基于SAMI2模式的电离层加热模拟

通过在SAMI2模式的电子能量方程中添加人工加热项,数值模拟了在加热条件下磁场线上电子温度与电子密度的扰动情况,并对比了不同加热条件下的扰动效应.结果表明,入射到电离层中的大功率无线电波与等离子体相互作用,能够有效造成整条磁场线上电子温度的升高而产生电子温度扰动,尤其是加热点处,温度可增加3倍多;由于电子温度升高,压力平衡受到破坏,引发等离子体扩散进而导致电子密度扰动;电子密度扰动使得垂直于磁场线的电子密度梯度发生变化,这有可能形成电离层管(Ionosphere duct);电子温度和电子密度的扰动幅度随着加热时间的推移而减小,即扰动逐渐趋于稳定.电子温度与密度的扰动与加热率存在一种非线性关系.     

耀斑-行星际激波结构与相应地磁扰动结构间关系的分析（Ⅰ）

利用297个耀斑-行星际激波-地磁扰动事件,统计研究了耀斑-行星际激波等离子体结构与相应磁扰结构间的关系,新的发现是:当激波面后的磁场南、北分量不大时,激波等离子体结构决定着相应磁扰的基本结构形态,特别是等离子体热状态与相应磁扰的恢复相关系十分密切.由本文定义的激波能量传输指数--FS指数对相应地磁扰动能给出较好的描述.推论:除磁重联这类能量传输机制外,对于行星际磁场南、北分量较小时,还可能存在以等离子体过程为基础的决定磁扰变化结构的太阳风-磁层能量传输机制,应进一步研究.     

磁尾等离子体片区氧离子丰度对离子剪切流的开尔文-赫姆霍茨不稳定性的影响

考虑等离子体片区存在源于电离层的氧离子,研究了离子剪切流在低频表面波扰动情况下的开尔文-赫姆霍茨(K-H)不稳定性.在氧离子流与质子流具有近似相同的宏观流速假定下,采用磁流体力学(MHD)近似,并且考虑在磁场方程中保留速度场涡量项,推导出沿磁场方向传播的表面波线性扰动的色散关系.在等离子体片边界层区,发现随着氧离子相对丰度的增加,产生K-H不稳定性的最大临界扰动波长可增大到20RE(地球半径).对于给定的氧离子丰度,临界剪切相对扰动波长的变化存在一个最小值.氧离子丰度越高,最小临界剪切值越小,对应的扰动波长(称最不稳定波长)也越长.高氧离子丰度的不稳定性增长率随速度剪切增加而增加,快于低氧离子丰度.不稳定性增长率随速度剪切增加的最大饱和值接近对应的离子回旋频率.在地磁活动期间,由等离子体片中氧离子丰度增加而增大的沿磁场传播的表面波不稳定性对于理解低频磁脉动事件和磁层亚暴过程也有着十分重要的意义.     

高邮4.9级地震前滁州地震台电磁扰动异常分析

采用超限率方法,分析滁州地震台2011-2013年电磁扰动数据,结果发现,2012年7月20日江苏高邮M4.9地震前,电磁扰动脉冲超限频次和超限幅度均出现明显增强;进一步分析该台电磁扰动子夜时段(00:00-04:00)的脉冲变化,结果显示,子夜时段的电磁扰动脉冲在震前明显增强.分析认为,2012年滁州地震台电磁扰动脉冲增强变化与高邮M4.9地震具有明显的相关性.     

太阳耀斑引起的地磁扰动与行星际参量的相关

本文讨论了耀斑发生前后的地磁指数与行星际参数之间的相关。结果论证了不同强度的K_p指数日频次是一种能很好反映行星际扰动特征的地磁指数。K_p=4.5级的中等扰动和K_p≥6级的强扰动和强烈扰动具有不同的变化规律,它们分别主要是由太阳风速和行星际磁场总强度增强所引起的从统计效应而言,A_p、AE和D_(st)指数对不同强度的扰动的响应是不相同的,AE和D_(st)指数对行星际参量的相关不如K_p和A_p指数的相关性好,利用地磁指数进行日地相关统计研究时必须注意到这种差别。     

地球磁尾不同位置处高速流的统计特性研究

使用2007~2011年THEMIS卫星数据,对位于地球磁尾(|YGSM|13RE,|ZGSM|5RE,–30REXGSM–6RE)等离子体片内的高速流及背景的等离子体特性和它们与太阳风参数之间的联系进行了统计研究.我们发现,距离地球越近,高速流温度的增加相较于其背景要更强一些;高速流与背景的离子数密度比值和离子温度比值也都有所升高;而我们的统计进一步表明,高速流密度与其发生前2 h的太阳风密度相关性最高,背景密度与其观测时刻前3.5 h的太阳风密度相关性最高,且二者的归一化密度(密度与太阳风密度之比)均与其前3 h的行星际磁场θ角(θ=arctan(Bz/sqrt(Bx2+By2)))相关性程度最大.行星际磁场越倾向于北向,高速流归一化密度越大,与磁尾背景等离子体的性质相似.     

正应力扰动对断层滑动失稳影响的实验研究

利用双轴伺服控制加载装置,采用三块花岗闪长岩标本组成的含有两个滑动面的直剪结构,开展了摩擦滑动实验.实验中通过在垂直滑动面的载荷上叠加正弦波状和方波状的扰动,研究了正应力扰动对断层黏滑失稳的影响.研究表明,在恒定的正应力和位移速率下,标本表现为规则的黏滑,叠加正应力扰动后,随扰动振幅的增加黏滑发生时间与扰动的相关性增大,黏滑应力降和时间间隔的分布趋于离散.黏滑应力降和时间间隔的平均值随平均正应力的增加呈线性增长,扰动叠加后黏滑应力降的离散度随平均正应力的增加而增大;黏滑应力降和时间间隔主要受应力变化幅度的影响,而与应力变化的速率关系不大.剪应力和正应力扰动都会对断层黏滑失稳产生影响,而正应力扰动的影响更明显.这两种扰动对断层黏滑失稳影响的机制存在差异,剪应力扰动只是改变断层滑动的推动力,而正应力扰动则改变了断层面上凹凸体的接触状态.     

场地黄土扰动前后的湿陷性与其物性指标的关系

黄土物性指标可以近似但较为简便快速地评价其湿陷性。原状黄土在不同荷载和浸水的扰动下,随着其物性指标的改变,湿陷性也随之变化,故为了更好地评价这类扰动性黄土的湿陷性,在兰州东岗某场地上进行的两次相隔四十多年室内试验的基础上,采用相关分析的方法,研究扰动前后湿陷性系数与干密度、含水率、孔隙比、饱和度和塑性指数之间的关系。结果表明:(1)扰动前后湿陷性系数和干密度、含水率、饱和度和塑性均呈负相关,和孔隙比呈正相关,且扰动后湿陷性系数整体上低于扰动前,各指标对湿陷性系数的影响减弱。(2)以干密度、含水率、孔隙比、饱和度和塑性指数作为反映扰动前后黄土湿陷性的因子进行多元线性回归和因子权重分析,得出用以评价扰动前后黄土湿陷性的回归公式和影响湿陷性的因子排序。研究结果对于研判扰动黄土的湿陷性并选择合适的地基处理方法具有一定参考价值。     

基于Weimer模型的高纬地磁扰动预测

地磁扰动是空间天气中的重要现象,对地基技术系统具有重要的影响.准确预报地磁扰动可以有效避免重大灾害发生.本文基于Weimer电势和磁势模型发展了高纬地区地磁扰动的模拟方法,并与地面台站观测数据进行了比较.地表磁场扰动主要受电离层电流系统的影响,利用Weimer模式计算出电离层等效电流分布后,基于毕奥-萨伐尔定律推导了地磁扰动三分量与电流的关系,最终计算出地磁扰动量.模型的输入参数为太阳风速度、太阳风密度、行星际磁场和磁偶极倾角.模型计算结果与不同纬度和经度的地磁台站观测结果对比表明本文的计算方法能有效地模拟地磁暴期间地磁扰动特征.本文结果对今后发展高纬地区地磁场预报模型奠定了重要基础.     

近磁尾TC-1观测到伴随有高速流的ULF波及不稳定性分析

2004年8月3日近地TC-1卫星在磁尾X_GSM~－12R_E的等离子体片内,观测到了伴随着高速流的低于离子回旋频率的波,即超低频波(ULF,Ultra Low Frequency).该波垂直分量的振幅在高速流及其振荡减速期间大致相当;而平行分量振幅在高速流时明显大于其振荡减速时. 利用一个扰动双流模型对完全磁化离子横场漂移驱动的电磁不稳定性计算后,预测结果表明:(1)对于垂直分量来说,横场漂移速度与Alfvén速度的比值影响不稳定性增长率和激发波频率,随其比值增加,增长率变大,激发波频率从负值增加到正值.(2)对于平行分量来说,温度各向异性时等离子体热速度与Alfvén速度比值只影响不稳定性增长率和激发波频率,未改变不稳定性模类别;而温度各向同性时离子横场漂移速度与Alfvén速度比值既影响不稳定性模的种类及其分支,又影响激发波频率.进一步将卫星观测到的等离子体密度、温度、整体流速和磁场代入模型方程,进行数值计算与上述预测结果对比后发现:卫星观测中垂直分量的功率谱密度(PSD,Power Spectrum Density)增强时间和频段与理论模型中由β_//、β_⊥和v_⊥/V_A引起不稳定性激发的波一致;卫星观测中平行分量的功率谱密度增强时间与理论模型基本相符,但是前者的频率明显地低于后者.因此,除了需考虑平行磁场的离子整体流速对不稳定性激发波频率的可能影响,还需要统计上进一步核实伴随有高速流的ULF波与不稳定性的相关性.     

Impacts of riparian zone plant water use on temporal scaling of groundwater systems

In this work, we study groundwater system temporal scaling in relation to plant water use and near‐river‐stage fluctuations in riparian zones where phreatophytes exist. Using detrended fluctuation analysis (DFA), we investigate the influence of regular diurnal fluctuations due to phreatophyte water use on temporal scaling properties of groundwater level variations. We found that groundwater use by phreatophytes, at the field site on the Colorado River, USA, results in distinctive crossovers (slope changes when the plots are fitted with straight lines) in the logarithm plots of root‐mean‐square fluctuations of the detrended water level time series versus time scales of groundwater level dynamics. For groundwater levels monitored at wells close to the river, we identified one crossover at ～1 day in the scaling characteristics of groundwater level variations. When time scale exceeds 1 day, the scaling properties decrease from persistent to close to 1/f noise, where f is the frequency. For groundwater levels recorded at wells further away from the river, the slope of the straight line fit (i.e. scaling exponent) is smallest when the time scale is between 1 and 3 days. When the time scale is < 1 day, groundwater variations become persistent. When the time scale is between 1 and 3 days, the variations are close to white noise, but return to persistent when the time scale is > 3 days. Copyright © 2011 John Wiley & Sons, Ltd.     

A method to detect and characterize sub‐daily flow fluctuations

Hydro peaking causes an important environmental impact on running water ecosystems. Many affected rivers have a poor ecological status. In rivers affected by hydro peaking, the flow conditions are highly complex and difficult to grasp. To develop a general framework for detecting and characterizing sub‐daily flow fluctuations, we analysed more than 500 Austrian hydrographs, covering the whole range from unimpacted to heavily impacted rivers. Different fluctuation types could be identified according to the potential source: e.g. sub‐daily flow fluctuations caused by hydro peaking, rainfall or snow and glacier melt. Additionally, the term ‘hydro fibrillation’ was established, to indicate frequently occurring artificial fluctuations with comparably low intensities. An automatic procedure was used to detect frequency and intensity of each flow fluctuation. Using variables based on duration curves of flow fluctuation rates (ramping rates), amplitudes, flow ratios, durations and daily numbers of fluctuations, a predictive model (linear discriminant analysis) was fitted to classify hydrographs into predominant fluctuation regimes. This is the basis for a detailed investigation of present sub‐daily flow regimes and to analyse the differences between the regimes. Based on the results, we finally propose a general framework that enables a standardized assessment of flow fluctuations regarding event intensities and/or event timing. The proposed framework offers a standardized selection of particular flow fluctuations referring to increase and decrease events separately. The selection of specific flow fluctuations can be defined with respect to several research questions (e.g. ecologically relevant fluctuations), which offers a wide range of applications. Copyright © 2015 John Wiley & Sons, Ltd.     

孕震系统宏观层次的单元体应力水平群体涨落模型

孕震系统是一个开放的复杂巨统统，系统具有层次结构。因此应分层次建立孕震系统的力学模型。作者从地球整体现出发，提出了单元体应力水平群体涨落模型，该模型为孕震系统宏观层次上的力学模型。这一模型可以作为几个地震带或几个地块内，地震活动频度、相关转移、时空分布及各类定点观测手段异常台项数群体涨落、时空转移、震后异常等研究的物理基础。     

Laboratory measurements of spatial fluctuation and attenuation of elastic waves by scattering due to random heterogeneities

To study the effects of strong scattering on elastic waves, spatial fluctuation and scattering attenuation ofP waves were examined by laboratory experiments for 2-D models of random media approximately characterized by a triangular correlation function in the range of 2<ka<33, wherek is the wave number anda is the correlation distance of the heterogeneities, i.e., the heterogeneity size. The results obtained are as follows: (1) Forka>10, both the intensity and the correlation distance of the amplitude fluctuation are approximate for any phase of theP-wave train. The correlation distance nearly agrees with the heterogeneity size. These fluctuation properties are quite consistent with the theoretical prediction by the forward-scattering approximation. (2) For 3<ka<6, the fluctuation intensity becomes stronger in later phases of theP-wave train. This shows that scattering is approximately isotropic, and therefore, the scattered energy increases with time within theP-wave train. The correlation distance of the amplitude fluctuation disagrees with the heterogeneity size, and it shows a frequency-dependent property decreasing from 7a to 4a with the increase ofka from 3 to 6. These properties for 3<ka<6 have not yet been predicted theoretically. (3) Forka<3, though the fluctuation is considerably smaller compared with that ofka>10 and 3<ka<6, the fluctuation property is considered similar to that of 3<ka<6. (4) The observed scattering attenuation,Q ^–1, increases withka forka<3, has a peak aroundka=35, and then decreases withka. (5) When _min = 15° and = 0.075, the theoreticalQ ^–1 curve, predicted by the approximate theory of Wu, roughly matches the observedQ ^–1 values, where _min is the minimum scattering angle measured from the propagation direction of theP waves and is the rms of fractional velocity fluctuation. This suggests that the energy scattered in the range of >15° is lost from theP waves, while the energy scattered in the range of <15° is retained; and that the approximate theory overestimates by about three times the value of the model media used owing to the neglect of multiple scattering. (6) When the size of velocity heterogeneities responsible for forward scattering at 3<ka<6 is estimated from the _min value of 15° on the basis of Wu's theory, it nearly agrees with the correlation distance for the initial phase of theP-wave train.     

全新世内蒙南缘黄旗海湖面的波动

黄旗海是一封闭湖泊,气候是控制其湖面变化的主要因素。地貌、沉积物、地球化学分析及历史考古资料均证实,一万年以来湖面在总体收缩下降过程巾不断地波动着。全新世初期,湖面扩张抬升,9000a B.P.前后湖面达最高(1340m),湖面面积也最大(约560km~2),其后,湖面持续地收缩下降。     

Analysis of the time-scaling behaviour in the sequence of the aftershocks of the Bovec (Slovenia) April 12, 1998 earthquake

Analysis of the temporal fluctuations, described by a power spectral density S(f) decaying as 1/f with exponent >0, in the sequence of aftershocks of the Bovec (Slovenia) earthquake of April 12, 1998 has been performed, using the Allan Factor (AF) method. The sequence of the occurrence times of the events with threshold magnitude M_th≥2.0 is characterised by a scale-invariant behaviour from the time scale τ2·10⁴ s with a scaling coefficient 0.9, evaluated by a least-square method. By gradually increasing the threshold magnitude up to M_th=2.9, the AF curves, associated, respectively with the processes of selected events with magnitude M≥M_th, indicate a monotonic decrease of the value of the scaling exponent , in the range of time scales stretching from 10² to 5·10⁵ s. For all the thresholds considered, the AF curves increase monotonically with the counting time and are well fitted by an increasing power-law function for counting times greater than approximately 2·10⁴ s. This monotonic power-law increase indicates the presence of fluctuations on many time scales and therefore of fractal clustering.     

东营凹陷波动古湖相烃源岩沉积特征

以东营凹陷牛38井为例,研究显示,该井沙河街组沙三段烃源岩的沉积特征具有明显的波动性．宏观上体现为, 构造因素控制湖盆的整体升降和沉积构造旋回,但季节性气候及其它因素的影响使湖盆呈现次级旋回的复合性沉积．微观上表现为纹层的不连续性及生物扰动构造等事件性沉积.古湖面不同幅度的波动和变化导致相对稳定的泥岩沉积的不稳定性,有机质的分布也呈现较显著的非均质性．湖泊的沉积过程影响了微量元素、有机质以及烃源物质的分布,水体较深、盐度较高的沙三段下部多数微量元素含量较高以及B／Ca、Sr／Ba呈现高值;水体较浅、盐度较低的沙三段中部各元素的分布较为稳定,B／Ca、Sr／Ba比值及Sr的含量均显著降低.波动性沉积导致烃源岩呈现明显的优劣性分布,沙三段下部中的有机质富集,为优质烃源岩;沙三段中部的有机质分布较为分散,生排烃的资源潜力有限．     

Influence of water level fluctuation on the spatial dynamic of the water chemistry at Lake Fertõ/Neusiedler See

Lake Fertõ/Neusiedler See is a steppe lake situated on the Hungarian-Austrian border with a surface area of 309 km². It is an extremely shallow lake with regulated outflow. 54% of the whole lake and 85% of the Hungarian part (75 km²) is covered by reed. There are numerous reedless areas (inner ponds) of variable size within the reed belt, which is enmeshed with canals connecting the inner ponds with the open water areas. Fundamental differences were recorded in the water chemistry of the three water type areas, open water, canals and inner ponds. The degree of these differences is basically determined by the distance from the open water areas and the water level of the actual years. An extremely high, an average and an extremely low water level year was examined, in order to present the spatial and temporal differences in the water chemistry of the investigated water bodies. Differences due to the water level fluctuation between years in the three different water types are discussed on the basis of electrical conductivity, cation, and anion concentration changes of the water. Our results support the concept of high instability of Lake Fertõ and describe habitats with remarkable temporal and spatial variability. The high influence of water level on habitat conditions at different sites of the lake recommend a carefull water level regulation strategy.     

Short‐term discharge and suspended sediment fluctuations in the proglacial Skeldal River,north‐east Greenland

The summer discharge pattern of the Skeldal River, which drains a 560 km² partly glacierized catchment in north‐east Greenland, is dominated by diurnal oscillations reflecting variations in the melt rate of snow and ice in the basin. Superimposed on this diurnal pattern are numerous short‐lived discharge fluctuations of irregular periodicity and magnitude. The larger fluctuations are described and attributed to both rainfall events and periodic collapse of the glacier margin damming flow from beneath the Skelbrae glacier. Other minor fluctuations are less readily explained but are associated with changes in the channelized and distributed reservoirs and possibly temporary blockage of subglacial conduits caused by ice melt with subsequent damming. Fluctuations in suspended sediment concentration (SSC) are normally associated with discharge fluctuations, although examples of ‘transient flushes’ were observed where marked increases in SSC occurred in the absence of corresponding discharge variations. A strong relationship between the event discharge increase and event SSC increase for rainfall‐induced events was established, but no such relationship existed for non‐rainfall‐induced events. There is some evidence for an exhaustion effect in the SSC patterns both at the event time‐scale and as the month proceeds. A mean suspended sediment load of 1765 ± 0·26 t day^?1 was estimated for the study period, which would be equivalent to a suspended sediment yield of 732 ± 4 t km^?2 year^?1. Copyright © 2001 John Wiley & Sons, Ltd.