A stochastic model of the Fourier phase of strong ground motion

ＡｓｔｏｃｈａｓｔｉｃｍｏｄｅｌｏｆｔｈｅＦｏｕｒｉｅｒｐｈａｓｅｏｆｓｔｒｏｎ　ｇｒｏｕｎｄｍｏｔｉｏｎＺｈｅｎ－ＰｅｎｇＬＩＡＯ；（廖振鹏）ａｎｄＸｉｎｇＪＩＮ（金星）（ＩｎｓｔｉｔｕｔｅｏｆＥｎｇｉｎｅｅｒｉｎｇＭｅｃｈａｎｉｃｓ，ＳｔａｔｅＳ...     

Pyramidal ice crystal scattering phase functions and concentric halos

Phase functions have been calculated using the Monte Carlo/geometric ray tracing method for single hexagonal pyramidal ice crystals (such as solid and hollow bullets) randomly oriented in space and horizontal plane, in order to study the concentric halo formations. Results from three dimensional model calculations show that 9° halo can be as bright as the common 22° halo for pyramidal angle of 28°, and the 18°, 20°, 24° and 35° halos cannot be seen due to the strong 22° halo domination in the scattering phase function between 18° and 35°. For solid pyramidal ice crystals randomly oriented horizontally, the 35° arc can be produced and its intensity depends on the incident ray solar angle and the particle aspect ratio.     

The statistical laws of strong seismic motion phase characteristics

ＴｈｅｓｔａｔｉｓｔｉｃａｌｌａｗｓｏｆｓｔｒｏｎｇｓｅｉｓｍｉｃｍｏｔｉｏｎｐｈａｓｅｃｈａｒａｃｔｅｒｉｓｔｉｃｓＸｉｎｇＪＩＮ（金星）ａｎｄＺｈｅｎ－ＰｅｎｇＬＩＡＯ（廖振鹏）（ＩｎｓｔｉｔｕｔｅｏｆＥｎｇｉｎｅｅｒｉｎｇＭｅｃｈａｎｉｃｓ，Ｓ...     

初始大扰动条件下双流系统的粒子相空间振荡

双流系统产生的不稳定性过程是近地空间中常见的等离子体不稳定性现象.地球磁尾、等离子体片边界层、地球弓激波、太阳风、极隙区和极光加速区观测到的静电孤立波被认为是由双流不稳定性产生.地球空间环境并非均匀稳态, 因此对双流系统演化过程的研究往往需要考虑初始的扰动.利用所建立的动理论粒子云模型方法, 我们研究了初始大扰动下双流系统的不稳定性现象, 发现初始大扰动条件下粒子相空间产生振荡现象, 且振荡频率与初始扰动的空间波数有关, 电场与电场能量也存在该频率成分.通过线性理论, 求解出了粒子相空间振荡频率.它与粒子云模拟得到的频率一致.该频率为朗缪尔振荡频率的基础之上叠加一个与初始扰动的空间波数有关的频率偏移量.我们改变等离子体频率, 进一步验证了上述结论.该研究结果表明初始扰动能够对双流系统的不稳定性现象产生重要影响, 对于加深理解地球磁层中双流系统的演化过程有重要参考意义.

     

Interplanetary scintillations of strong radio sources in the descending phase near the cycle 23 minimum

Observations of interplanetary scintillations of the 3C 298 and 3C 48 radio sources during low solar activity, performed with a BSA FIAN radio telescope at a frequency of 111 MHz, are presented. The radial dependences of the scintillation indices, where the effect of a low-latitude heliospheric current sheet is observed, have been obtained. Based on the scintillation temporal spectra, the solar wind velocity values have been obtained, and it has been indicated that these values are in good agreement with those found using the spaced measurements method.     

Probabilistic interpretation of forecasts of ice phase onset dates in Ob-Taz mouth area

The results of a posteriori probabilistic interpretation of forecasts of freezing and ice breaking dates in Ob-Taz mouth area are presented. The method of interpretation is based on the use of conditional distributions of errors in forecasting continuous variables. Parameter estimates of the distribution density of actual dates are given for forecasts grouped in periods. This creates sufficient conditions for the application of methods of continuous statistical optimization in planning measures the efficiency of which depends on dates of freezing and ice breaking in the mouth area.     

Growth of volcanic ash aggregates in the presence of liquid water and ice: an experimental approach

Key processes influencing the aggregation of volcanic ash and hydrometeors are examined with an experimental method employing vibratory pan aggregation. Mechanisms of aggregation in the presence of hail and ice pellets, liquid water (≤30?wt%), and mixed water phases are investigated at temperatures of 18 and ?20?°C. The experimentally generated aggregates, examined in hand sample, impregnated thin sections, SEM imagery, and X-ray microtomography, closely match natural examples from phreatomagmatic phases of the 27?ka Oruanui and 2010 Eyjafjallaj?kull eruptions. Laser diffraction particle size analysis of parent ash and aggregates is also used to calculate the first experimentally derived aggregation coefficients that account for changing liquid water contents and subzero temperatures. These indicate that dry conditions (<5–10?wt% liquid) promote strongly size selective collection of sub-63?μm particles into aggregates (given by aggregation coefficients >1). In contrast, liquid-saturated conditions (>15–20?wt% liquid) promote less size selective processes. Crystalline ice was also capable of preferentially selecting volcanic ash <31?μm under liquid-free conditions in a two-stage process of electrostatic attraction followed by ice sintering. However, this did not accumulate more than a monolayer of ash at the ice surface. These quantitative relationships may be used to predict the timescales and characteristics of aggregation, such as aggregate size spectra, densities, and constituent particle size characteristics, when the initial size distribution and water content of a volcanic cloud are known. The presence of an irregularly shaped, millimeter-scale vacuole at the center of natural aggregates was also replicated during interaction of ash and melting ice pellets, followed by sublimation. Fine-grained rims were formed by adding moist aggregates to a dry mixture of sub-31?μm ash, which adhered by electrostatic forces and sparse liquid bridges. From this, we infer that the fine-grained outer layers of natural aggregates reflect recycled exposure of moist aggregates to regions of volcanic clouds that are relatively dry and dominated by <31?μm ash.     

Rayleigh wave phase velocity tomography and strong earthquake activity on the southeastern front of the Tibetan Plateau

To investigate the relationship between velocity structure and earthquake activity on the southeastern front of the Tibetan Plateau, we make use of continuous observations of seismic ambient noise data obtained at 55 broadband stations from the regional Yunnan Seismic Network. These data are used to compute Rayleigh wave Green's Functions by cross-correlating between two stations, extracting phase velocity dispersion curves, and finally inverting to image Rayleigh wave phase velocity with periods between 5 and 34 s by ambient noise tomography. The results show significant lateral variations in crustal and uppermost mantle structures in the studied region. Phase velocity anomalies at short periods(5–12 s) are closely related to regional tectonic features such as sediment thickness and the depth of the crystalline basement. The Sichuan-Yunnan rhombic block, enclosed by the Honghe, Xiaojiang and Jianchuan faults, emerges as a large range of low-velocity anomalies at periods of 16–26 s, that inverts to high-velocity anomalies at periods of 30–34 s. The phase velocity variation in the vicinity of the Sichuan-Yunnan rhombic block suggests that the low-velocity anomaly area in the middle-lower crust may correspond to lower crustal channelized flow of the Tibetan Plateau. The spatial distribution of strong earthquakes since 1970 reveals that the Yunnan region is inhomogeneous and shows prominent characteristics of block motion. However, earthquakes mostly occur in the upper crust, with the exception of the middle-Yunnan block where earthquakes occur at the interface zone between high and low velocity as well as in the low-velocity zones, with magnitudes being generally less than 7. There are few earthquakes of magnitude 5 at the depths of 15–30 km, where gather earthquakes of magnitude 7 or higher ones which mainly occur in the interface zone between high and low velocities with others extending to the high-velocity abnormal zone.     

Daytime quasiperiodic geomagnetic pulsations during the recovery phase of the strong magnetic storm of May 15, 2005

Intense quasimonchromatic geomagnetic pulsations with a period of ～15 min, observed on the Earth’s surface in the near-noon sector at the beginning of the recovery phase of a very strong (Dst _min = ?260 nT) magnetic storm of May 15, 2005, are analyzed. The variations were registered at auroral latitudes only in the X field component, and wave activity shifted into the postnoon sector of the polar cap an hour later; in this case pulsations were observed in the X and Y field components. Within the magnetosphere the source of magnetic pulsations could be the surface waves on the magnetopause caused by the pulse of the solar wind magnetic pressure. Geomagnetic pulsations in the polar cap, observed in phase at different latitudes, could apparently reflect quasiperiodic variations in the NBZ system of field-aligned currents. Such variations can originate due to the series of pulsed reconnections in the postnoon outer cusp at large (～20 nT) positive B _z values and large (about ?40 nT) negative values of IMF B _x .     

强震中期阶段区域性形变异常的共性特征及其机制以青藏块体东北部为例

强震前中期阶段(1～3年或稍长)区域性形变异常往往表现出3个方面的共性特征: ① 区域垂直运动变形呈现与构造有关的异常隆起区、 垂直差异变形高梯度带(有的还呈“四象限”)分布特征; ② 水平运动变形呈现与活动地块及断裂构造有关的、 以剪切变形为主的高应变集中区(带)特征; ③ 区域性垂直形变异常区与水平形变的高应变分布区共生的特征。 分析这些异常共性特征的形成机制, 初步认为: 它们是在基本统一的大区域构造应力场控制下, 不同层次块体系统运动及其边界带变形的非平稳、 非协调性, 在活动地块边界地带和地块内部次级断裂构造部位产生变形差异而导致应力-应变积累、 孕育强震到一定阶段的结果。 在此基础上, 分析探讨了基于区域性形变异常共性特征、 结合地质构造活动背景进行强震中期预测的意义。     

Gradients and phase velocities of ULF geomagnetic disturbances used to determine the source of an impending strong earthquake

Results of studying the behavior of the vectors of gradients and phase velocities of ULF geomagnetic disturbances (F < 1 Hz) in the Japan seismic zone are presented. The gradient and phase velocity vectors along the Earth’s surface were determined using data of the group of three high-sensitivity three-component magnetovariation stations (MVC-3DS) located at triangle vertices at a small (～5 km) distance from one another (magnetic gradiometer). Two such groups of stations were installed in 1999 southwest and southeast of Tokyo at a distance of ～150 km from each other. It has been indicated that, several months before strong earthquakes (M > 5), the values of gradients and phase velocities start anomalously changing, and directions toward sources of impending strong earthquakes appear in the distribution of gradient vector directions. Directions from sources of impending earthquakes appear in the distribution of phase velocity vector directions. It is proposed to use gradients and phase velocities of ULF and ELF geomagnetic disturbances as one of the factors in a short-term prediction of strong earthquakes.     

Geomagnetic pulsations and magnetic disturbances during the initial phase of a strong magnetic storm of May 15, 2005

A very strong magnetic storm of May 15, 2005, was caused by an interplanetary magnetic cloud that approached the Earths’ orbit. The sheath region of this cloud was characterized by a high solar wind density (～25–30 cm^?3) and velocity (～850 km/s) and strong variations (to ～20 nT) in the interplanetary magnetic field (IMF). It has been indicated that an atypical bay-like geomagnetic disturbance was observed during the initial phase of this storm in a large longitudinal region at high latitudes: from the morning to evening sectors of the geomagnetic local time. Increasing in amplitude, the magnetic bay rapidly propagated to the polar cap latitudes up to the geomagnetic pole. An analysis of the global space-temporal dynamics of geomagnetic pulsations in the frequency band 1–6 mHz indicated that most intense oscillations were observed in the morning sector in the region of the equivalent ionospheric current at latitudes of about 72°–76°. The wavelet structure of magnetic pulsations in the polar cap and fluctuations in IMF was generally similar to the maximum at frequencies lower than 4 mHz. This can indicate that waves directly penetrated into the polar cap from the solar wind.     

Debris from the basal ice of the Agassiz ice cap,Ellesmere Island,arctic Canada

This article describes the characteristics of debris obtained from the basal ice in a borehole in the Agassiz ice cap, Ellesmere Island, Northwest Territories by the Canadian Polar Continental Shelf Project in 1979. The debris appears to have been incorporated by basal freezing at a time when the base of the glacier upstream was near the pressure melting point and some 19°C warmer than at the present site. Such an occurrence may be explained by a different flow regime, by a thicker ice sheet, by the influence of irregular bedrock topography on basal ice conditions at some stage in the past, or by a combination of these factors.     

乌梁素海冰封期湖泊冰盖组构特征对污染物分布的影响

为探究富营养化浅水湖泊季节性冰盖污染物分布规律,于2013-2014年冰封期,钻取乌梁素海湖泊冰盖冰芯试样,观测冰厚并对冰芯晶体结构、气泡含量、污染物浓度(总氮、总磷和COD_(Cr))进行分析.结果表明:冰盖可分为4层,中间2层冰晶体粒径较大且气泡含量较少,为冰盖热力生长区.冰盖以柱状晶体居多,粒径随深度增加而增加,气泡含量随冰盖密度增加而减少.冰盖结构特征与污染物分布具有相关关系,冰芯密度及气泡分布与总氮、总磷和COD_(Cr)相关关系分别为0.8965、0.8718、0.8184,并建立多元回归模型揭示冰封期湖泊水质特征,为季节性湖泊冰盖研究及冰封期湖泊水资源规划和管理提供理论依据.     

The structure of ice and ice cover in lower Amur reaches with branched channel

The study is focused on the specific features of ice regime in Amur lower reaches and the structure of ice surface in branches of different size and dynamic state. The main features of ice stratigraphy in different parts of the river have been identified, and ice cover characteristics have been found to show considerable heterogeneity across the channel. Quantitative data on the concentration of terrigenous material in the ice and its distribution within the ice mass have been collected. The amount of terrigenous material was estimated in the ice in Amur lower reaches, from where it is largely exported into the Sea of Okhotsk during spring ice drift.     

Unusual spatial-temporal dynamics of geomagnetic disturbances during the main phase of the extremely strong magnetic storm of November 7–8, 2004

The spatial dynamics of geomagnetic variations and pulsations, auroras, and riometer absorption during the development of the main phase of the extremely strong magnetic storm of November 7–8, 2004, has been studied. It has been indicated that intense disturbances were observed in the early morning sector of auroral latitudes rather than in the nighttime sector, as usually takes place during magnetic storms. The unusual spatial dynamics was revealed at the beginning of the storm main phase. A rapid poleward expansion of disturbances from geomagnetic latitudes of 65°–66° to 74°–75° and the development of the so-called polar cap substorm with a negative bay amplitude of up to 2500 nT, accompanied by precipitation of energetic electrons (riometer absorption) and generation of Pi2–Pi3 pulsations, were observed when IMF B _z was about ?45 nT. The geomagnetic activity maximum subsequently sharply shifted equatorward to 60°–61°. The spatial dynamics of the westward electrojet, Pi2–Pi3 geomagnetic pulsations, and riometer absorption was similar, which can indicate that the source of these phenomena is common.     

Modeling of ice phenomena in the mouth of the Vistula River

The mouth of the Vistula River, which is a river outlet located in tideless area, is analyzed. The Vistula River mouth is a man-made, artificial channel which was built in the 19th century in order to prevent the formation of ice jams in the natural river delta. Since the artificial river outlet was constructed, no severe ice-related flood risk situations have ever occurred. However, periodic ice-related phenomena still have an impact on the river operation. In the paper, ice processes in the natural river delta are presented first to refer to the historical jams observed in the Vistula delta. Next, the calibrated mathematical model was applied to perform a series of simulations in the Vistula River mouth for winter storm condition to determine the effects of ice on the water level in the Vistula River and ice jam potential of the river outlet.     

Modelling the poroelasticity of rocks and ice

For many geophysical and astrophysical applications the relationship between physical bulk properties and porosity is needed. As part of the preparation for the 'Rosetta' comet rendezvous mission, a simple model for the porosity dependence of the elastic properties of granular media, i.e. the elastic moduli and the propagation velocities of elastic waves, has been developed based on textural properties and the contact stiffness of the constituent particles. It is shown that the derived relationships fit very well with sandstone data. The model is also consistent with data for snow and ice and is in agreement with the transformation mechanisms from snow to ice. A short review shows the relevance to another physical bulk property, the thermal conductivity.     

Grain size record of microparticles in the Muztagata ice core

Dust grain size is a proxy for wind strength that en-trains it. Mineral aerosol blown from arid continent to remote sites has a broad diameter range, from less than 0.5 μm to larger than 75 μm[1]. For a long time, geolo-gists reveal the transport and sediment characteristics using grain size and size distribution. In loess research, grain size is widely used as the proxy for winter mon-soon strength[2,3]. Fractions entrained by the westerlies and winter monsoon can be discerned by grain size…     

Tephra layers in the Byrd Station ice core and the Dome C ice core, Antarctica and their climatic importance

Volcanic glass shards from tephra layers in the Byrd Station ice core were chemically analyzed by electron microprobe. Tephra in seven layers have similar peralkaline trachyte compositions. The tephra are believed to originate from Mt. Takahe, on the basis of their chemical similarity to analyzed rocks from Mt. Takahe and because dated rock samples from the volcano are younger than 250,000 years old. Glass shards from 726 m deep in the Dome C ice core, which is 2400 km from Byrd Station, are composed of peralkaline trachyte and may have also been derived from Mt. Takahe. The tephra could have resulted from eruptions which were triggered by increased ice loading during the late Wisconsin glaciation. Preliminary grain size data suggest the eruptions were only minor and they were unlikely to have instantaneously altered global climate as have explosive eruptions in the tropics. Nevertheless, the effect of this localized volcanic activity upon the Antarctic energy budget warrants further investigation.