共查询到19条相似文献，搜索用时 0 毫秒
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本文运用相似理论,在物理分析的基础上试图从统一的观点来讨论不同温度层结下的湍流运动。由强迫对流到自由对流的过渡趋势假定是连续的,对极端稳定层结时湍流运动的特点提出了看法。选取了符合物理分析所要求的通用函数的形式,设法确定了其中的参数的值,并进而建立了根据梯度观测资料计算湍流系数及各种湍流输送通量的公式及图表,并用不同资料进行了检验。 相似文献
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利用三维大涡模拟模式研究不同地面热力状况和风切变对湍流产生的影响，在对流层湍流发展过程中，这两种作用是同时存在的、同时起作用，水平风速的瞬时垂直切变可以在自由大气中激发湍流，但它不能维持很长时间，对流热泡也可以在自由大气中激发湍流，其湍流强度与地面的热量强度有关。 相似文献
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本文第一部分运用相似理論和因次分析对层結大气近地面层中湍流交換的問題作了分析,获得了与作者过去根据湍流能量平衡方程所得到的結果一致.第二部分根据新近国外发表的直接測量资料确定了普遍函数中的經驗系数D的大小;还确立了强迫对流向自由对流状态的过渡,与Priestley所指出的不同,它具有极平緩的性貭,計算結果与观測事实符合.在稳定情况下則沒有类似过渡发生.第三部分根据因次分析构成了特征尺度L_(R_i),并建立了以L_(R_i)为特征尺度的湍流交換的模式.討論結果表明,采用这一模式比前一模式合理一些,而且实用上更为方便。 相似文献
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Hu Yinqiao 《大气科学进展》2002,19(5):767-776
将边界层相似性理论同线性热力学理论结合，间接地以观测实验事实证明大气边界层内线性唯象关系是成立的，而且线性湍流输送系数同相应的线性唯象系数成正比关系。但实验事实表明，大涡对流的混合层线性唯象系数成正比关系。但实验事实表明，大涡对流的混合层线性唯象关系是不成立的，混合层内湍流输送过程是一种强的非线性过程。所以，对流边界层是一种远离平衡态非线性区的热力学状态。地转风和热成风是一种大气系统特有的动力过程和热力过程和交叉耦合现象，这是大气系统交叉耦合现象的一个实际例证。 相似文献
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利用大涡模式模拟了对流边界层结构演变以及深对流触发过程。通过改变鲍恩比的敏感性试验研究不同大气初始状况下湿润和干旱下垫面湍流特征及其对深对流触发过程的影响。结果表明:干旱下垫面的混合层干而暖,厚度较大;湿润下垫面相反。由于地表感热通量对热力湍流形成的作用更大,干旱下垫面上湍流混合和夹卷作用更强,使得水汽和相当位温在边界层内分布更均一,而在边界层顶有较大的负扰动;干旱下垫面上对流强度较湿润下垫面大,但均表现为泡状对流,水平方向上呈网状结构。不同下垫面上深对流的发生与大气初始状况有关,当初始时刻1—3 km的逆温强度较弱时（0.15 K/（100 m））,边界层内湍流迅速发展,深对流首先在干旱下垫面发生,但因对流有效位能较小,云层厚度小于湿润下垫面。当1—3 km的逆温强度增加到0.55 K/（100 m）时,云层形成时间较晚,云层厚度明显减小,仅当边界层顶的比湿较大时,有深对流发生,但仍首先发生在干旱下垫面,考虑贯穿对流在边界层顶引起的较强冷却作用,云层厚度大于湿润下垫面。 相似文献
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用自由大气实际风速取代地转风,得到了非定常均匀条件下阻力定律和边界层内参数的一些性质及相似性函数Ａ、Ｂ的特性。该方法和结果可应用于大气模式中的边界层参数化以及与相似性函数有关的一些研究。 相似文献
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晴空湍流(Clear Air Turbnlence,以下简称CAT)是指出现在9千米以上高空、且与对流云无关的湍流。它排除了与对流性不稳定边界层及深厚对流有关的湍流,却并未排除非对流性云(多指卷云)中存在的湍流。因此,有人认为采用“急流湍流”或“高空湍流”,的术语似更合适。 相似文献
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Significant improvements are occurring in the representation of physical processes in atmospheric convection models. They should go along with parallel improvements in the parameterization of subgrid scale turbulent processes. This problem appears to be particularly delicate in the presence of clouds, due to the local release of latent heat.Two important points are the choice of adequate turbulent thermodynamic variables and of the method for truncating the statistical moment equations. These topics are discussed here within the framework of the three-dimensional convection model under development at the Laboratoire de Météorologie Dynamique. Assuming the need for at least a simplified second-order closure, two improvements are tested on a numerical simulation of the Porto Rico experiment conducted by the National Center for Atmospheric Research (U.S.A.) in 1972. They concern the use of a rate equation for sub-grid scale turbulent kinetic energy and of specific variables which are approximately conserved in the condensation process. 相似文献
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Martin Claussen 《Boundary-Layer Meteorology》1983,27(3):209-215
Malkus' theory of turbulent shear flow and turbulent convection is extended to stably stratified shear flow. The local Richardson number is found to be close to its critical value throughout the turbulent flow. Assuming a strong interaction between velocity and density fields requires that their profiles depend linearly on height. From this, for stratified shear flow at sufficiently high Reynolds numbers, a combination of logarithmic and linear profiles is expected. The purely linear and the log-linear profile are both observed in laboratory channel flow and in atmospheric boundary layer flow.Work undertaken while at the Department of Meteorology and Physical Oceanography, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. 相似文献
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日间对流边界层最显著的结构特征是在热力作用下所形成的组织化对流。与小尺度湍涡不同的是，组织化对流具有边界层尺度的垂直相干性，可实现垂直贯穿边界层的非局地物质和能量传输。本文针对对流边界层中的动量混合，探究组织化对流对动量输送的贡献。以高精度大涡模拟数据为研究资料，通过傅里叶变换、本征正交分解和经验模态分解3种滤波方法，分离组织化对流和背景湍涡，计算与两者相关的非局地和局地动量通量，发现与组织化对流相关的非局地动量通量是总通量的重要组成部分，并主导混合层中的垂直动量输送。而后，基于协谱和相位谱分析，探究组织化对流的空间结构对动量传输的影响，发现在热力主导的不稳定环境中，单体型环流结构对动量的传输效率较低。而在风切较强的近中性环境中，滚涡型组织化结构可使垂直和水平流向扰动速度的相位差减小，从而提升动量传输效率。研究结果表明，边界层方案需要包含非局地动量通量项，其参数化应考虑整体稳定度对传输效率的影响。 相似文献
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Tracer transport in the atmosphere is controlled not only by synoptic-scale to mesoscale weather disturbances but also by microscale boundary-layer processes especially under fair-weather conditions. The present study investigates numerically the diurnal variation of boundary-layer convection and cumulus clouds and their role in transporting tracers by conducting high-resolution simulations that explicitly resolve turbulent eddies. The transport of dust aerosols in a desert area under two distinct stability conditions is specifically examined. Convection plays a significant role in transporting dust upward; in other words, the vertical depth of the dust transport is critically determined by the depth of convection. Deep convection is effective in transporting dust into the free atmosphere. The early morning stratification strongly regulates the temporal evolution and the vertical growth of convection and therefore the amount of tracer emission and transport. A sensitivity to model resolution of O (1 km) in a cloud-resolving simulation range is also examined. A proper parameterization for activating microscale convection is required for representing the diurnal variation of convection and tracer transport. 相似文献
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A method for calculating turbulent diffusion in the planetary boundary layer is developed based on Donaldson's second-order closure approach. The resulting partial differential equation for the turbulent mass flux has a hyperbolic character for early times when the plume scale is small compared with the ambient turbulent scale, with a smooth transition to a parabolic, gradient-diffusion-type character when the plume scale is large. Calculations are compared with available estimates from the literature for different values of Rossby number and Richardson number in the ambient atmosphere. Comparison of model predictions with laboratory simulation of diffusion in a free convection, mixed layer is good, with the model able to predict the maximum concentration rising from the ground as observed.This project has been funded in part with Federal funds from the Environmental Protection Agency under contract number EPA 68-02-1310. 相似文献
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M. J. Manton 《Boundary-Layer Meteorology》1980,19(3):337-358
A boundary-layer model, which incorporates an eddy diffusivity for turbulent transports, is presented. It is shown that this model can predict the appropriate behaviour for mixed layers produced by surface shear, free convection and mechanical mixing. The model is used to consider the development of cumulus clouds, which are shown generally to be convectively unstable at cloud top. Thus the entrainment of dry air leads to a very low cloud-water content in cumulus cloud. 相似文献
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陆气相互作用对中尺度对流系统影响的研究进展 总被引：1，自引：1，他引：0
文章回顾了大气对地表性质的敏感性研究,以及陆气相互作用对中尺度天气过程的影响,说明了地表性质与积云对流及对流降水之间的联系。地表性质的改变对行星边界层的热通量、水汽通量、对流有效位能产生影响,并通过湍流的垂直输送,进而影响到其上大气的性质。陆气之间存在着复杂的、非线性的相互作用。性质不均匀的下垫面造成地表向大气感热通量和潜热通量的差异,从而在近地层大气中形成温度和气压梯度,产生局地环流,在条件适合的情况下可以形成对流,并产生降水,而降水的不均匀分布,又维持了下垫面的不均匀性。土壤湿度对对流的影响受到多个因素的制约,其中天气尺度过程的影响是很显著的;由非均匀的下垫面所产生的局地环流能够触发积云对流。 相似文献
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J. A. Businger 《Boundary-Layer Meteorology》1973,4(1-4):323-326
The limiting condition of µ*, 0 in the unstable atmospheric boundary layer is usually referred to as free convection. Some of the similarity laws that are proposed for this condition do not agree with experiment. A mechanism is proposed in this paper to show why the asymptotic free convection condition is never completely reached near the surface. It is shown that local turbulent shear production plays an important role in shaping the temperature profile even when the average velocity is zero.Contribution No. 267, Dept. of Atmospheric Sciences, University of Washington. 相似文献
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H. L. Kuo 《Boundary-Layer Meteorology》1979,17(1):29-39
Previous theoretical and observational investigations have shown that vertical plumes are formed in the high Rayleigh number convection field over heated horizontal surfaces and that these plumes become unsteady and turbulent when the Rayleigh number is higher than about 20 times its critical value R
c. Based on these results, we conclude that the dissipation of kinetic energy takes place mainly in the surface boundary layer in high Rayleigh number laminar convection and mainly in the vertical plumes in turbulent convection, while the conversion of eddy potential energy into kinetic energy is accomplished mainly in the well-mixed main body of the fluid. On making use of these rather general conclusions concerning the kinetic energy generation and dissipation processes in the energy integrals, we are able to derive the well known 5/4 and 4/3 power laws of upward heat transfer by laminar and turbulent convections theoretically. 相似文献