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本文大用多普勒雷达垂直探测的速度估测大气垂直速度的方法－速度三阶中心短法（简称M3法）的基础上，利用雨滴谱资料，分析了降水粒子的最大直径Dmax对M3法的影响，并从实际工作出发，用反射率因子和多普勒谱宽拟合了Dmax和雨强（I),提高了大气垂直速度的估计精度。 相似文献
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An analysis of wind tunnel data of dispersion from elevated point sources over a flat floor and gently sloping, 2-D hills is performed. (The data were obtained by Khurshudyan et al., 1981.) Formulas for the mixing lengths and the Lagrangian time scales are tested, suitable for use in various dispersion models. Some expressions for the vertical first moments of the plume concentration distribution suitable for shear flow (Hunt, 1985) are also tested.Then, a normalization is suggested, based on the source mean flow and turbulence parameters, for the ground-level concentration maximum value and position along the plume centerline. Using this normalization, the maximum position is almost constant, regardless of source height variation and of whether the hill is present or not, at least for source positions upstream or over the top.The maximum values allow the determination of normalized terrain amplification factors TAFN, which are shown to be in most cases closer to one than the corresponding TAF obtained without normalization. 相似文献
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在区域酸沉积模式(RADM)基础上,设计了一个高分辨对流层(TL)物质交换模式(EM3)。EM3在以下五个方面明显不同于RADM:第一,增加行星边界层(PBL)的垂直网格层次;第二、TL内考虑分层的垂直涡旋扩散系数型;第三,使用TL内分层的水平涡旋扩散系数型;第四,采用包含有植物冠层垂直结构影响的新干沉积速度型;第五,使用数值扩散小的二阶矩守恒平流格式.用EM3和RADM对OSCAR Ⅳ实例作对比模拟,结果表明EM3能更好地预测出TL内的三维物质分布规律,在同样条件下,两模式预测的PBL低层中心浓度比值均大于1.8,最大值可大于3。 相似文献
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Weihua CHEN Weiwen WANG Shiguo JIA Jingying MAO Fenghua YAN Lianming ZHENG Yongkang WU Xingteng ZHANG Yutong DONG Lingbin KONG Buqing ZHONG Ming CHANG Min SHAO Xuemei WANG 《大气科学进展》2022,39(3):403-414
China experienced worsening ground-level ozone(O2) pollution from 2013 to 2019. In this study, meteorological parameters, including surface temperature(T2), solar radiation(SW), and wind speed(WS), were classified into two aspects,(1) Photochemical Reaction Condition(PRC = T2× SW) and(2) Physical Dispersion Capacity(PDC = WS). In this way, a Meteorology Synthetic Index(MSI = PRC/PDC) was developed for the quantification of meteorology-induced ground-level O2pollution. The positive linear relationship between the 90 th percentile of MDA8(maximum daily 8-h average) O2concentration and MSI determined that the contribution of meteorological changes to ground-level O-3 varied on a latitudinal gradient, decreasing from ~40% in southern China to 10%–20% in northern China. Favorable photochemical reaction conditions were more important for ground-level O2pollution. This study proposes a universally applicable index for fast diagnosis of meteorological roles in ground-level O2variability, which enables the assessment of the observed effects of precursor emissions reductions that can be used for designing future control policies. 相似文献
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采用与实测较接近的二次函数来表达Ｅｋｍａｎ层中的湍流粘性系数Ｋ，在圆形气压场条件下，求得了山地上空边界层中的风速，进而求得散度、涡度和垂直速度等场变量随高度的分布。并作图分析了这些场变量的一些动力学特征。改进了以往在求解析解时，略去运动方程中湍流粘性力项中的关于高度的一阶导数项，以及取山坡面上风速为零作下边界条件等欠合理欠精确的做法。所求得的风速、散度、涡度和垂直速度均用简单的初等函数表示出来，有助于边界层参数化和深化对边界层动力学的认识。 相似文献
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Eddy-correlation measurements over snow, wet bare soil, and lake water indicate very small vertical ozone fluxes. Adjustments to the small vertical fluxes are needed to take into account the effect of mean Stefan flow associated with evaporation at the surface and the effects of correlation between density variations and vertical wind fluctuations. For snow, the residual resistance calculated for the surface is about 34 s cm-1, indicating that the maximum deposition velocity is abut 0.03 cm s-1. For cold bare soil well saturated with water, the surface resistance is about 10 s cm-1 (maximum deposition velocity of about 0.1 cm s-1). The highest resistances obtained are for transfer to the surface of Lake Michigan, yielding values near 90 s cm-1 for resistance (0.01 cm s-1 for deposition velocity).Work supported by the U.S. Dept. of Energy and the U.S. Environmental Protection Agency. 相似文献
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气溶胶对台风“天兔”中闪电的影响 总被引：1，自引：2，他引：1
运用WRF模式配合对气溶胶更敏感的F-SBM微物理方案以及LPI闪电参数化方案对台风“天兔”进行模拟,通过改变F-SBM微物理方案中的云凝结核浓度得到不同气溶胶浓度下“天兔”中水凝物和闪电的分布情况,并从微物理过程出发讨论了气溶胶浓度对“天兔”中闪电的影响。WWLLN观测数据显示,“天兔”中的闪电主要呈现三圈分布,且“天兔”眼壁区闪电的爆发现象发生在其迅速加强阶段。对比发现,LPI指数与WWLLN观测实况的闪电分布形状有较好的对应,并且描绘出“天兔”中闪电的发展变化情况。通过气溶胶敏感性试验发现,随着气溶胶浓度的增加,“天兔”中过冷水含量及霰粒子浓度增加,垂直运动整体增强,为闪电的生成提供有利条件,此时LPI指数分布更加密集,强度增强。而冰晶粒子浓度始终较低,可初步推断“天兔”中闪电主要由霰粒子与雪粒子的非感应起电产生 相似文献
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A large-eddy simulation (LES) with a one-equation subgrid-scale (SGS) model was developed to investigate the flow field and
pollutant dispersion inside street canyons of high aspect ratio (AR). A 1/7th power-law wall model was implemented near rigid
walls to mitigate the demanding near-wall resolution requirements in LES. This LES model had been extensively validated against
experimental results for street canyons of AR = 1 and 2 before it was applied to the cases of AR = 3 and 5. A ground-level
passive pollutant line source, located in the middle of the street, was used to simulate vehicular emissions. Three and five
vertically aligned primary recirculations were developed in the street canyons of AR 3 and 5, respectively. The ground-level
mean wind speed was less than 0.5% of the free stream value, which makes it difficult for the pollutant to be transported
upward for removal. High pollutant concentration and variance were found near the buildings where the air flow is upwards.
It was found that the velocity fluctuation, pollutant concentration and variance were all closely related to the interactions
between the primary recirculations and/or the free surface layer. Several quantities, which are non-linear functions of AR,
were introduced to quantify the air quality in street canyons of different configurations. 相似文献
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不同垂直坐标系对垂直速度计算的影响 总被引：6，自引：2，他引：4
近年来,随着高精度中尺度数值预报模式和多尺度统一模式的发展,与之相关的一些非静力中尺度模式技术也随之提了出来,垂直坐标系的影响问题就是其中之一。本文借助于高精度美国新一代数值预报模式WRF(Weather Reseach and Forecast),模拟分析了两种不同的坐标系对模式大气中垂直速度计算的影响。试验结果表明,不同的坐标系对大气垂直速度大小计算存在着差异,特别是当分辨率提高时,不同垂直坐标系对大气垂直结构的刻画的差别更加明显。由于垂直速度与降雨过程密切相关,垂直速度的计算差异必然影响模式对降雨过程的描述。理想试验结果表明,在气压地形追随坐标中气压梯度力的计算对地表气压计算很敏感。 相似文献
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IMPACT STUDY ON THE CALCULATION OF VERTICAL VELOCITY IN DIFFERENT VERTICAL COORDINATE SYSTEMS 总被引：1，自引：1，他引：0
1 INTRODUCTION First, let’s have a review of various vertical coordinate systems used in numerical weather prediction (NWP). Richardson[1] (1922) first attempted to use the geometrical height z as the vertical coordinate system. Though geometrical height is easy to understand as a concept, it had not been applied in NWP until Kasahara and Washington (1967) rewrote his predictive equations and used state-of-the-art high-speed computers to conduct NWP in height coordinates. Eliassen[2]… 相似文献
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Summary The effects of atmospheric boundary-layer stability on urban heat island-induced circulation are numerically and theoretically
investigated using a nonlinear numerical model (ARPS) and a two-layer linear analytical model. Numerical model simulations
show that as the boundary layer becomes less stable, a downwind updraft cell induced by the urban heat island strengthens.
It is also shown that as the boundary layer becomes less stable, both the height of the maximum updraft velocity and the vertical
extent of the downwind updraft cell increase. Hence, in the daytime with a nearly neutral or less stable boundary layer the
urban heat island-induced circulation can become strong, even though the urban heat island is weak. It is suggested that these
findings can be a mechanism for urban-induced thunderstorms observed in the late afternoon or evening with a nearly neutral
or less stable boundary layer. The boundary-layer stability affects the spatial distribution of scalar concentration through
its influencing urban heat island-induced circulation. Analytical results from a two-layer model with different boundary-layer
stabilities in the lower and upper layers are in general qualitatively consistent with the numerical simulation results, although
the low-level maximum vertical velocity does not change monotonically with lower-layer stability. 相似文献
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P. K. Misra 《Boundary-Layer Meteorology》1980,19(4):501-507
This paper describes the verification of a dispersion model for a shoreline environment developed by the author in an earlier paper. It is shown that the observed concentration field reported in a case study agrees well with model predictions. Emphasis has been given to verification of the location of the maximum ground-level concentration and the downwind trend of the concentration field. This is because time-averaged concentrations are dependent on averaging time. Since a model generally predicts ensemble average concentrations which may not be achieved within half-hour periods within a convective boundary layer, numerical comparisons may not be very meaningful. Nevertheless, good agreement is found for the case study under consideration. 相似文献
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Characteristics of vertical turbulent velocities in the urban convective boundary layer 总被引：3，自引：0，他引：3
James M. Godowitch 《Boundary-Layer Meteorology》1986,35(4):387-407
Turbulence measurements of the vertical velocity component were obtained by an instrumented aircraft under fair weather conditions in the St. Louis, Missouri, metropolitan area. Time series of vertical velocity fluctuations from horizontal flight segments made in the lower part of and near the middle of the convective boundary layer (CBL) over the urban area and surrounding region were subjected to various statistical and objective analyses. Higher order vertical velocity moments, and positive and negative velocity statistics, were computed. The horizontal dimensions of updrafts and downdrafts, and related properties of these turbulent eddies were derived by conditional sampling analysis. Emphasis is on a comparison of the results from urban and selected rural measurements from the lower part of the CBL.The vertical velocity probability density distribution for each segment was positively skewed and the mode was negative. The means and standard deviations of positive and negative velocity fluctuations were greater over the urban area. The urban vertical velocity variance was 50% greater than rural values, and power spectra revealed greater production of vertical turbulent energy in the urban area over a wide frequency range.The mean and maximum widths of downdrafts were generally larger than the corresponding values for updrafts. Differences between urban and rural eddy sizes were not statistically significant. The widths of the largest updraft and downdraft are comparable to the boundary-layer depth, Z
i, and the mean value of the ratio of spectral peak wavelength to Z
iwas about 1.3 and 1.1 for urban and rural areas, respectively. Convective similarity scaling parameters appeared to order both the urban and rural measurements.On assignment from the National Oceanic and Atmospheric Administration, U.S. Dept. of Commerce. 相似文献
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It has been proved that there exists a cross coupling
between vertical heat turbulent transport and vertical velocity by
using linear thermodynamics. This result asserts that the vertical
component of heat turbulent transport flux is composed of both the
transport of the vertical potential temperature gradient and the
coupling transport of the vertical velocity. In this paper, the
coupling effect of vertical velocity on vertical heat turbulent
transportation is validated by using observed data from the
atmospheric boundary layer to determine cross coupling coefficients,
and a series of significant properties of turbulent transportation
are opened out. These properties indicate that the cross coupling
coefficient is a logarithm function of the dimensionless vertical
velocity and dimensionless height, and is not only related to the
friction velocity u*, but also to the coupling roughness
height zW0 and the coupling temperature TW0 of the
vertical velocity. In addition, the function relations suggest that
only when the vertical velocity magnitude conforms to the limitation
|W/u*|≠1, and is above the level zW0, then the
vertical velocity leads to the cross coupling effect on the vertical
heat turbulent transport flux. The cross coupling theory and
experimental results provide a challenge to the traditional
turbulent K closure theory and the Monin-Obukhov similarity
theory. 相似文献
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A stochastic model of particle dispersion in the atmosphere 总被引：2，自引：0，他引：2
Stochastic models of turbulent atmospheric dispersion treat either the particle displacement or particle velocity as a continuous time Markov process. An analysis of these processes using stochastic differential equation theory shows that previous particle displacement models have not correctly simulated cases in which the diffusivity is a function of vertical position. A properly formulated Markov displacement model which includes a time-dependent settling velocity, deposition and a method to simulate boundary conditions in which the flux is proportional to the concentration is presented. An estimator to calculate the mean concentration from the particle positions is also introduced. In addition, we demonstrate that for constant coefficients both the velocity and displacement models describe the same random process, but on two different time scales. The stochastic model was verified by comparison with analytical solutions of the atmospheric dispersion problem. The Monte Carlo results are in close agreement with these solutions.This work partially performed at Sandia National Laboratories supported by the U.S. Department of Energy under contract number DE-AC04-76DP00789. 相似文献
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Renellys C. Perez Verena Hormann Rick Lumpkin Peter Brandt William E. Johns Fabrice Hernandez Claudia Schmid Bernard Bourlès 《Climate Dynamics》2014,43(11):2943-2962
Ship-based acoustic Doppler current profiler (ADCP) velocity measurements collected by several major field programs in the tropical Atlantic are averaged and combined with estimates of the mean near-surface velocity derived from drifters and Argo float surface drifts (ADCP+D) to describe the mean cross-equatorial and vertical structure of the meridional currents along 23°W and 10°W. Data from moored ADCPs and fixed-depth current meters, a satellite-derived velocity product, and a global ocean reanalysis were additionally used to evaluate the mean ADCP+D meridional velocity. The dominant circulation features in the long-term mean ADCP+D meridional velocity in the upper 100 m are the tropical cells (TCs) located approximately between 5°S and 5°N, with near-surface poleward flow and subsurface equatorward flow that is stronger and shallower in the northern cell compared to the southern cell. The thickness of the surface limb of the TCs decreases and the northern cell is found to shift further south of the equator from the central to eastern tropical Atlantic. Analysis of two-season means estimated from the ship-based ADCP, near-surface drift, and moored velocity data, as well as the simulated fields, indicates that the maximum poleward velocity in the surface limb of the TCs intensifies during December–May along 23°W largely due to seasonal compensation between the geostrophic and ageostrophic (or wind-driven) components of the meridional velocity, whereas the maximum equatorward flow in the subsurface limb of the northern cell intensifies during June–November along both 23°W and 10°W due to the seasonality of the geostrophic meridional velocity. 相似文献