Comparison between measured and calculated tidal ellipses in the German Bight

Using a three-dimensional non-linear shelf model, the elliptical properties (ellipticity, inclination of the ellipse, major and minor semi-axis and phase) of the M₂ tide in the German Bight were calculated and compared with CODAR measurements. A series of barotropic and baroclinic calculations were carried out to investigate the influence of geometry, stratification and particularly inputs of freshwater on these parameters. The elliptical properties undergo stronger changes in zones of influence of embayments and in the deepening of the old Elbe Valley. Friction effects in the shallow areas are responsible for robust vertical variations of the ellipticity. The island of Helgoland induces wakes on its western and eastern sides. The discharge of freshwater of the rivers Elbe, Weser and Ems induced in general negative ellipticity. Although primarily determined by geography, baroclinic effects significantly modified the inclination of the ellipses. The calculated ellipses pattern of anticlockwise and clockwise tidal current rotation agrees quite well with CODAR measurements. The elliptical properties give a general idea of the interaction of tidal waves with coastal geometries.Responsible Editor: Hans Burchard     

Comparison of ionospheric parameters calculated with UAM and measured at Voeykovo observatory

The measurements of the critical frequencies of the ionospheric F2 layer based on vertical radiosounding, which was performed with a CADI digital ionosonde at the Voeykovo magnetic–ionospheric observatory in February 2013, have been considered. The observations have been compared with the upper atmosphere numerical model (UAM) data for three days that differ in the amplitude and the character of solar and magnetic activity and correspond to quiet and moderately disturbed states of the ionosphere. The work was performed in order to improve the methods for determining the ionospheric state by vertical sounding ionograms. The time variations in the F2 layer critical frequency, electric field vector zonal component, and thermospheric wind velocity meridional component have been analyzed. Calculations were performed with three UAM variants. The UAM version providing the best agreement with the CADI ionosonde data was the version in which the neutral temperature, neutral composition, and pressure gradients are calculated according to the MSIS empirical model and the horizontal neutral wind velocity is determined by the equation of motion with pressure gradients from MSIS. The calculated values corresponded to the measurements, except those for the evening, because the electron density at the ionospheric F2 layer maximum depends more strongly on electric fields and thermospheric wind velocities during this period. Thus, the indicated UAM version with the above limitations can be used to determine the state of the subauroral ionosphere.     

A comparison of gravity wave phase velocities calculated from the impedance equation and pressure data

Abstract

Marked oscillations in wind speed, wind direction and pressure with periods of between 5 and 15 minutes were recorded on a number of occasions and it is assumed that they were produced by atmospheric gravity waves. Gossard and Munk (1954) have shown that the phase velocity of a gravity wave can be calculated using wind and pressure fluctuation data from a single station by means of the “impedance equation”. It is also possible to measure the phase velocity of a gravity wave using an array of microbarovariographs. In this investigation, the phase velocity of gravity waves calculated using these two different methods are compared and the feasibility of deriving wave characteristics from single point measurements is discussed. The results show that, while in a few isolated cases the two velocities agree reasonably well, the application of the impedance equation to data from a single station is limited due to the superposition of local wind systems upon the wave-induced perturbations.     

FDE index for goodness‐of‐fit between measured and calculated response signals

A method is presented for determining the goodness‐of‐fit between measured and calculated structural response signals. The method is termed as the frequency domain error (FDE) index, which is a value between 0 and 1 where zero indicates a perfect correlation. The FDE is calculated from the Fourier spectra of the measured and calculated waveforms, using a relatively simple calculation procedure, readily implemented using standard fast Fourier transform (FFT) libraries. The FDE is demonstrated herein using three different types of problems: simple harmonic waves, a large number of earthquake response simulations, and a set of limited simulations. Along with the FDE concept, effective methods for displaying the results are presented. Copyright © 2009 John Wiley & Sons, Ltd.     

A comparison between measured and modelled open water evaporation from a reservoir in south-east England

Estimates of evaporation from large open water bodies are required for a variety of purposes in water resource management. The equilibrium temperature approach provides a means of taking into account the heat storage in the water body. The evaporation predicted by a model based on this method is tested against measured evaporation from a reservoir at Kempton Park, UK. The evaporation and water temperature predicted by the model are in good agreement with the measurements. The mean annual evaporation is predicted to almost the same accuracy as the measurements. Estimates of the monthly predicted evaporation have root mean square errors about three times those of the measurements. The error in the mean annual evaporation estimated without taking the heat storage into account is 16%. Copyright © 2001 John Wiley & Sons, Ltd.     

A comparison between simulated and measured CO2 and water flux in a subtropical coniferous forest

Using data from eddy covariance measurements in a subtropical coniferous forest, a test and evaluation have been made for the model of Carbon Exchange in the Vegetation-Soil-Atmosphere (CEVSA) that simulates energy transfers and water, carbon and nitrogen cycles based on ecophysiological processes. In the present study, improvement was made in the model in calculating LAI, carbon allocation among plant organs, litter fall, decomposition and evapotranspiration. The simulated seasonal variations in carbon and water vapor flux were consistent with the measurements. The model explained 90% and 86% of the measured variations in evapotranspiration and soil water content. However, the modeled evapotranspiration and soil water content were lower than the measured systematically, because the model assumed that water was lost as runoff if it was beyond the soil saturation water content, but the soil at the flux site with abundant rainfall is often above water saturated. The improved model reproduced 79% and 88% of the measured variations in gross primary production (GPP) and ecosystem respiration (R _e), but only 31% of the variations in measured net ecosystem exchange (NEP) despite the fact that the modeled annual NEP was close to the observation. The modeled NEP was generally lower in winter and higher in summer than the observations. The simulated responses of photosynthesis and respiration to water vapor deficit at high temperatures were different from measurements. The results suggested that the improved model underestimated ecosystem photosynthesis and respiration in extremely condition. The present study shows that CEVSA can simulate the seasonal pattern and magnitude of CO₂ and water vapor fluxes, but further improvement in simulating photosynthesis and respiration at extreme temperatures and water deficit is required.

     

A comparison between simulated and measured CO_2 and water flux in a subtropical coniferous forest

Using data from eddy covariance measurements in a subtropical coniferous forest, a test and evaluation have been made for the model of Carbon Exchange in the Vegetation-Soil-Atmosphere (CEVSA) that simulates energy transfers and water, carbon and nitrogen cycles based on ecophysiological processes. In the present study, improvement was made in the model in calculating LAI, carbon allocation among plant organs, litter fall, decomposition and evapotranspiration. The simulated seasonal variations in carbon and water vapor flux were consistent with the measurements. The model explained 90% and 86% of the measured variations in evapotranspiration and soil water content. However, the modeled evapotranspiration and soil water content were lower than the measured systematically, because the model assumed that water was lost as runoff if it was beyond the soil saturation water content, but the soil at the flux site with abundant rainfall is often above water saturated. The improved model reproduced 79% and 88% of the measured variations in gross primary production (GPP) and ecosystem respiration (Re), but only 31% of the variations in measured net ecosystem exchange (NEP) despite the fact that the modeled annual NEP was close to the observation. The modeled NEP was generally lower in winter and higher in summer than the observations. The simulated responses of photosynthesis and respiration to water vapor deficit at high temperatures were different from measurements. The results suggested that the improved model underestimated ecosystem photosynthesis and respiration in extremely condition. The present study shows that CEVSA can simulate the seasonal pattern and magnitude of CO2 and water vapor fluxes, but further improvement in simulating photosynthesis and respiration at extreme temperatures and water deficit is required.     

Kirchhoff prestack depth migration in 3-D simple models: comparison of triclinic anisotropy with simpler anisotropies

We use Kirchhoff prestack depth migration to calculate migrated sections in 3-D simple anisotropic homogeneous velocity models in order to demonstrate the impact of anisotropy on migrated images. The recorded wave field is generated in models composed of two homogeneous layers separated by one either non-inclined or inclined curved interface. The anisotropy in the upper layer is triclinic. We apply Kirchhoff prestack depth migration to velocity models with different types of anisotropy: a triclinic anisotropic medium, an isotropic medium, transversely isotropic media with a horizontal (HTI) and vertical (VTI) symmetry axis. We observe asymmetry in migration caused by triclinic anisotropy and we show the errors of the migrated interface caused by inaccurate velocity models used for migration. The study is limited to P-waves.     

A comparison of the estimated effective elastic thickness of the lithosphere using terrestrial and satellite-derived data in Iran

The effective elastic thickness of the lithosphere has an important role in constraining compositional structure, geothermal gradient and tectonic forces within the lithosphere and the thickness of this layer can be used to evaluate the earthquakes’ focal depth. Hence, assessment of the elastic thickness of the lithosphere by gravitational admittance method in Iran is the main objective of this paper. Although the global geopotential models estimated from the satellite missions and surface data can portray the Earth’s gravity field in high precision and resolution, there are some debates about using them for lithosphere investigations. We used both the terrestrial data which have been provided by NCC (National Cartographic Center of Iran) and BGI (Bureau Gravimetrique International), and the satellite-derived gravity and topography which are generated by EIGEN-GL04C and ETOPO5, respectively. Finally, it is concluded that signal content of the satellite-derived data is as rich as the terrestrial one and it can be used for the determination of the lithosphere bending.     

桩-土-结构相互作用分析的等效计算桩长简化模型

在一定程度上,桩长是影响桩-土-结构体系动力分析复杂程度的关键因素之一,在桩-土-结构相互作用的数值模拟中对桩长进行适当简化可以提高计算效率,尤其对具有大量长桩基础的结构体系。基于Boulanger模型和OpenSees软件,分析了软粘土地基-单桩结构体系地震反应中桩身的位移、弯矩、剪力的分布特点以及桩顶上部结构的加速度响应,探讨了结构体系振型及振型周期随桩长的变化特点,进一步提出了等效计算桩长的桩-土-结构模型。研究表明,当结构体系前3阶的振型周期的变化率控制到2.5%时,对应的等效计算桩长分析模型能实现较高的动力响应计算精度,其动力响应误差已降低至5%以内;等效计算桩长可以通过动力响应误差控制精度要求确定,对于软粘土地基中的单桩基础结构,建议将前3阶振型周期的变化率控制到2.5%时的计算桩长作为等效计算桩长。     

声波及弹性波地震模拟的无网格算法

波动方程方法是地震模拟和成像的基本方法之 一。本文利用无单元法(EFM)处理地震模拟中的 声波及弹性波波动方程。无单元法中没有单元的 概念,使节点完全摆脱了单元网格的束缚;此外, 采用滑动最小二乘(MLS)准则使得方程的解高次 连续。本文将分别针对声波方程和弹性波波动方 程详细讨论无单元法的原理及吸收边界问题。在 此基础上,通过几个叠前模型的试算验证无单元 法用于地震模拟的有效性。     

A statistical review of mudrock elastic anisotropy

Mudrocks, defined to be fine‐grained siliclastic sedimentary rocks such as siltstones, claystones, mudstones and shales, are often anisotropic due to lamination and microscopic alignments of clay platelets. The resulting elastic anisotropy is often non‐negligible for many applications in the earth sciences such as wellbore stability, well stimulation and seismic imaging. Anisotropic elastic properties reported in the open literature have been compiled and statistically analysed. Correlations between elastic parameters are observed, which will be useful in the typical case that limited information on a rock's elastic properties is known. For example, it is observed that the highest degree of correlation is between the horizontal elastic stiffnesses C₁₁ and C₆₆. The results of statistical analysis are generally consistent with prior observations. In particular, it is observed that Thomsen's ? and γ parameters are almost always positive, Thomsen's ? and γ parameters are well correlated, Thomsen's δ is most frequently small and Thomsen's ? is generally larger than Thomsen's δ. These observations suggest that the typical range for the elastic properties of mudrocks span a sub‐space less than the five elastic constants required to fully define a Vertical Transversel Isotropic medium. Principal component analysis confirms this and that four principal components can be used to span the space of observed elastic parameters.     

The BEAN experiment - An EISCAT study of ion temperature anisotropies

Results are presented from a novel EISCAT special programme, SP-UK-BEAN, intended for the direct measurement of the ion temperature anisotropy during ion frictional heating events in the high-latitude F-region. The experiment employs a geometry which provides three simultaneous estimates of the ion temperature in a single F-region observing volume at a range of aspect angles from 0° to 36°. In contrast to most previous EISCAT experiments to study ion temperature anisotropies, field-aligned observations are made using the Sodankylä radar, while the Kiruna radar measures at an aspect angle of the order of 30°. Anisotropic effects can thus be studied within a small common volume whose size and altitude range is limited by the radar beamwidth, rather than in volumes which overlap but cover different altitudes. The derivation of line-of-sight ion temperature is made more complex by the presence of an unknown percentage of atomic and molecular ions at the observing altitude and the possibility of non-Maxwellian distortion of the ion thermal velocity distribution. The first problem has been partly accounted for by insisting that a constant value of electron temperature be maintained. This enables an estimate of the ion composition to be made, and facilitates the derivation of more realistic line-of-sight ion temperatures and temperature anisotropies. The latter problem has been addressed by assuming that the thermal velocity distribution remains bi-Maxwellian. The limitations of these approaches are discussed. The ion temperature anisotropies and temperature partition coefficients during two ion heating events give values intermediate between those expected for atomic and for molecular species. This result is consistent with an analysis which indicates that significant proportions of molecular ions (up to 50%) were present at the times of greatest heating.     

二维弹性及粘弹性TTI介质中地震波场数值模拟:四种不同网格高阶有限差分算法研究

本文利用交错网格、辅助网格、旋转交错网格、同位网格有限差分方法分别模拟了二维弹性TTI介质和二维黏弹性TTI介质中的地震波传播.在稳定性条件内,选用不同的网格间距及时间间隔,通过波场快照、合成理论地震图较为系统分析对比了这四种不同网格有限差分数值模拟在计算精度、CPU时间、相移、频散、以及保幅方面的优缺点.数值模拟结果表明:1)这四种不同网格有限差分算法都是很好的波场数值模拟算法;2)就CPU计算时间而言,旋转交错网格有限差分算法的计算效率最高;3)从计算精度来看,同位网格有限差分的计算精度最高;4)从振幅保护方面来看,四种网格的保护振幅的能力相当;5)相移方面,当网格间距增大时,交错网格和旋转交错网格有可能出现相移现象;6)频散方面,同位网格的频散现象不明显.     

Observed and calculated short-periodPKIKP/PKP1 amplitude ratio

Summary The ratio of short-period PKIKP and PKP1 amplitudes of deep earthquakes in the Tonga region observed at the seismological station KHC is compared with the theoretical ratio computed for the probable geometry of the Tonga subduction zone and the Preliminary Reference Earth Model. Quantitatively good agreement of observed and calculated values was attained. The influence of the period of the signal and of a broad range of the source parameter rake on the calculated PKIKP/PKP1 amplitude ratio is investigated.

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Резюме С?rt;елaно срaвненuе оmнощенuŭ aмnлumу?rt; короmкоnерuо?rt;ных волн PKIKP u PKP1 оm лубокuх землеmрясенuŭ Тон a, зanuсaнных сеŭсмuческоŭ сmaцuеŭ HKC, с сооmвеmсmвующuмu mеореmuческuмu велuчuнaмu, рaссчumaннымu ?rt;ля верояmноŭ еомеmрuu зоны суб?rt;укцuu в рaŭоне Тон a u мо?rt;елu PREM. Нaблю?rt;енные u рaссчumaнные велuчuны ?rt;aюm колuчесmвенно хорощее со лaсuе. Обсуж?rt;aеmся влuянuе вaрuaцuŭ nерuо?rt;ов Т u уклонa л нa велuчuны рaссчеmных aмnлuму?rt; PKIKP u PKP1.

     

Effect of parameter uncertainty on calculated sediment yield

The modified Universal Soil Loss Equation combined with the U.S. Soil Conservation Service runoff calculation method is analysed with respect to parameter uncertainty. The case of agricultural watersheds, where the above method gives quite accurate estimates on the multiannual sediment yield, illustrates the methodology. Parameter uncertainty results in a coefficient of variation of the calculated sediment yield in the range (0.14–0.21). For the general case, five groups of statistical error bound for the parameters are distinguished, based on available information such as the scale of maps.     

脆塑性转化带Carrara大理岩断层稳定性的实验研究

为探究脆塑性转化带断层的力学性质和滑动稳定性,本文采用干燥的Carrara大理岩预切断层（saw-cut）样品,在气体介质三轴高温岩石力学实验仪上开展了摩擦实验研究,实验温度70~400℃,围压30~100 MPa,位移速率在0.08 μm·s^-1,0.4 μm·s^-1,2 μm·s^-1之间切换.实验力学数据揭示,不同围压下Carrara大理岩断层摩擦系数随温度变化规律不同：低围压（30 MPa）下,摩擦系数随温度升高先增大后减小,中高围压（≥70 MPa）下摩擦系数则表现为随温度先减小后增大.断层摩擦滑动行为在100~300℃的范围内表现出由稳定的速度强化转化为不稳定的速度弱化,且在400℃左右重新转变为稳定的速度强化.实验后断层滑动面形貌和微观结构分析表明,稳定滑动断层面为高反射镜面,擦痕清晰;黏滑断层面为有光泽的凹凸不平的表面;最高围压下蠕滑的断层面粗糙无光泽,擦痕不可辨别.本文认为受温度激活的塑性变形过程逐步主导了岩石变形,对断层激活发生不稳定滑动至关重要,而高围压则会抑制断层的不稳定滑动.本研究结果不仅为识别野外断层黏滑和蠕滑提供了实验证据,而且为探究强震孕育和发生机理等提供重要的参数.