A numerical study of the air flow within and around a single tree

A three-dimensional non-hydrostatic numerical model has been used to investigate the air flow and turbulence around a single tree.The results for velocity and turbulence distributions have been compared with available data from windtunnel experiments; the agreement is satisfactory.Simulations have been carried out for different meteorological conditions (wind speed, thermal stratification) as well as for different canopy characteristics (stem height, crown diameter, crown height, porosity).Dedicated to Prof. F. Wippermann on the occasion of his 65th birthday.     

荒漠绿洲边界层结构的数值模拟

陆-气相互作用和中小尺度天气系统的研究中,水平不均匀边界层和水平不均匀地表的强迫作用都是重要的物理过程.本文用已建立的陆面过程与大气边界层耦合模式(BLCM),较详细地研究了草地周围为荒漠(半沙漠)的地表植被不均匀而造成的边界层结构特征和局地环流及其昼夜变化.通过边界层顶影响自由大气不同尺度的运动.模式结果揭示出最强的上升和下沉运动是发生在荒漠-草地间动力和热力不连续的界面附近,且呈现出不对称性.     

An example of attenuation by wet snow on a radar dome

Abstract

A case study of the degradation of weather radar data by the accretion of wet snow on a radar dome is presented as a precautionary example to radar users. During the ERICA field program in 1989, accumulated precipitation on the radome at Halifax, Nova Scotia, attenuated signal in a distinctive, pie‐shaped sector on the upwind side of the radar.     

黄海夏季潮汐锋区环流的数值研究

基于Blumberg＆Mellor三维非线性环流模型(ECOM)并结合Mellor＆Yamada的湍封闭模型，对黄海M2分潮、密度环流、锋区环流等进行了的数值模拟：潮汐模拟结果较好的体现了黄、渤海M2潮波传播系统，验证了模型的可行性；模拟密度环流的量阶和方向均与夏季实测环流保持一致，体现了密度环流是夏季总环流的重要组成部分；两个断面锋区环流的模拟结果显示锋区位置不同环流特征也不相同，锋区对应的上升流特征与锋区表面通常观测到冷水现象吻合，锋区上层水体沿潮汐锋方向流速较强。另外，数值试验结果显示了地形和潮混合对潮汐锋的形成及锋区环流有重要影响。     

准后向散射对单点声雷达测量温度结构系数的影响

本文从湍流大气对声波散射方程出发,推导出静止大气和有水平运动两种情况下,有限接收面积上的平均准后向散射截面公式。从而分析了影响平均准后向散射截面的因子,同时还计算讨论了不同天线口径、风速和值的平均准后向散射截面。 计算结果表明:在一般情况下,边界层内用声雷达测得的温度结构系数[C_T~2(θ)]要比理论上纯后向温度结构系数[C_T~2(180°)]大些;C_T~2(θ)与C_T~2(180°)比值以及C_T~2(θ)随高度的变化都与天线口径、风速分布和m值等密切相关。因此对用不同声雷达在不同大气条件作对比测量,得到某些不一致的现象,可给予一定的解释。     

An example of fingerprint detection of greenhouse climate change

As an example of the technique of fingerprint detection of greenhouse climate change, a multivariate signal or fingerprint of the enhanced greenhouse effect is defined using the zonal mean atmospheric temperature change as a function of height and latitude between equilibrium climate model simulations with control and doubled CO₂ concentrations. This signal is compared with observed atmospheric temperature variations over the period 1963 to 1988 from radiosonde-based global analyses. There is a significant increase of this greenhouse signal in the observational data over this period.These results must be treated with caution. Upper air data are available for a short period only, possibly too short to be able to resolve any real greenhouse climate change. The greenhouse fingerprint used in this study may not be unique to the enhanced greenhouse effect and may be due to other forcing mechanisms. However, it is shown that the patterns of atmospheric temperature change associated with uniform global increases of sea surface temperature, with El NinoSouthern Oscillation events and with decreases of stratospheric ozone concentrations individually are different from the greenhouse fingerprint used here.     

建筑物高度对上行闪电触发以及传播影响的数值模拟

为了探讨建筑物高度对单个上行闪电触发以及传播的影响,设定了一个固定的背景电场,并结合自行触发的上行闪电随机放电参数化方案,进行了二维高分辨率上行闪电放电的模拟试验。结果表明:(1)上行闪电在初始阶段分支比较少;发展到离地面2 km左右后,闪电开始出现大量的分支,闪电通道开始出现明显的分叉:一部分通道继续向高电荷密度中心垂直传播,另一部分通道绕过高电荷密度中心,向外水平传播;模拟的上行闪电只能垂直传播到4 km处的负电荷中心,不能穿过0电势线向上方的正电荷区传播。(2)建筑物高度对上行闪电的触发起了关键作用,建筑物越高,越容易触发上行闪电。(3)建筑物高度对上行闪电传播具有一定的反作用,随着建筑物高度增高,模拟出的上行闪电的水平和垂直传播距离都有所减小,通道的分形维数变小,通道传播的总长度也逐渐减小。     

Retrieval of the microphysical properties in a CASP storm by integration of a numerical kinematic model

Abstract

A realistic kinematic model of cloud microphysical processes is presented. Heat and water substances in various phases are transported in the model by specific horizontal and vertical velocities using a semi‐Lagrangian numerical transport scheme. The model is applied to a CASP case study with horizontal and vertical velocities consistent with radiosondes and radar observations. The model is shown to capture the general observed features of the cloud and precipitation fields. In particular, it is shown that for the case studied stratiform clouds extend much higher than the top of detectable precipitation. This numerical model constitutes a useful tool for understanding the life cycle of hydrometeors as a function of their position within the storm system.     

A microscale model for air pollutant dispersion simulation in urban areas: Presentation of the model and performance over a single building

A microscale air pollutant dispersion model system is developed for emergency response purposes. The model includes a diagnostic wind field model to simulate the wind field and a random-walk air pollutant dispersion model to simulate the pollutant concentration through consideration of the influence of urban buildings. Numerical experiments are designed to evaluate the model's performance, using CEDVAL(Compilation of Experimental Data for Validation of Microscale Dispersion Models) wind tunnel experiment data, including wind fields and air pollutant dispersion around a single building. The results show that the wind model can reproduce the vortexes triggered by urban buildings and the dispersion model simulates the pollutant concentration around buildings well. Typically, the simulation errors come from the determination of the key zones around a building or building cluster. This model has the potential for multiple applications; for example, the prediction of air pollutant dispersion and the evaluation of environmental impacts in emergency situations; urban planning scenarios;and the assessment of microscale air quality in urban areas.     

An analysis of the turbulent structure in the unstable surface layer nearby a shelter belt

An analysis was performed of the turbulent data obtained from Yucheng experimental station in the Shandong Province in 1984. [t is shown that at variant wind speed, the spectra of streamwise velocity remain similar and the intensity of wind fluctuations is proportional to wind speed in the downwind area of shelter belt. Therefore, we may decide the similarity of wind fluctuations by a speed scale and a length scale which is not correlated with stability, σu /V0 = F(X / H). The -5/3 power range of temperature spectra extends to lower frequency. The variation of ratio σ0 /T. with stability becomes σ0 / T . = C(X / H)( - Z / L)-1/3 . There is not such an extension of -5 / 3 power range in the humidity spectra.     

Correlations of the evolution of a CCOPE squall line with surface thermodynamics and kinematic fields

A midlatitude squall line passed over the array of the Cooperative Convective Precipitation Experiment (CCOPE) on 1 August 1981. The structure and evolution of the squall line, and the correlations of the storm with surface thermodynamics and kinematic fields are investigated, mainly by using radar and surface mesonet data in CCOPE. The storm-wide precipitation efficiency is also estimated. The squall line was of an obvious process of metabolism. Thirty-four cells formed successively in front of the primary storm and eventually merged into it during the period 1700-2010 MDT. The newest cells formed near surface equivalent potential temperature maxima, and near surface moisture flux convergence zones or/ and the “temperature break lines”. The thunderstorm rainfall, with the precipitation efficiency of 54%, lags 25-30 min behind the moisture flux convergence on the average.     

Incorporating resilience into sustainability indicators: An example for the urban water sector

The development and use of indicators is common practice in efforts to promote urban sustainability. Indicators used to measure urban sustainability tend to focus narrowly on describing the current state of the urban system. Although a time series analysis using these indicators may lend insights into trends towards or away from certain ‘sustainability’ goals, existing indicators of urban sustainability do not provide information on the ability or the likelihood that the current system state can be maintained or improved over time. Indicators that incorporate a measure of system resilience would provide useful information on system sustainability. Through development of a new indicator, Water Provision Resilience (WPR), we provide an example of how measures of resilience could be incorporated into sustainability indicators. The new indicator adds six color codings to the existing indicator ‘percent of the population with access to safe water.’ Each color coding represents a measure of the ability of the water system to maintain or improve the current percent of the population with access to safe water in key areas of the water provision sector: supply, infrastructure, service provision, finances, water quality and governance. The metric is then applied to three cities. The goal in developing this metric is to provide a starting point for re-thinking the metrics used to measure progress and sustainability in order to incorporate the ability to absorb and adapt to stresses into sustainability analysis.     

2006年12月南京连续4天浓雾的微物理结构及演变特征

2006年12月24-27日南京地区出现了连续4天的浓雾天气,其中能见度小于50 m的强浓雾持续了40多个小时.利用FM-100型雾滴谱仪,连续观测了雾滴谱、数密度和含水量等微物理参量.结合自动气象站及能见度仪观测资料,分析了这次浓雾过程的微物理特征,并与1996年观测结果进行对比:雾滴的平均含水量和平均直径与1996年观测结果相当,含水量最大值比1996年观测结果大4倍,数密度比10年前小.认为前2个子过程的雾滴数密度、含水量很高,造成了南京奉次大雾能见度长时间低于50 m的恶劣天气.结合边界层探空资料,认为形成这种强浓雾的主要原因足近地层持续存在强盛的水汽平流,具有平流雾的特征.根据雾微物理参量的起伏变化,将浓雾过程分成4个子过稃,分析并比较了4个子过程的雾滴谱分布,总过程的谱分布及4个子过程的谱分布都服从Dcirmendjian分布,谱型都基本呈指数下降,雾滴主要集中存小滴段.最后,对第一个子过程微物理参量的变化特征进行了细致分析.发现这次浓雾是在夜间晴空辐射降温后形成的,午夜最强,日出后随着气温的升高逐渐减弱,反映了辐射雾的口变化特征.另外,还发现雾形成以后,开始变化不大,但随着进一步辐射降温,地面雾团不断产牛,雾爆发性发展.     

一个锢囚状中尺度对流系统的多尺度结构分析

利用多普勒雷达、气象卫星、自动气象站等监测资料、1°×1°NCEP再分析资料和4DVAR雷达反演低层风场资料,运用雷达拼图图形叠加、剖面和中尺度滤波等分析手段,对2007年7月18日华北东部一个锢囚状a中尺度对流系统(MaCS)的多尺度空间、动力结构及其演变进行了细致地分析.结果表明:(1) MaCS生命史分为发生发展...     

四川盆周山地暖季单站暴雨事件的精细特征

利用四川省2010—2019年2 165个气象站逐小时降水资料,分区统计了四川盆周山地暖季(5—9月)单站暴雨事件的精细特征。结果表明:(1)四川省单站暴雨事件频数在川西山地与川西南山地呈密集的带状分布。川西与川西南山地通常在降水开始不久就达到雨量最大值,而川东北山地的峰值时间集中在暴雨事件中段。(2)盆周山地的暴雨系统整体呈自南向北由前半夜向后半夜传播的特征。川西南山地和川东北山地的暴雨系统分别呈现较弱的自南向北和自西向东传播,而川西山地的暴雨系统则存在明显的自西向东的传播特征。(3)长历时暴雨事件的峰值出现时间略落后于短历时暴雨事件。暴雨持续时间在空间上存在显著的经向差异,大值区主要位于川西山地和川东北山地一带,暴雨雨量、频次和峰值基本不随持续时间变化,但川西南山地的暴雨峰值则随持续时间的加长而推迟。(4)在四川省大部区域,单站暴雨事件的降水量、频次和强度均表现出随海拔高度升高而减小的特征。在成都平原西南部、东部以及川东北山地,夜间暴雨事件持续时间越长,降水量和频次在较高海拔越易出现最大值。     

A multiparameter radar case study of the microphysical and kinematic evolution of a lightning producing storm

Summary We examine the co-evolving microphysical, kinematic, and electrical characteristics of a multi-cell thunderstorm observed on 21 May 1993 along the Front Range of Colorado using data collected with the 11 cm, multiparameter, CSU-CHILL Doppler radar. The measured polarimetric variables provide information on the size, shape, orientation, and thermodynamic phase of hydrometeors. Recent modeling and observational advances in weather radar polarimetry now permit the inference of bulk-hydrometeor types and mixing ratios, and the measurement of precipitation rate in mixed-phase (i.e., hail and rain) environments. We have employed these and other radar techniques, such as dual-Doppler analyses, to investigate the correlation between the convective life cycle of a multi-cell storm and the evolution of lightning type and flash rate.The observations suggest a strong correlation between the radar-inferred graupel volume suspended in a vigorous updraft in upper-portions of the storm and the in-cloud (IC) lightning flash rate. Our analyses reveal that maxima in the hail rate are related to peaks in the cloud-to-ground (CG) lightning flash rate. Both correlation's are consistent with the non-inductive charging mechanism which relies on collisions between graupel/hail particles and ice crystals in the presence of supercooled water. Peaks in storm outflow are shown to either lag or to coincide with maxima in both the CG flash rate and hail rate. The amount and vertical location of ice in this storm was also related to the strength and polarity of the electric field through observations of a Field Excursion Associated With Precipitation (FEAWP) and a subsequent microburst. We demonstrate that the FEAWP was coincident with the descent of graupel and small hail below the charge reversal level as explained by the non-inductive charging mechanism, and that the further descent of graupel and small hail below the melting level aided in the generation of a microburst near the surface. Using observations of the FEAWP, we present some comparative speculation on the microphysics of the associated lower positive charge center and the applicability of various laboratory charging studies.With 14 Figures     

An observational study of the structure of the nocturnal boundary layer

In an effort to describe the basic vertical structure of the nocturnal boundary layer, observations from four experiments are analyzed. During the night, the depth of significant cooling appears to increase with time while the depth of the turbulence and height of the low level wind maximum tend to remain constant or decrease with time. Since the inversion layer extends above the low level wind maximum and shear is small in the region of the low level jet, the Richardson number reaches a maximum at the jet level and then decreases again with height. As a result, turbulence is observed to be a minimum at the height of the low level wind maximum and then increases again above this height.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Part of this work was performed while a visiting scientist at Oregon State University.     

北半球大气臭氧层的遥相关结构分析

本文分析了北半球冬春季和夏秋季大气O_3层的遥相关结构.结果发现,O_3层存在一系列遥相关型,其时域特征与O_3层槽脊及大气环流型的变化有关,主要可分为:(1)O_3槽间型,(2)O_3槽脊型,(3)O_3脊间型.表明遥相关区域的空间分布具有波状结构.随着环流型的季节调整,冬春季与夏秋季O_3层的遥相关结构存在着差异.所得结果可显示出大气环流对O_3的输送作用以及环流系统振荡导致的O_3层异常分布,这对进一步揭示O_3层的时域演变特征具有重要意义.