X级耀斑过程中的磁剪切变化(英文)     

宗佰军  宋谊 《紫金山天文台台刊》2000,(1)

通过对活动区NOAA 6891中三个X级耀斑前后的向量磁场分析 ,研究耀斑发生条件与耀斑发生前后横向磁场和磁剪切变化的关系。我们发现与Hagyard的耀斑发生条件不同的是 ,强的横向磁场和磁剪切不是活动区中耀斑发生的充要条件。我们的结果表明 ,活动区NOAA 6891 1 991年 30日的耀斑发生在横向磁场和磁剪切剧烈下降后。尽管 1 0月 2 7日的耀斑发生后横向磁场和磁剪切变化很大 ,但由于有新磁流浮现 ,造成磁中性线的改变 ,使得横向磁场和磁剪切变化与耀斑发生的联系变得比较复杂。  相似文献   

Modelling of the retreat process of composite riverbank in the Jingjiang Reach using the improved BSTEM          下载免费PDF全文

Quanli Zong  Junqiang Xia  Meirong Zhou  Shanshan Deng  Yi Zhang 《水文研究》2017,31(26):4669-4681

Bank retreat in the Jingjiang Reach is closely related not only to the near‐bank intensity of fluvial erosion but also to the composition and mechanical properties of bank soils. Therefore, it is necessary to correctly simulate bank retreat to determine the characteristics of fluvial processes in the Jingjiang Reach. The current version of bank stability and toe erosion model (5.4) was improved to predict riverbank retreat, by inputting a dynamic water table, and calculating the approximation of the distribution of dynamic pore water pressure in the soil near the river bank face, and considering the depositional form of the failed blocks, which is assumedly based on a triangular distribution, with the slope approximately equalling the stable submerged bank slope and half of collapsed volume deposited in the bank‐toe region. The degrees of riverbank stability at Jing34 were calculated using the improved bank stability and toe erosion model. The results indicate the following trends: (a) the degrees of riverbank stability were high during the dry season and the rising stage, which led to minimal bank failure, and (b) the stability degrees were low during the flood season and the recession stage, with the events of bank collapse occurring frequently, which belonged to a stage of intensive bank erosion. Considering the effects of bank‐toe erosion, water table lag, and the depositional form of the collapsed bank soil, the bank‐retreat process was simulated at the right riverbank of Jing34. The model‐predicted results exhibit close agreement with the measured data, including the total bank‐retreat width and the collapsed bank profile. A sensitivity analysis was conducted to determine the quantitative effects of toe erosion and water table lag on the degree of bank stability. The calculated results for toe erosion indicate that the amount of toe erosion was largest during the flood season, which was a primary reason for bank failure. The influence of water table lag on the degree of stability demonstrates that water table lag was an important cause of bank failure during the recession stage.  相似文献   

CO2 absorption of sandy soil induced by rainfall pulses in a desert ecosystem          下载免费PDF全文

Ke‐Yu Fa  Jia‐Bin Liu  Yu‐Qing Zhang  Bin Wu  Shu‐Gao Qin  Wei Feng  Zong‐Rui Lai 《水文研究》2015,29(8):2043-2051

Soil CO₂ flux is strongly influenced by precipitation in many ecosystem types, yet knowledge of the effects of precipitation on soil CO₂ flux in semi‐arid desert ecosystems remains insufficient, particularly for sandy soils. To address this, we investigated the response of sandy soil CO₂ flux to rainfall pulses in a desert ecosystem in northern China during August–September 2011. Significant changes (P < 0.05) were found in diel patterns of soil CO₂ flux induced by small (2.1 mm), moderate (12.4 mm) and large (19.7 mm) precipitation events. Further analysis indicated that rainfall pulses modified the response of soil CO₂ flux to soil temperature, including hysteresis between soil CO₂ flux and soil temperature, with F_s higher when T_s was increasing than when T_s was decreasing, and the linear relationship between them. Moreover, our results showed that rainfall could result in absorption of atmospheric CO₂ by soil, possibly owing to mass flow of CO₂ induced by a gradient of gas pressure between atmosphere and soil. After each precipitation event, soil CO₂ flux recovered exponentially to pre‐rainfall levels with time, with the recovery times exhibiting a positive correlation with precipitation amount. On the basis of the amounts of precipitation that occurred at our site during the measurement period (August–September), the accumulated rain‐induced carbon absorption evaluated for rainy days was 1.068 g C m^?2; this corresponds approximately to 0.5–2.1% of the net primary production of a typical desert ecosystem. Thus, our results suggest that rainfall pulses can strongly influence carbon fluxes in desert ecosystems. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Tree ring-based temperature reconstruction over the past 186 years for the Miyaluo Natural Reserve,western Sichuan Province of China   总被引：2，自引：1，他引：1  

Zong Shan Li  Guo Hua Liu  Li Gong  Meng Wang  Xiao Chun Wang 《Theoretical and Applied Climatology》2015,120(3-4):495-506

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Mid-Holocene coastal hydrology and salinity changes in the east Taihu area of the lower Yangtze wetlands, China   总被引：1，自引：0，他引：1  

Yongqiang Zong  James B. Innes  Zhongyuan Chen 《Quaternary Research》2011,76(1):69-82

During the mid-Holocene the eastern Taihu area, on China's Yangtze delta plain, was populated by advanced late Neolithic cultures supported by intensive domesticated rice cultivation. This agricultural system collapsed around 4200 cal yr BP, with severe population decline, the end of the Liangzhu culture, and about half a millennium of very low-scale human activity in the area before the re-establishment of agricultural production. Microfossil analyses from six sedimentary sequences, supported by AMS ¹⁴C dating, has allowed reconstruction of mid-Holocene hydrological conditions and salinity changes which would have had a major influence on agricultural viability and cultural history in the coastal wetlands. These data, allied to existing stratigraphic and sea-level records, show that chenier ridges that developed after ca. 7000 cal yr BP in the east of the area sheltered it from marine inundation and, although still connected to the sea through tidal creeks, low-salinity conditions persisted throughout the Neolithic period. There is no evidence that marine flooding caused the collapse of Liangzhu culture. Marine influence was stable and evolved slowly. Social and cultural causes may also have been important, but if environmental change triggered the collapse of Neolithic agricultural society here, other natural forces must be sought to explain this event.  相似文献   

湖北武汉下志留统坟头组化石组合及沉积环境          下载免费PDF全文

纵瑞文  刘琦  龚一鸣 《古地理学报》2011,13(3):299-308

文中报道了在武汉市铁箕山新发现的下志留统坟头组剖面.该剖面所在位置交通方便,出露较好,化石丰富,发现有三叶虫、腕足类、双壳类、腹足类、头足类、喙壳类、海百合、锥石、海星、鱼类及遗迹化石等,初步鉴定出13属17种.根据该剖面中的化石组合面貌及与邻区的对比认为,武汉地区坟头组的时代应为早志留世(兰多维列世)特列奇期.通过对...  相似文献   

Research on the water use efficiency and foliar nutrient status of <Emphasis Type="Italic">Populus euphratica</Emphasis> and <Emphasis Type="Italic">Tamarix ramosissima</Emphasis> in the extreme arid region of China     

Sheng Kui Cao  Qi Feng  Yong Hong Su  Zong Qiang Chang  Hai Yang Xi 《Environmental Earth Sciences》2011,62(8):1597-1607

Seasonal variations in foliar stable carbon composition (δ¹³C) and nitrogen (N), phosphorus (P) and potassium (K) concentrations of Populus euphratica Olivier and Tamarix ramosissima Ledeb, as well as correlations between foliar δ¹³C values and N, P and K concentrations were studied in the Ejina oasis in the lower reaches of the Heihe River, northwestern China. Foliar δ¹³C values, and P and K concentrations significantly differed between species. Foliar δ¹³C signatures in T. ramosissima were significantly more enriched than those in P. euphratica, but P and K concentrations of P. euphratica were higher. The seasonal variations and patterns of these were similar. The total foliar δ¹³C values and N, P and K concentrations in both P. euphratica and T. ramosissima showed a descending trend. There were significantly positive correlations between foliar δ¹³C values and N and P concentration of both P. euphratica and T. ramosissima. For the relationship between foliar δ¹³C and K concentration, there appeared oppositely positive and negative correlations in P. euphratica and T. ramosissima, respectively, but they were not significant. The simple positive correlations of δ¹³C–P% and δ¹³C–N% suggested that N and P in P. euphratica and T. ramosissima behave in a similar manner. This study also showed that there were nutrient deficiencies; N and P nutriments were the co-limiting factors in P. euphratica, while it was P nutriment in T. ramosissima.  相似文献   

Burial of organic carbon in Holocene sediments of the Zhujiang (Pearl River) and Changjiang (Yangtze River) estuaries   总被引：1，自引：0，他引：1  

Shouye Yang  Min Tang  Wyss W.-S. Yim  Yongqiang Zong  Guangqing Huang  Adam D. Switzer  Yoshiki Saito 《Marine Chemistry》2011,123(1-4):1-10

The East Asian marginal seas are important sinks of terrigenous materials transported by large rivers. In this study two cores from the Changjiang (Yangtze River) and Zhujiang (Pearl River) estuaries and one core from the inner shelf off of Hong Kong were investigated to examine the burial of organic matter during the postglacial period and its possible links with paleoenvironmental changes. Based on a simple two end-member mixing model, the terrestrial organic matter supplied primarily from the Zhujiang and Changjiang dominates the estuarine areas while marine organic matter contributes more to the inner-mid shelf. The competing contributions of terrestrial and marine organic matter are responsible for the downcore variations of organic elemental compositions. The overall decreasing shifts of total organic carbon concentrations and total organic carbon to total nitrogen ratios in the Zhujiang estuarine sediments since 6.5 kaBP seems to support the notion that depth profiles of organic matter compositions deposited in the Zhujiang Estuary can aid in the reconstruction of monsoon history in the Holocene. Nevertheless, organic matter compositions in the Changjiang Estuary and inner shelf off of southeastern Hong Kong respond in a different and more complex way to freshwater discharges or precipitation changes (monsoon variability) in the catchments, owing to complex controls of deposition and preservation of organic matter in these estuarine and shelf environments. Caution is therefore needed in using organic elemental and isotopic compositions to decipher paleoenvironmental changes in East Asian continental shelves where intense river–sea interactions occur and sedimentary environments change drastically.  相似文献   

Characteristics of extreme daily minimum and maximum temperature over Northeast China, 1961–2009     

Haibo Du  Zhengfang Wu  Ming Li  Yinghua Jin  Shengwei Zong  Xiangjun Meng 《Theoretical and Applied Climatology》2013,111(1-2):161-171

In this study, the multifractal detrended fluctuation analysis method is employed to determine the thresholds of extreme events. Subsequently, the characteristics of extreme temperatures have been analyzed over Northeast China during 1961–2009. Approximately 58 % of stations have negative interdecadal trends of ?2.2 days/10 years to 0 days/10 years in extreme low minimum temperature (ELMT) frequency. Notable positive trend of 0–2.5 days/10 years in extreme high maximum temperature (EHMT) frequency of about 94 % stations are found. Approximately 58 % of stations have decreasing trend in ELMT intensity, whereas 69 % of stations have increasing trend of EHMT intensity. The trends are the range of ?0.72 °C/10 years to 0 °C/10 years and 0–0.7 °C/10 years, respectively. We propose the extreme temperatures indices, ELMT index (ELMTI) and EHMT index (EHMTI), which combined the frequency and intensity of extreme temperatures to represent the order of severity of extreme temperatures. According to this approach, serious ELMT mainly occur in the Songliao Plain and the Sanjiang Plain, especially in the Songliao Plain. Serious EHMT distinctly occur in the Sanjing Plain, and the southwestern and northwestern regions of Northeast China in recent five decades.  相似文献   

关中—天水经济区协调发展进程的社会网络分析   总被引：3，自引：0，他引：3  

王燕军  宗跃光  欧阳理  任崇强 《地域研究与开发》2011,30(6)

对城市间经济联系的分析能了解区域的协调发展状况.用修正后的引力模型分别计算出关中—天水经济区中6个城市在1999,2002,2005,2008年的经济联系值,采用社会网络分析软件Ucinet对关中—天水经济区各城市间经济联系值进行了网络密度、点的中心度、中心势、凝聚子群、凝聚子群密度、核心—边缘结构等指标分析.结果表明,关中—天水经济区的经济协调发展程度不高,有向着协调发展的趋势.因此,提出了关中—天水经济区早日实现成为全国内陆型经济开发区目标的一些建议.第一,加快推进西成一体化建设,着力打造西安国际化大都市,进一步做大增长极.第二,边缘区域中城市应充分发挥自己的角色,以实现经济区协调发展.第三,经济区内各城市要突破地理位置的束缚,形成网络开发的模式.  相似文献