关中盆地近地面风场和大气输送特征分析

利用2017年151个地面气象站的逐时观测数据和相关高空资料分析关中盆地近地面风场与输送特征。首先分析盆地内代表性站点的风速和风向观测事实,然后用CALMET风场诊断模式和轨迹计算模式获取当地逐小时风场和每日逐小时传输轨迹,分析风场类型。结果表明:关中盆地内日平均风速约1～3 m s?1,夏季风速高、秋冬季低;盆地中央的主导风向以沿地形走向的东北风和西南风为主,盆地四周测站的主导风向表现出顺着地形向盆地中央汇流的趋势。各站主导风向的季节变化不大。盆地内风场分为系统控制型、弱天气背景型和局地环流型3类,全年出现日数比例分别占8%、17.3%和74.7%。以山谷风日夜循环为特征的局地环流型风场最多。以西安城区为源点的大气输送轨迹显示,系统控制型风场以偏东北方向的输送为主,弱天气背景型和局地环流型风场的轨迹输送都大致以偏东北和偏西（以及偏西南）沿盆地走向以及偏东南朝向秦岭山地这三个方向为主。局地环流型的轨迹影响范围小,集中于盆地中央和南侧山地之间,表明这是一种不利于污染扩散的风场类型。     

ENSO in a hybrid coupled model. Part II: prediction with piggyback data assimilation

A hybrid coupled model (HCM) for the tropical Pacific ocean-atmosphere system is employed for ENSO prediction. The HCM consists of the Geophysical Fluid Dynamics Laboratory ocean general circulation model and an empirical atmospheric model. In hindcast experiments, a correlation skill competitive to other prediction models is obtained, so we use this system to examine the effects of several initialization schemes on ENSO prediction. Initialization with wind stress data and initialization with wind stress reconstructed from SST using the atmospheric model give comparable skill levels. In re-estimating the atmospheric model in order to prevent hindcast-period wind information from entering through empirical atmospheric model, we note some sensitivity to the estimation data set, but this is considered to have limited impact for ENSO prediction purposes. Examination of subsurface heat content anomalies in these cases and a case forced only by the difference between observed and reconstructed winds suggests that at the current level of prediction skill, the crucial wind components for initialization are those associated with the slow ENSO mode, rather than with atmospheric internal variability. A “piggyback” suboptimal data assimilation is tested in which the Climate Prediction Center data assimilation product from a related ocean model is used to correct the ocean initial thermal field. This yields improved skill, suggesting that not all ENSO prediction systems need to invest in costly data assimilation efforts, provided the prediction and assimilation models are sufficiently close. Received: 17 April 1998 / Accepted: 22 July 1999     

A numerical study on the meso-scale pollutant dispersion over a sloped surface in the stable boundary layer

A numerical model is used to study the properties of pollutant dispersion over a large uniformly-sloped surface in the stable atmospheric boundary layer. By simulating the structure of boundary layer flow to improve the advective wind field and vertical eddy diffusivities included in the advection-diffusion equa-tion, this numerical model permits an estimation of the distribution of pollutant concentration for more real-istic atmospheric diffusion conditions.     

南海海域海-气耦合模式及其数值模拟试验

在ＮＣＡＲ区域气候模式ＲｅｇＧＭ２和普林斯顿海洋模式ＰＯＭ基础上发展适用于区域海－气相互作用研究的区域海－气耦合模式,模式采用同步耦合、海洋模式将海表温度提供给大气模式,大气模式为海洋模式提供太阳短波辐射、感热能量、潜热通量。海洋与大气模式每１５ｍｉｎ交换一次通量。耦合过程没有使用通量校正。使用该模式对中国南海区域１９９５年５－７月大气和海洋进行了模拟试验,将模拟结果与ＣＯＡＤＳ通量强迫的模拟结果     

Evolving Turbulence Realizations of Atmospheric Flow

A significant difference exists between estimates of contaminant atmospheric transport and dispersion calculated by an ensemble-averaged model and the turbulent details of any particular atmospheric transport and dispersion realization. In some cases, however, it is important to be able to make inferences of these realizations using ensemble-averaged models. It is possible to make such inferences if there are sensors in the field to report contaminant concentration observations. Any information determined about the atmospheric transport and dispersion realization can then be assimilated into a forecast model. This approach can enhance the accuracy of the atmospheric transport and dispersion forecast of a particular event. This work adopts that approach and reports on a genetic algorithm used to optimize the variational problem. Given contaminant sensor measurements and a transport and dispersion model, one can back-calculate unknown source and meteorological parameters. In this case, we demonstrate the dynamic recovery of unknown meteorological variables, including the transport variables that comprise the “outer variability” (wind speed and wind direction) and the dispersion variables that comprise the “inner variability” (contaminant spread). The optimization problem is set up in an Eulerian grid space, where the comparison of the concentration field variable between the predictions and the observations forms the cost function. The transport and dispersion parameters, which are determined from the optimization, are in Lagrangian space. This calculation is applied to continuous and instantaneous releases in a horizontally homogeneous wind field such as that observed during traditional transport and dispersion field experiments. The method proves to be successful at recovering the unknown transport and dispersion parameters for a numerical experiment.     

下坡运动的分析解

本文采用二层模式,在一个斜坡地形上,求解大气波动方程,得出了下坡运动的普遍分析解,并对解在不同大气条件和地形条件下的物理意义做了分析。当下层大气厚而稳定、风速较强时,得到的是背风坡大风。而当下层大气强稳定、小风时,得到的是泄流风。对各类下坡运动近地面风速和大气层结、流场结构及Scorer参数之间的关系也做了讨论。     

North Atlantic atmospheric circulation and surface wind in the Northeast of the Iberian Peninsula: uncertainty and long term downscaled variability

The variability and predictability of the surface wind field at the regional scale is explored over a complex terrain region in the northeastern Iberian Peninsula by means of a downscaling technique based on Canonical Correlation Analysis. More than a decade of observations (1992–2005) allows for calibrating and validating a statistical method that elicits the main associations between the large scale atmospheric circulation over the North Atlantic and Mediterranean areas and the regional wind field. In an initial step the downscaling model is designed by selecting parameter values from practise. To a large extent, the variability of the wind at monthly timescales is found to be governed by the large scale circulation modulated by the particular orographic features of the area. The sensitivity of the downscaling methodology to the selection of the model parameter values is explored, in a second step, by performing a systematic sampling of the parameters space, avoiding a heuristic selection. This provides a metric for the uncertainty associated with the various possible model configurations. The uncertainties associated with the model configuration are considerably dependent on the spatial variability of the wind. While the sampling of the parameters space in the model set up moderately impact estimations during the calibration period, the regional wind variability is very sensitive to the parameters selection at longer timescales. This fact illustrates that downscaling exercises based on a single configuration of parameters should be interpreted with extreme caution. The downscaling model is used to extend the estimations several centuries to the past using long datasets of sea level pressure, thereby illustrating the large temporal variability of the regional wind field from interannual to multicentennial timescales. The analysis does not evidence long term trends throughout the twentieth century, however anomalous episodes of high/low wind speeds are identified.     

A high-resolution 44-year atmospheric hindcast for the Mediterranean Basin: contribution to the regional improvement of global reanalysis

A 44-year (1958–2001) high-resolution atmospheric hindcast for the whole Mediterranean Basin was performed within the EU-funded Hindcast of Dynamic Processes of the Ocean and Coastal Areas of Europe (HIPOCAS) Project. The long-term hindcasted data set, which comprises several atmospheric parameters at different levels, was produced by means of dynamical downscaling from the NCEP/NCAR global reanalysis using the atmospheric limited area model REMO. The REMO hindcast has been exhaustively validated. On that score, various hindcasted surface parameters, such as 10-m wind field, 2-m temperature and mean sea level pressure, have been compared to satellite data (ERS-1/2 scatterometer) and in-situ measurements from offshore stations. In addition, two ocean models (waves and sea level) have been forced with REMO hindcasted fields (mean sea level pressure and 10-m wind field). The validation of these ocean runs, performed through comparisons of simulated waves and sea level with oceanographic measurements, allows to evaluate "indirectly" the quality of the REMO hindcasted data used as atmospheric forcing. Once the quality of the hindcasted data was verified, the efficiency of the regional enhancement performed through dynamical downscaling on the NCEP global reanalysis was assessed. The regional improvement was evaluated through comparisons of REMO and NCEP performance in reproducing observations. The important improvement obtained in the characterization of extreme wind events is particularly remarkable.     

不同阶曲线拟合扰动场对下平流层重力波气候特征影响研究

重力波参数气候特征是确定大气模式中重力波参数化方案的重要条件之一,高垂直分辨率探空资料扰动场是获取重力波参数气候特征的基础数据;目前,获取扰动场的方法较多,但基于不同方法计算的扰动场对重力波参数气候特征影响的研究较少.基于2014—2017年山西太原气象台高垂直分辨率探空资料,利用2—4阶曲线拟合方法获取下平流层(17...     

Thermally induced wind patterns in the Sahelian city of Ouagadougou, Burkina Faso

The urban surface wind field in the dry-tropical city of Ouagadougou, Burkina Faso was studied based on data collected at one urban and one suburban station during early dry season. An intra-urban thermal breeze, creating almost opposite wind directions at the two sites, was found during nights with high atmospheric stability. The high atmospheric stability suggests a decoupling of the surface wind layer from the layer above, allowing the wind system to develop due to the strong intra-urban temperature gradients in the city. Frequent temporary breakdowns of the thermal wind system were noticed, generally generating a turn in wind direction towards that of the regional wind, thus indicating a re-coupling with a stronger wind flow in the wind layer above.     

局地废气排放污染影响的实验模拟

本文给出了一项在南京大学NJU环境风洞中实施的实验模拟研究。试验模拟一座位于城市街区的排放塔的废气排放，通过流场测量，放烟显示和示踪气体扩散试验，分析气流分布与污染物浓度分布，得出对局地环境影响的一些结论。文中还以模拟扩散试验资料为实验基础，建立修正的扩散模式，探讨污染物浓度预测的可靠途径。研究结果表明，风洞流体模拟手段是有成效且实用的。     

Case study and numerical simulation of the summer regional circulation in São Paulo,Brazil

The three-dimensional mesoscale circulation in the vicinity of the city of São Paulo is examined through model simulations validated by observational data obtained during a field experiment. The complex terrain surrounding the plateau where the city is located, plus proximity to the sea, represent the local controls on the wind field with implications for boundary-layer transport of atmospheric constitutents. The coupling of a regional-scale circulation with slope and sea-breeze circulations is an important feature which determines the wind regime in São Paulo in a summer situation not influenced by frontal systems.     

Observations of atmospheric boundary layer evolution above the Gulf Stream frontal zone

Ship borne measurements of atmospheric boundary layer (ABL) parameters, sea-surface temperature and radar signals are analyzed to reveal the effects of the ABL transformation above the Gulf Stream temperature frontal zone. It was found that local changes in vertical gradients of wind speed and air temperature are well correlated with sub-mesoscale (~ 10 km) sea surface temperature variations. These effects are accompanied by appropriate variations in surface wind stresses that were identified from microwave backscatter.For steady atmospheric conditions the same effects were observed on spatial scales of 100 km, demonstrating positive radar signal contrast of the Gulf Stream warm waters with respect to surrounding Sargasso sea and shelf water areas. A simplified model of the ABL, accounting for an effect of spatial inhomogeneity by introducing an internal boundary layer, is used to analyze field observations. The model is able to reproduce both sub-mesoscale and mesoscale ABL evolution.     

北京地区不同天气条件下近地面大气电场特征

利用2004年8月—2005年11月近地面大气电场仪的观测资料, 对北京地区不同天气条件下近地面大气电场特征进行分析。结果表明:北京地区晴天近地面大气电场日变化呈双峰双谷, 谷值分别出现在北京时05:00和12:00, 峰值分别出现在07:00和23:00, 并且表现出一定的季节变化; 晴天大气电场的变化与气溶胶含量的变化有密切关系, 两者呈正相关; 晴天大气电场与绝对湿度之间也表现出很强的相关性, 在一定程度上反应了水汽对大气电场的作用; 沙尘天气下风速均达到一定强度, 近地面大气电场为负值, 并且变化剧烈, 电场强度与PM₁₀之间呈现较强的负相关, 而电场强度与风速之间没有表现出明显的相关性。     

温坨子区域地面水平流场分布特征研究

利用辽东湾温坨子地区冬夏两季大气扩散试验资料，采用风场诊断模式，对拟建核电站厂区水平风场的分布特征进行了研究, 以为评估该地区拟建核电站的大气污染扩散状况提供基本参数与依据。结果表明:冬季该地区水平风场分布主要有3种形式:1) 呈偏南风型的风场；2) 偏北风型的风场；3) 厂址附近位于高低压中心之间，或整个区域是一均压场, 这时系统风弱，局地风 (包括山谷风及海陆风) 明显，整个区域地面风场比较混乱。夏季该地区水平风场分布主要有4种形式:1) 受季风控制，呈偏南风型的风场；2) 系统风较弱，呈海陆风型的风场；3) 锋前低压控制，产生切变型的风场；4) 受季风控制，呈偏北风型的风场。     

Evaluation of wind fields for storm events in the black sea region using a numerical regional atmospheric circulation model

A method of the NCEP/NCAR reanalysis wind data recalculation using a regional atmospheric circulation model is described. A comparison of model results and satellite measurements is performed. The results of wind wave computation using the reanalysis and model winds are presented and their comparison is made. It is shown that the NCEP/NCAR reanalysis wind recalculation using a regional atmospheric circulation model removes the underestimation in the reanalysis winds, provides a better representation of the wind regime, and, consequently, gives a possibility to create the reanalysis of wind regime in the Black Sea region to be used in climate estimates.     

A Statistical Model for the Prediction of Wind-Speed Probabilities in the Atmospheric Surface Layer

Wind fields in the atmospheric surface layer (ASL) are highly three-dimensional and characterized by strong spatial and temporal variability. For various applications such as wind-comfort assessments and structural design, an understanding of potentially hazardous wind extremes is important. Statistical models are designed to facilitate conclusions about the occurrence probability of wind speeds based on the knowledge of low-order flow statistics. Being particularly interested in the upper tail regions we show that the statistical behaviour of near-surface wind speeds is adequately represented by the Beta distribution. By using the properties of the Beta probability density function in combination with a model for estimating extreme values based on readily available turbulence statistics, it is demonstrated that this novel modelling approach reliably predicts the upper margins of encountered wind speeds. The model’s basic parameter is derived from three substantially different calibrating datasets of flow in the ASL originating from boundary-layer wind-tunnel measurements and direct numerical simulation. Evaluating the model based on independent field observations of near-surface wind speeds shows a high level of agreement between the statistically modelled horizontal wind speeds and measurements. The results show that, based on knowledge of only a few simple flow statistics (mean wind speed, wind-speed fluctuations and integral time scales), the occurrence probability of velocity magnitudes at arbitrary flow locations in the ASL can be estimated with a high degree of confidence.     

双多普勒天气雷达反演大气三维风场的个例研究

根据笛卡尔坐标系下双多普勒天气雷达反演大气三维风场的理论，以2003年7月5日发生在安徽省的一次强降水过程为例，反演大气三维风场。结果表明：利用双多普勒天气雷达反演大气风场能够更加详细地反映出大气风场的三维结构。     

Response Process of Oceanto AtmosphericForcing and Optimal Response Frequency in the CZ Ocean Model

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基于不同资料的影响南海热带气旋环流背景对比北大核心CSCD

利用1981—2020年中国热带气旋最佳路径数据集、中国大气再分析资料(CMA-RA)、欧洲中期天气预报中心ERA5及美国NCEP/NCAR再分析资料(NCEP-Ⅰ),对比不同资料在表征影响南海热带气旋活动环流背景的能力,探讨CMA-RA的适用性。结果表明:不同资料基本刻画出与热带气旋活动密切相关的环流特征,包括南方涛动、菲律宾至南海低层纬向风、热带低层纬向风反向分布型、菲律宾至南海中东部低层涡度、热带西太平洋垂直风切变及南海至菲律宾以东海域中层湿度。它们对南方涛动、关键区纬向风和中层湿度的刻画较相似,CMA-RA和ERA5对南方涛动、低层纬向风及其与热带气旋关系的描述一致性高,较NCEP-Ⅰ密切,但低层经向风、关键物理量差异较大。对极端年环流具有相似的表现能力,但异常程度存在差异,海平面气压、低层纬向风高度一致,以CMA-RA与ERA5最接近;中层湿度CMA-RA与ERA5接近,较NCEP-Ⅰ偏小;关键物理量差异较大。CMA-RA对南海热带气旋环流的刻画具有与ERA5和NCEP-Ⅰ相当的性能,并与ERA5一致性较高,可为相关工作提供可替换的再分析资料集。