海上风的边界层模式

由于航海、海上开发作业等对海洋上风和海浪的预报提出越来越高的要求,而海浪、风暴潮等海洋水文要素的数值计算和预报,迫切需要解决海洋上风场的精确计算。但是,复杂的海面结构,大气稳定度的影响以及风、浪之间动量的交换等,使海上风的理论计算遇到很多困难,至今大部分工作是依靠统计方法。利用天气预报的形势场计算地转风或梯度风,以及它与海面摩擦、大气稳定度的经验订正关系。     

Effect of air-sea temperature difference on the momentum exchange between air and sea for fetch-limited cases

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Numerical modeling of hydrophysical fields of the Black Sea under the conditions of alternation of atmospheric circulation processes

The hydrological regime of the Black Sea in the conditions of permanent alternation of atmospheric circulation processes was investigated on the basis of a baroclinic prognostic model of the sea dynamics. In the model, variations in the wind action were expressed as permanent alternation of 24 wind types characteristic of the Black Sea basin throughout the year. Thermohaline impact of the atmosphere was taken into account by specifying the annual trends of temperature and salinity at the sea surface, which was established from multiyear means of these parameters. The problem was solved numerically on the basis of the method of two-cycle splitting with the use of the grid with a horizontal spacing of 5 km. Results of the numerical experiment showed that, under the influence of a strong nonstationarity of atmospheric processes, the water circulation in the upper layer of the Black Sea changes qualitatively and quantitatively. The upper 20–30-m layer of the sea is particularly sensitive to atmospheric circulation variations. For any character of atmospheric circulation, the Black Sea circulation below this layer is nearly always cyclonic with internal cyclonic rotations.     

海面状态参数化对海上大气边界层数值模拟的影响研究

由于海上大气边界层的下垫面是复杂多变的海面,因此海面状态的参数化对海上大气边界层数值模拟起到十分关键的作用.采用高分辨率的大气边界层模式进行敏感性试验研究,讨论了不同海面参数化方案对海上大气边界层数值模拟产生的影响.结果表明:几种海面粗糙度参数化方案在中低风速下模拟垂直结构主要的差异出现在边界层和自由大气分界面上;考虑...     

Wave-tide-surge coupled simulation for typhoon Maemi

The main task of this study focuses on studying the effect of wave-current interaction on currents, storm surge and wind wave as well as effects of current induced wave refraction and current on waves by using numerical models which consider the bottom boundary layer and sea surface roughness parameter for shallow and smooth bed area around Korean Peninsula. The coupled system (unstructured-mesh SWAN wave and ADCIRC) run on the same unstructured mesh. This identical and homogeneous mesh allows the physics of wave-circulation interactions to be correctly resolved in both models. The unstructured mesh can be applied to a large domain allowing all energy from deep to shallow waters to be seamlessly followed. There is no nesting or overlapping of structured wave meshes, and no interpolation is required. In response to typhoon Maemi (2003), all model components were validated independently, and shown to provide a faithful representation of the system’s response to this storm. The waves and storm surge were allowed to develop on the continental shelf and interact with the complex nearshore environment. The resulting modeling system can be used extensively for prediction of the typhoon surge. The result show that it is important to incorporate the wave-current interaction effect into coastal area in the wave-tide-surge coupled model. At the same time, it should consider effects of depth-induced wave breaking, wind field, currents and sea surface elevation in prediction of waves. Specially, we found that: (1) wave radiation stress enhanced the current and surge elevation otherwise wave enhanced nonlinear bottom boundary layer decreased that, (2) wind wave was significantly controlled by sea surface roughness thus we cautiously took the experimental expression. The resulting modeling system can be used for hindcasting (prediction) the wave-tide-surge coupled environments at complex coastline, shallow water and fine sediment area like areas around Korean Peninsula.     

海浪搅拌混合对北太平洋海表面温度模拟的影响

利用NCEP再分析风场驱动WAVEWATCH III海浪模式对北太平洋海域的海浪过程进行模拟,利用浮标观测资料对模拟出的海浪要素有效波高进行验证,发现他们之间具有很好的一致性。基于模式输出的有效波高等波浪要素,利用特征波参数化理论,在海洋环流模式中引入海浪搅拌混合作用,分析其对北太平洋海表面温度模拟的影响,初步数值模拟结果表明,sbPOM模式在考虑海浪搅拌混合作用以后,模拟精度进一步提升,这对提供一个准确的大气模式下边界条件具有重要作用。     

高海况海洋遥感信息提取技术研究进展

中等海况下,星载合成孔径雷达(Synthetic Aperture Radar,SAR)已经广泛应用于海洋动力环境要素的监测(风场、波浪、流场)。近年来,SAR高海况遥感,尤其是探测台风海面风场、巨浪、流场已经成为国内外研究热点,并突破了一些关键技术。利用SAR多极化成像模式对海观测和新发展的地球物理模式函数,可以提取高海况下的海面风速、风向、有效波高、流速和流向等海洋表面关键物理参数。这些环境要素可以用于海洋灾害监测预警;为海洋和大气数值模式提供准确的初始场和同化源,改进模式预报精度;为研究全球气候变化提供有力的观测依据。     

海—气相互作用与海流、风暴潮

从方法论上说,除潮汐以外,通常在处理海洋动力学问题时,大多撇开海洋对大气的影响,强调大气对海洋的主导作用,把大气运动当作诱发海水运动的唯一原动力,视海面风场为给定条件,而后用经验或半经验公式算出海面风应力场,作为施加于海水的强迫力。因此,一个成功的海浪、海流或风暴潮的预报,除了具备反映海水运动的主要物理性能的数学模型外,还必须以客观的、准确的海面风场的数值计算和预报为前提。由于问题的复杂性,迄今为止似乎还不能说在实用上已经提供了海面风的一种足够精确的估算或预报方法。海上气象观测资料,尤其是测风资料的稀少,给海面风应力的实际计算带来不少困难。     

The concentration and distribution of dimethyl sulfide in the marine atmospheric boundary layer near the equator

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Atmospheric frontal gravity waves observed in satellite SAR images of the Bohai Sea and Huanghai Sea

In the satellite synthetic aperture radar (SAR) images of the Bohai Sea and Huanghai Sea, the authors observe sea surface imprints of wave-like patterns with an average wavelength of 3.8 km. Comparing SAR observations with sea surface wind fields and surface weather maps, the authors find that the occurrence of the wave-like phenomena is associated with the passing of atmospheric front. The authors define the waves as atmospheric frontal gravity waves. The dynamical parameters of the wave packets are derived from statistics of 9 satellite SAR images obtained from 2002 to 2008. A two-dimensional linear physical wave model is used to analyze the generation mechanism of the waves. The atmospheric frontal wave induced wind variation across the frontal wave packet is compared with wind retrievals from the SAR images. The CMOD-5 (C-band scatterometer ocean geophysical model function) is used for SAR wind retrievals VV (transmitted vertical and received vertical) for ENVISAT and HH (transmitted horizontally and received horizontally) for RADARSAT-1. A reasonable agreement between the analytical solution and the SAR observation is reached. This new SAR frontal wave observation adds to the school of SAR observations of sea surface imprints of AGWs including island lee waves, coastal lee waves, and upstream Atmospheric Gravity Waves (AGW).     

A simplified model for the transformation of the atmospheric planetary boundary layer overlying a thermal front in the sea

This paper discusses a simplified model for the evolution of the atmospheric planetary boundary layer overlying a thermal front in the sea. The model provides local values of the friction/heat transfer geostrophic coefficients and the direction of surface wind stress, as well as the wind/temperature profiles at any point on the front. With the running over a warm front, the baroclinicity of the internal boundary layer leads to the generation of a near-surface current of air directed down the front. The model can be used to interpret radar imagery of the sea surface with the purpose of determining its mesoscale variability. Translated by Vladimir A. Puchkin.     

简单海-气边界层模式中的埃克曼流动Ⅰ——无限深海的情形

近十余年来,海洋和大气相互作用这一课题日益受到人们的关注。从海-气边界层结构以及通过海面的物理量和化学量输送机制的研究到大尺度海洋和大气相互作用的研究都取得了可喜的成果。此外,还从海洋和大气相互作用的观点探索了风暴潮预报的新的可能途径[2]。然而,由于问题的复杂性,通过海面以及海-气边界层的物理量的小尺度输送机制迄未得到澄清,企图从本质上改善大尺度海洋和大气相互作用的理论是不现实的。     

风浪和海洋飞沫对海表面拖曳系数和风廓线的影响

基于埃克曼理论,本文将波致应力和飞沫应力引入到海-气边界层的界面应力中,来研究海表面风浪和海洋飞沫对海-气边界层动量交换的影响,并得到修改后的埃克曼模型的理论解。波致应力是由风浪谱和波增长函数估计,并得到在中低风速下,波致应力、飞沫应力与湍流应力相比,对海表面拖曳系数和风廓线的影响非常小。当风速高于25米/秒时,海洋飞沫通过飞沫应力对海-气界面应力的作用远高于波致应力,以至于波致应力可以忽略。海表面拖曳系数在高风速下,随着风速的增大而减小。通过采用风浪谱的不同波龄,得到海洋飞沫的产生会导致海-气边界层风速的增加。最后,理论解与现场的观察数据进行了对比。对比后的数据表明,在中高风速下,飞沫对海-气边界层的影响远大于表面风浪。     

有限区域海面风场数值模式的建立

目前,国内外大尺度天气预报数值模式已经取得很大成就,如在预报地面气旋系统的移动和发展等方面。然而,这些模式的铅直分辨率一般不高,通常不包括边界层的动力过程,因而,在预报海面风场上,数值天气预报模式还没有令人满意的效果。目前所用的边界层预报模式尽管具有较高的水平分辨率和垂直分辨率,但要求大量的计算和资料,很难用于日常业务预报;另一种边界层诊断模式,用到的风场数据是气象工作者从天气形势(大尺度)分析中,通过差值等方法获得的,缺乏针对性,而且精度较低(WMO,1988;WMO,1990)。 作者认为,适于海洋要素预报的风场模式应是定位于有限区域,或称中尺度模式,并根据台站的具体资料来源和工作状况力争建立一套适于海洋要素预报的中尺度风场数值模式。鉴于以上,作者建立了一个适于海洋要素预报的有限区域海面风场数值模式。模式采用符合动力及热力学条件的简化方程组对大尺度风场进行加密,通过数值模拟得到适于海洋要素预报的有限区域海面风场。并将该模式运用于渤海这一有限区域,获得了良好的效果,说明该模式对海洋要素预报具有很好的应用前景。     

The atmospheric hinder for intraseasonal sea-air interaction over the Bay of Bengal during Indian summer monsoon in CMIP6

The surroundings of the Bay of Bengal (BoB) suffer a lot from the extreme rainfall events during Indian summer monsoon (ISM). Previous studies have proved that the sea-air interaction is an important factor for the monsoonal precipitation. Using the 6th Coupled Modol Inter-comparison Project (CMIP6) models, this study examined the biases of surface heat flux, which is the main connection between atmosphere and ocean. Results show that although CMIP6 have a better simulation of intraseasonal sea surface temperature (SST) anomalies over BoB than the previous ones, the “atmospheric blockage” still delays the response of latent heat flux to the oceanic forcing. Specifically, during the increment of positive latent heat flux in CMIP6, the negative contribution from wind effects covers most of the positive contribution from humidity effects, due to the underestimate of humidity effects. Further diagnostic analysis denote that the surface air humidity has a quarter of a phase ahead of warm SST in observation, but gets wet along with the warm SST accordingly in most CMIP6 models. As a result, the simulated transfer of intraseasonal moisture flux is hindered between ocean and atmosphere. Therefore, as a bridge between both sides, the atmospheric boundary layer is essential for a better sea-air coupled simulation, especially when the atmospheric and the oceanic variabilities involved in a climate model becomes increasingly sophisticated. The surface air humidity and boundary layer processes require more attention as well as better simulations.     

The role of surface waves in the ocean mixed layer

Previously, most ocean circulation models have overlooked the role of the surface waves. As a result, these models have produced insufficient vertical mixing, with an under - prediction of the ,nixing layer （ML） depth and an over - prediction of the sea surface temperature （SST）, particularly during the summer season. As the ocean surface layer determines the lower boundary conditions of the atmosphere, this deficiency has severely limited the performance of the coupled ocean - atmospheric models and hence the climate studies. To overcome this shortcoming, a new parameterization for the wave effects in the ML model that will correct this systematic error of insufficient mixing. The new scheme has enabled the mixing layer to deepen, the surface excessive heating to be corrected, and an excellent agreement with observed global climatologic data. The study indicates that the surface waves are essential for ML formation, and that they are the primer drivers of the upper ocean dynamics; therefore, they are critical for climate studies.     

Fine structure of the turbulent atmospheric boundary layer over the water surface

In this paper, the results of a laboratory experiment on investigating the wind-velocity field over a water surface using the PIV method are described. The use of a rapid CCD-camera made it possible to perform a detailed study of the eddy structure of airflow. We have measured the velocity fields over a flat plate by wind waves and waves induced by a wave generator. The model of a turbulent boundary layer over a rough surface was directly verified. It has been shown that the wind-velocity profiles over waves obtained by averaging the instantaneous fields over the ensemble of samples and horizontal coordinate are satisfactorily consistent with the profiles calculated within the frameworks of the model of wind flow over rough water surface.     

Modeling a neutrally stratified turbulent air flow over a horizontal rough surface

The neutrally stratified boundary layer over a smooth rough surface is consider. The turbulent flow is simulated using a finite-difference eddy-resolving model of the atmospheric boundary layer (ABL). The model includes different turbulence closure schemes and numerical approximations for advection components of the momentum balance equation. We investigate the quality of reproduction of spectral characteristics of the turbulent flow and the model’s capabilities to reproduce the observed profile of mean wind velocity near the rough surface. It is shown that the best result is obtained by coupling a numerical scheme of higher order of accuracy with a mixed closure scheme based on an adaptive estimation of the mixing length for subgrid-scale fluctuations. Here, we are able to reproduce the asymptotics of the fluctuation spectrum of the longitudinal component of wind velocity near the surface and within the boundary layer as well as the logarithmic profile of mean velocity near the surface.     

Measurements of the atmospheric turbulence in the coastal zone of the sea during weak wind from a mountainous coast

Results of measurements of the atmospheric turbulence in the layer between 1.5 and 21 m above sea level and the drag coefficient of the sea surface as the wind blows from a 4-km-long mountainous slope with a mean inclination of 11° are presented. The measurements of wind-speed profiles and its fluctuations at several levels, waves, and the main meteorological parameters were carried out in autumn 2005 and 2008 from a stationary platform located in the Black Sea at a distance of approximately 1 km from the southern coast of Crimea. It is shown that during weak synoptic wind a low-level wind jet develops at night over the sea with a maximum velocity up to 5–6 m/s at a level of approximately 6 m over the sea induced by the katabatic wind over the coastal slope. According to the approximate estimates, the horizontal scale of the low-level jet can reach a few tens of kilometers. This flow is characterized by the dissipation rate of the turbulence energy independent of height and low-frequency velocity fluctuations related to the gravity waves and advection of turbulence from the coast. It is shown that the lower part of the boundary layer (up to a height of 3 m) is adjusted to the sea-surface roughness. The dependencies of the drag coefficient on the wind speed or wave age are steadier than in the data for the open sea. However, the age of the waves is not a universal parameter at long and short fetches.     

2016年苏北近海风场和波浪场多时间尺度变化的数值模拟研究

利用高分辨率的大气和波浪数值模式,模拟了2016年苏北近海的风场和波浪场,并与卫星高度计资料、散射计风场、再分析资料以及实测浮标资料进行了比较,验证了模式的准确性。基于这套模式结果,系统地分析了江苏近海的风场和波浪场的多时间尺度变化:季节变化、日变化以及季节内变化(台风、寒潮)。分析结果表明:苏北近海海域的风速、有效波高和涌浪在冬季和秋季较大、春季和夏季较小;冬季盛行西北风,常浪向为西北向,夏季盛行东南风,常浪向为东南向。风场和波浪场还具有显著的日变化特征,且日变化存在季节变化规律,离岸越近海域日变化特征越明显。同时,江苏近海还会经历季节内尺度的强天气过程的影响,比如台风和寒潮。