2007/2008和2008/2009冬季平流层强、弱极涡事件对应的行星波活动的对比分析

在对逐日气象资料进行纬向谐波分析的基础上, 对比和讨论了2007/2008年冬季强极涡期间和2008/2009冬季弱极涡期间平流层和对流层不同波数的行星波的变化特征, 特别关注强极涡或弱极涡发生之后, 500 hPa 沿60°N和30°N行星波1波和2波振幅和位相的差异, 以及相应的500 hPa位势场的差异, 进而讨论为什么不同的平流层极涡异常会对东亚有不同的影响, 特别讨论为什么同一种极涡异常, 对我国南北方近地面气温的影响会不同。结果表明:平流层极涡发生异常时, 平流层行星波活动有明显的异常。随着极涡异常的下传, 对流层行星波的振幅和位相也有明显的变化, 而且, 对于不同的纬度带, 其变化又有不同, 表现为:2008年1月强极涡发生之后, 500 hPa行星波1波和2波的扰动都向南伸, 而2009年1月的弱极涡(SSW)期间和之后, 1波和2波的扰动都偏北; 在对流层, 强极涡和弱极涡发生之后不但行星波1波和2波的振幅有所差异, 其位相也有明显的不同。特别是, 其位相的差异还随纬度而变化。就同一年(或者说对于同是强极涡或者同是弱极涡)而言, 无论是1波还是2波, 在60°N和30°N附近的扰动相比, 几乎反位相。这样就使得它们的500 hPa 位势场也有明显不同:在东半球, 主要表现为乌拉尔高压和东亚大槽的强度和位置不同。2008年1月强极涡发生之后, 乌拉尔高压和东亚大槽东移, 不利于冷空气向欧亚大陆北部(包括我国北方)的输送, 使这些地区的温度偏高;而2009年1月弱极涡之后, 东亚大槽西退, 利于冷空气向欧亚大陆北部输送, 导致这些地区较冷。对于同一种极涡异常(如2008强极涡或者2009弱极涡)由于南方和北方行星波扰动的位相不同, 对南方和北方冷暖空气的输送也就不一样。所以同一种极涡异常对(我国)南北地区的温度影响是不同的。     

Rheological properties of the upper mantle of Northern Eurasia and nature of regional boundaries according to the data of long-range seismic profiles

Deep seismic investigation carried out in Russia in long-range profiles with peaceful nuclear explosions allowed clarifying in details the structure of the upper mantle and the transition zone down to the depth of 700 km within the huge territory of old and young platforms of Northern Eurasia. Variability of horizontal heterogeneity of the upper mantle depending on the depth serves to qualitative estimation of its rheological properties. The upper part of the mantle to the depth of 80–100 km is characterized by the block structure with significant velocity steps of seismic waves at the blocks often divided by deep faults. This is the most rigid part of lithosphere. Below 100 km horizontal heterogeneity is insignificant, i.e., at these depths the substance is more plastic and not capable to retain block structure. On the lithosphere bottom at the depth of 200–250 km plasticity increase is observed as well but the zone of the lower velocities that might have been bound with the area of partial melting (asthenosphere) has not been found. These three layers with different rheological properties are divided by seismic boundaries presented by thin layering zones with alternating higher and lower velocities. At the specified depths any phase boundaries have been distinguished. These thin layering zones are assumed to form due to higher concentration of deep fluids at some levels of depths where mechanical properties and permeability of substance change. Insignificant number of fluids may result in appearance of streaks with partial or film melting at relatively low temperature—to the rise of the weakened zones where subhorizontal shifts are possible. According to seismic data in many world regions seismic boundaries are also observed at the depth of about 100 and 200 km; they may be globally spread. There are signs that areas of xenoliths formation and earthquake concentration, i.e., zones of high deformations, are confined to these depths.     

Evidence for significant clockwise rotations of the Korean Peninsula during Cretaceous

In an effort to evaluate the Cretaceous magnetostratigraphy for the Korean Peninsula and to establish the tectonic coherence of its various elements, we collected paleomagnetic data from 121 samples from 20 sites within the Chilgok Formation (108.3–109.9 Ma) in the Gyeongsang Basin. Together with previously published data, we evaluate the results from a total of 163 sites in the basin.We combine our age model with results from recent stratigraphic, paleomagnetic and radiometric geochemical studies. In this study, we found that two distinct declination shifts decrease with younging direction, indicating two clockwise rotational events of the Korean Peninsula with respect to the Eurasia continent. The earlier event took place during 130–100 Ma (Phase I, newly termed “Goguryeo Disturbance”) and a later one during 80–50 Ma (Phase III, belonging to “Bulguksa Orogeny”). The mean rotation rate in the interval from 115.2 to 103.8 Ma (Phase I) is about 0.74°/Ma, while the rate from 90.9 to 79.8 Ma (Phase II) is 0.19°/Ma. Based on paleolatitude change during Phase I, we infer that the Korean Peninsula (eastern part of the Sino-Korea Block) migrated southward about 300 km after the complete amalgamation of the Sino-Korea Block into the Eurasian continent resulting in N–S compression within the Korean peninsula and Manchuria. Large-scale strike-slip faults (e.g., Tan-Lu Fault, Okcheon Boundary Fault) were probably rejuvenated in the Sino-Korea Block during Phase I.     

欧亚大陆春季植被对同年中国西北夏季大气环流和气候的影响研究

利用1982—2006年欧亚大陆月归一化植被指数（NDVI）,NCAR/NCEP月高度场和风场以及中国西北地区248个气象台站的逐日降水、温度资料,通过SVD及合成分析等方法,分析了欧亚大陆春季植被同同年中国西北夏季大气环流乃至干湿特征的关系.结果表明：欧亚大陆春季植被覆盖状况对预测我国西北地区同年夏季的干湿特征具有较...     

CMIP3模式对未来50a欧亚大陆雪水当量的预估

为研究预估未来50a欧亚大陆雪水当量,基于遥感数据,用误差百分率、空间相关和误差标准差等统计方法,评估了14个CMIP3模式在20C3M的雪水当量产品,诊断各模式对欧亚大陆雪水当量的模拟能力,在此基础上对模拟效果较好的10个模式产品进行多模式集合,分析了A2和B1情景下2002—2060年欧亚大陆雪水当量的变化．结果表...     

Reconstruction of fire spread within wildland fire events in Northern Eurasia from the MODIS active fire product

Russian boreal forests have been reshaped by wildland fire for millennia. While fire is a natural component of boreal ecosystems, it impacts various aspects of the environment and affects human well-being. Often fires occur over large remote areas with limited access, which makes their ground-based observation difficult. A significant progress has been made in mapping burned area from satellite imagery, which provides consistent and fairly unbiased estimates of fire impact on areas of interest at multiple scales. Although the information provided by burned area products is highly important, the spatio-temporal dynamics of individual fire events and their impact are less known. In high northern latitudes of Northern Eurasia, MODIS (Moderate Resolution Imaging Spectroradiometer) makes up to four daily observations from each of the Terra and Aqua satellites providing consistent data on fire development with high temporal frequency. Here we introduce an approach to reconstruct the development of fire events based on active fire detections from MODIS. Fire Spread Reconstruction (FSR) provides a means for characterization of fire occurrence over large territories from remotely sensed data. Individual fire detections are clustered within a GIS environment based on a set of rules determining proximity between fire observations in space and time. FSR determines the number of fire events, their approximate size, duration, and fire spread rate and allows for the analysis of fire occurrence and spread as a function of vegetation, fire season, fire weather and other parameters. FSR clusters were compared to burned scars mapped from Landsat7/ETM+ imagery over Yakutia (Russia). While some smaller burn scars were found to be formed through a continuous burning of a single fire event, large burned areas in Siberia were created by a constellation of fire events incorporating over 100 individual fire clusters. Geographic regions were found to have a stronger influence on the rates of fire activity in the area compared to vegetation zones. In addition, fire spread rates do not directly correlate with the intensity of a given fire season. FSR is also used to identify the points of ignition for individual fire events in spatio-temporal domain for fire danger and fire threat modeling. This approach presents another step towards the more complete characterization of fire events from remotely sensed data.     

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历史地理视角下丝绸之路空间格局及影响研究

已有的“一带一路”相关研究已逐步引起了学界对历史文化资源于今日发展影响的关注,然而作为“一带一路”倡议的历史依托和出发点,丝绸之路相关量化研究仍处于起步阶段。从文明的角度来说,如何认识丝绸之路是当代中国理解全球的关键。运用OLS、Logistic回归等手段,定量探讨了丝绸之路路线的形成动因以及其对历史及当代的影响。结果表明：① 丝绸之路道路密度分布总体处于波动状态,在以罗马、长安、大都为代表的交通网络起始点以及撒马尔罕、塔什干为代表的内线重要中转枢纽处密度数值大幅提高。② 作为商业贸易通道,丝绸之路路线选择影响最大的因素是地理因子,主要倾向于低坡度、高起伏度的地区,这一点在中亚复杂山地地形中表现得尤为明显。③ 丝绸之路的开辟与通畅,对当时社会经济、城市发展起到了显著的作用。丝绸之路道路密度同距最近海岸距离、纬度、历史文明指数等指标一道构成了古代城市分布的主要影响因素。④ 丝绸之路对区域经济发展的正面影响具有一定的持续性,其对今日经济的发展仍起着难以否认的支撑作用。丝绸之路道路密度每增加1%,所在区域夜间灯光指数增加0.373。本文通过横跨历史学、地理学、经济学的探索能够很好地提供差异化理论视角和技术手段助益,为相关研究的开展起到一定的参考与启发作用,同时也为“一带一路”相关理论的完善提供理论支撑与历史证明。     

Late glacial and Holocene environmental change in the Lake Baikal region documented by oxygen isotopes from diatom silica

We investigate late glacial and Holocene climate change recorded in Lake Baikal using the oxygen isotope composition of diatom silica (δ¹⁸O_DIAT). Evaporation from the lake is minor, and the temperature fractionations of δ¹⁸O are unable to explain variations in the δ¹⁸O_DIAT record alone. Isotopically, low meltwater input from glaciers may have some influence on δ¹⁸O_DIAT, but the assumed periods of climatic warming and wastage do not coincide with large shifts in δ¹⁸O_DIAT. There is a gradual oxygen isotope lowering from 27.0‰ to 20.6‰ over the late glacial, while, during the Holocene, δ¹⁸O_DIAT values return to relatively high values. Previous studies of the modern oxygen and hydrogen isotope composition of Lake Baikal's inputs reveal that fluvial input to the lake's North Basin are isotopically lower than fluvial input from South Basin rivers. This north–south gradient of river δ¹⁸O and δD is mainly due to the greater input from isotopically low winter precipitation in the north and isotopically higher summer precipitation in the south. As a result, the δ¹⁸O_DIAT record from Lake Baikal can at least in part be explained by varying input from these sources related to seasonal changes in precipitation. Changes in atmospheric conditions may have a role in altering seasonality and the distribution of precipitation over Lake Baikal's catchment. A feedback mechanism is well known linking higher Eurasian spring snow cover extent (ESSC) to the development of anticyclonic conditions and low precipitation the following summer in the areas south of Lake Baikal. A simultaneous increase in the importance of depleted water (snowmelt) input from the north and decreased enriched summer precipitation in the south is needed to explain depletions in δ¹⁸O of lake water and subsequently δ¹⁸O_DIAT during colder periods. The opposite of this situation is required to enrich lake water during warmer periods. The analysis of δ¹⁸O from diatom silica is a useful proxy for environmental change, especially in lakes, like Lake Baikal, where carbonates are absent or diluted. However, analysis must be based on near pure diatom samples as even trace amounts of silt can have a dominating effect on δ¹⁸O_DIAT values.