新疆伊犁盆地黄土古气候记录与Heinrich事件对比分析   总被引：1，自引：0，他引：1  

张文翔  史正涛  刘勇  苏怀  牛洁 《冰川冻土》2015,37(4):973-979

伊犁盆地作为中国黄土高原与欧洲黄土区的过渡区域,其第四纪古气候研究对于揭示全球气候驱动及耦合机制具有重要的意义.通过对伊犁盆地塔勒德晚更新世黄土-古土壤剖面粒度、低频磁化率及地球化学元素分析,探讨了西风区黄土-古土壤序列中古气候指标变化特征及记录的全球气候突变事件.结果表明:古土壤层中粒径10μm颗粒物含量明显高于黄土层,与之相反的是古土壤层中的低频磁化率、Zr/Rb值和元素Ti含量均小于黄土层,且元素Ti含量与Zr/Rb间具有较高的相关性.黄土-古土壤剖面中古气候代用指标清晰的记录了6次Heinrich(H)事件及Younger Drays(YD)事件,但YD事件、H1、H2、H5和H6事件变幅较H3和H4事件显著,古气候指标与格陵兰冰芯δ18O、季风区李家塬粒度和洛川、西峰及环县Zr/Rb值均具有较好的一致性,所记录的气候事件较李家塬、洛川、西峰更为显著.结合已有研究说明,Heinrich和D-O旋回等气候事件是由西风区向季风区传递的,MIS3阶段温度的升高和常年受西风的影响是造成塔勒德气候环境变化特征的主要控制因素.  相似文献   

JJI甚低频台站信号对太阳耀斑事件的响应特性   总被引：1，自引：0，他引：1  

顾旭东  罗凡  彭锐  李光剑  陈欢  王市委  易娟  李志鹏  倪彬彬  赵正予  王琛  袁丁 《地球物理学报》2021,64(5):1508-1517

太阳耀斑发生时,日地空间的X射线通量会随之增大,进而影响到地球电离层的电子密度分布,导致地球-电离层波导状态发生改变,因此接收到的甚低频(VLF,Very Low Frequency)信号会表现出对应的扰动现象.2017年9月8日,位于湖北省内武汉和随州两站点的VLF接收机分别监测到与X射线太阳耀斑相关的来自日本宫崎县(130°49′E,32°04′N)的JJI甚低频台站信号(22.2 kHz)的振幅异常事件.分析当日的数据发现JJI信号的振幅对不同的太阳耀斑出现不同的响应类型,而且对于同一个耀斑,两地的信号响应类型不尽相同.通过统计2017—2019年间与太阳耀斑相关的JJI信号振幅扰动事件,发现两接收站点的JJI信号响应类型都与耀斑强度及其发生时间存在一定的关系,且呈现出四种响应类型,即两次上升下降型、先上升后下降型、下降型和上升型,但是四种响应类型的事件占比不同.拟合结果表明信号的扰动幅度与X射线通量的积分成正相关,但是两站点的线性拟合斜率存在差异.JJI信号到武汉和随州均属于近似沿纬度方向的短距离传播,且两接收站点相距较近,因此两传播路径大致相似.研究两路径上JJI信号对太阳耀斑响应的差异性有助于理解VLF信号的传播以及探索其在太阳活动监测方面的应用.  相似文献   

天山中段地区重复地震时空特征研究          下载免费PDF全文

唐兰兰  张艺峰  姚道平 《地震学报》2021,43(5):551-568

基于2009—2017年新疆区域数字地震台网记录的地震波形数据,利用波形互相关技术及主事件定位方法识别并重新定位了新疆天山中段及其周缘的重复地震。以波形互相关系数0.9作为阈值来确定研究区的重复地震事件,统计结果显示3万零181个事件中的1万1 618个为重复地震事件,这些重复地震事件组成了2395组重复地震对和重复地震丛,占总事件数的38.5%。根据重复地震重定位前后地震对之间距离的统计结果推测,该区域的系统定位误差约为5—10 km。进一步结合该区域最新的震源分类结果对不同震源类型重复地震的时空分布特征予以分析,结果显示:重复矿山爆破事件在空间上呈丛集性分布,且其中的93.6%发生于白天,同时呈现季节性发生模式,即爆破多发生于夏季,而冬季较少;而重复构造地震在空间上大多沿断层分布,24小时内呈随机分布的特征,且研究时段内每个月的活动水平相对平稳;重复诱发地震成丛分布于靠近油气田和水库的区域,但其中部分诱发地震的位置与构造地震重叠,发震时间特征与构造地震相似,为随机分布。   相似文献   

Using isotopes to understand landscape-scale connectivity in a groundwater-dominated,lowland catchment under drought conditions     

Lukas Kleine  Doerthe Tetzlaff  Aaron Smith  Tobias Goldhammer  Chris Soulsby 《水文研究》2021,35(5):e14197

The Demnitzer Millcreek catchment (DMC), is a 66 km² long-term experimental catchment located 50 km SE of Berlin. Monitoring over the past 30 years has focused on hydrological and biogeochemical changes associated with de-intensification of farming and riparian restoration in the low-lying landscape dominated by rain-fed farming and forestry. However, the hydrological function of the catchment, which is closely linked to nutrient fluxes and highly sensitive to climatic variability, is still poorly understood. In the last 3 years, a prolonged drought period with below-average rainfall and above-average temperatures has resulted in marked hydrological change. This caused low soil moisture storage in the growing season, agricultural yield losses, reduced groundwater recharge, and intermittent streamflows in parts of an increasingly disconnected channel network. This paper focuses on a two-year long isotope study that sought to understand how different parts of the catchment affect ecohydrological partitioning, hydrological connectivity and streamflow generation during drought conditions. The work has shown the critical importance of groundwater storage in sustaining flows, basic in-stream ecosystem services and the dominant influence of vegetation on groundwater recharge. Recharge was much lower and occurred during a shorter window of time in winter under forests compared to grasslands. Conversely, groundwater recharge was locally enhanced by the restoration of riparian wetlands and storage-dependent water losses from the stream to the subsurface. The isotopic variability displayed complex emerging spatio-temporal patterns of stream connectivity and flow duration during droughts that may have implications for in-stream solute transport and future ecohydrological interactions between landscapes and riverscapes. Given climate projections for drier and warmer summers, reduced and increasingly intermittent streamflows are very likely not just in the study region, but in similar lowland areas across Europe. An integrated land and water management strategy will be essential to sustaining catchment ecosystem services in such catchment systems in future.  相似文献   

Scientists' warning on extreme wildfire risks to water supply     

François-Nicolas Robinne  Dennis W. Hallema  Kevin D. Bladon  Mike D. Flannigan  Gabrielle Boisramé  Christian M. Bréthaut  Stefan H. Doerr  Giuliano Di Baldassarre  Louise A. Gallagher  Amanda K. Hohner  Stuart J. Khan  Alicia M. Kinoshita  Rua Mordecai  João Pedro Nunes  Petter Nyman  Cristina Santín  Gary Sheridan  Cathelijne R. Stoof  Matthew P. Thompson  James M. Waddington  Yu Wei 《水文研究》2021,35(5):e14086

2020 is the year of wildfire records. California experienced its three largest fires early in its fire season. The Pantanal, the largest wetland on the planet, burned over 20% of its surface. More than 18 million hectares of forest and bushland burned during the 2019–2020 fire season in Australia, killing 33 people, destroying nearly 2500 homes, and endangering many endemic species. The direct cost of damages is being counted in dozens of billion dollars, but the indirect costs on water-related ecosystem services and benefits could be equally expensive, with impacts lasting for decades. In Australia, the extreme precipitation (“200 mm day −1 in several location”) that interrupted the catastrophic wildfire season triggered a series of watershed effects from headwaters to areas downstream. The increased runoff and erosion from burned areas disrupted water supplies in several locations. These post-fire watershed hazards via source water contamination, flash floods, and mudslides can represent substantial, systemic long-term risks to drinking water production, aquatic life, and socio-economic activity. Scenarios similar to the recent event in Australia are now predicted to unfold in the Western USA. This is a new reality that societies will have to live with as uncharted fire activity, water crises, and widespread human footprint collide all-around of the world. Therefore, we advocate for a more proactive approach to wildfire-watershed risk governance in an effort to advance and protect water security. We also argue that there is no easy solution to reducing this risk and that investments in both green (i.e., natural) and grey (i.e., built) infrastructure will be necessary. Further, we propose strategies to combine modern data analytics with existing tools for use by water and land managers worldwide to leverage several decades worth of data and knowledge on post-fire hydrology.  相似文献   

A simple mechanism for the climatological midsummer drought along the Pacific coast of Central America     

K.B. Karnauskas  R. Seager  A. Giannini  A.J. Busalacchi 《Atmósfera》2013,26(2):261-281

The global distribution, seasonal evolution, and underlying mechanisms for the climatological midsummer drought (MSD) are investigated using a suite of relatively high spatial and temporal resolution station observations and reanalysis data with particular focus on the Pacific coast of Central America and southern Mexico. Although the MSD of Central America stands out in terms of spatial scale and coherence, it is neither unique to the Greater Caribbean Region (GCR) nor necessarily the strongest MSD on Earth based on an objective analysis of several global precipitation data sets. A mechanism for the MSD is proposed that relates the latitudinal dependence of the two climatological precipitation maxima to the biannual crossing of the solar declination (SD), driving two peaks in convective instability and hence rainfall. In addition to this underlying local mechanism, a number of remote processes tend to peak during the apex of the MSD, including the North American monsoon, the Caribbean low-level jet, and the North Atlantic subtropical high which may also act to suppress rainfall along the Pacific coast of Central America and generate interannual variability in the strength or timing of the MSD. However, our findings challenge the existing paradigm that the MSD owes its existence to a precipitation-suppressing mechanism. Rather, aided by the analysis of higher-temporal resolution precipitation records and considering variations in latitude, we suggest the MSD is essentially the result of one precipitation-enhancing mechanism occurring twice.  相似文献   

Exceptionally favourable life conditions for macrobenthos during the Late Cenomanian OAE-2 event: Ichnological record from the Bonarelli Level in the Grajcarek Unit,Polish Carpathians     

《Cretaceous Research》2013

Pelagic and hemipelagic sediments of the Bonarelli Level (uppermost Cenomanian) in the Sztolnia section (Grajcarek Unit, Polish Carpathians) contain trace fossils of the Zoophycos ichnofacies, including (in descending order of abundance): Chondrites (smaller and larger forms), Planolites, Thalassinoides, Palaeophycus, Taenidium, Teichichnus, and Zoophycos. They occur in thick bioturbated layers, which are interbedded with rare, thin layers of unbioturbated black shales. The black shale layers mark the Bonarelli Level and are interpreted as a record of anoxia or dysoxia. Coeval sections in the Western Tethys contain similar trace fossils but they are less abundant and these sections are characterized by thicker unbioturbated black shale layers and thinner bioturbated layers. This confirms the exceptionally favourable life conditions in sediments of the Sztolnia section, which do not record strong global anoxia during the OAE-2 event. Such favourable conditions were probably caused by effective oxygenation of pore waters and deep burial of organic matter, which are a consequence of high rates of accumulation and the palaeogeographical location of the section on a flank of a submarine high, under strong circulation.  相似文献   

广义最短路径在街区人员疏散中的应用研究     

欧斌  解正明  孙睿英 《测绘与空间地理信息》2013,(10)

选择广度优先遍历算法,以事发地点为起始对所有路段进行编号。通过分析影响街区人员疏散的几个因素,研究了人员疏散的相关模型,并对广义最短路径在人员疏散过程中的模拟做了一些研究。最后对全文内容进行了小结,并对值得进一步研究的问题给出了建议。  相似文献   

DIE TECHNISCHE UND WIRTSCHAFTLICHE BEDEUTUNG DER GLETSCHER / The Role of Glaciers in the Economy and Technical Development of Alpine Countries     

Otto LANSER Dipl. Ing. Dr. techn. 《水文科学杂志》2013,58(1):83-93

English Summary

In former times the inhabitants of alpine regions looked upon glaciers as an uncanny and dangerous realm which they avoided as far as possible. It was only around the middle of the 18th Century that man became gradually aware of the beauty of the mountains, and approximately at the same time science started to take an interest in glaciers. Most of the questions raised in this field have been solved since. However, even in our times it is not sufficiently well known that glaciers, which are responsible for the characteristics of the regime of alpine rivers, are interesting not only from the point of view of physical geography, but are also of great importance for the economy and technical development of alpine countries.

Torrents which are fed by the melted ice, carry great quantities of water at periods when other streams frequently run dry. Nevertheless, in the terms of hydraulic power economy, it would be an over simplification to consider glaciers as reservoirs. It must not be forgotten, that in the Alps precipitation is highest during the summer months, and consequently that rivers carry more water during that season than during any other period of the year. The presence of glaciers adds to the extreme situation, and therefore the equalisation of seasonal differences in the runoff of glaciers necessary for power economy requires more storage capacity than is needed for catchment areas without glaciers.

On the other hand, there are also arid zones in the Alps, where conditions are entirely different. I am thinking of the deep valleys, running east to west, which are screened from rain by high mountain ranges, as for instance in the Wallis, the Vintschgau, parts of Western Tyrol and the Engadine. In these valleys it is particularly the slopes open to the south and exposed to constant insolation which show the typical characteristics and vegetation of arid zones. Precipitation during the growing season is often far less than the 600mm which is considered as the minimum needed for most types of cultivation, so much so that artificial irrigation has been practised for many generations. Whenever possible, the aqueducts, often very primitive, are fed by the glacier runoff of the large mountain massifs which never run dry. In some parts of the Wallis and in the South and West Tyrol, the water had to be conducted long distances and across difficult terrain; the construction of these primitive aqueducts was therefore a truly difficult task, as financial and technical resources available for that purpose were very inadequate.

This additional water-supply produced by glaciers in summer has a very definite effect on the large rivers rising in the Alps and flowing down in all directions, to name a few of them, the Rhine, the Inn, the Drave, the Rhône, the Adige etc. Not a single one of them has a low water level record in summer equal to that of the Weser or the Elbe and many other rivers of Central Europe which are not fed by glaciers. This low water level in summer has naturally a very detrimental effect on the navigation of rivers, and also on their capacity to replenish ground-water resources. The abundance of glacier runoff assures a fairly steady supply of water to the first mentioned rivers even in their lower courses, a fact which is of special importance for hydraulic economy in general and for hydraulic energy economy in particular. The rich potential of hydraulic energy in Jugoslavia, for instance, suffers from the fact that the quantity of water carried by the karst-rivers is considerably smaller in summer than it is in winter. The river Drave with its tributaries fed by glacier runoff from the Alps in Carynthia and East Tyrol, is practically the only river in Jugoslavia used to a considerable extent for the production of hydraulic power. It carries even more water in summer than during other seasons. This river, which serves to equalise the seasonal production of energy is therefore most valuable for the power economy of the country.

Short-term changes in the size of glaciers which are the subject of our present symposium, are causing the development of glacier lakes of which there exist several types. Most dangerous are those in larger valleys, caused by the tongue of a side glacier forming a dam, for instance here in the Ötztal Alps, at the Gurgler and at the Rofener Eissee near Vent. Other lakes develop in the basins left behind by the tongues of former glaciers. Water suddenly released from glacier lakes due to a breach of the ice or moraine dam, has frequently been the cause of terrible catastrophes. Attempts have therefore been made to protect the valleys against floods by the construction of flood reservoirs suitably situated below the glacier. An example of this type is the reservoir dam which the Austrian torrent-control authorities constructed in the Martellvalley (South Tyrol) in 1898/99 to prevent damage from an eventual breach in the banks of a glacier lake which had developed. Nowadays the large reservoirs constructed for hydro-electric power provide even greater protection.

Reservoirs for power plants in the Alps, which are created by the construction of large dams, require the existence of basins hollowed out by former glaciers during a long geological period. Outside of the glaciated areas, such basins can generally be created only by artificially blocking up a river-valley. This type of reservoir can be easily distinguished from that described above by its entirely different outline.

It must finally be remembered that the large load of sediment carried by glacial rivers has its economic and technical problems. Although it will probably take centuries to fill up the largest hydro-electric reservoirs, or even to considerably reduce their storage capacity, there are many smaller lakes in which this development will take no more than decades. Deposits of mud, for instance in the reservoir of the Margaritze, in the “Tauernfraftwerke” area had, after a mere decade accumulated to the extent that the power-plant administration had to install a floating suction dredger to remove at least part of the sediment. In this connection it was, however, important not to overload the river downstream with mud to such a degree as to cause damage to the fish population. Careful observation was needed to find out to what extent the river was able to cope with the artificial inflow of mud, and to follow the dispersion of the peak values of the suspesion load.

Nowadays waters destined for the generation of hydro-electric power are collected at the highest possible altitudes. An interesting example of the application of modern methods of this type is the collection of the runoff from beneath the Brandner Ferner in the Silvretta from where it is conveyed to the Lünersee. As a water intake on the surface was impossible due to the difficult terrain, a tunnel had to be driven through the rock bed of the glacier and there, immediately underneath it, in an ice cave, the water flows into a cage consisting of strong steel girders. This cage retains the large bolders, while the water from the bottom of the glacier runs off into the tunnel.  相似文献   

Direct relationships of discharges to the mean and standard deviation of the intervals between their exceedences     

Arie Ben-Zvi  Benjamin Azmon 《水文科学杂志》2013,58(4):565-577

Abstract

This article paves a way for assessing flood risk by the use of two-parameter distributions, for the intervals between threshold exceedences rather than by the traditional exponential distribution. In a case study, the apparent properties of intervals between exceedences of runoff events differ from those anticipated for exponentially distributed series. A procedure is proposed to relate two statistical parameters of the intervals to threshold discharges. It considers partial duration series (PDS) with thresholds equal to all high enough observed discharges. To avoid unnecessary assumptions on the behaviour of those parameters and effects of dependence between parameters for different PDS, a non-parametric trend-free pre-whitened scheme is applied. It leads to power-law relationships between a discharge and the mean and standard deviation of the intervals between its exceedences. Predicted mean inter-exceedence intervals, for the highest observed discharges at the stations, are closer to the observational periods than those predicted by GEV distributions fitted to AMS, and by GP distributions to fitted PDS. In the present case, the latter predictions are longer than the observational periods whereas some of the predicted mean inter-exceedences are shorter than the corresponding observational periods and some others are longer.

Citation Ben-Zvi, A. & Azmon, B. (2010) Direct relationships of discharges to the mean and standard deviation of the intervals between their exceedences. Hydrol. Sci J. 55(4), 565–577.  相似文献