The effect of rainfall on the wind in the surface layer

Raindrops falling into a wind-shear zone do not adjust their horizontal speeds immediately to the new wind. Thus, stresses develop which accelerate the air. The effect of raindrops falling into a layer with a logarithmic wind profile is investigated numerically. We find the adjustment of the wind to this situation to be quite small and only barely detectable, even in heavy rain conditions. The effect on the stress distribution is greater. Stress variations of 10–20 % and greater in the lowest 10 m are possible under certain conditions.     

The relative performance of various cup anemometers in a gusty wind

Summary Wind data collected during the Great Plains Turbulence Field Experiment of 1953 are used to study the relative performances of various types of cup anemometers subjected to air flow of known gustiness. Scatter diagrams which relate differences in the indicated mean speeds of two anemometers to gustiness are prepared. Although the instruments compared represent a wide range of moments of inertia, no relationship between gustiness and anemometer performance is noted. This result is examined in light of Schrenk's parameter which describes anemometer performance.

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Zusammenfassung Windbeobachtungen, welche während des Great Plains Turbulence Field Program im Jahre 1953 gewonnen wurden, werden zu einem Vergleich verschiedener Typen von Schalenkreuzanemometern in einem Windfeld von bekannter Böigkeit verwendet. Die Ergebnisse werden in Form von Streubildern veranschaulicht, in denen die Geschwindigkeits-unterschiede von verschiedenen Anemometern als Funktion des Böigkeitsgrades aufgetragen sind. Obgleich die verglichenen Anemometer erheblich verschiedene Trägheitsmomente besitzen, ergibt sich keine Abhängigkeit der Anzeigedifferenzen von der Böigkeit des Windes. Dieser Befund wird mit Hilfe des Schrenkschen Parameters näher beleuchtet.

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Résumé Les observations anémométriques effectuées dans le cadre du Great Plains Turbulence Field Program en 1953 sont utilisées ici dans le but de comparer différents types d'anémomètres à cupules placés dans un champ de mouvement de turbulence connue. Les résultats sont donnés sous forme d'essaims de points dans un système de référence: écarts individuels de l'indication et degré de turbulence. Bien que les instruments comparés présentent des moments d'inertie notablement différents, les écarts observés ne dépendent pas de la turbulence du vent. Ce résultat est encore examiné à l'aide du paramètre de Schrenk.

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With 4 Figures     

三类测风仪测量近地层小尺度风场比较

用LSF1-1型测风仪测量一分钟一次瞬时风速记录分析表明,该测风仪可以粗略测量比较长周期的风速脉动变化,但精度较差。FL和Dyne测风仪由于它们灵敏度低,精度不够,不太合适测量小尺度风场的脉动变化。     

湍流频散对边界层风廓线的影响

应用包括湍流粘性和频散的新的Reynolds平均动量方程，分析了边界层的垂直风速廓线，发现包含湍流频散的地面层的风速廓线对经典的风廓线指数规律有一个对数规律的修改；而且在不稳定层结下比在稳定层结下，湍流的频散效应更为显；在中性条件下，指数规律退化为对数规律并且Karman常数被另外一个常数所代替，而这个新常数也可以通过相似理论来获得。     

新疆风区有自记风记录参照站风速的均一化订正

为了较好地开展风能资源的详查与综合评价工作,对新疆风区有自记风记录的4个参照站2min与10min时距的风速统计序列在参考测站“元数据”直接进行迁站前后一致性订正、时次一致性检验与订正、高度一致性订正以及观测、测量系统一致性订正基础上,采用SNTH、POTTER、CUSUM等手段进行了客观的非均一性检验与均一化订正。结果表明：（1）对于达坂城与阿拉山口站而言,EL型感应仪使用期,2min与10min时距年平均风速序列并未因风的观测与记录系统由EN型测风处理仪替代而间断。EN型测风处理仪使用期,10min时距平均风速序列也并未因感应仪的变更而间断。（2）达坂城、哈巴河、托克逊站2min时距统计序列均在1980s年代存在间断现象;（3）阿拉山口、达坂城、哈巴河站2min时距统计序列在2005年观测系统改变前后的间断具有一定不确定性;（4）EL-J电接式自记仪使用期,哈巴河气象站10min时距平均风速统计序列在1992年前后出现了有别于2min时距统计序列的间断现象;（5）阿拉山口、哈巴河、托克逊参照气象站的年平均风速序列经客观均一化订正后,仍然存在显著的减小趋势。     

“黄蜂”边界层风速分析—— 台风平均风速的时距选取与强度估计

通过对热带风暴(TC)"黄蜂"登陆的一次边界层观测所得到风速资料的分析计算,取得不同时距下平均风速序列.比较不同时距选取时登陆TC的平均风速、风向和台风强度,发现1 min平均比10 min平均水平最大风速大25.30%,风向变化不大,TC强度指数1 min与10 min相差2%～4%.时距选取较小时,TC平均风速和强度变大,所测得风速区域也变大,而风向与时距的选取没有明显关系.只是在阵风变化比较大的情况下选取小的时距可以更好的表示这种特征.所以时距选取需要对所研究问题的需要进行分析,对不同的问题选取不同的时距以得到更好的结果.     

孟加拉湾的叶绿素a,海表温度和风速的趋势

孟加拉湾（BoB）是一个高能量活跃的地区,其短期内的动态变化将对浮游环境产生巨大影响."风泵"能够在BoB海域导致垂直的混合从而影响海表温度和叶绿素浓度.本文对2006——2016年的月平均Aqua-MODIS叶绿素a （chl-a）浓度数据和Sea WiFS月度气候态数据进行了分析,研究了叶绿素浓度的时间/季节变化和温度以及风速的关系.基于季风期间的chl-a变异与海表温度（SST）,评估了在BoB海域它们之间的关系和变化.chl-a浓度值的趋势分析表明,该区域的垂直混合非常低,冬季最高,夏季最低.冬季最大chl-a浓度值为0.50 mg/m³,并且从2月开始下降到夏季季风期间.与冬季季风相比,夏季季风期间叶绿素表现出较低的浓度.在夏季季风期间,特别是在7月和8月,由于云层密集,卫星传感器无法准确捕获chl-a浓度值.chl-a浓度和SST之间相关系数R²值为0.218 1.     

城市化对近地层风速概率分布及参数的影响

通过地面风速Weibull概率分布参数的阶段变化来描述城市化对地面风速的影响,并通过理论分析得出城市化进程导致其尺度参数c缩小,位置参数r增大的趋势效应的结论。将北京等8个城市1982—2005年地面天气资料定时数据按时间划分为前、后两个时段,分别拟合分布曲线的参数,对比前、后两个时段的拟合结果,验证了理论分析所得结论,即随城市的发展,各城市风参数c不同程度地缩小,r不同程度地增大,同时概率密度曲线的峰值均增大;不同城市的风速概率密度函数曲线变化特征有所不同,根据前、后时段概率密度曲线变化的特征,8个城市风速概率分布变化大致可分为A、B两种类型,两者的主要差异是A型变化特征为在曲线两端(大风和静风)的概率都减少,曲线分布更加集中;B型则是大风概率减少而静风的概率则增大,曲线向左移动;A型变化城市的r参数平均增大46.3%,明显大于B型城市的15.7%。初步资料分析还表明,风参数c和r变化幅度与城市化扩张速度有关。     

The association of surface wind stresses over Indian Ocean with monsoon rainfall

Summary Variability of Indian summer monsoon rainfall is examined with respect to variability of surface wind stresses over Indian Ocean. The Indian Ocean region extending from 40°–120° E, and 30° S–25° N, has been divided into 8 homogeneous subregions, viz (1) Arabian Sea (AS), (2) Bay of Bengal (BB), (3) West-equatorial Indian Ocean (WEIO), (4) Central-equatorial Indian Ocean (CEIO), (5) East-equatorial Indian Ocean (EEIO), (6) South-west Indian Ocean (SWIO), (7) South-central Indian Ocean (SCIO), and (8) South-east Indian Ocean (SEIO). The period of study extends for 13 years from 1982–1994. Monthly NCEP surface wind stress data of five months – May through September, have been used in the study. The spatial variability of seasonal and monthly surface wind stresses shows very low values over CEIO and EEIO and very high values over AS, SWIO, and SEIO regions. On the seasonal scale, all India summer monsoon rainfall (AISMR) shows concurrent positive relationships with the surface wind stresses over AS, BB, WEIO, SWIO and SCIO and negative relationships with the surface wind stresses over EEIO and SEIO. The relationships of AISMR with the surface wind stresses over AS and WEIO are significant at 5% level. The concurrent relationships between monthly surface wind stresses over these 8 oceanic sub-regions and monthly subdivisional rainfalls over 29 sub-divisions have been studied. The rainfalls over the subdivisions in the central India and on the west coast of India are found to be significantly related with surface wind stresses over AS, SWIO, SCIO. Monthly subdivisional rainfalls of four subdivisions in the peninsular India show negative relationship with BB surface wind stresses. May surface wind stresses over AS, BB, WEIO, CEIO and SWIO have been found to be positively related with ensuing AISMR. The relationship with AS wind stresses is significant at 5% level and hence may be considered as a potential predictor of AISMR. Received May 21, 2001 Revised October 8, 2001     

Reduction of horizontal wind speed in a boundary layer with obstacles

The reduction of horizontal wind speed at hub height in an infinite cluster of wind turbines is computed from a balance between a loss of horizontal momentum due to the drag and replenishment from above by turbulent fluxes. This reduction is derived without assumptions concerning the vertical wind profile above or below hub height, only some basic assumptions on turbulent exchange have been made. Two applications of the result are presented, one considering wind turbines and one pressure drag on orographic obstacles in the atmospheric boundary layer. Both applications are basically governed by the same kind of momentum balance.     

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.     

城市化对石家庄站近地面风速趋势的影响

利用1972—2012年石家庄城市站和4个乡村站地面风速资料,采用城乡对比方法,对石家庄城市站地面风速序列中的城市化影响进行分析,结果表明,石家庄站年和季节平均地面风速和平均10 min最大风速的长期下降趋势,主要是由城市化因素引起。具体结论如下：(1)石家庄站年和四季平均风速、平均10 min最大风速和大风日数均呈极显著的减少趋势,年平均减少速率分别为-0.15 (m/s)/10a、-1.05 (m/s)/10a和-2.90 d/10a;乡村站年平均风速呈微弱下降趋势,年平均10 min最大风速减少较为明显,年大风日数减少趋势非常显著,减少速率分别为-0.02 (m/s)/10a、-0.21 (m/s)/10a和-2.19 d/10a。(2)石家庄站年平均风速下降趋势中的城市化影响为-0.13 (m/s)/10a,城市化影响非常显著,城市化贡献率达到86.0%。该站春、夏、秋、冬季平均风速变化的城市化影响分别为-0.16 (m/s)/10a、-0.10 (m/s)/10a、-0.13 (m/s)/10a和-0.15 (m/s)/10a,城市化贡献率分别为82.8%、87.6%、88.6%和85.4%。(3)石家庄站年平均10 min最大风速变化趋势中的城市化影响为-0.84 (m/s)/10a,城市化贡献率为79.7%;春、夏、秋、冬季平均10 min最大风速变化趋势中的城市化影响分别为-0.94 (m/s)/10a、-0.80 (m/s)/10a、-0.60 (m/s)/10a和-1.01 (m/s)/10a,城市化贡献率分别达到90.4%、78.6%、64.9%和79.1%。(4)城市化对石家庄站年大风日数减少的影响不显著,但冬季大风日数减少仍明显与城市化过程有关。     

低层风场在暴雨发生中的动力作用

通过对两次中尺度暴雨过程的计算,分析研究了风的散度与涡度的变化以及与暴雨的关系。指出散度场比涡度场的变化快、尺度小。辐合增加的地区与暴雨区配合最好。对于中尺度系统、完全的散度方程中风速平流的散度项是一个重要的项,它的正值分布区与暴雨区的位置比其他各项有较好的对应。低层流场中大风速中心或低空急流的出现直接导致了散度方程中A项及带有风速垂直切变项的增大,构成了暴雨发生的不可忽视的动力因素。     

Transport rate of drifting snow and the mean wind speed profile

Transport rates, measured by weighing snow blown into a filter fabric trap, were greater over hard snow or ice than for the same wind speed over soft, fresh snow surfaces. Analysis of wind speed profiles from nine blizzards showed that friction between moving particles and the surface was less, and particle speeds were greater over hard surfaces. Transport rates at a given wind speed increased rapidly as aerodynamic roughness decreased in the rough-smooth transition region. Bagnold's theory for bed load transport provided a useful framework for the analysis.     

Characteristics of wind speed and wind direction in the atmospheric boundary layer on the southern coast of Bulgaria

The characteristics of wind speed and wind direction in the boundary atmospheric layer measured at the meteorological station in Akhtopol (Bulgaria) are presented. The measurements were carried out with the Scintec sodar and MK-15 automatic meteorological station. The sodar measurement data on wind parameters at different heights in different months are presented as well as the frequency of inshore and offshore wind directions, that enables to trace the intensity of the breeze circulation. The frequency of calms and wind speeds at the heights of 50, 100, and 200 m according to gradations for different months and the probability of wind of various speeds depending on the direction are also given. The breeze front characteristics in June–September of 2009 are computed from the speed and direction of surface wind measured with the acoustic anemometer of MK-15 complex.     

ASCAT近岸风在山东沿海的适用性分析

利用2013年1月—2014年12月山东近海的8个浮标站、海岛站和自动站资料与ASCAT近岸风速和风向进行对比,以分析ASCAT反演风场在山东沿海的适用性。研究发现：总体上看,ASCAT近岸风速与代表站实况风速正相关,ASCAT近岸风速在山东沿海误差较小,风向有明显的偏离。ASCAT近岸风在渤海、渤海海峡和黄海北部的适用性优于黄海中部。风力不同时,ASCAT近岸风速与实况偏差有明显差别,表现为当实况出现6级及以上的大风,ASCAT近岸风速小于实况;当实况出现6级以下的风,ASCAT近岸风速大于实况。就ASCAT风速偏差而言,6级以下的风速偏差小于6级及以上风。ASCAT近岸风向与实况偏差也有明显差别,当实况出现6级及以上的大风,ASCAT近岸风向与实况的偏离变小;当实况出现6级以下的风,ASCAT近岸风向与实况的偏离变大。因此,ASCAT近岸风速在山东沿海有较好的适用性,6级以下风更优;ASCAT近岸风向也有一定的适用性,6级及以上风向可用性比6级以下强。