系留气艇探测风速的误差订正及其应用评估

使用系留气艇探空系统在常州、苏州、南京市区对边界层风速、温度、湿度廓线进行了观测,原始数据表明探测结果存在明显的系统误差。本文主要讨论风速订正问题,分析发现风速误差与高度和风速有关,据此提出了依据高度和依据风速的两种订正方案。对比结果表明:两种方案都能有效修正系留气艇测量风速的系统误差,高度订正方案表现更好。本文还用订正后的系留气艇探测结果与苏州市气象局的风廓线雷达资料进行对比,结果显示风廓线雷达探测结果在500 m以下系统偏小。     

On the deep‐water fetch laws for wind‐generated surface gravity waves

Abstract

With the object of providing an accurate set of open‐sea wave spectra in a variety of conditions, we deployed, in conjunction with CASP, an array of 9 wave buoys (3 directional, 6 non‐directional) along a 30‐km line offshore from Martinique Beach, N.S. A large set of high‐quality wave spectra was collected in conjunction with extensive meteorological information. The data set is unique in the sense that a large onshore swell component was normally present.

Offshore‐wind cases for three windows: ±5°, ±15° and ±30° with respect to the shore normal, have been considered. Wind speed was found to be a strong function of fetch, and attempts were made to allow for this in the analysis. Power‐law regressions have been produced of dimensionless sea energy, peak frequency and high‐frequency spectral level (the Kitaigorodskii “alpha” parameter) vs dimensionless fetch and wind speed (inverse wave age). The regressions are compared with earlier work: the Joint North Sea Waves Project (Jonswap) and the Canada Centre for Inland Waters (CCIW) Lake Ontario study.

The comparisons indicate that dimensionless wave energies, peak frequencies and alpha values in this experiment are comparable with those from earlier experiments; in spite of different wind analysis methods, the CASP and CCIW fetch‐limited growth laws are consistent within the contexts of the two experiments. Differences among the estimated parameters are as large within the analyses of the three windows as they are among the three experiments we compare.     

On calculation of wind speed in tornado

A formula is obtained for calculation of wind speed in tornado, as proportional to the speed of convective updraft. Results are presented of wind speed calculation using the formula for 57 tornadoes observed at different time and in different regions of the world. Possibilities are shown of tornado wind speed forecasting taking into account criteria of tornado danger of the Cb clouds.     

On estimating the return values for time series of wind speed and wind wave height

In order to estimate the return values ofthe time series ofwind speed and wind wave height, it is proposed to use the extrapolation of polynomial approximation constructed for the small part of the tail of probability function of the series considered. The method is based on the optimization of the accuracy of polynomial approximation implemented by varying the length and shift of the used part of probability function and the polynomial exponent. Optimization includes control over quality criteria for approximation that are aimed at increasing approximation accuracy. On the example of wind reanalysis data and the results of numerical simulation of wind waves in the Indian Ocean for the period of 1980-2010, the proposed method is applied to obtain the return value estimates of the mentioned parameters at several fixed points in the ocean.     

On fitting the log-linear model to wind speed and temperature profiles over a melting glacier

The profile structure of wind speed and temperature in katabatic flow over a melting glacier is analyzed within the log-linear framework. Similarity between windspeed and temperature profiles is indicated but the log-linear model should be restricted to heights within 1.5 m of the ice. Marked deviation from the model occur at greater heights, probably due to the effects of flux divergence.Unlike results from other stable atmospheres, a decreases with increasing stability. This may arise from the use of the Obukhov length L. When the height H at which the wind speed reaches its maximum value is used instead, does not vary with stability. It has mean values of 4.5 and 4.3 for windspeed and temperature profiles, respectively.     

On extraction of time-varying mean wind speed from wind record based on stationarity index

We have proposed in a previous study a non-stationary wind model to represent the typhoon record as a summation of a time-varying mean wind speed (TVM) and a stationary turbulence. This note further suggests a quantitative scheme, rather than the previous qualitative method, to find the best TVM for any given wind record. Trial TVMs are first extracted from the wind record by a data-processing technique named empirical mode decomposition. For each TVM, its corresponding turbulent component is computed by removing the TVM from the original wind record, and the degree of stationarity of the turbulence component is checked. The best TVM is taken as the one that leads to the maximum degree of stationarity. The degree of stationarity of turbulence is quantified by two indicators: ?? the ratio of horizontal wind variability and wind speed; and ?? the ratio of friction velocity at different Reynolds averaging periods. The applicability of the suggested scheme is validated with 550 typhoon and 3300 monsoon records of 10 minute duration and at different measurement heights. Threshold values for the two stationary indicators ?? and ?? are determined using field measurements and their sensitivities to the Reynolds averaging periods are discussed. Observations in this study demonstrate that the suggested scheme is proper for finding the TVM of a wind record. For a stationarity quantification of 10 minute duration record, the ?? indicator with 30 second Reynolds averaging period is recommended.     

High-frequency radar observations of sea waves travelling in opposition to the wind

High-frequency (HF) radar observations of sea waves apparently travelling against the wind are discussed. In some cases, it appears that the wave angular spectrum does contain components travelling against the wind. Some data taken on the Barbados Island during BOMEX have been analyzed, and they show that such components increase in amplitude with distance from a windward shore. It is shown that the order of magnitude of the observed growth rates can be explained by resonant non-linear interaction within the wave spectrum.     

多普勒雷达与L波段雷达垂直风廓线对比分析北大核心

利用2012-2017年阜阳多普勒雷达与L波段雷达测风数据进行对比分析,统计两者的相关性和测量误差,进一步了解多普勒雷达风廓线产品的准确性和可信度。结果表明:两者测风结果一致性较好,风向和风速相关系数分别为0.97和0.94,标准差分别为19.5°和2.65 m·s^(-1)。多普勒雷达风速总体上在同一高度比L波段雷达风速偏小,两者风速相对偏差平均为24.48%;风速标准差随高度增高呈增大趋势,在降水期间对比差值小于非降水;风向标准差在7 km以下呈递减趋势,8 km以上有小幅增加趋势;风速相关系数随高度增加呈增大趋势,除低空偏低以外,其他高度相关系数均较高。     

风廓线雷达在高空风场分析中的应用

利用大连风廓线雷达高时空分辨率风场观测资料,统计2011年雷达站上空各层水平及垂直风速的分布特征.通过分析发现:最大水平风速通常出现在12 km上下,受高空急流的影响,各季节高空最大水平风速出现高度不同,4 km以下高空水平风速随高度的变化各月份存在一定差异,4 km以上至最大风速层,水平风速随高度的升高而增大,最大风速层以上至雷达测量的上限水平风速随高度增加先减小后增大;高空垂直风速在夏季较为明显,秋季次之,冬春季节最小;6月是全年月均垂直风速最大的月份,在500～1300 m高度层存在一个上升气流中心,平均风速大于0.6 m/s,2月各高度平均垂直风速全年最小.     

华南暴雨试验期间香港风廓线雷达资料的评估

联合应用5部风廓线雷达、多普勒天气雷达组网观测资料,并结合海河流域自动气象站资料详细分析了2012年7月21日海河流域强降水发生、发展过程中温度场、风场演变特征。结果表明：这次强降水天气具有明显的中尺度天气特征,强降水主要发生在露点温度梯度区内。低空急流指数变化对短时强降水的峰值有一定的指示作用,它的快速增加意味着强降水将要开始。垂直风切变对短时强降水的形成具有参考价值：降水开始前,2 500-3 000 m的风速和风切变首先开始增大,之后大风向1 000 m以下扩散,风切变梯度增强预示着短时强降水开始;1 000-1 500 m风速迅速减小,高层也随之减小,强降水趋于减弱或结束。风廓线雷达中风向风速的变化能够指示系统的过境时间, 以上结论对预报强降水的起始及降水的持续时间具有使用价值。

     

风廓线雷达资料质量控制及其同化应用

为更好地同化风廓线雷达观测资料开展了相应的质量控制与同化应用研究。针对2013年5月广东地区13部风廓线雷达的观测数据,采用经验正交函数(EOF) 分析方法对其进行质量控制。相比原始观测,经过质量控制的风场提高(降低)了来自时空大(小)尺度的贡献,较好地滤除了小尺度高频脉动,也较好地保留了大尺度平均状态与局地中小尺度系统的共同影响,并且更加接近ECMWF再分析场。此外,还对质量控制后的数据进行了垂直稀疏化。分别计算了质量控制前、后风廓线雷达观测与NCEP 6 h预报场的差值,对比差值的特征发现,经过质量控制的数据的观测增量更好地满足了高斯分布与无偏假设。针对一个实际天气个例,基于GRAPES 3D-Var同化系统,分析了质量控制后的风廓线雷达资料对模式分析与预报的影响。试验表明,在循环同化过程中加入风廓线雷达资料可以更好地描述模式初始场低层风场的特征,从而对强降水的位置与强度做出更好的预报。针对2013年5月的批量试验表明,同化风廓线雷达资料使短期降水预报有明显的改善。     

风电场风速数值预报的误差分析及订正

使用WRF模式对内蒙古某风电场区域内的2011年1-6月,50m高度的风速进行了模拟,并结合实测风速对模拟结果进行了评估。在此基础上再利用自回归模型(AR模型)和持续法对WRF模式模拟结果进行了订正预报,订正结果表明:AR模型和持续法都能有效地减小WRF模式风速的模拟误差,AR模型订正效果优于持续法。为能对订正预报时效进行延长,提出了"假设观测值"概念。在AR模型的基础上建立一种新的订正模型称之为New AR模型。其订正预报结果表明:新模型能在12h时效内,改善WRF模式风速模拟精度,其中6h的改进效果较好。     

济南边界层风廓线雷达与L波段雷达探空测风资料对比研究

采用统计、相关分析等方法,对2014年济南站边界层风廓线雷达观测资料和L波段雷达探空资料进行了长期时空变化规律的对比,进而研究了地面无降雨、有降雨时段两者的风向、风速数据的相关关系及差值。结果得出全年有降雨、无降雨时段两者的风向、风速总体一致性较好,相关性较高,并具有较好可比性和互补性的结论,对了解固定式边界层风廓线雷达探测的准确性,改进观测资料质量控制方法等具有很好的参考价值。     

典型风场的多普勒天气雷达速度图象模拟与识别及暴雨实例分析

使用湖北新一代天气雷达平均散度反演产品,结合高空、地面和雷达观测资料,统计分析了短时强降水发生发展过程中大气低层辐合的演变特征,检验低层辐合的预警指示意义,并解释其天气意义。结果表明：低层辐合演变一般具有单波谷或双波谷特征,且中尺度特征明显。在强降水前期低层散度为辐合或由辐散转为辐合,强降水集中期低层辐合发展至最强,之后逐渐减弱,强降水后期低层转为辐散。低层辐合且明显增强可能具有预警指示意义。雷暴冷出流和低空急流加强对低层辐合有重要贡献。

     

On theoretical wind speed and temperature profiles over the sea with applications to data from sable island,Nova Scotia

Abstract

In October 1985, the Boundary‐Layer Research Division of the Atmospheric Environment Service conducted an experiment on Sable Island, Nova Scotia, where 10‐m wind measurements were made at a number of locations. Wind data were also collected at 4 levels on one of the 10‐m masts and at 6 levels on a 26‐m mast, both located on the South Beach. Other data used in the present study consisted of air temperature measured at 9 m and sea temperature measured at the beach.

The theory for wind speed and temperature profiles over the sea is reviewed. A method of deriving over‐sea profile parameters (u_*, θ_*, Z₀, L) from wind data at one level and the air‐sea temperature difference is described. The method is limited to applications either over homogeneous open ocean or, provided measurements are taken above the internal boundary layer generated by the change of roughness at the coastline, over a flat beach (without coastal orography). The heights at which the method is applied must be within the surface layer which must not have any discontinuities in wind speed or temperature in the vertical, such as are often associated with inversion layers. An application to data collected at beach sites in onshore flow during the October 1985 experiment is illustrated.

Once the above parameters are obtained, theoretical wind profiles may be computed and compared with observed profiles. In order to make a proper comparison it is essential to account for internal boundary layers generated at the shoreline by the step‐change in surface roughness. Only the data measured above the internal boundary layer are representative of over‐sea conditions and may, therefore, be used for verifying the theoretical profiles. The agreement between calculated and measured data is generally very good. One complication, however, is a slight upstream‐blockage effect due to a 7‐m high dune located about 140 m downwind of the 26‐m mast. Estimates of the magnitude of this effect partially account for small discrepancies in the results at the 26‐ and 10‐m mast locations.

An estimation of the most probable errors in the calculated parameters, based on assumed measurement errors, is included in the computer program. Results suggest that small measurement errors can explain the above discrepancies.     

风廓线雷达风场资料质量控制初探

基于2016年2月和8月江西宜春风廓线雷达探测水平风场数据,分别利用扩展经验正交函数(EOF)分析重构法和高斯滤波法对其进行质量控制。结果发现,相比原始观测风场,EOF分析重构法和高斯滤波法均能有效过滤风廓线雷达原始风场的高频脉动。两种方法对比分析发现,对于空间尺度的瞬时扰动,EOF分析重构法质控效果优于高斯滤波法;对于时间尺度的瞬时扰动,高斯滤波法质控效果优于EOF方法。