteorological stations (Wudaoliang, Tuotuohe, Naqu, Bange) of the nearby Geladaindong and ice core drilling at the flat firn basin in the Guoqu glacier, the northern of Mt. Geladaindong by Sino-US cooperation expedition in October-November, 2005, the variations of air temperature and precipitation in the source region of Yangtze River are analyzed. Major ions of ice core are also used to investigate the variations in atmospheric dust. The main conclusions were listed as follows: In the past 50 years (1959-2007), there is a clearly warming trend in the source region of Yangtze River. In this region, the warming rate annual mean air temperature is 0.35 ℃/10a, and the air temperature has raised 1.72 ℃. The warming rate for annual mean maximum air temperature (0.15 ℃/10a) was far less than the annual mean minimum air temperature (0.58 ℃/10a). This indicates the main characteristic of warming in the source region of Yangtze River is showing the sharp increasing of the annual mean minimum air temperature. The warming rates in winter (January, 0.35 ℃/10a) is also bigger than it in summer (July, 0.14 ℃/10a). The annual precipitation also has an obviously increasing trend, and the increasing trend is 14.8 mm/10a. The variation of precipitation days is 4.58 d/10a with significance level at 0.01, but precipitation intensity doesn’t show the clearly trend. δ18O time series is recovered as proxy of air temperature from Geladaindong ice core. Based on the correlation between δ18O and summer air temperature from nearby meteorological stations, a 70-year history air temperature (1935-2004) in the source region of Yangtze River was reconstructed. Air temperature was relatively low in 1940s and high in 1950s to the middle of 1960s. The lowest temperature occurred in the middle of 1970s. Temperature was low in 1980s and dramatically increased since 1990s, keeping the trend to the beginning of the 21st century. The warming rate recorded in the ice core with 0.5 ℃/10a, and it becomes 1.1 ℃/10a since 1990s. This reflected an accelerated warming and a more sensitive response to global warming in the high elevation region. A 7-year period was found in the temperature time series with the significance level at 0.05, and it was same to the NAO (North Atlantic Oscillation). This coincidence may reflect the potential influence by NAO in this region. The seasonal variations of δ18O time series are also discussed. The δ18O recorded in the non-monsoon period has the same trend with April air temperature in Amdo meteorological station, and in the monsoon season, it has high correlation to July-September air temperature. This showed the non-monsoon δ18O recorded the spring air temperature variation, while monsoon δ18O for summer. Annual accumulation records covering 1935 to 2004 were reconstructed using Geladaindong ice core. A significant positive correlation between annual accumulation and precipitation from nearby meteorological stations was found, suggesting ice core accumulation could be taken as a precipitation proxy. By using Mann-Kendall rank statistical test method, a change point for precipitation was determined in 1967. Analysis of the atmospheric circulation over the Tibetan Plateau suggested that, compared with the southwest wind during the low precipitation period (before 1967), it extended about 2 latitudes northward during high precipitation period (after 1967). Moreover, during the high precipitation, the trough over the Bal Karshi Lake was also enhanced, and both the meridional wind and vapor transporting displayed a remarkable aggrandizement. The major ions of Geladaindong ice core and snowpit were analyzed, and the results showed the crustal originated ions vary seasonally, and peak dust concentrations occur during winter and spring, which are consistent with dust days observed at nearby stations. However, both similarities and differences exist between the decadal variations of dust records in the Geladaindong core and data of dust days from the stations, due to effects of local environment of stations on dust days. Taking 1980s and 1970s as the case periods for high and low dust aerosols, enhanced atmospheric circulation (with strengthened wind speed) in 1970s caused more dust aerosols transported to the central TP. Moreover, a significant correlation between Geladaindong dust concentrations and the Total Ozone Mapping Spectrometer (TOMS) aerosol index in March indicates that dust loading over central Tibetan Plateau is closely correlated with dust aerosols in the regions around 35ºN over the Northern Hemisphere, demonstrating that dust aerosols over the Tibetan Plateau can be transported over the hemispheric scale as suggested by others, and also implying that variability of crustal ions in the central Tibetan Plateau ice core could be considered as one of indices for reconstructing a history of atmospheric dust loading not only in the TP, but also in the Northern Hemisphere by using the deep ice core records.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.itpcas.ac.cn/handle/131C11/1239
Appears in Collections:图书馆_学位论文

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Recommended Citation:
张拥军.青藏高原中部长江源区的冰芯气候环境记录研究[博士].北京.中国科学院研究生院.2009
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