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1.
Two Gill Solent Ultrasonic anemometers, models 1012R2 and 1210R3, weretested in field parallel measurements against a windvane based hot-film anemometerwith additional sensors for temperature and wet-bulb temperature, the MIUU (MIUU:Meteorology Institute, Uppsala University) instrument. This instrument was shown toretain its precision from laminar wind-tunnel tests when used in atmospheric turbulentflow. This contrasts strongly to the observed results for the two sonic anemometers,which were first calibrated in laminar wind-tunnel flow. Individual three-dimensionalcalibration matrices were constructed, and were shown to reduce the remaining calibration uncertainty for the wind speed to 0.4–0.8% for all azimuths and for angles of attack within ±40°. In the field intercomparison tests of the sonics against the MIUU instrument, it was found that the precision not only of the mean wind speed but of all second-order moments studied (variances and covariances, with and without temperature) deteriorated by a factor of typically three to four. Most of the scatter appears to be random, but in the case of the wind speed, a clear dependence on wind direction is found as well. It is concluded that the correction for the effect of the vertical supporting rods of the R2 and R3 instruments, which gives nearly perfect agreement for laminar flow, does not work entirely satisfactory in the natural turbulent flow. This, in turn, is likely to be so because of high sensitivity of the wake behind the cylindrical supporting rods to the character of the approach flow. 相似文献
2.
Another Simple Method of Spectral Correction to Obtain Robust Eddy-Covariance Results 总被引：3，自引：0，他引：3
The eddy-covariance method is the state-of-the-art tool to measure mass and energy fluxes, though many measuring systems (particularly
closed-path systems) show strong spectral attenuation that causes significant underestimates of actual mass fluxes. The standard
way to correct these underestimates is to use theoretically derived transfer functions. Practical implementation has shown
that the attenuation, especially of closed-path systems, is underestimated by this method, even when the additional tube damping
is considered. This paper introduces and tests three alternative site-specific and hardware specific correction methods based
on spectral analysis, which typically enhance—additionally to the classical correction—the calculated mass fluxes based on
closed-path analysers, as their inevitable tubing and the filters used cause additional flow attenuation. Two of the three
methods are based on a site-specific and hardware specific transfer functions, the third uses direct comparison of cospectra.
Primarily the methods based on transfer functions proved to be easy-to-handle once established for the specific set-up and
measurement site. They represent practical and robust methods to correct for spectral attenuation. 相似文献
3.
在中尺度WRF-EnSRF系统中最新引入的采样误差订正局地化方法不仅考虑了回归系数偏差,而且计算量较小。该方法基于状态变量和对应观测值的相关系数的分布关系,根据离线蒙特卡洛技术制作的关于集合数和样本相关系数的查找表格确定局地化系数因子,进而订正由集合数选取有限造成的背景误差协方差被低估引起的采样误差。本文利用风暴过程的雷达观测资料做了一系列风暴尺度的资料同化理想试验,探讨了采样误差订正局地化方法在风暴尺度集合卡尔曼滤波同化中的技术特点和同化效果。结果表明:相比于经验局地化方法,采样误差订正局地化方法能够有效地改善集合同化的效果,对距离的敏感度更低,尤其在天气系统发展变化较快的阶段,新方法优势更大。并且,对不同观测变量以及在风暴发展的不同阶段使用不同的局地化方法,所得的结果都存在一定的差异,因此需要根据同化对象合理地选择局地化方法。 相似文献
4.
A widely used method of evaluating effects of climate change on flow regime is to perturb the climate inputs to a rainfall–runoff model and examine the effect on a statistic of the modelled flows. Such studies require four elements: a method of perturbing the climate, a rainfall–runoff model, a study catchment and a flow index. In practice the direction and magnitude of the estimated effects depend on each of the four elements, leading to concern over the usefulness and generality of the results. To investigate these uncertainties two climate scenarios and eight climate sensitivity tests have been applied to three UK catchments using two conceptual rainfall–runoff models in order to quantify effects of climate change on three flow indices representing mean runoff, flood magnitudes and low flows. The sensitivity tests were found to be useful to assess the suitability of the models to simulate flows outside the conditions experienced in their calibration. Both models gave internally consistent results but, on close examination, one model was found inappropriate for this application. Results show that the effect of climate change on flow varies between catchments and that different flow response indices can change in opposite directions, e.g. floods increased in magnitude while low flows reduced. Contrasting results were obtained from the two climate scenarios. 相似文献
5.
《Dynamics of Atmospheres and Oceans》2001,33(2):135-156
Symmetry properties of steady solutions of the barotropic quasigeostrophic vorticity equation are explored using mirror reflections with respect to mid-basin longitude and latitude. The analysis is conducted by perturbing the fully inertial solution, the zeroth-order solution or the Fofonoff mode, by introducing forcing and dissipation as a first order correction. In the context of a classical square-basin and single-gyre circulation subject to bottom friction, it is shown numerically and analytically that the full solution can be approximated by the superposition of three components each having definite symmetry properties under longitude and latitude reflections: the north–south symmetric and antisymmetric components of the zeroth-order solution and the east–west antisymmetric component of the first-order correction. The flow patterns of the individual components are discussed. 相似文献
6.
Tilt corrections over complex terrain and their implication for CO<Subscript>2</Subscript> transport
Jielun Sun 《Boundary-Layer Meteorology》2007,124(2):143-159
Observational data from sonic anemometers are commonly rotated from sonic to streamline coordinates, a procedure that is called
tilt correction. Tilt corrections are often used to post-process air velocity data collected from sonic anemometers to allow
objective interpretation of air flow data relative to the Earth. Since streamline coordinates depend on dynamical characteristics
of the flow, the tilt correction depends not only on temporal and spatial variations of the flow, but also on local circulations.
We found that ensemble- averaged slope flows are approximately parallel to the terrain slope close to the ground within the
canopy layer, but not above, due to the influence of the diurnal variation of local vertical circulations. As a result, the
diurnal variation of the observed vertical velocity in streamline coordinates at 21.5 m above the ground over 11-m tall forest
canopies can be opposite to that calculated from the continuity equation. To estimate CO2 transport over sloping terrain, a workable reference coordinate system is needed such that multiple sonic anemometers have
a common reference relative to the Earth. Streamline coordinate systems can be the choice of the common reference coordinate
system only if flow, at least ensemble-averaged flow, is parallel to terrain slopes. The choice of the reference coordinate
system and its implication in investigation of CO2 transport are discussed.
The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
7.
8.
The impact of ground heating on flow fields in street canyons under different ambient wind speed conditions was studied based on numerical methods.A series of numerical tests were performed,and three factors including height-to-width(H/W) ratio,ambient wind speed and ground heating intensity were taken into account.Three types of street canyon with H/W ratios of 0.5,1.0 and 2.0,respectively,were used in the simulation and seven speed values ranging from 0.0 to 3.0 m s 1 were set for the ambient wind speed.The ground heating intensity,which was defined as the difference between the ground temperature and air temperature,ranged from 10 to 40 K with an increase of 10 K in the tests.The results showed that under calm conditions,ground heating could induce circulation with a wind speed of around 1.0 m s 1,which is enough to disperse pollutants in a street canyon.It was also found that an ambient wind speed threshold may exist for street canyons with a fixed H/W ratio.When ambient wind speed was lower than the threshold identified in this study,the impact of the thermal effect on the flow field was obvious,and there existed a multi-vortex flow pattern in the street canyon.When the ambient wind speed was higher than the threshold,the circulation pattern was basically determined by dynamic effects.The tests on the impact of heating intensity showed that a higher ground heating intensity could strengthen the vortical flow within the street canyon,which would help improve pollutant diffusion capability in street canyons. 相似文献
9.
利用大邑、西岭雪山滑雪场及周边区域自动站2005～2017年每年10月～次年2月逐日最低温度资料，通过统计分析区域自动站与大邑站候平均最低温度差值，建立以大邑本站最低温度预报值为基础，加上逐候最低温度差值后得到区域各站的日最低温度预报的候最低温度差值订正方法；用距滑雪场最近的格点温度预报数据代替滑雪场站点温度预报，选出最低温度，以气温预报变化量，建立最低气温预报的模式温度订正方法；建立以候最低温度差值订正和模式温度订正进行加权平均的最低温度集成订正方法。通过对以上三种最低温度预报方法进行检验，发现最低温度集成订正方法预报准确率最高。基于最低温度集成订正方法预报西岭雪山滑雪场的最低温度，结合智能网格降水预报结果和降雪最低温度阈值判别，建立西岭雪山降雪的订正预报方法。 相似文献
10.
Flow distortion is a universal consideration in the measurement of wind. Usually the distortion results from deflection of the flow by the support. Instruments mounted on airplanes, however, experience an additional deflection associated with lift, which changes rapidly and continuously during flight. In front of the airplane, this deflection appears as upwash. Characteristic upwash contamination ranges from 0.5 to 2.5 m s-1, depending on wing loading, flight speed, and forward distance from the wing to the measurement location. On pressure-radome installations the distance from the wing is usually small and the potential for upwash contamination large. Sensors mounted at the end of long probes attached to smaller airplanes with light wing loading are less susceptible to upwash contamination. Since wing loading also depends on the local vertical wind velocity the upwash velocity is directly correlated with vertical wind velocity. Generally, empirical corrections are derived from flight tests. We develop a simple method from principles of aerodynamics which explains these corrections in terms of upwash. The applicability of our approach to moderate upwash is demonstrated with data collected from the NOAA Long-EZ research airplane. More severe upwash conditions require a more sophisticated correction beyond the scope of this paper, but basically derived from the same principles.Oak Ridge Associated Universities, assigned to NOAA/ATDD 相似文献
11.
风沙流中风速廓线的数值模拟与实验验证 总被引：2，自引：0，他引：2
如何描述风沙流中被风沙运动改变了的风速廓线是风沙相互作用研究中的关键问题之一.该文中将跃移风沙流视为一种颗粒拟流体,将跃移颗粒对气流产生的阻力用颗粒流的阻力系数来表达,建立了描写两场相互作用的数学模型.颗粒流的阻力系数采用了前人在液态流化床研究中得出的阻力系数表达形式,通过引入一个修正系数,使其适用于风沙流(气-固两相流).将风沙边界层划分为跃移颗粒所产生的阻力不可忽略的内边界层和跃移颗粒阻力可以忽略但受内边界层影响的外边界层,分别建立了内边界层和外边界层的风速廓线表达式.应用所建立的数学模型,根据由风洞实验测定的跃移风沙流的浓度分布和速度分布资料,计算了跃移风沙流中的风速廓线,并与风洞实测结果进行了对比.结果表明,计算风速廓线与实测风速廓线吻合得比较好,在半对数图上均为上凸的曲线,有别于无风沙运动时的直线.跃移边界层外风速分布可较好地用对数函数来描述.对风沙流中风速廓线的进一步分析证实了风沙物理学奠基人Bagnold在其早期观测风沙流中的风速廓线时提出的"结点现象"(Bagnold结),该结点的高度随风速的增大而升高,随颗粒粒径的增大而降低.根据数值模拟和模拟实验,可以认为有风沙运动的动床剪切风速是综合反映风场与跃移层以及地表之间相互作用的物理量. 相似文献
12.
K. H. Papadopoulos N. C. Stefantos U. S. Paulsen E. Morfiadakis 《Boundary-Layer Meteorology》2001,101(1):77-107
Four commercial and one research cup anemometers were comparatively tested in a complex terrain site to quantify the effects of turbulence and flow inclination on the wind speed measurements. The difference of the mean windspeed reading between the anemometers was as much as 2% for wind directions where the mean flow was horizontal. This difference was large enough to be attributed to the well-known overspeeding effect related to the differing distance constant (ranging from 1.7 to 5 m) of the cup anemometers. The application of a theoretical model of the cup-anemometer behaviour in athree-dimensional turbulent wind field proved successful in explaining theobserved differences.Additional measurements were taken with the anemometers tilted at known angles into and out of the incident wind flow. Thus, a field-derived angular response curve is constructed for each anemometer and the deviations from publishedwind-tunnel results are discussed.The uncertainties of, or false assumptions about, the angular response characteristics of the anemometers contribute the largest amount inthe observed errors of mean wind speed even for a horizontal mean flow. The angular response curves are finally used to correct the 10-min mean windspeed. The necessary information for the correction is the turbulent intensity (preferably in the vertical direction) and the mean flow inclination.For demanding applications, the angular response parameters of cup anemometers should be taken into account. The incorporation of the angular response parameters in a correction scheme would be most robustly applied if their variation with inclination and wind speed was smooth. 相似文献
13.
Ship-board measurements and estimations of air-sea fluxes in the western tropical pacific during TOGA COARE 总被引：1，自引：0，他引：1
Direct air-sea flux measurements were made on R/V Kexue #1 at 4 ° S, 156 ° E during the Tropical Ocean Global Atmosphere (TOGA)
Coupled Ocean-Atmospheric Response Experiment (COARE) Intensive Observation Period (IOP). An array of six accelerometers was
used to measure the motion of the anchored ship, and a sonic anemometer and Lyman-α hygrometer were used to measure the turbulent
wind vector and specific humidity. The contamination of the turbulent wind components by ship motion was largely removed by
an improvement of a procedure due to Shao based on the acceleration signals. The scheme of the wind correction for ship motion
is briefly outlined. Results are presented from data for the best wind direction relative to the ship to minimize flow distortion
effects. Both the time series and the power spectra of the sonic-measured wind components show swell-induced ship motion contamination,
which is largely removed by the accelerometer correction scheme. There was less contamination in the longitudinal wind component
than in the vertical and transverse components. The spectral characteristics of the surface-layer turbulence properties are
compared with those from previous land and ocean results. Momentum and latent heat fluxes were calculated by eddy correlation
and compared to those estimated by the inertial dissipation method and the TOGA COARE bulk formula. The estimations of wind
stress determined by eddy correlation are smaller than those from the TOGA COARE bulk formula, especially for higher wind
speeds, while those from the bulk formula and inertial dissipation technique are generally in agreement. The estimations of
latent heat flux from the three different methods are in reasonable agreement. The effect of the correction for ship motion
on latent heat fluxes is not as large as on momentum fluxes. 相似文献
14.
基于2008—2017年全国自动气象观测站逐旬土壤相对湿度观测数据,综合评估中国气象局陆面数据同化系统（CMA Land Data Assimilation System,CLDAS）0～20 cm层融合土壤相对湿度产品在中国地区的适用性,评估表明CLDAS土壤相对湿度产品在中国东北、西北、江南大部及华南等地区存在较大系统性误差,总体上适用性较差。为消除CLDAS土壤相对湿度产品的系统性误差,采用回归订正法、7旬滑动平均订正法和临近加权前旬订正法对CLDAS土壤相对湿度产品进行误差订正处理,对订正结果评估发现：订正处理后CLDAS土壤相对湿度产品与站点观测的相关性显著增加,系统偏差基本消除,适用性明显提高,3种订正方法中临近加权前旬订正法的订正效果最优。最后,采用经不同方法订正后的CLDAS土壤相对湿度产品对2017年5月东北—华北地区一次气象干旱个例进行重现,对比验证表明：相对其他两种订正方法,经临近加权前旬订正法处理后的CLDAS土壤相对湿度产品能更为精准地重现2017年5月东北—华北地区气象干旱的落区和强度。〖JP〗 相似文献
15.
Kefeng ZHU Ming XUE Yujie PAN Ming HU Stanley G. BENJAMIN Stephen S. WEYGANDT Haidao LIN 《大气科学进展》2019,36(12):1308-1326
A regional ensemble Kalman filter (EnKF) data assimilation (DA) and forecast system was recently established based on the Gridpoint Statistical Interpolation (GSI) analysis system. The EnKF DA system was tested with continuous threehourly updated cycles followed by 18-h deterministic forecasts from every three-hourly ensemble mean analysis. Initial tests showed negative to neutral impacts of assimilating satellite radiance data due to the improper bias correction procedure. In this study, two bias correction schemes within the established EnKF DA system are investigated and the impact of assimilating additional polar-orbiting satellite radiance is also investigated. Two group experiments are conducted. The purpose of the first group is to evaluate the bias correction procedure. Two online bias correction methods based on GSI 3DVar and EnKF algorithms are used to assimilate AMSU-A radiance data. Results show that both variational and EnKF-based bias correction procedures effectively reduce the observation and background radiance differences, achieving positive impacts on forecasts. With proper bias correction, we assimilate full radiance observations including AMSU-A, AMSU-B, AIRS, HIRS3/4, and MHS in the second group. The relative percentage improvements(RPIs) for all forecast variables compared to those without radiance data assimilation are mostly positive, with the RPI of upper-air relative humidity being the largest. Additionally, precipitation forecasts on a downscaled 13-km grid from 40-km EnKF analyses are also improved by radiance assimilation for almost all forecast hours. 相似文献
16.
17.
基于中国气象局(China Meterological Administration,CMA)高分辨率数值预报产品、欧洲中期数值预报中心(the European Center for Medium-range Weather Forecast,ECMWF)精细化数值预报产品和国家级地面观测站数据,采用小波分析方法及滑动训练、最优融合等技术对模式误差序列进行时频处理,实现了对模式系统误差和局地误差的订正,发展了西北区智能网格气温客观预报方法(northwest intelligent grid temperature objective prediction method,NWTM)。以2017年3月—2018年2月数据作为训练样本,对2018年3月—2019年1月西北区239个国家基本站进行检验。结果表明:1)NWTM对CMA和ECMWF两种模式产品的气温预报能力有显著的提升;随着预报时效增长,两种模式订正产品的误差增大。2)NWTM对ECMWF西北区最高气温的订正效果要明显优于CMA,但就最低气温而言,NWTM对CMA的订正效果更为显著。其中,就24 h最高气温而言,ECMWF在宁夏的订正效果最好,CMA在青海的订正效果最好;而对于24 h最低气温的预报,CMA在西北4省的订正效果相差不大,ECMWF在陕西的订正效果最好。3)空间误差检验表明:针对最高气温的预报,ECMWF订正产品的订正能力明显优于CMA,特别是在甘肃河西走廊和中东部、陕西北部和南部、宁夏中南部及青海大部。就最低气温的预报而言,ECMWF和CMA对甘肃河东和陕西南部的订正能力较好;ECMWF订正产品在宁夏中南部及青海南部的订正能力高于CMA,而CMA订正产品在陕西中部的订正能力更优。 相似文献
18.
利用2016—2019年ECMWF（European Centre for Medium-Range Weather Forecasts）降水预报资料和江西省93个国家气象站降水资料,基于频率匹配法进行降水偏差订正,采用4种方法统计降水频率对降水预报进行订正试验（不分区试验）,根据江西省汛期暴雨气候特征对汛期降水进行分区订正试验,并对典型强降水个例进行分析。结果表明: 频率匹配法降低了模式预报小雨的空报率和大雨、暴雨的漏报率,预报技巧改进明显。在4种降水频率统计方法中,准对称滑动平均法效果最好。分区试验对强降水的订正效果优于不分区试验,该试验对模式预报正技巧暴雨过程的订正能力大于无技巧过程。对于模式预报效果差（TS=0）、一般（0 < TS < 0.2）、好（TS≥0.2）的暴雨过程,分区试验改善的概率分别为40.8%、89.1%和65.3%。频率匹配分区订正后强降水面积更加接近实况,但强降水落区不能得到明显的改善。订正方法对模式预报强降水形态、位置与实况较接近的过程,效果较好。 相似文献
19.
Surface turbulent flux measurements over the Loess Plateau for a semi-arid climate change study 总被引：2，自引：0，他引：2
In order to provide high quality data for climate change studies, the data quality of turbulent flux measurements at the station
of SACOL (Semi-Arid Climate & Environment Observatory of Lanzhou University), which is located on a semi-arid grassland over
the Loess Plateau in China, has been analyzed in detail. The effects of different procedures of the flux corrections on CO2, momentum, and latent and sensible heat fluxes were assessed. The result showed that coordinate rotation has a great influence
on the momentum flux but little on scalar fluxes. For coordinate rotation using the planar fit method, different regression
planes should be determined for different wind direction sectors due to the heterogeneous nature of the ground surface. Sonic
temperature correction decreased the sensible heat flux by about 9%, while WPL correction (correction for density fluctuations)
increased the latent heat flux by about 10%. WPL correction is also particularly important for CO2 fluxes. Other procedures of flux corrections, such as the time delay correction and frequency response correction, do not
significantly influence the turbulent fluxes. Furthermore, quality tests on stationarity and turbulence development conditions
were discussed. Parameterizations of integral turbulent characteristics (ITC) were tested and a specific parameterization
scheme was provided for SACOL. The ITC test on turbulence development conditions was suggested to be applied only for the
vertical velocity. The combined results of the quality tests showed that about 62%–65% of the total data were of high quality
for the latent heat flux and CO2 flux, and as much as about 76% for the sensible heat flux. For the momentum flux, however, only about 35% of the data were
of high quality. 相似文献
20.
J. Egger 《Climate Dynamics》1997,13(4):285-292
Flux correction schemes are used in order to suppress the drift of coupled ocean atmosphere models. This technique is tested
for a simple box model of the climate system. Two “perfect” models of the ocean and the atmosphere are available. These are
coupled to form an ocean-atmosphere model representing the true climate system. This climate system is simulated by a climate
model which is also constructed by coupling those two perfect models. This time, however, both models are run first separately
as models of the atmosphere and the ocean. In that case, “observations” from the climate system are prescribed at the ocean
surface in the uncoupled models. It is assumed that these observations are imperfect. A drift results, when these models are
coupled to form an ocean-atmosphere stimulation model. A flux adjustment scheme is implemented to remove this drift. It is
argued that the merits and shortcomings of the flux correction technique can be assessed more clearly this way than by coupling
imperfect models as is done normally. Sensitivity tests are performed where either radiation parameters are changed or a salt
anomaly is implanted. Model parameters are chosen such that the ocean has a thermally direct circulation in the unperturbed
climate state. It is found that the flux correction technique is performing satisfactorily as long as the imposed perturbations
are small enough so that the ocean circulation does not change its sense. If, however, the model climate is close to the transition
to an indirect circulation, then the flux correction technique is unreliable. The predictions of the coupled model with flux
correction may deviate substantially from the response of the climate system in that case.
Received: 4 December 1995/Accepted: 15 October 1996 相似文献