共查询到19条相似文献,搜索用时 55 毫秒
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行星波传播理论虽然已有很多研究,但是大多以纬向对称基流为主,无法解释东西风带之间相互作用的事实.鉴于此,本文从理论上系统讨论了纬向对称和水平非均匀基流中定常和非定常波动的传播特征.首先,对纬向对称基流中波动传播的周期特征进行分析后发现,西风中位相东传超长波周期大于30 d,而东风中位相西传超长波的周期则小于30 d.之后,从传播的空间以及周期特征等方面系统研究了水平非均匀基流中球面波动传播理论,得到以下结论:经向基流使得定常波可以穿越东风带,在南北两半球间传播,为东西风带之间的相互作用提供了理论解释;强的经向流使得波动传播具有单向性;亚澳季风区低层纬向1波呈低频特征. 相似文献
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本文提出了一种利用反射波走时曲线计算垂向非均匀介质速度和反射界面深度的方法。当在地球表面没有获得来自地下某一深度范围内介质的任何信息时,可以认为这一深度范围内的地震波速度具有连续性。利用来自其底部反射界面的反射波走时曲线,可以计算出该深度范围的地震波速度结构。对三种模型进行了理论计算,所得反演解与真实值较为一致,其中计算出的反射界面深度最为精确。利用本文提出的方法可以计算两个相邻反射面之间的垂向非均匀速度结构,如低速层等。 相似文献
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利用现有大气本底站的大气CO2浓度观测信息,综合考虑不同经济区划与土地覆盖类型对应的CO2浓度差异及其季节变化规律,构建模式区域内以月为单位的网格化大气CO2浓度非均匀动态分布数据模型.由此数据模型驱动RegCM4-CLM3.5区域气候模式运行,对东亚区2000年3月—2009年2月之间的气候变化特征进行了模拟,进而对大气CO2浓度非均匀动态分布可能引起的区域气候效应进行了初步研究.结果表明:目前气候模式中CO2浓度的常态均匀分布假设可能将温室效应夸大了10%左右.对大气CO2浓度非均匀动态分布影响气温变化的可能机制进行研究表明:CO2的自身效应(改变大气透射率)并不是导致Exp2试验温度降低的主要原因.大气CO2浓度的变化影响了大气与植物胞间CO2分压差,陆地植被通过改变气孔阻力适应这种变化,气孔阻力的变化直接影响到植物与大气间水分的交换,这种作用一方面通过蒸发冷却改变环境温度,另一方面,蒸发水分改变了近地面层湿度,进而水汽扩散到空中影响低云的分布.冬季,植物处于非生长季,对大气CO2浓度变化响应微弱,湿度和低云变化不明显;夏季,植物生长旺盛,由CO2生理学强迫激发的云反馈效应强烈,其效果是使中低云趋于增加,进而减弱了到达对流层低层的太阳短波辐射,造成温室效应减弱. 相似文献
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利用现有大气本底站的大气CO2浓度观测信息,综合考虑不同经济区划与土地覆盖类型对应的CO2浓度差异及其季节变化规律,构建模式区域内以月为单位的网格化大气CO2浓度非均匀动态分布数据模型.由此数据模型驱动RegCM4-CLM3.5区域气候模式运行,对东亚区2000年3月—2009年2月之间的气候变化特征进行了模拟,进而对大气CO2浓度非均匀动态分布可能引起的区域气候效应进行了初步研究.结果表明:目前气候模式中CO2浓度的常态均匀分布假设可能将温室效应夸大了10%左右.对大气CO2浓度非均匀动态分布影响气温变化的可能机制进行研究表明:CO2的自身效应(改变大气透射率)并不是导致Exp2试验温度降低的主要原因.大气CO2浓度的变化影响了大气与植物胞间CO2分压差,陆地植被通过改变气孔阻力适应这种变化,气孔阻力的变化直接影响到植物与大气间水分的交换,这种作用一方面通过蒸发冷却改变环境温度,另一方面,蒸发水分改变了近地面层湿度,进而水汽扩散到空中影响低云的分布.冬季,植物处于非生长季,对大气CO2浓度变化响应微弱,湿度和低云变化不明显;夏季,植物生长旺盛,由CO2生理学强迫激发的云反馈效应强烈,其效果是使中低云趋于增加,进而减弱了到达对流层低层的太阳短波辐射,造成温室效应减弱. 相似文献
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地球物理成像解释的一个重要问题是,地震波传播时其本身受到地质体中小尺度非均匀性的影响,对该问题的研究具有重要的意义且备受关注. 据此,本文首先从统计意义上的表示形式来描述小尺度非均匀性,给出一种拓展了小尺度非均匀性择优取向的随机介质建模新方法,重点阐述了建模过程中对误差处理的重要性. 其次讨论了地震波在水平层状介质中传播时的长波长理论,并指出对该理论的适用条件进行研究的重要意义.且还基于1D随机层状介质,从局部各向异性因子曲线的角度对长波长理论进行了研究,并讨论了密度及泊松比扰动对曲线形态的影响. 最后,从对1D和2D随机介质进行数值模拟的角度重点研究长波长理论不能满足的情况下地震记录的特点,为了便于对比分析,文中也计算了1D随机介质在不同平均化长度下,通过长波长理论得到的等效介质的理论走时(走时的计算是在弱各向异性假设条件下完成的),并给出有指导意义的结论. 相似文献
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地球物理成像解释的一个重要问题是,地震波传播时其本身受到地质体中小尺度非均匀性的影响,对该问题的研究具有重要的意义且备受关注. 据此,本文首先从统计意义上的表示形式来描述小尺度非均匀性,给出一种拓展了小尺度非均匀性择优取向的随机介质建模新方法,重点阐述了建模过程中对误差处理的重要性. 其次讨论了地震波在水平层状介质中传播时的长波长理论,并指出对该理论的适用条件进行研究的重要意义.且还基于1D随机层状介质,从局部各向异性因子曲线的角度对长波长理论进行了研究,并讨论了密度及泊松比扰动对曲线形态的影响. 最后,从对1D和2D随机介质进行数值模拟的角度重点研究长波长理论不能满足的情况下地震记录的特点,为了便于对比分析,文中也计算了1D随机介质在不同平均化长度下,通过长波长理论得到的等效介质的理论走时(走时的计算是在弱各向异性假设条件下完成的),并给出有指导意义的结论. 相似文献
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转换点位置的计算是转换波资料处理中的一个关键问题. 本文提出了分别基于速度随深度线性变化、速度随垂直走时线性变化、慢度随深度线性变化和慢度随垂直走时线性变化四种等效垂向非均匀介质情况下转换点位置的计算方法. 研究了通过速度拟合、走时近似和相似系数谱三种方式选择合适的等效速度方法. 结合理论模型对非均匀介质转换点计算方法、渐进转换点计算方法、Thomsen近似公式和均匀介质解析计算方法的误差进行了分析,结果表明非均匀介质转换点计算方法能更准确地计算转换点位置. 相似文献
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相对于单频衍射层析成像而言,垂向非均匀背景多频背向散射层析成像方法大大提高了图像的分辨率和质量;其计算速度比其它诸如多频全息术、叠前偏移等多频方法快得多;用反传播进行成像时,该方法的计算速度与有关文献提出的均匀背景相应的方法几乎相同,但该方法适用于垂向非均匀背景,因而更适于实际应用.本文还提出了垂向非均匀背景中空间域Born散射数据的一种快速形成方法. 相似文献
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Sheet flow hydrodynamics over a non-uniform sand bed channel 总被引:1,自引:0,他引:1
The current study experimentally investigates the flow characteristics and temporal variations in the sheet flow profile of a non-uniform sand bed channel. Experiments were done to explore turbulent structures in the presence of a sheet flow layer with and without seepage. The turbulent events, such as stream wise velocity, Reynolds shear stresses, and turbulence intensities were found to be increasing and vertical velocity was found decreasing with a sheet layer. The presence of a sheet layer also effects the turbulent energy production and energy dissipation. All the turbulence parameters with and without a sheet layer have also been influenced by the presence of downward seepage. The rate of sheet flow movement is increased with seepage, owing to increased turbulence with seepage. The current study used wavelet analysis on temporally lagged spatial bed elevation profiles obtained from a set of laboratory experiments and synchronized the wavelet coefficients with bed elevation fluctuation at different spatial scales. A spatial cross correlation analysis at multiple scales, based on the wavelet coefficients, has been done on these bed elevation datasets to observe the effect of downward seepage on the dynamic behavior of sheet flow at different length scales. It is found that seepage increases average bed celerity and also increases the celerity of sheet flow of similar length scales. This increase in the celerity has been hypothesized as the increase of sheet flow movement as well as the increase in turbulent parameters with seepage, which destabilizes the bed particles resulting in a disruption in the continuous propagation pattern of the sheet flow. The increase of sheet flow celerity with seepage is confirmed from the saturation level of the wavelet power spectra of the bed elevation series. The presence of seepage also affects the non-uniformity of collective sheet material. 相似文献
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Existing analytical solutions to 2D and 3D contaminant transport problems are limited by the mathematically convenient assumption of uniform flow. An approximate method is developed herein for coordinate mapping of 2D (vertically-averaged) transport solutions to non-uniform steady-state irrotational and divergence-free flow fields in single-layer aquifers. The method enables existing analytical transport solutions to be applied to aquifer systems with wells, non-uniform saturated thickness, surface water features, and (to a limited degree) heterogeneous hydraulic conductivity and recharge. This mass-conservative coordinate mapping approach is inexact in its approximation of the dispersion process but is still sufficiently accurate for many simple flow systems. The degree of model error is directly proportional to the variation of velocity magnitude within the domain. These mapped analytical solutions are compared to numerical simulation results and the coordinate mapping errors are investigated. The methods described herein may be used in the traditional capacity of analytical transport models, i.e., screening and preliminary site assessment, without sacrificing accuracy by assuming locally uniform flow conditions or applying an ad-hoc coordinate transformation. The solutions benefit from the traditional advantages of analytical methods, particularly the removal of artifacts due to spatial and temporal discretization: no time-stepping or numerical discretization is required. 相似文献
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S. M. Churilov 《地球物理与天体物理流体动力学》2013,107(3):159-175
Abstract The development of initially small perturbations in a weakly supercritical zonal shear flow on a β-plane is studied. Two different scenarios of evolution are possible. If the supercriticality is sufficiently small, the growth of a perturbation is stopped in the viscous critical layer regime; for this case the evolution equation (corrected by the inclusion of a quintic nonlinearity) is derived. At greater supercriticality the nonlinearity cannot stop the growth of the perturbation in a linear (viscous or unsteady) critical layer regime, and the evolution is more complicated. Transition to a nonlinear critical layer regime leads to a reduction in the growth rate and to a slowing (but not a stopping) of the increase in amplitude, A. These are connected to the formation of a plateau (S=constant) of width L=O(A ½) in the profile of absolute vorticity, S. Careful analysis reveals that the growth in amplitude ceases only when the whole instability domain (where the slope of unperturbed S-profile is positive) becomes covered again by the plateau. 相似文献
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Abstract A study is made of the nonlinear stability of a weakly supercritical zonal shear flow in the β-plane approximation. The dynamics of initially small disturbances are examined. The main nonlinear effects are associated with the rearrangement of the critical layer. It is shown that as the wave grows in amplitude, linear regimes of the critical layer (viscous and nonstationary) change over to a nonlinear regime while the exponential law of disturbance growth becomes a power-law. 相似文献
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本文利用热层-电离层-中间层能量和动力学卫星TIMED中宽带发射辐射计SABER观测的临边大气长波红外背景辐射数据来研究平流层增温效应,基于2012/2013年1—3月在20~100 km高度内的临边大气长波红外背景辐射数据,采用微扰方法,得到辐射扰动的时空分布.结果显示:大气长波红外背景辐射扰动数据能够更精细的展示平流层增温事件的发生,2013年平流层爆发性增温效应下最大辐射扰动幅度出现在40 km处可达160%,而利用温度扰动数据表征此事件的发生时最大温度扰动幅度出现在40 km处只有21%.针对2012年弱平流层增温效应,温度扰动幅度最大值出现在40 km处为16.4%,而辐射扰动幅度的最大值在40 km处可达91%.大气长波红外背景辐射的纬度分布体现出此事件发生于高纬度地区;其经度分布在20~50 km范围内呈现"w"形状;而50 km和80 km处大气长波红外背景辐射的极值区域范围随着事件的发生在高纬度地区都是先扩大随后缩小的过程.这表明高层大气临边红外辐射信号可用于研究平流层增温效应,尤其是对于温度弱起伏的小扰动事件.这对于掌握临近空间环境辐射形成机理及其变化特性亦具有重要意义. 相似文献
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本文利用热层-电离层-中间层能量和动力学卫星TIMED中宽带发射辐射计SABER观测的临边大气长波红外背景辐射数据来研究平流层增温效应,基于2012/2013年1—3月在20~100 km高度内的临边大气长波红外背景辐射数据,采用微扰方法,得到辐射扰动的时空分布.结果显示:大气长波红外背景辐射扰动数据能够更精细的展示平流层增温事件的发生,2013年平流层爆发性增温效应下最大辐射扰动幅度出现在40 km处可达160%,而利用温度扰动数据表征此事件的发生时最大温度扰动幅度出现在40 km处只有21%.针对2012年弱平流层增温效应,温度扰动幅度最大值出现在40 km处为16.4%,而辐射扰动幅度的最大值在40 km处可达91%.大气长波红外背景辐射的纬度分布体现出此事件发生于高纬度地区;其经度分布在20~50 km范围内呈现"w"形状;而50 km和80 km处大气长波红外背景辐射的极值区域范围随着事件的发生在高纬度地区都是先扩大随后缩小的过程.这表明高层大气临边红外辐射信号可用于研究平流层增温效应,尤其是对于温度弱起伏的小扰动事件.这对于掌握临近空间环境辐射形成机理及其变化特性亦具有重要意义. 相似文献
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The last two decades have witnessed the development and application of well-balanced numerical models for shallow flows in natural rivers.However,until now there have been no such models for flows with non-uniform sediment transport.This paper presents a 1D well-balanced model to simulate flows and non-capacity transport of non-uniform sediment in alluvial rivers.The active layer formulation is adopted to resolve the change of bed sediment composition.In the framework of the finite volume Slope Llmiter Centred(SLIC) scheme,a surface gradient method is incorporated to attain well-balanced solutions to the governing equations.The proposed model is tested against typical cases with irregular topography,including the refilling of dredged trenches,aggradation due to sediment overloading and flood flow due to landslide dam failure.The agreement between the computed results and measured data is encouraging.Compared to a non-well-balanced model,the well-balanced model features improved performance in reproducing stage,velocity and bed deformation.It should find general applications for non-uniform sediment transport modelling in alluvial rivers,especially in mountain areas where the bed topography is mostly irregular. 相似文献