京津冀城市群地区夏季低层大气风速谱特征分析

利用京津冀城市群地区6个观测站风廓线雷达夏季一个月同步观测资料,对其进行了风功率谱和小波分析.越接近地面,测站之间风的周期变化特征差异越明显,离地面越远,差异不显著.各站大于1天周期的频谱特征差异小,而小于1天周期的频谱特征差异大.各站频谱在几百米高度有明显日变化.不同位置的测站其日变化周期信号随高度分布表现为不同程度的地形影响效应.部分测站1km高度以下风功率谱在大于1天高频区近似满足-5/3幂分布规律.降水过程风频谱在低层普遍有小于1天的高频周期,这与降水过程高低空风速起伏和变化密切相关.各站平均风矢量日变化在5∶00—6∶00、20∶00—21∶00有明显风速变化和风向转换,1500m以下风向变化差异显著,偏南风出现时间及影响高度与该地区的山谷风和海陆风相联系.各站之间风速相关系数随高度分布呈现出低层低、上层高的特点.最后还给出了风廓线雷达布网建议.     

总体样本风速风向联合概率分析方法

提出了针对总体样本的风速风向联合分布的实用统计分析方法。假定任意给定风向上的风速符合某一概型分布、风向间的关联以风速资料的相对发生频率反映、不同风向间的概型参数及频率分布的变化满足谐波函数,在此基础上,利用风速风向资料的总体样本可以得到一个能够反映任意方向的风速风向联合分布函数。利用澳门地区的百年风资料与某风站连续5年的风速观测记录,对该方法的可行性进行了验证。分析表明,该方法具有一定的适用性,便于结构的抗风可靠性分析,具有一定的工程应用价值。     

YSU边界层参数化方案中不同地形订正方法对地面风速及温度模拟的影响

为了修正中尺度气象模式WRF(Weather Research and Forecasting model)对低层风速模拟的系统性误差,有学者在新版本WRF模式的YSU(Yonsei University)边界层参数化方案中加入了两个地形订正方法:Jiménez方法和UW(University of Washington method)方法.本文利用这两个地形订正方法,选取了两个时间段,对北京地区的地面气象要素以及气象要素垂直廓线进行了个例模拟研究,模拟结果和观测数据的比对表明在北京地区:是否采用地形订正,对地面温度的模拟几乎没有影响;采用地形订正后,模式对地面风速的模拟有明显的改进,两种方法对风速模拟的差别主要体现在山/丘陵地区;Jiménez方法在山/丘陵地区的模拟风速明显偏大,而采用UW方法进行订正后,模拟的风速减小,更接近观测值;两种方法在山谷地区对风速均有一定的过度订正.通过分析气象要素的垂直廓线发现,不同地形订正方法主要影响的是2000m以下的低层风速.总体而言,UW地形订正方法在北京地区更为适用,采用UW方法后,模拟得到的地面气象要素的各项统计参数基本达到了统计基准值.     

风速风向联合概率密度分布的一种经验函数模型

对风速与风向边缘分布采用统一的极值概型描述,提出了一种可适用于多峰极值以及总体样本的风速风向联合概率分布函数的经验解析表达式。模型包括7个参数,可由实测数据利用非线性最小二乘方法拟合得到。对模型参数拟合时的初值选取方法提出了建议,并对典型的风向双峰值情况,给出了峰向区间的划分方法;利用双峰总体、双峰极值以及单峰极值3种不同类型的实测数据,检验了模型的适用性。结果表明,该模型可以较好地描述不同类型总体样本或极值样本的风速风向联合概率密度特性,可供风向设计风速的确定、风速评估及场地风能评估等工程问题参考。     

长江三角洲城市热岛与太湖对局地环流影响的分析研究

发展了一个适合于长江三角洲地区的细网格区域气象模式, 利用这个模式成功模拟了长江三角洲地区海陆风、湖陆风、城市热岛等小尺度天气现象, 并研究了该地区地面风切变线形成的特征和机理, 指出海风和湖风的相互作用, 是地面切变线形成、维持的一个主要因素.     

数值模式延伸期可预报分量提取及预报技术研究

针对延伸期尺度的可预报分量,借鉴了CNOP相关算法,形成了在数值模式中提取可预报分量的实用方法和预报技术.从模式预报误差增长的角度将模式变量分为可预报分量和不可预报的混沌分量,将可预报分量定义为在预报时段内误差增长较慢的分量.基于现有的国家气候中心月动力延伸预报业务模式,建立了针对可预报分量的数值模式.同时结合历史资料有用信息,对数值模式的可预报分量,在历史资料的可预报分量中寻找相似场,降低了相似判断过程中变量的维数,进一步对可预报分量的预报误差进行订正.对混沌分量利用历史资料,通过集合预报方法得出其期望值和方差.数值试验结果表明,该方法能有效提高10～30天延伸期数值模式大气环流场的预报技巧,具有良好的业务应用前景.     

北冰洋及其邻近海域极昼期间大气边界层结构特征试验研究

1年7-月中国"雪龙"号破冰船首航北极科学考察期间,利用TMT(系留式气象塔)大气边界层探测系统,对北冰洋及其邻近海域不同下垫面进行较长时间的连续多次观测. 观测到的大气边界层廓线,其中包括比湿廓线的多层、逆湿结构(逆湿强度最强为0.7g/(10m·kg));风向、风速廓线的切变结构(风向切变为1.1°/m,风速切变为0.11(m·s^-1)/m. 特别是持续数日、厚达几百米、其平均逆温强度有时高达1.4℃/10m的逆温结构,这种北冰洋海域特有的大气边界层结构,与地球气候系统中其他圈层的大气边界层结构有明显差别. 据此,提出了对该海域大气-海冰-海洋间动量、感热和潜热等湍流通量垂直交换以及热量平衡等有重要影响的大气逆温的屏障过程. 这为研究北极地区对全球气候影响、模拟北极地区现代气候和未来气候等提供一条新的思路. 此外,文中还给出该海域不同下垫面稳定大气边界层的高度.     

延伸期可预报分量的预报方案和策略

延伸期时间尺度虽然超过逐日天气预报时效理论上限,但仍然存在可预报的气象场特征.本文针对延伸期尺度的可预报分量,提出了有针对性的预报方案和策略.基于大气系统的混沌特性,从误差增长的角度在数值模式中分离了可预报分量和不可预报的随机分量,将可预报分量定义为在预报时段内误差增长较慢的分量,它对初值小的误差不极其敏感.通过在预报过程中滤除随机分量,保留可预报性较高的分量,建立起针对可预报分量的数值模式,避免小尺度分量预报误差的快速增长对预报效果的影响.同时,结合历史资料,利用相似-动力方法对可预报分量的预报误差进行订正,达到减小模式误差和从统计角度考虑随机分量对可预报分量影响的目的.结果表明,该方法能有效提高数值模式对可预报分量的预报技巧,从空间分布上体现为对可预报性较高的地区改进更为明显;从空间尺度上看,改进最为明显的是0波,其次是超长波和天气尺度波,与各尺度的可预报性有很好的一致性.该方法能有效减小可预报分量的模式误差,提高预报技巧,显示出良好的业务应用前景.     

太湖北部风浪波高计算模式观测分析

通过用无量纲分析和线性回归方法对2002-2003年太湖4测点1000多组波浪资料的分析,给出了太湖不同时段风浪平均波高(H)与风区长度(F)、水深(d)、风速(v)6个关系模式.在此基础上,开展了模式的误差分析及与前人模式对比.结果表明,太湖北部不同区域风浪平均波高的计算应选用不同计算模式,但是可用如下形式表示:其中,a1-a8为和地形及水生植物覆盖度等相关的参数.误差分析结果显示:离岸距离大于1km区域的参数a1-a8的取值分别为0.217456、1、0.15、0.6、0.09、0.6、1.0、0.0052,模式估算平均波高的误差小于24％;近岸区参数a7大于1,a8取0,a4取值介于0.6-0.72,a5介于0.00131-0.00168,模式估算平均波高的误差较大,表明近岸区波浪还需进行进一步的观测研究.     

一种用于微波辐射计遥感海表面盐度和温度的反演算法

海面的微波辐射除了与海表面温度和盐度有关外, 还受海面风的影响. 海面风的观测误差严重地影响了海表面温度和盐度的遥感精度. 通过研究海面风因子对海表面辐射影响, 建立了海面风(包括风速和风向)与海表面的微波亮温T以及风导致的亮温修正量DT之间的关系; 在此基础上, 提出了利用微波辐射计的单卫星、多角度观测数据反演海表面盐度和温度的算法. 在这个算法中, 风对海表面辐射影响已经被剔除, 风速和风向不再是反演算法的输入参数. 因此, 该算法不受制于海面风速和风向的影响导致的误差. 这样, 为利用单卫星、多角度微波辐射计遥感海表面盐度和温度提供了一个新途径.     

海南岛海风雷暴结构的数值模拟

本文利用高分辨率WRF模式对2012年7月20日发生在海南地区的一次海风雷暴过程进行模拟,探讨了海南岛复杂地形下海风雷暴的结构、发展演变过程及其触发机制.结果表明,海南岛北部向内陆传播的海风与南部受地形阻挡的海风相遇后会形成海风辐合带,辐合带能影响当地的散度和涡旋特征,为雷暴的发生发展提供有利的动力和热力学条件.海南岛受热带海洋的影响较大,当地的水汽条件和对流潜势长期保持着有利于对流发展的状态,自由对流高度始终处于较低的位置,一旦海风辐合带来的抬升运动克服对流抑制到达自由对流高度后,对流就能自主地发展起来,所以单纯的海风辐合也常常能触发当地的强雷暴.雷暴发生发展过程中对流参数存在明显的变化,其演变曲线的突变位置对雷暴的发生有一定的指示作用.海南岛的海风雷暴过程与当地的复杂地形密切相关,地形的动力阻挡作用影响着低层海风的辐合以及对流的发展.     

辐射参数化对海南岛海风雷暴结构模拟的影响

本文利用高分辨率WRF模式探讨了两组短波、长波辐射参数化方案(Dudhia+RRTM、RRTMG+RRTMG)对海南岛一次海风雷暴模拟的影响及其可能的物理机制.结果表明,辐射参数化能影响大气的加热程度和近地面能量,决定海陆温差和气压差,改变海南岛的海风特征,最终影响海风雷暴的发生发展.Dudhia+RRTM方案模拟的短波、长波综合加热率、感热通量以及潜热通量都大于RRTMG+RRTMG方案,造成了前者模拟的近地面能量偏高,大气层结也表现得更加不稳定,进而使得该方案下的海陆温差和气压差相对较大,Dudhia+RRTM方案模拟的海风明显强于RRTMG+RRTMG方案,能提供更好的水汽输送和抬升条件,有利于海风雷暴的发生发展,因此其模拟的雷暴活动范围和对流中心强度都要大于RRTMG+RRTMG方案.     

On mesoscale characteristics of bora conditions in Yugoslavia

The local wind bora is a well-known phenomenon on the eastern coast of the Adriatic Sea, where steep mountains, the Dinaric Alps, closely follow the coast. In a relatively undisturbed atmosphere the coastal thermal effect and the dynamic effect of orography give rise to a cool downslope land breeze, theborino, which develops at night-time, and particularly in the winter season, when the land-sea temperature contrast is large. The causes ofcold bora, with strong and gusty winds, are then attributed to the synoptic scale effects upon the local flow intensification and inland cold air supply. Since the interaction processes on various scale motions are involved in a sequence of bora spells, it is shown how the large scale anomalies may subsequently change the mesoscale characteristics of the bora environment and eventually make the bora appear as a relatively warm wind.     

Analysis of the effect of the coastal discontinuity on near-surface flow

Conditional sampling is used herein to examine the effect of fetch, stability, and surface roughness changes on wind speeds in the coastal zone. Using data from an offshore wind farm it is shown that at a distance of 1.2–1.7 km from the coast, up to a height of 20 m above the surface, differences in wind speed distributions from onshore and offshore masts are statistically significant for flow moving offshore under all stability conditions. In contrast, differences between the distribution of wind speeds at 38 and 48 m at masts located at the coast and in the coastal zone are not significant for flow moving offshore, indicating that flow at these heights is not fully adjusted to the change in surface roughness (land to sea). These findings are in accordance with calculations of the internal boundary layer (IBL) height which indicate that the IBL would frequently be below the two upper measurement heights at 1.2–1.6 km from the coast. The analyses presented here indicate that the wind speed distribution at a potential offshore wind farm site is not solely dependent on fetch (distance from the coast) but also depends on the stability climate.     

Bagnold's kink: A physical feature of a wind velocity profile modified by blown sand?

Bagnold (1941) made detailed measurements of the wind profile modified by blown sand. He noted that each velocity profile appeared to be kinked and suggested that the position of the kink corresponded to the height at which an average or a characteristic trajectory extracted the bulk of its momentum from the wind. However, Anderson and Haff (1988) have shown that in aeolian sand transport the grain cloud is made up from a distribution of trajectory paths and that it was an over-simplification to attempt to describe the complex behaviour of the grain cloud in terms of a single representative trajectory. These recent developments leave the nature and even the existence of the kink observed by Bagnold (1941) open to question. This paper shows that a kink is indeed a physical feature of the modified wind velocity profile and that it is caused, as Bagnold (1941) suggested, by a maximum, occurring at some height above the surface, in the momentum extracted by the grains from the wind. Further comments are made on both the form of the modified wind velocity profile and the fluid shear stress profile in the grain layer. In particular these comments, based upon a theoretical analysis, suggest an experimental means to measure the mean surface fluid shear stress and to gain, from accurately measured wind profiles, a greater insight into the grain cloud which caused the modification.     

The effect of wind averaging time on wind erosivity estimation

The Wind Erosion Prediction System (WEPS) and Revised Wind Erosion Equation (RWEQ) are widely used for estimating wind‐induced soil erosion at a field scale. Wind is the principal erosion driver in the two models. Wind erosivity, which describes the capacity of wind to cause soil erosion, is defined as erosive wind power density (WPD) in WEPS, and wind value (W) in RWEQ. In this study, the daily average WPD (AWPD) and the daily average W (Wf) were chosen to investigate the effect of averaging time on wind erosivity estimation based on observed wind data. We compare the daily AWPD and Wf calculated from 1, 5, 10, 15, 30, and 60 minute average wind speed data. The results of comparisons indicate that averaging wind speed can significantly influence estimates of wind erosivity. Compared with the daily AWPD and Wf calculated from one minute average wind speed data, all daily AWPD and Wf values calculated from 5, 10, 15, 30, and 60 minute averaged wind speeds tend to be significantly lower than values calculated from one minute values. In general, longer averaging times tend to produce smaller values of daily AWPD or Wf, which may lead to an under‐estimation of wind erosion. Further studies are needed to extend and apply the findings obtained in this study to actual wind erosion predictions. Copyright © 2012 John Wiley & Sons, Ltd.     

近地层参数化对海南岛海风降水模拟的影响

利用WRF模式探讨了两种近地层参数化方案(MM5方案和Eta方案)对2013年5月31日海南岛一次海风降水过程模拟的影响.结果表明,改变近地层方案可对当地的海风环流及相应的降水特征产生明显影响,两个试验最重要的差别主要体现在模拟的海风及降水的强度差异上,与MM5试验相比,Eta试验的低层海风及辐合程度更强,相应的降水也更强,表现为岛屿总格点降水量、大于10mm的降水区域、最大格点降水三个量化指标均比较大.通过分析两种方案在不同降水阶段的地表通量及近地层变量场,发现Eta试验模拟的降水前环境场更有利于对流的启动,随着午后热力湍流的不断增强,将MM5方案替换为Eta方案可使近地层感热通量、潜热通量分别增加约3.57%、5.65%,动量通量减小约10.79%,感热、潜热的增加使Eta试验中近地层大气的加热加湿作用更加明显,相应的低层大气不稳定度更高,再配合海风锋前较强的辐合上升运动,局地不稳定能量的释放变的更加容易,因此降水强度更大.     

Using wind run to predict sand drift

Conventional aeolian sand transport models relate mass transport rate to wind speed or shear velocity, usually expressed and empirically tested on a 1-s time scale. Projections of total sand delivery over long time scales based on these models are highly sensitive to any small bias arising from statistical fitting on empirical data. We analysed time series of wind speed and sand transport rate collected at 14 independent measurement stations on a beach during a prior field experiment. The results show that relating total sand drift to cumulative above-threshold wind run yields models which are more statistically robust when fitted on empirical data, generating smaller prediction errors when projected to longer time scales. Testing of different power exponents indicates that a linear relationship between sand drift and above-threshold wind run yields the best results. These findings inspire a speculative novel phenomenological model relating the mass flow of air in the boundary layer to the mass transport of sand over the surface. © 2020 John Wiley & Sons, Ltd.     

Analysis of the influence of Taihu Lake and the urban heat islands on the local circulation in the Yangtze Delta

The influences of human activities on regional climate and weather are tremendous. The re-gional temperature and the distributing of wind field are influenced, whereas the precipitation in-tensity and the spatial and temporal distribution of the precipita…