华南暴雨试验期间香港风廓线雷达资料的评估

风廓线雷达资料无论对暴雨等中尺度现象还是对季风等大尺度现象的研究都很有科学价值。为有效地利用香港天文台提供的1998年华南暴雨和南海季风科学试验期间的风廓线资料，简要介绍了资料的性质和数据结构，并对资料的有效性进行了初步评估。给出了风廓线资料有效率随高度的分布及不同天气状况对资料有效率的影响。指出每10分钟一次的资料的有效率在相邻时次之间存在很大的差别，应使用多时次平均以增强其代表性。另外，通过了一致性检验的有效资料中仍可能存在少数代表性较差的资料。风廓线资料与探空资料对比发现两者所得的垂直风场精度相当。上述结果可作为应用风廓线雷达资料时的参考。     

Evaluating the NOAA Coastal and Marine Ecological Classification Standard in estuarine systems: A Columbia River Estuary case study

A common first step in conservation planning and resource management is to identify and classify habitat types, and this has led to a proliferation of habitat classification systems. Ideally, classifications should be scientifically and conceptually rigorous, with broad applicability across spatial and temporal scales. Successful systems will also be flexible and adaptable, with a framework and supporting lexicon accessible to users from a variety of disciplines and locations. A new, continental-scale classification system for coastal and marine habitats—the Coastal and Marine Ecological Classification Standard (CMECS)—is currently being developed for North America by NatureServe and the National Oceanic and Atmospheric Administration (NOAA). CMECS is a nested, hierarchical framework that applies a uniform set of rules and terminology across multiple habitat scales using a combination of oceanographic (e.g. salinity, temperature), physiographic (e.g. depth, substratum), and biological (e.g. community type) criteria. Estuaries are arguably the most difficult marine environments to classify due to large spatio-temporal variability resulting in rapidly shifting benthic and water column conditions. We simultaneously collected data at eleven subtidal sites in the Columbia River Estuary (CRE) in fall 2004 to evaluate whether the estuarine component of CMECS could adequately classify habitats across several scales for representative sites within the estuary spanning a range of conditions. Using outputs from an acoustic Doppler current profiler (ADCP), CTD (conductivity, temperature, depth) sensor, and PONAR (benthic dredge) we concluded that the CMECS hierarchy provided a spatially explicit framework in which to integrate multiple parameters to define macro-habitats at the 100 m² to >1000 m² scales, or across several tiers of the CMECS system. The classification's strengths lie in its nested, hierarchical structure and in the development of a standardized, yet flexible classification lexicon. The application of the CMECS to other estuaries in North America should therefore identify similar habitat types at similar scales as we identified in the CRE. We also suggest that the CMECS could be improved by refining classification thresholds to better reflect ecological processes, by direct integration of temporal variability, and by more explicitly linking physical and biological processes with habitat patterns.     

街谷环流和热力结构的数值模拟

文章介绍一种用于模拟街谷流场和温度场的动力学模式和热力学模式.应用动力模式模拟了方柱体塔楼和圆柱体塔楼形成的流场,应用动力和热力模式模拟了街谷中流场和温度场的日变化过程.计算实例表明,上述模式可用于城市街谷和建筑群风环境和热力环境研究以及街谷中空气污染物传输和扩散的计算.     

一次台风残涡引发的天津局地暴雨中尺度对流过程分析

本文利用欧洲中心再分析资料、FY-2G卫星云导风资料,多普勒雷达组网资料、风廓线、加密自动站资料,分析了2017年8月2日由北上台风残涡引起的天津局地暴雨过程中的中尺度对流过程,研究其触发条件,并探讨了形成原因。结果表明:在局地对流发生前,天津中北部地面附近并没有较好的动力以及湿度条件,且存在扰动逆温,扰动温度负值区(冷垫)厚度达到50 hPa以上,较大的水平风垂直切变在东南斜升气流下,水平涡管发生扭曲,产生垂直涡度,在边界层以上正负涡度之间形成辐合线,触发条件不稳定能量释放,在天津中北部产生局地对流,对流在触发后不断发展并向西北方向移动,与其西北侧线状多单体合并,导致天津北部的短时强降水天气。     

现代风成沉积物磁化率各向异性与风向关系的研究

通过对风洞及室内模拟定向风条件下的风成沉积物磁化率各向异性与风向之间关系的研究,发现风成沉积物磁化率各向异性的长轴方向的偏角不仅与风向有关,而且与粉尘沉积量有关。风成沉积物磁化率各向异性的长轴方向的偏角在α95（α95≤20°）的区间范围内与粉尘沉积量大的风向一致．在干旱、半干旱区,现代风成沉积物（沙丘、黄土的表层土）的磁化率各向异性的长轴方向的偏角在此范围区间内与常年盛行风向一致,尤其与沉积物沉降时的盛行风向一致．     

青藏铁路沿线砾石方格固沙机理风洞模拟研究

通过对青藏铁路沿线砾石方格内风速特征、固沙效率的风洞模拟实验研究发现,当气流运行至砾石方格前缘,水平风速迅速降低,砾石方格对风速的削弱作用非常显著,达到50%左右。气流在沿砾石方格向下风向移动过程中,水平梯度风速逐渐减小,但其减小幅度比较缓慢。砾石方格中风速随高度的分布遵循对数规律,各方格间风速变化趋势相对稳定。砾石方格地表粗糙度在5.2cm左右,摩阻速度为2.4 cm/s。砾石方格中固沙量随着进口风速的增加而增加,在相同风速下,固沙量随离沙源距离的增加呈指数关系递减。     

风向的统计方法研究

在核安全分析和环境影响评价中,必须使用到的是小时气象数据。对自动气象站小时风向的计算方法和小时数据如何统计,地面气象规范中和核安全导则中还没有定论,因此本文对小时风向统计方法展开讨论。目前小时风向值的计算方法有算术平均法、滑动平均法、矢量平均法和频率最高法,针对算术平均法和滑动平均法对经过0°的风向统计容易出现误差,本文提出对此的修正方法并对4种计算方法进行了比较。结果表明：文中过零风向修正方法简便准确,小时数据统计方法为正点前10min数据时,修正算术平均法更可靠,但该方法对风速为零时的判断容易出现误差,因此在小风、静风频率高的地方推荐矢量平均法。关于小时数据的划分方法,美国核管会RG1.23与我国核安全导则及地面气象规范中的规定不同,因此文中利用实测资料对不同小时数据统计方法所得结果比较,分析表明,取整点前或其他时段的10min和15min的数据进行平均的风向相关矩阵一致性为97.87%;取4个15min平均值的平均或6个10min数据平均值的平均作为小时值的风向相关矩阵一致性为99.96%,这两种统计方法与取10min和15min的一致性为86.00%,相对较差;取60min时段的平均值作为小时值则与其余方法一致性最差。     

高原和开阔山地风资源的估算

本文着重介绍了在高海拔地区如何利用短期梯度考察资料估算风源资的一种计算方案。     

The effect of wave-induced turbulence on intertidal mudflats: Impact of boat traffic and wind

Semi-diurnal and fortnightly surveys were carried out to quantify the effects of wind- and navigation-induced high-energy events on bed sediments above intertidal mudflats. The mudflats are located in the upper fluvial part (Oissel mudflat) and at the mouth (Vasière Nord mudflat) of the macrotidal Seine estuary. Instantaneous flow velocities and mudflat bed elevation were measured at a high frequency and high resolution with an acoustic doppler velocimeter (ADV) and an ALTUS altimeter, respectively. Suspended particulate matter concentrations were estimated by calibrating the ADV acoustic backscattered intensity with bed sediments collected at the study sites. Turbulent bed shear stress values were estimated by the turbulent kinetic energy method, using velocity variances filtered from the wave contribution. Wave shear stress and maximum wave–current shear stress values were calculated with the wave–current interaction (WCI) model, which is based on the bed roughness length, wave orbital velocities and the wave period (T_S). In the fluvial part of the estuary, boat passages occurred unevenly during the surveys and were characterized by long waves (T_S>50 s) induced by the drawdown effect and by short boat-waves (T_S<10 s). Boat waves generated large bottom shear stress values of 0.5 N m⁻² for 2–5 min periods and, in burst of several seconds, larger bottom shear stress values up to 1 N m⁻². At the mouth of the estuary, west south-west wind events generated short waves (T_S<10 s) of H_S values ranging from 0.1 to 0.3 m. In shallow-water environment (water depth <1.5 m), these waves produced bottom shear stress values between 1 and 2 N m⁻². Wave–current shear stress values are one order of magnitude larger than the current-induced shear stress and indicate that navigation and wind are the dominant hydrodynamic forcing parameters above the two mudflats. Bed elevation and SPM concentration time series showed that these high energy events induced erosion processes of up to several centimetres. Critical erosion shear stress (τ_ce) values were determined from the SPM concentration and bed elevation measurements. Rough τ_ce values were found above 0.2 N m⁻² for the Oissel mudflat and about 1 N m⁻² for the Vasière Nord mudflat.     

Wind environment in the Lee of Kauai Island,Hawaii during trade wind conditions: weather setting for the Helios Mishap

On 26 June 2003 (approximately 1030 local time) the Helios ultralight aircraft broke apart off the west coast of Kauai Island, Hawaii as it was climbing out of the Kauai wind shadow. Following the aircraft mishap, a study was carried out to understand the conditions on the day of the crash and to better characterize the wind in the lee of Kauai. As part of this effort, both aircraft measurements and numerical modelling studies were carried out. Measurements and models showed the trade wind flow was enhanced around the island creating a region of wind shear surrounding the leeside calm zone. This wind shear region was found to be vertically oriented along the south side but tilted northward with height along the northern side of the calm zone. Several other factors on the day of the crash were investigated including water vapour gradients, diurnal Island heating, and gravity waves but their possible influences on the crash could not be confirmed. While the numerical model captured the general features of the Kauai leeside winds, the orientation of the calm zone was north of the observed one.