Babin模式特征分析及应用

讨论了气象条件对Babin模式的影响，对比分析了Babin模式模拟结果与典型的P—J模式模拟结果，前者一般小于后者；还计算了南海海区的蒸发波导高度，平均结果与现有文献上的此海区统计结果基本一致，这为Babin模式用于研究蒸发波导气候变化提供了基础。     

基于局地相似理论的蒸发波导计算方案及敏感性试验

蒸发波导是海洋环境中最常出现的异常大气折射结构,具有很高的利用价值.利用局地相似理论代替 Monin-Obukhov 相似理论来确定近地层温度、湿度垂直分布廓线,并借助热带海洋全球大气-海气耦合响应试验(TOGA COARE) 中提出的总体通量算法,对 Local 模式和 New 的推导过程和算法设计进行了详细的阐述和说明.通过比较不同模式的计算结果和敏感性试验发现,在较强逆温和低风速(强稳定层结) 条件下,除 P-J 模式外,基于 Monin-Obukhov 相似理论的蒸发波导模式计算的高度值均出现异常突变;而基于局地相似理论的 Local 模式能够有效抑制这种异常突变的现象,且与加入人为修正的 P-J 模式结果比较接近.New 模式集 Babin 模式与 Local 模式的优点于一身,应该说是目前理论上最为完善的模式.     

水平非均匀性蒸发波导诊断及其对雷达探测的影响

蒸发波导是发生在海气边界层的一种异常折射现象,因为其分布广、发生概率大,所以被认为是对海上电子装备影响最为显著的波导类型。然而由于其形成机制复杂,且在近岸地区存在水平不均匀性,使得目前非均匀蒸发波导的诊断及其应用还未能落实到实际工作中。针对这一现状,首先利用G L Geernaert的方法修正了Monin-Obukhov相似理论,将其扩展到海洋大气表面边界层不均匀条件下;其次在Babin模式的基础上引入张强普适函数的非线性修正因子与阵性风速,从而将蒸发波导诊断模式的适用范围拓展到近海沿岸地区和甚低风速条件下。并在此基础上研究了蒸发波导水平非均匀性对雷达探测的影响,得到了水平非均匀蒸发波导能够改变均匀波导环境下雷达的探测距离及其盲区的分布。     

利用WRF模式对海上蒸发波导的数值模拟研究

以WRF中尺度模式为基础,耦合Babin蒸发波导模式,建立了一种海洋蒸发波导预报模式,对南海2010年3月26日至28日的蒸发波导高度进行48h的数值模拟。通过与NCEP再分析资料FNL数据计算得出的蒸发波导高度对比分析发现,WRF模拟结果与FNL计算结果拟合的较好,并且变化规律基本一致,该模式可以用来预报海上蒸发波导。     

基于非迭代海-气通量算法的蒸发波导预测模型研究

蒸发波导易发生在海洋等水体之上.为了深入研究蒸发波导预测模型的诊断预报技术,本研究依据目前最新的非迭代海-气通量算法,建立了非迭代通量算法蒸发波导预测模型-NEW模型,进而对新模型进行了敏感性试验,且用我国近海试验数据进行了检验.最后将NEW模型与目前使用广泛、效果较好的4种蒸发波导模型(即P-J模型、Babin模型、NPS模型和伪折射率模型)进行了对比分析,得到了不同模型蒸发波导高度随气象海洋要素变化的规律,结果表明非迭代通量算法模型与传统模型对不同海洋气象要素的敏感性响应是一致的.不稳定层结条件下NEW模型对蒸发波导的诊断结果接近于Babin模型和NPS模型,而稳定条件下略高于NPS模型.试验表明NEW模型可以有效地诊断预报蒸发波导.本研究系统阐述了非迭代通量算法模型的建立和适用情况,为蒸发波导预测诊断算法的更新和模型发展提出了新的思路.     

近海面蒸发波导和大气负折射的统一监测模型研究

近海面的蒸发波导和大气负折射都是海洋大气表面层的异常折射结构,两者对电磁波传播都具有重要影响。利用M-O近地层相似理论推导了蒸发波导的模型,利用等效蒸发波导高度推导了大气负折射与蒸发波导的统一监测模型及其廓线结构参数的bulk计算方法,比较分析了蒸发波导与大气负折射在廓线结构方面的特征和差异,并利用2002年5月福建平潭岛的试验数据验证分析了大气负折射监测模型机廓线计算方法的适用性。     

应用湍流通量理论分析蒸发波导机理

蒸发波导是近海面经常出现的大气结构.从湍流运动方程出发,基于近海面海-气耦合湍流通量理论和算法分析了蒸发波导机理.对气象要素变化时,蒸发波导高度和感热、蒸发潜热和动量通量间的关系进行了分析,表明蒸发波导的形成和湍流通量具有明显相关性,为蒸发波导机理研究提供了新途径.     

基于大气湍流效应的蒸发波导PJ 模型研究

本文基于海洋大气近地层相似理论和一维Kolmogorov 谱函数, 建立考虑各向同性和各向异性湍流效应的蒸发波导模型, 并基于相对误差理论, 将数值模拟的大气修正折射率与根据试验采集数据计算得到的修正折射率进行对比分析。研究结果表明： 湍流效应对蒸发波导模型的预测结果有影响, 且考虑各向异性湍流效应的蒸发波导模型预测精度更高。因此在构建蒸发波导模型时, 需要考虑各向异性湍流对大气折射率的扰动影响, 才能得到更准确的大气修正折射率廓线。通过引入各向异性大气湍流理论, 能够有效提升蒸发波导模型的适用性, 为后续反演大气波导提供较好的模型基础。     

蒸发波导条件下风速风向对电磁波传播的影响

海洋蒸发波导是重要的军事敏感要素,严重影响着海上电磁波的传播。风向、风速是决定蒸发波导强弱的重要因素,为精确模拟蒸发波导条件下的电磁波传播,准确评估预报雷达、通信等电子设备的性能,文中利用抛物线方程模型,结合粗糙度参数和蒸发波导条件下大气修正折射指数廓线模型来求解电磁波波动方程,基于电磁波传播的数值模拟结果,重点研究蒸发波导条件下风速和风向对电磁波传播的影响。并得到如下结论:在同一传播距离处,风速越大,海面粗糙度越大,海面电磁波传播损耗就越大;当电磁波传播方向与风向夹角为0°时,其传播路径损耗远远大于在45°或90°条件下,即顺风条件下电磁波传播损耗大于侧风。     

中国近海蒸发波导的数值模拟与预报研究

利用中尺度大气模式MM5对2007年中国近海大气蒸发波导进行了全年的高分辨的数值模拟.模拟结果统计表明,整个海域蒸发波导的平均出现概率约为90%.本文重点关注强度较大的蒸发波导,详细分析了其季节分布特征及其与海洋环流和海面气象条件的相关关系.研究发现,25°N以南的开阔海域的蒸发波导出现概率全年都较高,面以北的东海西北部、黄海与渤海,蒸发波导的出现概率呈现明显的季节特征;蒸发波导的空间分布受中国近海海洋环流的强烈影响,存在1个与黑潮区域相一致的带状波导高出现概率区域,台湾暖流、黄海暖流和对马暖流使得在某些季节相应海域蒸发波导出现概率高于其周围海域.此外,本文还基于WRF模式及其3DVAR系统构建了大气波导数值预报系统,尝试对中国东南海域的蒸发波导进行数值预报.     

一个嵌套于MM5下的蒸发波导预报模式

Evaporation duct is an abnormal refractive phenomenon in the marine atmosphere boundary layer. It has been generally accepted that the evaporation duct prominently affects the performance of the electronic equipment over the sea because of its wide distribution and frequent occurrence. It has become a research focus of the navies all over the world. At present, the diagnostic models of the evaporation duct are all based on the Monin-Obukhov similarity theory, with only differences in the flux and character scale calculations in the surface layer. These models are applicable to the stationary and uniform open sea areas without considering the alongshore effect.This paper introduces the nonlinear factor av and the gust wind item wg into the Babin model, and thus extends the evaporation duct diagnostic model to the offshore area under extremely low wind speed. In addition, an evaporation duct prediction model is designed and coupled with the fifth generation mesoscale model(MM5).The tower observational data and radar data at the Pingtan island of Fujian Province on May 25–26, 2002 were used to validate the forecast results. The outputs of the prediction model agree with the observations from 0 to 48 h. The relative error of the predicted evaporation duct height is 19.3% and the prediction results are consistent with the radar detection.     

二维大气模型在海上电波传播中的应用

电磁波在海上波导环境下传播特性的研究对提升舰载雷达探测性能有重大意义。通用的波导环境折射率模型是基于莫宁相似理论的5参数经验模型,其缺陷在于将折射率的水平结构看作是均匀的。本文运用的二维波导环境10参数模型克服了先前模型的缺陷,对实际波导环境有更近似的描述。最后运用基于离散傅里叶正弦变换的抛物方程方法具体分析了波导环境中折射率水平方向的变化对电波传播产生的影响,结果表明折射率水平变化会改变电磁波的空间场强分布,二维折射率模型更具实用价值。     

Calculations of the evolution of the upper ocean based on the similarity theory

Several schemes of turbulent mixing in the upper ocean are considered, including a modified scheme based on the modified Monin-Obukhov similarity theory. The schemes have been used for the calculation of the evolution of the upper ocean. The results are compared with the data of automated buoys. It is shown that the scheme based on the similarity theory gives a result not worse than the commonly used ones and has several advantages, which makes it the most appropriate for including in the ocean circulation models and climate models.     

Modelling ocean waves in ice-covered seas

Over the past decade there has been a rapid growth of interest in wave propagation through ice covers. This paper summarizes the author’s observation of the modeling efforts on this topic. Models can be theory-based, data-driven, or a combination of the two. A pure data-driven model relies on a large amount of observations and is only becoming available recently. Theory-based models on the other hand have a long history. They are always a simplified version of the reality. As our knowledge grows, theories become more complicated. A theory for waves-in-ice that captures all possible processes does not exist. However, when integrated with observation through calibration, these combined theory + data-based models may be used with some confidence. In this paper, different models, their basic concepts, their calibration and validation are discussed. The present theory-based models do not have the correct spectral attenuation trend as observed from field or laboratory experiments. Hence, through calibration they may fit different parts of the wave spectra but not all. Pure data-driven models can reproduce the correct trend, but its dependability outside the situation where the data are collected is uncertain. In addition to offering tools to forecast waves-in-ice, these model building and validating efforts point to missing mechanisms that should be carefully studied. Despite the many challenges towards building a satisfactory general waves-in-ice model, significant progress has been made for models that work reasonably well in the marginal ice zone. We anticipate much more data will become available in the coming years to help us improve the existing models.     

Verification of numerical wave propagation models for simple harmonic linear water waves

When applying numerical methods to study short-wave propagation in the horizontal plane (refraction and/or diffraction problems) it is important to know which method can best be used with respect to accuracy, computer costs and practical flexibility.In this paper three models, indicated as the refraction model, the parabolic refraction-diffraction model and the full refraction-diffraction model, are briefly described, together with a comparison of the computational results of these models with measurements in a hydraulic scale model. Conclusions with respect to the practical use of the models are also given.     

A depth-integrated model for weakly dispersive, turbulent, and rotational fluid flows

A set of weakly dispersive Boussinesq-type equations, derived to include viscosity and vorticity terms in a physically consistent manner, is presented in conservative form. The model includes the approximate effects of bottom-induced turbulence, in a depth-integrated sense, as a second-order correction. Associated with this turbulence, vertical and horizontal rotational effects are captured. While the turbulence and horizontal vorticity models are simplified, a model with known physical limitations has been derived that includes the quadratic bottom friction term commonly added in an ad hoc manner to the inviscid equations. An interesting result of this derivation is that one should take care when adding such ad hoc models; it is clear from this exercise that (1) it is not necessary to do so – the terms can be included through a consistent derivation from the viscous primitive equations – and (2) one cannot properly add the quadratic bottom friction term without also adding a number of additional terms in the integrated governing equations. To solve these equations numerically, a highly accurate and stable model is developed. The numerical method uses a fourth-order MUSCL-TVD scheme to solve the leading order (shallow water) terms. For the dispersive terms, a cell averaged finite volume method is implemented. To verify the derived equations and the numerical model, four cases of verifications are given. First, solitary wave propagation is examined as a basic, yet fundamental, test of the models ability to predict dispersive and nonlinear wave propagation with minimal numerical error. Vertical velocity distributions of spatially uniform flows are compared with existing theory to investigate the effects of the newly included horizontal vorticity terms. Other test cases include comparisons with experiments that generate strong vorticity by the change of bottom bathymetry as well as by tidal jets through inlet structures. Very reasonable agreements are observed for the four cases, and the results provide some information as to the importance of dispersion and horizontal vorticity.