冬季雪深再分析资料在欧亚中高纬地区的适用性评价

欧亚中高纬地区的积雪是影响气候的重要因子,但是观测台站稀疏且记录只到1996年,导致积雪观测资料严重缺乏。基于目前国际上应用较为广泛的3套再分析资料:美国国家大气海洋局(NOAA)的20世纪再分析资料(NCAR-20th century reanalysis)、欧洲中期天气预报中心(ECMWF)的再分析资料(ERA-Interim)及日本气象厅(JMA)的全球大气再分析资料(JRA-55),利用前苏联站点观测的雪深资料评估雪深再分析资料在欧亚大陆区域的适用性。结果表明:3套再分析资料对积雪的时空变化均具有一定的描述能力;其中,尤以JRA-55再分析资料与观测事实最为接近,能较好揭示欧亚中高纬雪深变化的空间分布特征,反映雪深的长期变化趋势。JRA-55再分析资料揭示的欧亚雪深与169站观测有90%吻合,20世纪再分析资料有76%一致,而ERA-Interim再分析资料只有一半。区域尺度上,JRA-55再分析资料揭示的欧洲、西伯利亚南部雪深在1961~1990年的变化与观测是正相关,相关系数达到0.91、0.87,而20世纪再分析资料仅有0.77、0.32。长时间序列的雪深资料(JRA-55)表明欧亚大陆积雪存在年代际的变化特征:1960年代积雪偏少;1970年代偏多;从1980年代开始呈现减少趋势,持续至20世纪末,并且积雪的减少是高纬度积雪变化造成的。     

欧亚大陆积雪与亚洲季风关系研究进展

系统回顾了欧亚大陆积雪和亚洲季风之间联系的国内外研究进展,并对研究中存在的一些问题做出评述。积雪可以显著影响地表温度、土壤湿度以及地表辐射状况,从而影响亚洲夏季风的建立和发展。普遍认为,积雪增加会导致亚洲夏季风减弱或者爆发推迟,在众多诊断分析和模拟研究中都发现了这种积雪和季风的负相关关系。但这种关系是十分复杂的,不同区域的积雪以及雪盖或者雪深都对亚洲季风有不同的影响,而且积雪和季风之间的关系也存在年代际的变化。积雪和亚洲季风的联系还受到ENSO以及北大西洋涛动等因素的影响。目前的研究工作中,有关积雪和季风的关系以及积雪影响季风的机制和过程,还存在很多的分歧和疑问,有待于进一步的研究。     

欧亚大陆及西太平洋边缘海瑞利面波层析成像研究

利用亚洲、欧洲及西太平洋边缘海地区台网114个数字地震台,搜集了400W～1800E,400S～800N范围内近万个地震事件,并从中挑选出1982～2006年间震级在5.0～7.0之间、震源深度小于100㎞的1800余个事件.经过筛选,共得到周期在8～200s之间10450余条质量较高的瑞利面波频散曲线,这些面波所通过的大圆路径很好地覆盖了欧亚大陆及西太平洋.本文首先对原始记录进行预处理,测定面波频散曲线,包括截取Rayleigh面波,进行频率时域分析等,以得到实际频散数据.然后对研究区域进行网格划分,反演网格点附近的纯路径频散曲线.即采用网格化纯路径频散反演方法得到各块的纯频散数据.最后由得到的每块纯频散数据作为观测数据,并利用LSQR、SVD等广义线性反演方法,对每一块的纯频散曲线进行反演求取该单元的S波速度随深度的分布.     

Plate tectonic evolution of the southern margin of Eurasia in the Mesozoic and Cenozoic

Thirteen time interval maps were constructed, which depict the Triassic to Neogene plate tectonic configuration, paleogeography and general lithofacies of the southern margin of Eurasia. The aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework. The Hercynian Orogeny was completed by the collision of Gondwana and Laurussia, whereas the Tethys Ocean formed the embayment between the Eurasian and Gondwanian branches of Pangea. During Late Triassic–Early Jurassic times, several microplates were sutured to the Eurasian margin, closing the Paleotethys Ocean. A Jurassic–Cretaceous north-dipping subduction boundary was developed along this new continental margin south of the Pontides, Transcaucasus and Iranian plates. The subduction zone trench-pulling effect caused rifting, creating the back-arc basin of the Greater Caucasus–proto South Caspian Sea, which achieved its maximum width during the Late Cretaceous. In the western Tethys, separation of Eurasia from Gondwana resulted in the formation of the Ligurian–Penninic–Pieniny–Magura Ocean (Alpine Tethys) as an extension of Middle Atlantic system and a part of the Pangean breakup tectonic system. During Late Jurassic–Early Cretaceous times, the Outer Carpathian rift developed. The opening of the western Black Sea occurred by rifting and drifting of the western–central Pontides away from the Moesian and Scythian platforms of Eurasia during the Early Cretaceous–Cenomanian. The latest Cretaceous–Paleogene was the time of the closure of the Ligurian–Pieniny Ocean. Adria–Alcapa terranes continued their northward movement during Eocene–Early Miocene times. Their oblique collision with the North European plate led to the development of the accretionary wedge of the Outer Carpathians and its foreland basin. The formation of the West Carpathian thrusts was completed by the Miocene. The thrust front was still propagating eastwards in the eastern Carpathians.During the Late Cretaceous, the Lesser Caucasus, Sanandaj–Sirjan and Makran plates were sutured to the Iranian–Afghanistan plates in the Caucasus–Caspian Sea area. A north-dipping subduction zone jumped during Paleogene to the Scythian–Turan Platform. The Shatski terrane moved northward, closing the Greater Caucasus Basin and opening the eastern Black Sea. The South Caspian underwent reorganization during Oligocene–Neogene times. The southwestern part of the South Caspian Basin was reopened, while the northwestern part was gradually reduced in size. The collision of India and the Lut plate with Eurasia caused the deformation of Central Asia and created a system of NW–SE wrench faults. The remnants of Jurassic–Cretaceous back-arc systems, oceanic and attenuated crust, as well as Tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems.     

冬半年欧亚雪盖变化对东亚环流的影响

对１９７３～１９９４年期间欧亚雪盖和东亚５００ｈＰａ高度距平资料进行旋转扩展主成分分析,研究了冬半年欧亚雪盖异常与后期夏半年东亚环流分布连续演变的关系及其可能机制。结果表明前期秋冬春季欧洲、中亚和东亚中高纬雪盖异常不同的动态变化激发出具有不同持续性的东亚低频流型,而夏半年东亚副热带环流纬向扩展型演变与前期冬半年欧亚雪盖异常无关。     

Potential forest fire danger over Northern Eurasia: Changes during the 20th century

Significant climatic changes over Northern Eurasia during the 20th century have been reflected in numerous variables of economic, social, and ecological interest, including the natural frequency of forest fires. For the former USSR, we are now using the Global Daily Climatology Network and a new Global Synoptic Data Network archive, GSDN, created jointly by U.S. National Climatic Data Center and Russian Research Institute for Hydrometeorological Information. Data from these archives (approximately 1500 of them having sufficiently long meteorological time series suitable for participation in our analyses) are employed to estimate systematic changes in indices used in the United States and Russia to assess potential forest fire danger. We use four indices: (1) Keetch–Byram Drought Index, (KBDI; this index was developed and widely used in the United States); (2) Nesterov, (3) Modified Nesterov, and (4) Zhdanko Indices (these indices were developed and widely used in Russia). Analyses show that after calibration, time series of the days with increased potential forest fire danger constructed using each of these three indices (a) are well correlated and (b) deliver similar conclusions about systematic changes in the weather conditions conducive to forest fires. Specifically, over the Eastern half of Northern Eurasia (Siberia and the Russian Far East) statistically significant increases in indices that characterize the weather conditions conducive to forest fires were found. These areas coincide with the areas of most significant warming during the past several decades south of the Arctic Circle. West of the Ural Mountains, the same indices show a steady decrease in the frequency of “dry weather summer days” during the past 60 yr. This study is corroborated with available statistics of forest fires and with observed changes in drought statistics in agricultural regions of Northern Eurasia.     

A mass balance model for the Eurasian Ice Sheet for the last 120,000 years

We present a mass balance model for Eurasia which is based on the calculation of accumulation from a moisture balance concept. The model is forced with 500 hPa temperatures from GCM time slices at LGM and present day. The model simulates key characteristics, such as control on the size of ice sheets through the advection of moisture, asymmetric ice sheets due to advection of moisture and orography, and the drying of ice sheets when they grow. A simulation of the Eurasian Ice Sheet through a full glacial cycle shows that the model reproduces realistic ice sheets that compare well with geomorphological data. During the Middle Weichselian and the Late Weichselian, the model picks up the trend that the Scandinavian part of the ice grows towards the south and east whilst the ice sheet covering the Barents and Kara Seas remains relatively stable. However, the model seriously underestimates the observed ice extent in the Baltic area. Uncertainties in the temperature and the wind field limit the reliability of regional modelling results.     

Paleomagnetic study on orogenic belt: An example from Early Cretaceous volcanic rocks,Inner Mongolia,China

Since the 1990s, a large number of paleomagneticstudies have been carried out in the North China block(NCB) and Tarim block[1-8], and more and more geo-physicists recently believe that the last collision andconvergence between Siberia and the Mongolia-NorthChina plate happened in the Late Jurassic, which wascontributed to a paleomagnetic study on these areas byZhao and his colleagues[2]. However, we lack paleo-magnetic results obtained directly from the orogenicbelt between Siberia and th…