Wave-mean flow interaction and its relationship with the atmospheric energy cycle with diabatic heating

In a linear system, the wave characteristics depend strongly on the distributions with height of wind ve-locity and static stability. The simplest case is for con-stant wind and static stability (e.g., isothermal atmos-phere with pressure and density exponentially de-creasing with height). In such circumstances there is no convergence or divergence in wave energy flux, therefore, no energy exchange between the wave and mean flow. In the atmosphere wind speed varies with increasing height, inte…     

基于能量密度的自解耦互相关成像条件

基于能量密度构建的弹性波能量成像条件,可以准确提取弹性波场的能量信息,并可以有效压制背向散射.但是该成像条件得到的成像结果将所有弹性波场能量信息耦合在一起,难以区分纯波模式的能量信息.为此,我们从势能及动能两方面将能量场解耦,得到纯纵波（PP）、纯横波（SS）、转换波（C）能量场.根据能量守恒定律,基于Helmholtz原理对位移场的空间导数进行因式分解,将弹性势能自解耦得到纯纵波、纯横波及转换波势能;引入体应力构建得到P波及S波速度,将弹性动能分解为纯纵波、纯横波和转换波动能.从而,构建基于能量密度自解耦得到纯波能量互相关成像条件.数值实验表明自解耦成像条件可实现弹性波场能量的分解,并得到背向散射压制、振幅有效保持的PP波、SS波和C波成像结果.     

Japan's 2011 Tsunami: Characteristics of Wave Propagation from Observations and Numerical Modelling

We use a numerical tsunami model to describe wave energy decay and transformation in the Pacific Ocean during the 2011 Tohoku tsunami. The numerical model was initialised with the results from a seismological finite fault model and validated using deep-ocean bottom pressure records from DARTs, from the NEPTUNE-Canada cabled observatory, as well as data from four satellite altimetry passes. We used statistical analysis of the available observations collected during the Japan 2011 tsunami and of the corresponding numerical model to demonstrate that the temporal evolution of tsunami wave energy in the Pacific Ocean leads to the wave energy equipartition law. Similar equipartition laws are well known for wave multi-scattering processes in seismology, electromagnetism and acoustics. We also show that the long-term near-equilibrium state is governed by this law: after the passage of the tsunami front, the tsunami wave energy density tends to be inversely proportional to the water depth. This fact leads to a definition of tsunami wave intensity that is simply energy density times the depth. This wave intensity fills the Pacific Ocean basin uniformly, except for the areas of energy sinks in the Southern Ocean and Bering Sea.     

煤巷小构造Rayleigh型槽波超前探测数值模拟

对煤巷小构造地震波场进行了数值模拟研究,分析了层状煤层中地震波的传播特征.研究表明:(1)在煤巷迎头前方煤层内以纵波震源激发的Rayleigh型槽波相对于体波能量较强,波列较长,波速较低.(2)沿煤层传播的Rayleigh型槽波在小构造面上产生Rayleigh型槽波反射波,反射Rayleigh型槽波垂直分量相对于水平分量能量较强.沿煤层反向传播的反射Rayleigh型槽波在煤巷迎头面上转换为沿煤巷底板传播的Rayleigh面波.沿煤巷底板可以接收到能量较强的反射Rayleigh型槽波产生的Rayleigh面波,其可以作为超前探测小构造面的特征波.在地震记录上反射Rayleigh型槽波产生的Rayleigh面波波至最迟,在时间域与其他波列时间间隔较大,其垂直分量能量相对于水平分量较强,在地震记录上容易识别.(3)在相同的地质条件下应用反射地震超前探测方法,标志煤巷迎头前方存在小构造面的反射地震波能量较弱,受煤巷顶、底板界面和采煤迎头面的强反射波干扰,在地震记录中难以识别.     

南亚高压区Rossby波能量向上穿越对流层顶传播的特征与机制

夏季平流层盛行强东风,Rossby波能量难以从对流层向上传播至平流层,而冬季平流层盛行西风,Rossby波能量容易上传,因此以往对Rossby波能量向平流层传播的研究多考虑冬季的情况.而事实上,因为夏季高原上空南亚高压反气旋环流,并非只有强东风存在,所以Rossby波能量也可能在南亚高压区向上传播,从而影响平流层的温度、风场及大气成分等.因此,本文利用ERA-interim逐日再分析资料,分析了1979—2015年夏季南亚高压区Rossby波能量穿越对流层顶传播的特征与机制.结果表明:Rossby波能量可以从南亚高压西北部的窗口区上传至平流层,最高可到达平流层顶,而在南亚高压的其他部分,Rossby波能量均不能穿越对流层顶上传或穿越对流层顶后无法继续上传.南亚高压西北区Rossby波能量可以穿越对流层顶传播的原因是盛行西风,且西风急流出现的频率很小,同时涡动热量通量异常引起的垂直分量的第一项对其上传有很大贡献.南亚高压东北区也盛行西风,然而Rossby波能量不能向上穿越对流层顶的原因是强西风出现频率较高,且温度脊与高度脊位相相近,不利于上传.南亚高压南部均盛行东风,在平流层中下层均为稳定层结,因此Rossby波能量很难上传.南亚高压西南区在对流层位于青藏高原环流的伊朗高原下沉区附近,层结稳定,并且温度脊超前于高度脊,所以Rossby波能量很难上传.而南亚高压东南区在对流层位于南海-西太平洋热带幅合带,层结不稳定,存在Rossby波能量较弱的上传,达到对流层顶后无法继续上传,该区域温度脊落后于高度脊的温压场配置也为Rossby波能量在对流层内的传播提供了条件.     

基于小波分解的能量谱分析方法及其在汶川地震中的应用

利用小波分解将地震波分解成不同频带的小波分量,进而对地震波输入结构的总能量EI进行分解,得到能量在频域上的分布,这是一个有意义的结果。通过对各分量能量谱峰值的分析,可以从另一个方面得到地震波的频谱特性,能量谱峰值出现的结构固有周期与地震波傅里叶谱的卓越周期相同,也可以作为估算卓越周期的一种方法。     

Wave energy input into the Ekman layer

This paper is concerned with the wave energy input into the Ekman layer, based on 3 observational facts that surface waves could significantly affect the profile of the Ekman layer. Under the assumption of constant vertical diffusivity, the analytical form of wave energy input into the Ekman layer is derived. Analysis of the energy balance shows that the energy input to the Ekman layer through the wind stress and the interaction of the Stokes-drift with planetary vorticity can be divided into two kinds. One is the wind energy input, and the other is the wave energy input which is dependent on wind speed, wave characteristics and the wind direction relative to the wave direction. Estimates of wave energy input show that wave energy input can be up to 10% in high-latitude and high-wind speed areas and higher than 20% in the Antarctic Circumpolar Current, compared with the wind energy input into the classical Ekman layer. Results of this paper are of significance to the study of wave-induced large scale effects.     

真实基流中非线性Rossby波演变特征(二):能量、结构演变及初始场影响

针对非线性的准地转正压位涡方程,利用自行设计的差分格式和高斯函数拟合得到的真实基流分布,数值研究了线性和非线性Rossby波流场结构和总能量的演变以及初值对总能量演变的影响.发现在非线性的真实基流中,线性和非线性Rossby波的相对总能量出现振荡型增长或衰减,非线性波动的振荡周期明显小于线性波动,非线性项不仅抑制能量的...     

Wave to wave and wave to zonal mean flow kinetic energy exchanges during contrasting monsoon years

Fourier analysis of the monthly mean northern hemispheric geopotential heights for the levels 700 mb and 300 mb are undertaken for the months of April through to August. The wave to wave and wave to zonal mean flow kinetic energy interactions are computed for specified latitude bands of the northern hemisphere during the pre-monsoon period (April to May) and monsoon period (June through to August) for bad monsoon years (1972, 1974, 1979) and for years of good monsoon rainfall over India (1967, 1973, 1977). Planetary scale waves (waves 1 to 4) are the major kinetic energy source in the upper atmosphere during the monsoon months. Waves 1 and 2 in particular are a greater source of kinetic energy to other waves via both wave to wave interactions as well as wave to zonal mean flow interactions in good monsoon years than in bad monsoon years. The zonal mean flow shows significantly larger gains in the kinetic energy with a strengthening of zonal westerlies in good monsoon years than in bad monsoon years.     

不同散射模式下S波包络合成

为揭示地震波在地壳小尺度非均匀介质中的散射过程,更准确地描述地震波的包络展宽现象,本文基于多次各向异性散射理论,采用离散波数法求解能量密度积分方程,选取高斯型自相关函数表征的散射模式,得到S波能量密度包络.基于此,本文首先分析了单次散射和多次散射在形成S波能量密度包络中的贡献规律;然后探讨了吸收系数和总散射系数对合成S...     

The behaviour of beach elevation contours in response to different wave energy environments

Within the context of a warming climate, there are wide and increasing concerns about the way beaches respond to different wave energy environments. However, behavioural differences in changes in beach elevation contours (including shorelines) in different wave energy environments remain unknown. Thus, it is unilateral to evaluate the changes in beaches based on a single elevation contour (e.g. shoreline) in coastal engineering and management applications. In this study, based on the collected shoreline and wave energy data of two international beaches, as well as the measured beach elevation contour data from Yintan Beach and the corresponding wave energy data simulated by Xbeach, our results show that frequency distributions of beach elevation contour changes exhibit distinct features under different wave energy environments. Under high wave energy environments, the frequency distributions of beach elevation contour changes show a Gaussian distribution. However, frequency distributions of beach elevation contour changes present a power law, intermediate between the logarithmic and Gaussian distributions under low and moderate wave energy environments, respectively. Furthermore, the conceptual model of beach elevation contour changes constructed by this study indicates that the relative importance of the wave energy and sediment resistance determines this phenomenon. © 2020 John Wiley & Sons Ltd     

热带气旋Rossby波能量频散问题研究进展

热带气旋是发生在热带洋面上的强烈气旋性涡旋.由于地转涡度梯度的存在,热带气旋在移动过程中不断发生Rossby波能量频散,并在热带气旋运动方向的后部激发出反气旋和气旋交替排列的Rossby波能量频散波列.多热带气旋共存和热带气旋的异常运动是当前国际热带气旋研究领域的热点问题,热带气旋Rossby能量频散被证实与多个热带气...     

Experimental study of near-bed concentration and sediment vertical mixing parameter for vertical concentration distribution in the surf zone

Two formulae for the near-bed concentration(C_a) and the sediment vertical mixing parameter(m) are established based on a large scale wave flume experiment.The advantage of the new formulae is that the turbulent kinetic energy induced by wave breaking can be taken into account;the formula for C_a is in terms of the near-bed,time-averaged turbulent kinetic energy,and the formula for m is in terms of depth-and time-averaged turbulent kinetic energy.A new expression for suspended sediment load also is established by depth integration of the vertical distribution of the suspended sediment concentration obtained on basis of the new formulae.Equation validation is done by comparing the predicted C_a and m to measurements for different types of waves(regular wave,wave group,and irregular wave),and good agreement is found.The advantages of the proposed formulae over previous formulae also are discussed.     

数字地震波时频分析

选取具有较高分辨率和较低交叉项的赵—阿特拉斯—马克斯(ZAM)方法,进行数字化地震波时频处理。结果显示:(1)S波高能量密度区域处于低频段,其频带比P波高能量密度区域窄,且S波能量密度比P波大1个数量级;(2)天然地震的高能量密度分布较为离散,爆破的高能量密度分布较为集中。     

Bimodal wave spectra in lower Chesapeake Bay, sea bed energetics and sediment transport during winter storms

The transition zone separating estuarine environments from the coastal ocean is characterized not only by distinctive morphological and sedimentary trends but by unique hydrodynamic forces as well. Lower Chesapeake Bay, a large coastal estuary within the Mid-Atlantic Bight of the U.S. East Coast, experiences complex wave and current-induced forces produced during winter storms. Wave and current measurements made near Thimble Shoal Light over five winter seasons show that most storms simultaneously produce both ocean and bay-generated wave trains that appear as distinct bimodal peaks in directional spectra. Analysis of selected storm wave records reveal that lower-frequency ocean waves, although nominally lower in amplitude than higher-frequency bay waves, are roughly equivalent to bay waves in terms of energy expended on beds of fine- to medium-grained sand at either end of the Thimble Shoal Channel. Grain-friction energy dissipation estimates calculated for waves and currents suggest that waves provide more net energy capable of transporting bottom sediment than currents, although strong barotropic flows briefly encountered during a major storm on 13–14 March 1993, exceeded wave energy expended at the bed by almost an order of magnitude. From analyses of wave orbital velocity spectra, it is shown that dual wave trains characterized by differences in peak frequency and direction may assist each other through interactions that increase their combined contribution to frictional energy dissipation and inferred sediment transport at the bed.     

长江三峡地区盐关微地震群的成因机制

盐关微地震群的活动局限在矿区内,地震都是微震和极微震。地震分两种类型:一种是微震活动,初动呈象限分布的双力偶滑动型震源机制,S波能量高于P波能量。另一种是极微震,初动几乎全负,P波能量高于S波能量,呈非双力偶的张破裂向内爆炸型的震源机制。两种地震的成因都是采矿诱发地震,不能做为仙女山断层向北延伸的证据     

天然地震与人工爆破的波形小波特征研究div

研究了如何从天然地震和人工爆破事件的波形记录中提取出有效、适用的波形特征,以用于对爆破事件的识别．首先对波形记录进行了4层小波包变换;然后对变换得到的最后一层小波包系数提取3种波形特征:能量比特征、香农熵特征及对数能量熵特征;最后利用upsilon;-SVC支持向量分类机对这3种特征的分类能力进行了外推检验．通过选用不同地区、不同台站、不同震级的天然地震与人工爆破的波形记录,力求提取的特征量能尽可能地反映天然地震与人工爆破波形的本质区别,尽量弱化震中距、震级等因素对识别效果的影响．结果表明,上述３种特征中以香农熵特征的识别效果最好,能反映天然地震与人工爆破的本质区别,可作为识别天然地震与人工爆破的一个有效判据．      

重力波非共振激发的数值研究

应用二阶算子分裂格式,采用全非线性模式,对可压大气中重力波波包非共振激发进行数值模拟和分析.研究表明：两个向上传播的重力波波包,通过非共振相互作用,也能激发出一个向下传播的重力波波包.生成波的能量几乎正比于主波的能量,也随次波的能量增大而增大.能量传递方向主要表现为从高频的主波向次波和生成波转移,这与共振相互作用不完全相同.非共振作用的特征时间由主次波的初始位置和波长频率决定,与主次波的初始振幅无关.生成波的波矢量并不严格满足弱非线性相互作用理论预言的波矢量匹配条件,而且生成波的波长和频率在传播的过程中会随时间发生变化,这表明了弱非线性相互作用理论的局限性.     

Non-hydrostatic and non-linear contributions to the internal wave energy flux in sill regions

A three-dimensional non-linear, non-hydrostatic model in cross-sectional form is used to determine the factors influencing the relative importance of the linear, non-hydrostatic and non-linear contributions to the internal wave energy flux in sill regions due to tidal forcing. The importance of the free surface elevation term is also considered. Idealised topography representing the sill at the entrance to Loch Etive, the site of a recent measurement programme, is used. Calculations show that the non-linear terms in the energy flux become increasingly important as the sill Froude Number (F _s) increases and the sill aspect ratio is increased. The vertical profile of the stratification, in particular its value close to the sill crest where internal waves are generated, has a significant influence on unsteady lee wave and mixed tidal–lee wave generation and the non-linear contribution to the energy flux. Calculations show that as F _s increases, the energy flux due to the non-linear and non-hydrostatic terms increases more rapidly than the linear term. The importance of the non-linear terms in the energy flux also increases as the sill aspect ratio is increased. Increasing the buoyancy frequency reduces the contribution of the non-hydrostatic and non-linear terms to the total energy flux. Also, as the buoyancy frequency is increased, this reduces unsteady lee wave and mixed tidal–lee wave generation. In essence, these calculations show that the energy flux due to the non-hydrostatic and non-linear terms is appreciable in sill regions.     

A study of dissipation of wind-waves by mud at Cassino Beach,Brazil: Prediction and inversion

The impact of a non-rigid seafloor on the wave climate at Cassino Beach, Brazil, May–June 2005 is studied using field measurements and a numerical wave model. The measurements consist of wave data at four locations; rheology and mud thickness from grab samples; and an estimate of the horizontal distribution of mud based on echo-soundings. The dissipation of waves by a non-rigid bottom is represented in the wave model by treating the mud layer as a viscous fluid. Applied for 431 time periods, the model without this type of dissipation has a strong tendency to overpredict nearshore wave energy, except during a period of large storm waves. Two model variations which include this dissipation have a modest tendency to underpredict the nearshore wave energy. An inversion methodology is developed and applied to infer an alternate mud distribution which, when used with the wave model, yields the observed waveheights.