WRF模式对福建沿海风电场风速预测的效果分析

在WRF模式中选取不同的边界层、近地面层以及陆面过程参数化方案,设计了4种不同物理过程参数化方案,组合模拟福建沿海某测风塔站2010年1月1—11日和7月1—11日的逐时风速,将数值模拟结果和同期测风塔观测数据进行对比,以寻求最佳参数化方案。经分析比较,采用MYJ边界层方案,Monin-Obukhov近地面层方案以及Noah陆面过程方案的方案2模拟效果最好。使用该方案对2010年1月和7月的风速进行模拟,按不同风速级别分别对数值模拟结果进行对比分析,结果表明:方案2对6~15m/s风速模拟的平均相对误差在20%左右,能够满足风电预测的精度需求;而对0~6m/s风速模拟的误差相对较大,这可能是由于模式地形分辨率不够精细以及风塔所处海陆交界处的特殊位置,使低风速容易受地面扰动以及海陆气流影响所致。     

Deriving Changjiang coastal zone wind from C-band SAR and its application to salinity simulation

Wind plays an important role in hydrodynamic processes such as the expansion of Changjiang （Yangtze） River Diluted Water （CDW）, and shelf circulation in the Changjiang estuary. Thus, it is essential to include wind in the numerical simulation of these phenomena. Synthetic aperture radar （SAR） with high resolution and wide spatial coverage is valuable for measuring spatially inhomogeneous ocean surface wind fields. We have collected 87 ERS-2 SAR images with wind-induced streaks that cover the Cbangjiang coastal area, to verify and improve the validity of wind direction retrieval using the 2D fast Fourier transform method. We then used these wind directions as inputs to derive SAR wind speeds using the C-band model. To demonstrate the applicability of the algorithms, we validated the SAR-retrieved wind fields using QuikSCAT measurements and the atmospheric Weather Research Forecasting model. In general, we found good agreement between the datasets, indicating the reliability and applicability of SAR- retrieved algorithms under different atmospheric conditions. We investigated the main error sources of this process, and conducted sensitivity analyses to estimate the wind speed errors caused by the effect of speckle, uncertainties in wind direction, and inaccuracies in the normalized radar cross section. Finally, we used the SAR-retrieved wind fields to simulate the salinity distribution off the Changjiang estuary. The findings of this study will be valuable for wind resource assessment and the development of future numerical ocean models based on SAR images.     

一次典型高压型海雾过程中海上大气波导的数值模拟

2009年4月9—12日黄海海域发生了一次受高压系统影响的海雾过程。利用卫星观测与探空数据、WRF模式(Weather Research and Forecasting Model)对此次海雾过程及相伴的大气波导进行了观测分析与数值模拟。海雾与波导发展可分为3个阶段:(1)大气波导先于海雾存在于黄海海面;受高压下沉影响,黄海上空存在逆温层和较强的湿度梯度,表现为较强的贴海表面波导和非贴海表面波导。(2)海雾始于高压西部,并随高压系统逐渐东移减弱,向黄海北部扩展;辐射冷却虽然使雾顶附近逆温增强,但海雾的机械湍流使其顶部湿度梯度减小,雾顶附近对应弱悬空波导或波导消失。(3)高压系统影响使干空气下沉到雾区导致黄海海雾消散;雾顶附近逆温仍存在,同时湿度梯度增大,黄海上空逐渐变为非贴海表面波导。本研究结果表明:高压系统不仅极易为波导的发生提供有利条件,而且有利于海雾的生成,在海雾演变过程中主要是雾顶水汽梯度的变化导致了波导类型及强度的变化。     

WRF_Lake湖气模式对我国太湖的湖温模拟应用评估

文章把一维热扩散湖模式成功地耦合到中尺度天气研究和预报模式WRF3.2中,建立了湖气耦合模式。并用太湖区梅梁湾获得的2010年8月11—28日的观测资料对该耦合模式模拟湖温的能力进行了初步评估。设计了3组方案进行对照试验,分别为:(1)没有加入湖模块的WRF模式试验(WRF);(2)没有对参数进行优化的原始耦合模式试验(WRF_Lake_Old);(3)对3个参数进行优化后的耦合模式试验(WRF_Lake_New)。结果表明耦合了湖泊模块并且参数优化后的湖气耦合模式(WRF_Lake_New)比没有包含湖面方案的WRF模式对太湖水温的模拟能力有了很大的改进。WRF_Lake_New能够合理地模拟出太湖梅梁湾上湖表温度的日变化,模拟的湖表温度误差范围平均在±1℃左右,模拟的空气温度平均误差范围在±0.5℃以内,模拟的感、潜热通量也与观测更为接近。该耦合模式在太湖的初步评估结果表明,该湖气耦合模式为下一步研究湖泊过程和湖气相互作用提供了重要的工具。     

云中积冰过程微物理参量演变规律的数值模拟

利用耦合Thompson参数化物理方案的WRF（weather research and forecasting）中尺度数值模式,对发生在2008/2009年和2009/2010年冬季恩施雷达站处三次积冰过程的边界层特征和云雾微物理量进行了模拟,并与实测结果进行了对比分析.模拟结果较好地反映了恩施雷达站上空多逆温影响的温度层结特征;云水质量浓度和云雾滴中值体积直径的模拟值与观测值的平均绝对误差分别为10-2g·m-3和3.8μm;恩施雷达站上空存在一个质量浓度为0.3g ·m-3左右的高值中心,其逐渐下移接地,给积冰过程带来充足水汽,且此时通常也有降雨出现.     

背景场和物理过程对WRF模式在新疆区域预报性能的影响

为了优选考虑新疆气候和地形特征的背景场和物理过程,设计WRF模式的Lin、WSM6、Thompson微物理过程和KF、Grell 3D积云参数化敏感性试验方案,使用T639和GFS两种背景场,进行了回算和对比检验,确定了在新疆预报能力最优的物理过程和背景场方案,并对WRF模式在新疆的预报能力和不足之处有了较为清晰的认识。     

A multi-scale urban atmospheric dispersion model for emergency management

To assist emergency management planning and prevention in case of hazardous chemical release into the atmosphere,especially in densely built-up regions with large populations,a multi-scale urban atmospheric dispersion model was established.Three numerical dispersion experiments,at horizontal resolutions of 10 m,50 m and 3000 m,were performed to estimate the adverse effects of toxic chemical release in densely built-up areas.The multi-scale atmospheric dispersion model is composed of the Weather Forecasting and Research （WRF） model,the Open Source Field Operation and Manipulation software package,and a Lagrangian dispersion model.Quantification of the adverse health effects of these chemical release events are given by referring to the U.S.Environmental Protection Agency＇s Acute Exposure Guideline Levels.The wind fields of the urban-scale case,with 3 km horizontal resolution,were simulated by the Beijing Rapid Update Cycle system,which were utilized by the WRF model.The sub-domain-scale cases took advantage of the computational fluid dynamics method to explicitly consider the effects of buildings.It was found that the multi-scale atmospheric dispersion model is capable of simulating the flow pattern and concentration distribution on different scales,ranging from several meters to kilometers,and can therefore be used to improve the planning of prevention and response programs.     

广东一次飑线过程中一个雷暴单体成熟阶段的电荷结构演变特征的数值模拟

为了进一步印证以往观测反推得到的广东地区雷暴云多偶极性电荷结构的结论,利用加入了起放电参数化方案的WRF模式,模拟了广东在2017年5月8日发生的一次飑线过程,并对这次飑线过程中一个雷暴单体成熟期的电荷结构演变特征进行分析,通过分析动力、云水含量、各水成物粒子混合比及携带电荷情况,讨论了电荷结构的形成及演变机制。结果表明,成熟阶段的单体,电荷结构从三极性逐渐演变为偶极性。这是因为在成熟初期,霰粒子在有效液态水含量适中且温度较高的地方与冰晶/雪花粒子发生了非感应碰撞,因此底部霰粒子携带正电,雷暴云底部形成次正电荷区,电荷结构为三极性。而在成熟后期,由于丰富的云水含量,使冰粒子的凇附过程增强,霰不断增加,冰晶和雪花不断被消耗,温度较暖区域与霰共存的冰晶和雪花急剧减少,使得该区域大小冰粒子的非感应碰撞起电急剧减少,此处霰粒子不能再通过非感应碰撞获得正电荷,底部次正电荷区随之消失,雷暴云的电荷结构转变为偶极性。此结果和以往观测反推得到的结论不同,这表明,对南方雷暴电荷结构还需继续深入认识。      

地表利用城市化在一次极端高温过程数值模拟中的影响

地表种类的城市化对城市区域的热力结构和局地环流都会产生巨大的影响。利用地面、高空观测资料和MODIS地表覆盖资料,使用耦合城市冠层模式(UCM)的区域中尺度数值模式(WRF),对2013年8月8日福州地区的一次极端高温天气过程进行数值模拟,研究地表利用变化对福州城市热岛效应及其对福州城市区域局地环流的影响。结果表明:地表利用的城市化使得午后城市热岛现象更加明显而夜间热岛效应呈现出减小的趋势;地表利用城市化后,中心城区的近地面风速减小,但城区与山区以及城区与海洋之间的局地热力环流明显加强,促进了山谷风和海陆风环流的发展;同时地表加热效应增强,促进了垂直运动的发展。      

High-Resolution Hindcast of Record-Breaking Rainfall in Beijing and Impact of Topography

In this paper,a hindcast study of the record-breaking rainfall event occurring in Beijing on 21July 2012,is conducted by using the Weather Research and Forecasting(WRF)model forced by National Centers for Environmental Prediction(NCEP)Global Forecasting System(GFS)outputs,paired with an investigation of the impact of topography in this region.The results indicate that WRF can reasonably predict the salient features of orographic precipitation;the 24-h rainfall amount and spatial distribution compare reasonably well with the observations.The hindcast simulation also indicates that rainfall events can be predicted approximately 36 h ahead.When the topography is removed,the spatial distribution of rainfall changes remarkably,suggesting the importance of the topography in determining rainfall structure.These results also indicate that prediction of such city-scale heavy rainfall events would benefit from a high-resolution prediction system.