Determining the drift velocity of ionospheric irregularities by analyzing three mutually orthogonal projections of the HF radio signal field vector

This paper presents results of an experimental verification of our earlier suggested spectral-polarization method of measuring the interference pattern velocity by analyzing three mutually orthogonal projections of the radio signal field vector using a single receiving antenna. The measurements were made on an HF radio path about 100 km in length, with a simultaneous monitoring of the ionospheric situation using an oblique-incidence sounding chirp–ionosonde. In an effort to eliminate multipath effects, in the analysis we used nighttime intervals, for which a stable one-mode reflected radio signal was observed. It is shown that the proposed method gives the mean values of the azimuth and zenith angle which differ by no more than 2 to 5° from calculated values. Mean values of the velocity of travelling ionospheric disturbances (of order 50 m/s) and propagation directions (north-westward changing to northward by the morning hours) obtained for these time intervals are consistent with existing published data.     

月球射电探测仪天线特性分析

本文介绍月球射电探测仪的基本原理,通过讨论所使用的电偶极天线的特性,得到了月球地层上方不同频率及不同距地高度的天线方向图,为最终选择出最佳方案提供了参考.     

Plasma inhomogeneities and radiowave scattering in experiments with electron pulses in the ionosphere

The absorption of telemetry radiosignals at frequencies of 250 and 75 MHz, transmitted from rockets, was observed in the ARAKS and Zarnitza 2 rocket experiments, respectively, with electron pulses in the ionosphere. The signals were registered with ground receivers. Four cases of complete signal absorption on the propagation path were observed in the ARAKS experiment. The radio absorption at frequencies substantially higher than the plasma and upper hybrid frequencies can be related to wave scattering by plasma inhomogeneities. It has been indicated that plasma inhomogeneities were generated when electrostatic oscillations damped in the region with decreased plasma density at a decrease in the natural oscillation phase volume in the frequency-wave vector space with decreasing plasma density. The observed radio absorption could be related to reflectionless wave scattering in an inhomogeneous plasma structure.     

Vertical distribution features of atmospheric water vapour in the Po valley area

Two sets of radiosounding measurements, taken at different hours from some stations in the Po Valley area, were examined in order to obtain the values of precipitable waterw and determine the shapes of the vertical distribution curves of absolute humidity. From these curves, we calculated the bestfit values of scale heightsH ₁ andH ₂ in the 0÷5 km and 5÷10 km altitude intervals, respectively. The analysis of the radiosounding data clearly shows that parametersw andH ₁ are closely related to the evolutionary features of the meteorological conditions on synoptic scale and are influenced, to a lesser extent, by the diurnal variations in the atmospheric ground layer. Seasonal average curves of temperature and absolute humidity, as functions of altitude, were also defined from the radiosounding measurements taken at various hours of the day. Moreover, interpolation methods in time (applied to a 12-hour range) and in space (range of about 300 km) were proposed for determining parametersw andH ₁ from the radiosounding measurements taken at different hours from the same station or from different stations at the same hour. Reliability tests, made by comparing the same station or from different stations at the same hour. Reliability tests, made by comparing the values given by the interpolation methods with those directly obtained from the radiosounding measurements, show that these evaluations ofw andH ₁ are affected by standard errors of estimate, which are comparable to the errors usually made in analyzing the radiosounding data.     

Using microwave links to adjust the radar rainfall field

The final stage in processing radar data so as to arrive at an estimated rain field typically involves a comparison of the preliminary radar-derived estimates of hourly rainfall with those observed by ground-based gauges. Often a mean field bias adjustment will then be applied using an age-weighted average of the individual gauge–radar comparisons. In this paper, a mean field bias adjustment is presented that uses the path-integrated rainfall estimates provided by microwave links together with information from gauges. It is shown to be at least as efficient as the current gauge-based procedure used by the UK Met Office to improve the accuracy of radar-based estimates of rainfall at the ground.     

Key structural parameters affecting earthquake ground motion in 2D and 3D sedimentary structures

Alluvial valleys generate strong effects on earthquake ground motion (EGM). These effects are rarely accounted for even in site-specific studies because of (a) the cost of the required geophysical surveys to constrain the site model, (b) lack of data for empirical prediction, and (c) poor knowledge of the key controlling parameters. We performed 3D, 2D and 1D simulations for six typical sedimentary valleys of various width and depth, and for a variety of modifications of these 6 “nominal models” to investigate sensitivity of EGM characteristics to impedance contrast, attenuation, velocity gradient and geometry. We calculated amplification factors, and 2D/1D and 3D/2D aggravation factors for 10 EGM characteristics, using a representative set of recorded accelerograms to account for input motion variability. The largest values of the amplification and aggravation factors are found for the Arias intensity and cumulative absolute velocity, the lowest for the root-mean-square acceleration. The aggravation factors are largest for the vertical component. For each model, at least one EGM characteristic exhibits a significant 2D/1D aggravation factor, while all EGM characteristics exhibit significant 2D/1D aggravation factor on the vertical component. For all investigated sites, there is always an area in the valley for which 1D estimates are not sufficient. 2D estimates are insufficient at several sites. The key structural parameters are the shape ratio and overall geometry of the sediment-bedrock interface, impedance contrast at the sediment-bedrock interface, and attenuation in sediments. The amplification factors may largely exceed the values that are usually considered in GMPEs between soft soils and rock sites.     

The Influence of Path Corrections and a Three-dimensional Global <Emphasis Type="Italic">P</Emphasis>-wave Velocity Model on Seismic Event Location in Kazakhstan

We relocate 81 large nuclear explosions that were detonated at the Balapan and Degelen Mountain subregions of the Semipalatinsk test site in Kazakhstan during the years 1978 to 1989. The absolute locations of these explosions are available, as well as very accurate estimates of their origin times. This ground truth information allows us to perform a detailed analysis of location capability. We use a sparse network of stations with highly accurate first arrival picks measured using a waveform cross-correlation method. These high quality data facilitate very accurate location estimates with only a few phases per event. We contrast two different approaches: 1) a calibration-based approach, where we achieve improved locations by using path corrections, and 2) a model-based approach, where we achieve improved locations by relocating in a recently published global 3-D P-velocity model. Both methods result in large improvements in accuracy of the obtained absolute locations, compared to locations obtained in a 1-D reference earth model (ak135). The calibration-based approach gives superior results for this test site, in particular when arrival times from regional stations are included. Estimated locations remain well within a 1000 km² region surrounding the ground truth locations when the path corrections for the Balapan and Degelen Mountain subregions are interchanged, but even for the short separation between these two regions, we find variations in the path corrections that cause systematic mislocations. The model-based approach also results in substantially reduced mislocation distances and has the distinct advantage that it is, in principle, transportable to other source regions around the world.     

Specific features of variations in the characteristics of VLF signals when the lunar shadow propagated along the path during the solar eclipse of March 29, 2006

The effects of the solar eclipse of March 29, 2006, in the signals of ULF radio stations, in the intensity of regular radio noise at frequencies of 0.3–10 kHz, and in the number of atmospherics received in Yakutsk mostly from the west have been considered. The observations were performed using a multichannel parallel analyzer-recorder (11 channels in the frequency band 0.47–8.7 kHz), one-point lightning direction and range finder (0.3–100 kHz), narrow-sector radio noise direction-finder (0.3–10 kHz), recorder of signals from VLF radio stations, and broadband radio noise recorder (0.3–100 kHz). A GPS clock was used to synchronize a recorder of signals from VLF radio stations. The effect was observed in radio signals, radio noise, and number of atmospherics from the direction 270° ± 20° counted off clockwise from the north during the last stage of the eclipse (～ 1100–1200 UT), when the lunar shadow approached the line of the nighttime terminator and obscured part of the signal propagation path. The effect was observed as an enhancement of the received signals by a factor of ～1.2, a factor of ～1.4 increase in the number of atmospherics, and a change in the radio station phase values.     

3D Modelling of the electromagnetic response of geophysical targets using the FDTD method1

A publicly available and maintained electromagnetic finite-difference time domain (FDTD) code has been applied to the forward modelling of the response of 1D, 2D and 3D geophysical targets to a vertical magnetic dipole excitation. The FDTD method is used to analyse target responses in the 1 MHz to 100MHz range, where either conduction or displacement currents may have the controlling role. The response of the geophysical target to the excitation is presented as changes in the magnetic field ellipticity. The results of the FDTD code compare favourably with previously published integral equation solutions of the response of 1D targets, and FDTD models calculated with different finite-difference cell sizes are compared to find the effect of model discretization on the solution. The discretization errors, calculated as absolute error in ellipticity, are presented for the different ground geometry models considered, and are, for the most part, below 10% of the integral equation solutions. Finally, the FDTD code is used to calculate the magnetic ellipticity response of a 2D survey and a 3D sounding of complicated geophysical targets. The response of these 2D and 3D targets are too complicated to be verified with integral equation solutions, but show the proper low- and high-frequency responses.     

Sliding fragility of block‐type non‐structural components. Part 2: Restrained components

This paper focuses on seismic vulnerability assessment of restrained block‐type non‐structural components under sliding response on the basis of seismic inputs specified by current seismic codes. The general representation of restrained equipment considered in this study consists of a rigid block restrained by four post‐tensioned, symmetrically arranged cables. Two sliding‐related failure modes are considered: restraint breakage and excessive absolute acceleration. Fragility analysis is proposed as an appropriate tool to evaluate these failure modes. Sample fragility curves developed through Monte‐Carlo simulations show that the restraint breakage limit state is sensitive to the parameters of the equation of motion. For instance, fragility estimates obtained without taking into account vertical base accelerations can be significantly unconservative for relatively large values of the coefficient of friction. In contrast, the excessive absolute acceleration limit state exhibits little sensitivity to the parameters of the equation of motion. Peak absolute acceleration response is almost always equal to or greater than the horizontal peak base acceleration. Representative results suggest that reasonable response estimates for blocks located at stories other than the ground in multistorey buildings can in general be obtained by simply scaling the ground acceleration to the peak acceleration at the corresponding storey. Copyright © 2002 John Wiley & Sons, Ltd.     

地震前氡衰变引起大气温度与湿度异常问题讨论

强地震前地震区域会出现卫星热红外增温异常现象,S A Pulinets提出了一种新的解释,认为是震前地表大量析出的222Rn衰变产生的高能α粒子使得空气电离,这些离子很容易吸附水蒸气分子,导致大气中潜热的释放,使得空气温度、湿度发生显著变化.本文分析了高能α粒子对空气辐射电离后的主要物理、化学作用,估算了放热和吸附水蒸气分子数量的极大值,结果表明空气温度、湿度的变化是微不足道的.由此认为,地震前出现的温度升高、湿度下降的现象可能与氡浓度变化无关.     

Sliding fragility of block‐type non‐structural components. Part 1: Unrestrained components

Motivated by the development of performance‐based design guidelines with emphasis on both structural and non‐structural systems, this paper focuses on seismic vulnerability assessment of block‐type unrestrained non‐structural components under sliding response on the basis of seismic inputs specified by current seismic codes. Two sliding‐related failure modes are considered: excessive relative displacement and excessive absolute acceleration. It is shown that an upper bound for the absolute acceleration response can be assessed deterministically, for which a simple yet completely general equation is proposed. In contrast, fragility curves are proposed as an appropriate tool to evaluate the excessive relative displacement failure mode. Sample fragility curves developed through Monte‐Carlo simulations show that fragility estimates obtained without taking into account vertical base accelerations can be significantly unconservative, especially for relatively large values of the coefficient of friction. It is also found that reasonable estimates of relative displacement response at stories other than the ground in multistorey buildings cannot in general be obtained by simply scaling the ground acceleration to the peak acceleration at the corresponding storey. Failure modes considered in this study are found to be essentially independent of each other, a property that greatly simplifies assessment of conditional limit states. Copyright © 2002 John Wiley & Sons, Ltd.     

Ground truthed performance of single‐and dual‐polarized radar rain rates at large ranges

Radar accuracy in estimating qualitative precipitation estimation at distances larger than 120 km degrades rapidly because of increased volume coverage and beam height. The performance of the recently upgraded dual‐polarized technology to the NEXRAD network and its capabilities are in need of further examination, as improved rainfall estimates at large distances would allow for significant hydrological modelling improvements. Parameter based methods were applied to radars from St. Louis (KLSX) and Kansas City (KEAX), Missouri, USA, to test the precision and accuracy of both dual‐ and single‐polarized parameter estimations of precipitation at large distances. Hourly aggregated precipitation data from terrestrial‐based tipping buckets provided ground‐truthed reference data. For all KLSX data tested, an R(Z,ZDR) algorithm provided the smallest absolute error (3.7 mm h^?1) and root‐mean‐square‐error (45%) values. For most KEAX data, R(ZDR,KDP) and R(KDP) algorithms performed best, with RMSE values of 37%. With approximately 100 h of precipitation data between April and October of 2014, nearly 800 and 400 mm of precipitation were estimated by radar precipitation algorithms but was not observed by terrestrial‐based precipitation gauges for KLSX and KEAX, respectively. Additionally, nearly 30 and 190 mm of measured precipitation observed by gauges were not detected by the radar rainfall estimates from KLSX and KEAX, respectively. Results improve understanding of radar based precipitation estimates from long ranges thereby advancing applications for hydrometeorological modelling and flood forecasting. Copyright © 2016 John Wiley & Sons, Ltd.     

高层建筑被动混合控制的波动分析

本文提出了一种将基础隔震系统与调频质量阻尼器（ＴＭＤ）相结合的被动混合控制系统,计算了带有基础隔震系统,调频质量阻尼器（ＴＭＤ）及其混合控制系统的高层建筑在地面水平运动作用下的振动波及其功率大小,文中比较了不同控制结构在１９４０ＥｌＣｅｎｔｒｏ地震动作用下的加速度峰值,层间位移峰值和最大层间剪力值。理论及数值结果表明：这种被动混合控制系统能够非常有效地抑制地面运动作用下高层建筑的振动,它不仅大大地     

On the interpretation of recharge estimates from steady-state model calibrations

Ground water recharge is often estimated through the calibration of ground water flow models. We examine the nature of calibration errors by considering some simple mathematical and numerical calculations. From these calculations, we conclude that calibrating a steady-state ground water flow model to water level extremes yields estimates of recharge that have the same value as the time-varying recharge at the time the water levels are measured. These recharge values, however, are a subdued version of the actual transient recharge signal. In addition, calibrating a steady-state ground water flow model to data collected during periods of rising water levels will produce recharge values that underestimate the actual transient recharge. Similarly, calibrating during periods of falling water levels will overestimate the actual transient recharge. We also demonstrate that average water levels can be used to estimate the actual average recharge rate provided that water level data have been collected for a sufficient amount of time.     

内蒙古区域背景噪声特征分析

应用PDF方法,计算了内蒙古现运行48个测震台站0.01~20 Hz频带范围内的功率谱密度(PSD)和1~20 Hz频带范围内噪声均方根(RMS)值,定量分析了内蒙古区域背景噪声水平。结果显示:平均噪声水平属于Ⅰ类的台站有45个,Ⅱ类有3个;台站背景噪声在1 Hz以上频段内,主要受公路和人为影响;在0.6~1 Hz频段内背景噪声水平差异较小;在低频段,水平向受温度和湿度影响大于垂直向,山洞台受影响小于地面台。     

Comparative performance analysis of climate re-analysis approaches in Angola

This paper examines the performance of three climate re-analysis datasets in Angola, namely the ERA-40, NCEP-r1 and JRA-55, by comparing annual and seasonal estimates of precipitation, surface air temperature and evaporation with ground observation measurements. The observational dataset describes a region poorly covered by international climate databases and it is believed that most of its data have not been used in the data assimilation procedures of the climate models. This paper therefore provides a fresh look at the performance of these climate re-analysis datasets in a vast area where distance and civil war have hindered ground monitoring efforts. The re-analysis exercises offer better temperature estimates than precipitation estimates. When offered, the evaporation estimates from all three products are very poor. The three products are able to describe the main features of the spatial distribution of average annual precipitation and temperature, but struggle to reproduce the temporal changes of these variables. The results from a set of performance criteria show that the correlation between the observed ground measurements and re-analysis estimates is poor overall and the NSE values indicate that the average measured value at each location is usually a better estimate than the re-analysis estimate.

EDITOR A. Castellarin

ASSOCIATE EDITOR S. Kanae     

Effects of reservoir bottom absorption on earthquake response of concrete gravity dams

A procedure is presented to analyse the response of concrete gravity dams due to horizontal and vertical earthquake ground motion components considering dam-water interaction and partial absorption of hydrodynamic pressure waves at the reservoir bottom into the foundation medium. The effects of reservoir bottom absorption on the hydrodynamic force on a rigid dam are examined first. The harmonic response of an idealized dam cross-section is presented for a wide range of parameters characterizing the properties of the dam, the impounded water and the foundation medium. Based on these frequency response functions the effects of dam-water interaction and of reservoir bottom absorption in the response of dams due to horizontal and vertical components of ground motion are investigated.     

Airborne EM footprints

As frequency-domain airborne electromagnetic (AEM) studies move towards more detailed assessments of the near-surface, the behaviour of system footprints, and hence the spatial averages involved in the measurement, becomes important. Published estimates suffer from two main limitations: first, they are based on perfectly conducting, thin sheet models and, secondly, they are system specific. The present study is a revision of footprint estimates based on (i) a finitely conducting half-space and (ii) an at-surface scale estimate that uses the spatial equivalent of the conventional electromagnetic skin depth. In order to remove the system dependence, a transmitter footprint is defined in terms of electromagnetic skin distance. Only the limiting cases of vertical and horizontal magnetic dipole sources then require analysis. Electromagnetic skin distances, two for each of the coil orientations, are defined. The revised definition makes it possible to investigate the footprint behaviour of both towed-bird and fixed-wing AEM systems over an altitude range from 20 to 100 m. The footprint/altitude ratio has a primary dependence on altitude and a secondary dependence on both resistivity and frequency. The analysis covers a frequency range from 1 to 100 kHz and results are presented for two specific resistivity values that represent conductive (10 Ωm) and resistive (1000 Ωm) environments. The revised footprint parameters display a quasi-linear behaviour with altitude, particularly for mid-range frequencies. This behaviour enables the coefficients of linear, least-squares relationships to be obtained, thus assisting with the prediction of footprint estimates for survey planning and interpretation. A comparison of the new estimates with published values suggests that existing footprint values for a vertical magnetic dipole should be revised downward.     

Observations of the solar radio emission with the Callisto spectrometer

In the framework of the program for setting the Callisto spectrometer network into operation, the spectral measurements were carried out at the sites of spectrometer locations in India and Russia in winter 2006. The results achieved at Badary, the site where the Siberian Solar Radio Telescope (SSRT) is located, are presented. The measurements were performed using a broadband log-periodic antenna connected to the Callisto spectrometer developed at the Institute of Astronomy (Zurich). The results of these measurements should explain whether spectral studies at frequencies below 1 GHz can be performed using such antennas or new antennas should be developed. The presented results are compared with the similar results obtained in Switzerland in the frequency intervals of interest for radio astronomy. Concerning electromagnetic noise, Badary is a better site for observing the Sun in the 50–800 MHz frequency range as compared to observatories in Switzerland.