Geophysical phenomena during an ionospheric modification experiment at Tromsø, Norway

We present an analysis of phenomena observed by HF distance-diagnostic tools located in St. Petersburg combined with multi-instrument observation at Tromsø in the HF modified ionosphere during a magnetospheric substorm. The observed phenomena that occurred during the Tromsø heating experiment in the nightside auroral E_s region of the ionosphere depend on the phase of substorm. The heating excited small-scale field-aligned irregularities in the E region responsible for field-aligned scattering of diagnostic HF waves. The equipment used in the experiment was sensitive to electron density irregularities with wavelengths 12–15 m across the geomagnetic field lines. Analysis of the Doppler measurement data shows the appearance of quasiperiodic variations with a Doppler frequency shift, f_d and periods about 100–120 s during the heating cycle coinciding in time with the first substorm activation and initiation of the upward field-aligned currents. A relationship between wave variations in f_d and magnetic pulsations in the Y-component of the geomagnetic field at Tromsø was detected. The analysis of the magnetic field variations from the IMAGE magnetometer stations shows that ULF waves occurred, not only at Tromsø, but in the adjacent area bounded by geographical latitudes from 70.5° to 68° and longitudes from 16° to 27°. It is suggested that the ULF observed can result from superposition of the natural and heater-induced ULF waves. During the substorm expansion a strong stimulated electromagnetic emission (SEE) at the third harmonic of the downshifted maximum frequency was found. It is believed that SEE is accompanied by excitation of the VLF waves penetrating into magneto-sphere and stimulating the precipitation of the energetic electrons (10–40 keV) of about 1-min duration. This is due to a cyclotron resonant interaction of natural precipitating electrons (1–10 keV) with heater-induced whistler waves in the magnetosphere. It is reasonable to suppose that a new substorm activation, exactly above Tromsø, was closely connected with the heater-induced precipitation of energetic electrons.     

Interpretation of cosmogenic nuclides in meteorites on the basis of accelerator experiments and physical model calculations

Cosmogenic nuclides in extraterrestrial matter provide a wealth of information on the exposure and collision histories of small objects in space and on the history of the solar and galactic cosmic radiation. The interpretation of the observed abundances of cosmogenic nuclides requires detailed and accurate knowledge of their production rates. Accelerator experiments provide a quantitative basis and the ground truth for modeling cosmogenic nuclide production by measurements of the relevant cross sections and by realistic simulations of the interaction of galactic protons with meteoroids under completely controlled conditions, respectively. We review the establishment of physical model calculations of cosmogenic nuclide production in extraterrestrial matter on the basis of such accelerator experiments and exemplify this approach by presenting new experimental and theoretical results for the cosmogenic nuclide⁴⁴Ti. The model calculations describe all aspects of cosmogenic nuclide production and allow the determination of long-term solar and galactic cosmic ray spectra and a consistent interpretation of cosmogenic nuclides in extraterrestrial matter.     

A comparison of estimated and calculated effective porosity

 Effective porosity in solute-transport analyses is usually estimated rather than calculated from tracer tests in the field or laboratory. Calculated values of effective porosity in the laboratory on three different textured samples were compared to estimates derived from particle-size distributions and soil–water characteristic curves. The agreement was poor and it seems that no clear relationships exist between effective porosity calculated from laboratory tracer tests and effective porosity estimated from particle-size distributions and soil–water characteristic curves. A field tracer test in a sand-and-gravel aquifer produced a calculated effective porosity of approximately 0.17. By comparison, estimates of effective porosity from textural data, moisture retention, and published values were approximately 50–90% greater than the field calibrated value. Thus, estimation of effective porosity for chemical transport is highly dependent on the chosen transport model and is best obtained by laboratory or field tracer tests. Received, March 1997 · Revised, August 1997 · Accepted, August 1997     

Runoff and erosion processes and rates in the Zin valley badlands,northern Negev,Israel

Badland areas are usually regarded as impermeable zones which generate high runoff and are very vulnerable to sheetwash and rainsplash. To test those considerations sprinkling experiments using two rainfall simulators were carried out on slopes of varying aspect in the northern Negev (Israel). For one unit 1·5 m² plots were used with rainfall of natural characteristics at 36 mm/hr intensity and 43–48 minute duration, runoff being recorded and water/sediment samples taken every 5 minutes. The second unit was used on 30–50 m² plots but rainfall energy production was below that of natural rainfall. Results show that due to the high stability and strong flocculation of clay-rich aggregates rainsplash is ineffective in surface sealing so that infiltration capacities remain high despite intense, prolonged rainfall. Aspect differences are reflected in variation of surface properties despite homogenous bed-rock, which cause marked differences in hydrological response. North-facing slopes respond more quickly, more frequently and produce more runoff than south-facing slopes. Non-uniform runoff generation is also seen within plots of one aspect reflecting subtle variations in surface properties. Comparison of rainfall intensity and duration used during the experiments with those prevailing under natural conditions shows that under present day conditions surface flow in the Zin valley badlands must be extremely infrequent and denudation rates very low.     

湖泊水位资料与模型模拟恢复的6000年前全球湿润状况的对比研究

本项研究是ＰＭＩＰ（ＰａｌａｅｏｃｌｉｍａｔｅＭｏｄｅｌｉｎｇＩｎｔｅｒｃｏｍｐａｒｉｓｏｎＰｒｏｊｅｃｔ）国际合作项目中有关模型模拟与观测资料对比的一部分。模型试验对象是６０００ｙｒ．ＢＰ的全球湿润状况。模拟试验以检测太阳辐射变化对全球大尺度气候系统的影响为主要目的。观测资料是利用地质证据恢复的古湖泊水位变化,实际上是某一地区的有效降水（降水减蒸发）的变化。通过两者的比较发现,所有模拟试验均能重现６０００ｙｒ．ＢＰ在亚洲南部与非洲北部的湿润环境,从而证实了因太阳辐射变化导致的亚洲与非洲季风的增强。但模拟的季风增强无论是强度还是范围均小于地质记录。原因很可能是模拟试验中下垫面特征用“现代”的来处理。模拟试验对北半球夏季辐射增加造成的西风带北移及由此引起的中纬度地区的气候变化不够成功。绝大多数模拟对受洋流与海温影响较大的地区是失败的。主要原因可能是所有ＰＭＩＰ中的模拟试验都未考虑海洋的作用。     

历次核试验进入海洋的~(137)Cs对中国近海影响的模拟研究

1945年以来,世界各主要核国家进行了数千次核试验,这些核试验产生的绝大部分放射性物质通过多种途径进入海洋,对海洋环境造成放射性污染。本文建立了一个准全球海洋的放射性物质输运和扩散数值模式,通过数值模拟手段评估了历史核试验释放的放射性物质137 Cs对中国近海海洋环境的影响。本文借助前人工作评估了核试验释放137Cs进入海洋的途径和总量;通过比较模拟结果与观测资料,表明本文建立的放射性物质模式能够较好地模拟出137Cs在中国近海及其邻近海域的分布情况和随时间演变特征;模拟结果表明中国近海里的137Cs浓度在20世纪50年代中期达到最大,其中吕宋海峡海域137Cs浓度最高,达80.99Bq/m3;进一步分析了2011年3月份日本福岛核事故前中国近海137Cs浓度分布状况,2011年整个中国近海137Cs浓度介于1.0~1.6Bq/m3间,且其浓度垂向分布较均匀,相对封闭的南海浓度略高于其他海域。     

卡尔曼滤波器在卫星遥感影像大地校正中的应用

在卫星遥感图像的预处理中,通过系统校正可以基本上消除影像内部的变形误差。然而,整幅影像的大地定位误差仍然是很大的,甚至几百米至1公里的数量级。本文介绍利用少量的地面控制点,采用递归算法而不是批处理算法,大大地提高大地定位精度。在单幅影像处理中,可以重新对卫星的轨道参数与姿态参数进行估值,从而提高影像的大地定位精度。在一条轨道上连续的多幅影像中,可以预报下一幅影像的大地位置,从而对那些不具有地面控制点的影像的大地校正中,实现外推计算。文中介绍并推导了卡尔曼滤波器方程中的转移矩阵和测量矩阵的系数,并推荐用数值回归的办法求得其数值解。文中最后介绍模拟试验及算法计算结果,并讨论其优缺点。     

黄河入海泥沙沉积固结过程抗侵蚀性变化研究

河口入海泥沙沉积固结过程中抗侵蚀性的变化直接决定着沉积物的再悬浮和二次迁移,对河口岸滩的稳定具有重要决定作用。在现代黄河三角洲潮滩模拟入海泥沙快速沉积,现场测试不同固结时间沉积物的抗侵蚀性和物理力学指标的变化。研究发现,黄河入海泥沙沉积物的抗侵蚀性随固结时间增长迅速提高,当沉积固结时间达8h时,其临界侵蚀切应力就超过了原状潮滩表层沉积物;新沉积泥沙的临界侵蚀切应力与其重度、贯入阻力、剪切强度呈良好的正相关关系,与含水率呈良好的负相关关系。黄河入海泥沙临界侵蚀流速的试验值随固结时间的增长速率要高于各泥沙起动公式计算值的增长速率,前者是后者的1.5～4.1倍。     

虚拟地理环境研究进展与理论框架

阐述虚拟地理环境的形成、发展与研究现状,并从"虚拟现实技术"与"虚拟现实"的相互关系探讨虚拟地理环境基本概念.从基本思想、系统结构、在线参与者社会组织水平、与GIS/数字地球的关系等角度,分析虚拟地理环境的特征.从数据、模型、表现以及协同4个方面,讨论了虚拟地理环境系统建设的关键技术与研究前沿.尝试建立了一个虚拟地理环境基本理论初步研究框架,认为在地理哲学思想层次应该重点研究复杂性人地系统、地理虚/实关系论、地理/遥感信息本体论,在地理/地理信息科学层次需要重点研究地理认知与思维、地理相似原理、地理计算模拟;同时讨论虚拟地理环境与面向"人"的地理信息科学、基于虚拟地理环境地理科学方法论,以及可计算人地关系的相关理论问题.     

沂源县田庄水库农业面源氮素淋滤行为研究

受农业面源影响,典型山区水库-田庄水库氮素超标,通过模拟土壤在不同降雨强度与不同降雨类型下的淋滤行为,探讨氮素淋溶释放规律,并对田庄水库农业面源氮素入库量进行了计算。结果表明,降雨类型和降雨强度只影响土壤中氨氮峰值浓度出现的时间,对其数值影响不大,由于土壤中硝氮含量较高,使降雨强度和类型对其淋出液中的硝氮峰值浓度产生的时间和数值都有所影响;农业面源氮污染通过田庄水库四条入库河流年均排入水库中的硝氮总量高达604．49t,氨氮为23．85t。