On Experience in using the remote acoustic method of partial reflections in studies of the lower troposphere

Using the phenomenon of the partial reflection of acoustic waves from anisotropic wind-velocity and temperature inhomogeneities in the lower troposphere is justified in determining the structure of these inhomogeneities. The data (obtained with the method of bistatic acoustic sounding) on signals reflected from stratified inhomogeneities in the lower 600-m layer of the troposphere are given. A detonation-type pulsed acoustic source was used. The methods of isolating a small (in amplitude) reflected signal against the background of noise and determining the reflecting-layer height and the partial-reflection coefficient from the measured parameters (time delay and amplitude) of a reflected signal are presented. The method of estimating the vertical gradients of the effective sound speed and the squared acoustic refractive index from the partial-reflection coefficient previously calculated is described on the basis of an Epstein transition-layer model. The indicated parameters are experimentally estimated for concrete cases of recording reflected signals. A comparison of our estimates with independent analogous data simultaneously obtained for the same parameters with monitoring instruments (a sodar and a temperature profiler) has yielded satisfactory results.     

Physical modeling of long-range infrasonic propagation in the atmosphere

The results of experiments on the physical modeling of long-range infrasonic propagation in the atmosphere are given. Such modeling is based on the possible coincidence between the forms of the vertical profiles of the effective sound speed stratification in the atmospheric boundary layer (between 0 and 600 m for the case under consideration) and in the atmosphere as a whole (from the land surface up to thermospheric heights (about 150 km)). The source of acoustic pulses was an oscillator of detonation type. Owing to the detonation of a gas mixture of air (or oxygen) and propane, this generator was capable of producing short, powerful (the maximum acoustic pressure was on the order of 30 to 60 Pa at a distance of 50 to 100 m from the oscillator), and sufficiently stable acoustic pulses with a spectral maximum at frequencies of 40 to 60 Hz and a pulsing period of 20 to 30 s. The sites of acoustic-signal recording were located at different distances (up to 6.5 km) from the source and in different azimuthal directions. The temperature and wind stratifications were monitored in real time during the experiments with an acoustic locator—a sodar—and a temperature profiler. The data on the physical modeling of long-range sound propagation in the atmosphere are analyzed to verify the physical and mathematical models of predicting acoustic fields in the inhomogeneous moving atmosphere on the basis of the parabolic equation and the method of normal waves. A satisfactory agreement between calculated and experimental data is obtained. One more task was to compare the theoretical relations between variations in the azimuths and angles of tilting of sound rays about the horizon and the parameters of anisotropic turbulence in the lower troposphere and stratosphere with the experimental data. A theoretical interpretation of the experimental results is proposed on the basis of the theory of anisotropic turbulence in the atmosphere. The theoretical and experimental results are compared, and a satisfactory agreement between these results is noted.     

Structure of the mesoscale variability of the troposphere and stratosphere found from radio refraction measurements via CHAMP satellites

Data of an experiment on radio occultation sounding of the atmosphere with the use of GPS signals were used to obtain global distributions of the variances of mesoscale variations in the refractive index in the troposphere and stratosphere. The experiment was carried out with the CHAMP satellite during the period 2001–2005. Measured vertical profiles were smoothed inside 5–10-km-thick layers centered at different altitudes in the troposphere and stratosphere with the use of second-degree polynomials. Deviations from the smoothed quantities and the corresponding variances were obtained for each profile and averaged for each month during the analyzed interval of the CHAMP experiment. Altitude-longitude-latitude inhomogeneities in the distribution of refractive index variances were analyzed. Altitude and latitude distributions of maxima and minima of refractive index variances depend on altitude and season. Turbulence and acoustic gravity waves can be the causes of small-scale and mesoscale variations in the refractive index of the troposphere and stratosphere. The variances of variations in the refractive index are greater in the regions of tropospheric jet streams and in the zones of near-equatorial deep convection. Atmospheric disturbances increase over mountain systems.     

On acoustic N-wave reflections from atmospheric layered inhomogeneities

The nonlinear propagation of acoustic pulses from a point source of an explosive character (surface explosion or volcano) throughout the atmosphere with stratified wind-velocity and temperature inhomogeneities is studied. The nonlinear distortions of acoustic pulse and its transformation into an N-wave during its propagation to the upper atmosphere are analyzed in the context of a modified Burgers’ equation which takes into account a geometric ray-tube divergence simultaneously with an increase in both nonlinear and dissipative effects with height due to a decrease in atmospheric density. The problem of reflection of a spherical N-wave from an atmospheric inhomogeneous layer with model vertical wind-velocity and temperature fluctuations having a vertical spectrum that is close to that observed within the middle atmosphere is considered. The relation between the parameters (form, length, frequency spectrum, and intensity) of signals reflected from an atmospheric inhomogeneous layer and the parameters of the atmospheric fine layered structure at reflection heights is analyzed. The theoretically predicted forms of signals reflected from stratified inhomogeneities within the stratosphere and the lower thermosphere are compared to the observed typical forms of both stratospheric and thermospheric arrivals from surface explosions and volcanoes in the zones of an acoustic shadow.     

Role of Vertical Resolution in Numerical Models Towards the Intensification,Structure and Track of Tropical Cyclones

The impact of vertical resolution on the evolution and movement of tropical cyclones was studied using NCAR MM5 model with a horizontal resolution of 9 km. Four numerical experiments were performed with different vertical resolutions, that is, with 23 vertical levels as control experiment, and 36 vertical levels with high resolution in the lower troposphere, 33 vertical levels with high resolution in the upper troposphere and 46 vertical levels with increased vertical resolution throughout the troposphere as relative to base experiment. The results indicate that increased vertical resolution in the lower troposphere produces efficient intensification and better structure in terms of eye and eyewall. Increased vertical resolution at lower levels improves the prediction of vertical shear of horizontal wind. Experiments with high resolution in the lower troposphere and high resolution throughout the troposphere simulate better track up to 72 hours.     

Analysis of the weekly cycle in the atmosphere near Moscow

Using the spectral method and the method of grouping by days of week, we analyzed the weekly cycles by standard air sounding data obtained at the Dolgoprudny station near Moscow and by the results of measurements of NO₂ content in the stratosphere and the atmospheric boundary layer at the Zvenigorod Research Station of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, in 1990–2010. We revealed weekly cycles of the NO₂ content in the vertical column of the stratosphere, temperature, geopotential, meridional wind velocity in the troposphere and lower stratosphere, and the tropopause height in the warm half of the year (mid-April to mid-October). The weekly variations in temperature in the troposphere are positive in the first half of the week and negative in the second half, and the variations in temperature in the tropopause layer and in the lower stratosphere are opposite in sign to the tropospheric variations. The weekly cycle of the tropopause height is approximately in phase with the cycle of tropospheric temperature, and the weekly cycle of the NO₂ content in the stratospheric column is opposite in phase to the cycle of the tropopause height. Weekly variations were also observed in the total ozone content over Moscow. This finding was confirmed by calculations based on regression relationships between the vertical distribution of ozone and tropopause height. Conceptual mechanisms of weekly cycles were proposed.     

长江河口南港河段沙波观测研究

利用Sea Bat 7125多波束测深系统,对长江河口南港河段进行了沙波的高分辨率观测研究。结果表明:南港河段沙波发育广泛。统计的沙波中,最小波高0.12m,最大波高达3.12m;最小波长为3.12m,最大波长为127.89m。其中,南港上段、南港中段主航道、南港下段沙波陡坡有向海倾斜的趋势,而南港中段主航道南侧沙波陡坡有向陆倾斜的趋势。     

The propagation of an acoustic pulse in a near-ground atmospheric waveguide

A wave theory of propagation of an acoustic pulse in a moving stratified atmospheric layer above the ground with a finite impedance of an underlying ground surface is developed. The shapes of acoustic signals in a near-ground atmospheric waveguide, which are formed due to temperature inversion and a vertical shear of the wind velocity, are calculated based on this theory. These signals are compared with those measured during the experiments where vertical profiles of the wind velocity and temperature in an atmospheric boundary layer have been continuously controlled using a sodar, a temperature profile meter, and acoustic anemometers or thermometers mounted on a 56-meter-high mast. The joint action of a near-ground acoustic waveguide, the impedance of the underlying surface, and a vertical layered structure of the boundary atmospheric layer on a signal shape far from the acoustic source are studied.     

北冰洋80°～85°N浮冰区对流层大气的垂直结构

利用2008年夏季中国第3次北冰洋考察所获取的GPS探空资料对北冰洋(79°～85.5°N,144°～170°W)浮冰区对流层大气的垂直结构进行了研究.结果表明:北冰洋浮冰区对流层中部大气的平均温度递减率为6.47℃/km;对流层顶高度为8.0～10.7 km,平均为9.3 km,对流层顶温度为-59.4～-43.5℃...     

Using artificial neural networks in the temperature and humidity sounding of the atmosphere

The application of the radiative data inversion technique based on artificial neural networks (ANN) for the meteorological satellite sounding of the atmosphere is described. To increase the efficiency of solving inverse problems, the principal component method is used for the temperature and humidity profiles, as well as for IR radiation spectra, which allows the problem dimensionalities to be reduced substantially. Based on numerical experiments, errors of the temperature and humidity sounding are analyzed from the spectra of outgoing IR radiation (that were measured by the IKFS-2 instrument onboard the Meteor Russian satellite) using the iterative physical-mathematical (IPM) algorithm, multiple linear regression (MLR), and ANN-based methods. Appreciable advantages of the ANN-based method are revealed as compared to the MLR method. Therefore, in temperature sounding, the MLR method has a markedly large error at heights of 1–12 km (a difference of up to 1 K), while the IPM algorithm has almost the same error as the ANN method. The humidity determination error is about 10% when the ANN method is used at heights of 0–12 km. The IPM approach yields approximately the same error in the lower troposphere, but as the height increases the advantages of the ANN method grow.     

Space and time variations in the fine structure of the upper atmosphere according to acoustic sounding data

The results of studying variations in the fine layered structure of the upper atmosphere (heights of 20–140 km) according to data obtained from acoustic sounding within the range of infrasonic waves are given. The sources of infrasounds were surface explosions equivalent to 10 kg to 70 t of TNT. These explosions were set off in different seasons in different regions of Russia. Experimental data obtained in 1981–2011 have been analyzed. It has been found that the fine structure in the form of vertically distributed layered formations occurs in the upper atmosphere in all seasons. Moreover, the vertical distribution of both air-temperature and wind-velocity inhomogeneities in the upper atmosphere may be invariable over a time interval of no less than several hours. It has also been found that, throughout the entire atmospheric thickness from the stratopause to the lower thermosphere heights (up to 140 km), the instantaneous height distribution of layered air-temperature and wind-velocity inhomogeneities may remain almost unchanged during a time interval of no less than 20 min.     

深水声学拖曳系统

介绍了我国自主设计和研制的深水声学拖曳系统,它的最大工作水深4000m,安装有高分辨率测深侧扫声纳,可在近海底工作获得高分辨率的海底地形地貌和温盐深等数据.它的测深覆盖范围600m,侧扫覆盖范围800m,垂直航迹分辨率5cm,最小可检测高度10cm,测深分辨率高于目前的多波束测深系统.该系统已进行了湖试和海上锚泊试验.该系统的研制成功将对开展大陆架勘查,探测和开发国际海底资源发挥重要作用,拖曳系统中高分辨率测深侧扫声纳还可装船安装,在大陆架水域进行高分辨率海底地形地貌测绘.     

About the relationship between acoustic fields and hydrological fields in the area of a mesoscale eddy in the Black Sea

This paper discusses the application of acoustic sounding with the purpose of identifying vortical features in the sea. Analysis of the results of a multidisciplinary acoustic/hydrological experiment conducted in the Black Sea has revealed a stable recurrent correlation between the amplitudinal variance of echo signals, on the one hand, and the peculiarities of water temperature fields, on the other. Given these characteristics, the peripheral and the central areas of a mesoscale eddy essentially differed. This allows us to apply acoustic sounding to identify mesoscale eddies in the sea. Translated by Vladimir A. Puchkin.     

The vertical structure of the atmospheric boundary layer over the central Arctic Ocean

The tropopause height and the atmospheric boundarylayer （PBL） height as well as the variation of inversion layer above the floating ice surface are presented using GPS （global position system ） radiosonde sounding data and relevant data obtained by Chinas fourth arctic scientific expedition team over the central Arctic Ocean （86°-88°N, 144°-170°W） during the summer of 2010. The tropopause height is from 9.8 to 10.5 km, with a temperature range between -52.2 and -54.10C in the central Arctic Ocean. Two zones of maximum wind （over 12 m/s） are found in the wind profile, namely, low- and upper-level jets, located in the middle troposphere and the tropopause, respectively. The wind direction has a marked variation point in the two jets from the southeast to the southwest. The average PBL height determined by two methods is 341 and 453 m respectively. These two methods can both be used when the inversion layer is very low, but the results vary significantly when the inversion layer is very high. A significant logarithmic relationship exists between the PBL height and the inversion intensity, with a correlation coefficient of 0.66, indicating that the more intense the temperature inversion is, the lower the boundary layer will be. The observation results obviously differ from those of the third arctic expedition zone （800-85° N）. The PBL height and the inversion layer thickness are much lower than those at 870-88° N, but the inversion temperature is more intense, meaning a strong ice- atmosphere interaction in the sea near the North Pole. The PBL structure is related to the weather system and the sea ice concentration, which affects the observation station.     

南海北部声散射季节变化

声散射是重要的声学现象,海洋水体产生的高频声散射信号既可用于开展多种目的的声学海洋学研究,也可能对水下声学设备产生干扰,而海洋水体背景声散射具有显著的时空变异特征,因此针对特定海区开展声散射时变观测具有重要意义。本文利用在南海北部布放的锚系系统所搭载的声学多普勒流速剖面仪,获取了覆盖4个季节的累计约80 d的声散射数据,数据包括75 kHz和300 kHz两个频段,观测水深几乎覆盖了从海面到约600 m水深的整个水体。结果表明,水体在垂向上分布着上散射层和深散射层2个主要散射层。上散射层分布深度在冬夏较浅,位于约100 m以浅,在春秋较深,位于约200 m以浅;深散射层分布深度同样为冬季最浅,位于约300 m以深,但夏季则最深,位于约400 m以深。因此,两散射层的距离在夏季最远,在春秋最近。2个散射层的声散射强度（Sv）同样具有明显的季节变化,上散射层散射强度夏秋较强而春冬较弱,深散射层则正好相反。     

An active source electromagnetic sounding system for marine use

Instrumentation has been developed for carrying out active source electromagnetic sounding experiments in the deep oceans. Experiments of this type are directly and uniquely sensitive to the presence of molten or partially molten material, to temperature structure and to the porosity of upper crustal rocks such as those that accommodate hydrothermal circulation systems. Electromagnetic sounding experiments therefore represent an extremely desirable addition to the existing range of geophysical techniques for studying geological processes in thermally, hydrothermally or magmatically active regions—for example, at oceanic spreading centres.The instruments can be operated in regions of rugged, unsedimented sea bottom terrain, and are designed for investigating the distribution of electrical conductivity within the oceanic crust and uppermost mantle. The instrumentation consists of a deep towed, horizontal electric dipole transmitter and a set of free-fall, sea bottom, horizontal electric field recording devices.The transmitter is a deep-towed instrument, which is provided with power from the towing ship through a conducting cable. The transmitter package is fitted with an integral echo sounder, which allows it to be towed safely a short distance above the seabed. Electromagnetic signals are transmitted from a neutrally-buoyant antenna array, which is streamed behind the deep tow.The sea bottom receiving instruments each consist of a recoverable package which contains the instrumentation and digital recording system, an acoustic release unit, four low-noise, porous electrodes arranged in two orthogonal, horizontal dipoles, and a disposable bottom weight.The instruments have been used at sea on three occasions. On their most recent use, active source signals were successfully recorded during an experiment to investigate crustal magmatism and hydrothermal circulation beneath the axis of the East Pacific Rise.     

台阶式变深水槽造波的解析研究

利用特征函数展开法对台阶式变深水槽中推板式造波机造波问题进行了研究,建立了相应速度势和波面的解析表达式。与高阶边界元方法(HOBEM)数值结果进行了对比,验证了本解析解的正确性。通过数值试验,研究了台阶对入射波的影响,同时分析了造波板所在位置(上部台阶)水深、水槽工作区(下部台阶)水深、造波板运动周期和造波板水平位置等因素对生成波浪高度的影响。由此选择合适的造波板所在位置及水深来得到所需要的波浪高度,进而根据需要生成波浪的周期和波幅来反演造波板的运动。     

华北冷涡背景下青岛三次混合型对流天气环境场条件对比分析

利用探空观测资料,对比分析华北冷涡背景下青岛三次混合型对流天气过程环境场条件,揭示出现短时强降水、雷暴大风和冰雹天气时的水汽、稳定度和垂直风切变差异特征.分析结果表明:500 hPa上冷涡中心位于42°N的华北冷涡、850 hPa低涡系统和偏南风急流以及地面气旋是这三次混合型对流天气的影响系统;在这三次混合型对流过程中...     

声学方法进行海底沉积物遥测分类:综述

本文讨论利用声学遥测方法进行海底沉积物分类的目的、用途及该项技术的发展背景和现状。重点介绍目前主要的用于浅、表层沉积物分类的声学遥测方法，包括选通等幅脉冲、宽频带脉冲、连续线性扫频脉冲等正入射方法和侧扫声呐、多波束测深等斜入射方法。回顾它们的发展历史，评述它们的技术现状，并讨论它们的进一步发展     

Frequency Selectivity Analysis Based on Inductively Coupled Channel for Current Transmission Through Seawater

Inductively coupled channels are based on the electromagnetic induction principle and realize long-distance current signal transmission through seawater. Due to a few difficulties in performing actual experiments, it is unclear how the seawater medium affects the frequency selectivity of the current signal. In this paper, a dual dipole model of the inductively coupled seawater transmission channel is established for the traditional short-distance current field transmission mode. The transmission characteristics of electrical signals in seawater are theoretically derived. A platform is used to measure the amplitude-frequency and phase-frequency characteristics of the current signal transmission in seawater with transmission frequencies ranging from 30 kHz to 1 MHz, and transmission distances in the vertical range of 4 m. The COMSOL Multiphysics simulation and practical test analysis are carried out to analyze the frequency selectivity of seawater conductivity. It is proved that the seawater resistance increases as the frequency increases, which is the key problem that affects the current signal. This study provides an important theoretical support and experimental evidence for improving the transmission performance of long-distance underwater current signals.