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1.
Ulf Högström Anna Rutgersson Erik Sahlée Ann-Sofi Smedman Tihomir S. Hristov W. M. Drennan K. K. Kahma 《Boundary-Layer Meteorology》2013,147(1):139-163
A systematic comparison of wind profiles and momentum exchange at a trade wind site outside Oahu, Hawaii and corresponding data from the Baltic Sea is presented. The trade wind data are to a very high degree swell dominated, whereas the Baltic Sea data include a more varied assortment of wave conditions, ranging from a pure growing sea to swell. In the trade wind region swell waves travel predominantly in the wind direction, while in the Baltic, significant cross-wind swells are also present. Showing the drag coefficient as a function of the 10-m wind speed demonstrates striking differences for unstable conditions with swell for the wind-speed range 2 m s?1 < U 10 < 7 m s?1, where the trade-wind site drag values are significantly larger than the corresponding Baltic Sea values. In striking contrast to this disagreement, other features studied are surprisingly similar between the two sites. Thus, exactly as found previously in Baltic Sea studies during unstable conditions and swell, the wind profile in light winds (3 m s?1) shows a wind maximum at around 7–8 m above the water, with close to constant wind speed above. Also, for slightly higher wind speeds (4 m s?1 < U 10 < 7 m s?1), the similarity between wind profiles is striking, with a strong wind-speed increase below a height of about 7–8 m followed by a layer of virtually constant wind speed above. A consequence of these wind-profile features is that Monin–Obukhov similarity is no longer valid. At the trade-wind site this was observed to be the case even for wind speeds as high as 10 m s?1. The turbulence kinetic energy budget was evaluated for four cases of 8–16 30- min periods at the trade-wind site, giving results that agree very well with corresponding figures from the Baltic Sea. 相似文献
2.
Characteristics of the Drag Coefficient in the Roughness Sublayer over a Complex Urban Surface 总被引：2，自引：1，他引：1
The statistics of momentum exchange in the urban roughness sublayer are investigated. The analysis focuses on the characteristics of the dimensionless friction velocity, \({u_{*}}/U\) , which is defined as the square root of the drag coefficient. The turbulence observations were made at a height of 47 m above the ground on the 325-m meteorological tower, which is located in a very inhomogeneous urban area in Beijing. Under neutral conditions, the dependence of the drag coefficient on wind speed varies with wind direction. When the airflow is from the area of densely built-up buildings, the drag coefficient does not vary with wind speed, while when the airflow is from the area covered by vegetation, the drag coefficient appears to decrease with increasing wind speed. Also, the drag coefficient does not vary monotonically with the atmospheric stability. Both increasing stability and increasing instability lead to the decrease of the drag coefficient, implying that the roughness length and zero-plane displacement may vary in urban areas. 相似文献
3.
本文使用欧洲中期天气预报中心（European Center for Medium Range Weather Forecasting,ECMWF）近30年（1982～2011年）全球再分析资料（ECMWF 40 Year Re-analysis Interim）中的风场及海浪场资料,对全球海表10 m风场、有效波高、平均周期和平均波向进行了统计分析,并定义了一种计算季节变率的方法。研究发现,有效波高和平均周期均存在明显的季节变化,且北半球大洋比南半球大洋季节变化更为明显,印度季风区则例外。另外尝试用波龄揭示风浪、涌浪的分布特征,证实了全球海洋为涌浪占主导及太洋东部存在涌浪强化,同时发现了涌浪的分布在春夏季变化明显的特征。 相似文献
4.
利用美国国家海洋大气总局/美国国家环境预报中心（NOAA/NCEP）发布的最新版WAV-EWATCHⅢ（version3.14）海浪模式对0801号台风＂浣熊＂进行数值模拟,并在此基础上对台风浪的发展过程和台风影响下的海面有效波高、风浪场及涌浪场的分布特征进行分析。结果表明：海面有效波高的分布和演变受台风系统强度和移动的影响;台风过程中所产生的大浪主要为风浪;涌浪场的分布与风浪场的分布几乎相反,涌浪场基本分布在远离台风中心的外围海域;涌浪场波高比风浪场波高要小。 相似文献
5.
Xiaoli Guo Lars n Vladimir K. Makin Ann-Sofi Smedman 《Journal of Atmospheric & Ocean Science》2003,9(3):97-120
Measurements from the Baltic Sea and a wind-over-wave coupled model are used to study the wave impact on the sea drag. The study has been carried out for different wave conditions, namely a pure wind-sea, following-swell/ mixed sea and cross-swell/ mixed sea. Measurements reveal the fact that the sea drag is dependent on the sea-state. In stationary conditions and in the absence of severe cross-swell, swell reduces drag compared to wind-sea at the same wind speed. The cross-swell enhances the drag as compared to the following-swell case and the magnitude of the drag coefficient is increased with increasing the angle of swell propagation to the wind. It is shown that the agreement between the model results and measurements is good for pure wind-sea and stationary mixed-sea cases. Discrepancies occur at light winds, where most of the data represent pure swell conditions. During these pure swell conditions the data are characterized by a large variation of the drag coefficient. The variation is caused by mesoscale variability in the stress co-spectra, wind-cross-swell effects and nonstationarity in the wave and wind fields not represented in the model. 相似文献
6.
Wave-dependence of friction velocity,roughness length,and drag coefficient over coastal and open water surfaces by using three databases 总被引：3，自引：0，他引：3
The parameterization of friction velocity, roughness length, and the drag coefficient over coastal
zones and open water surfaces enables us to better understand the physical processes of air-water interaction.
In context of measurements from the Humidity Exchange over the Sea Main Experiment (HEXMAX), we recently proposed
wave-parameter dependent approaches to sea surface friction velocity and the aerodynamic roughness by using the
dimensional analysis method. To extend the application of these approaches to a range of natural surface conditions,
the present study is to assess this approach by using both coastal shallow (RASEX) and open water surface measurements
(Lake Ontario and Grand Banks ERS-1 SAR) where wind speeds were greater than 6.44 m s-1. Friction velocities,
the surface aerodynamic roughness, and the neutral drag coefficient estimated by these approaches under moderate wind
conditions were compared with the measurements mentioned above. Results showed that the coefficients in these approaches
for coastal shallow water surface differ from those for open water surfaces, and that the aerodynamic roughness length
in terms of wave age or significant wave height should be treated differently for coastal shallow and open water surfaces. 相似文献
7.
Kusuma G. Rao 《Boundary-Layer Meteorology》2004,111(2):247-273
For the first time, the exchange coefficient of heat CH has been estimated from eddy correlation of velocity and virtual temperature fluctuations using sonic anemometer measurements made at low wind speeds over the monsoon land atJodhpur (26°18' N, 73°04' E), a semi arid station. It shows strong dependence on wind speed, increasing rapidly with decreasing wind speed, and scales according to a power law CH = 0.025U10
-0.7 (where U10 is the mean wind speed at 10-m height). A similar but more rapid increase in the drag coefficient CDhas already been reported in an earlier study. Low winds (<4 m s-1) are associated with both near neutral and strong unstable situations. It is noted that CH increases with increasing instability. The present observations best describe a low wind convective regime as revealed in the scaling behaviour of drag, sensible heat flux and the non-dimensional temperature gradient. Neutral drag and heat cofficients,corrected using Monin–Obukhov (M–O) theory, show a more uniform behaviour at low wind speeds in convective conditions, when compared with the observed coefficients discussed in a coming paper.At low wind convective conditions, M-O theory is unable to capture the observed linear dependence of drag on wind speed, unlike during forced convections. The non-dimensional shear inferred from the present data shows noticeable deviations from Businger's formulation, a forced convection similarity. Heat flux is insensitive to drag associated with weak winds superposed on true free convection. With heat flux as the primary variable, definition of new velocity scales leads to a new drag parameterization scheme at low wind speeds during convective conditionsdiscussed in a coming paper. 相似文献
8.
In this paper,the observational data from Marine and Meteorological Observation Platform(MMOP)at Bohe,Maoming and buoys located in Shanwei and Maoming are used to study the characteristics of air-sea temperature and specific humidity difference and the relationship between wind and wave with the tropical cyclones over the South China Sea(SCS).The heat and momentum fluxes from eddy covariance measurement(EC)are compared with these fluxes calculated by the COARE 3.0 algorithm for Typhoon Koppu.The results show that at the developing and weakening stages of Koppu,both these differences between the sea surface and the near-surface atmosphere from the MMOP are negative,and data from the buoys also indicate that the differences are negative between the sea surface and near-surface atmosphere on the right rear portion of tropical cyclones(TCs)Molave and Chanthu.However,the differences are positive on the left front portion of Molave and Chanthu.These positive differences suggest that the heat flux is transferred from the ocean to the atmosphere,thus intensifying and maintaining the two TCs.The negative differences indicate that the ocean removes heat fluxes from the atmosphere,thus weakening the TCs.The wind-wave curves of TCs Molave and Chanthu show that significant wave height increases linearly with 2-min wind speed at 10-m height when the wind speed is less than 25 m/s,but when the wind speed is greater than 25 m/s,the significant wave height increases slightly with the wind speed.By comparing the observed sensible heat,latent heat,and friction velocity from EC with these variables from COARE 3.0 algorithm,a great bias between the observed and calculated sensible heat and latent heat fluxes is revealed,and the observed friction velocity is found to be almost the same as the calculated friction velocity. 相似文献
9.
New evidence for a relation between wind stress and wave age from measurements during ASGAMAGE 总被引：7，自引：0，他引：7
Data from the 1996 ASGAMAGE experiment, performed in the southern North Sea at research platform Meetpost Noordwijk (MPN), are analysed for the parameters affecting the momentum flux. The stress turns out to be quadratically related to the 10-m wind speed and linearly to the wind speed at a wavelength related level. The Charnock parameter (dimensionless roughness length) shows a pronounced correlation with wave age. This implies, due to a coupling between wave age and the steepness of the waves, a connection between the stress and the steepness. We find that our North Sea results are consistent withopen ocean observations. For a given wind speed the mean stress at MPN turns out to be higher because the wave age there is in general lower. We define and give an expression for a drag coefficient at a wavelength related level that can be calculated straightforwardly from the wave age and then reduced to a standard level. 相似文献
10.
KARL F. Rieder 《Boundary-Layer Meteorology》1997,82(3):355-377
Data from the Surface Waves and Processes Program (SWAPP) are employed to test current sea-surface drag parameterizations in open ocean conditions. General trends in the data indicate that drag increases with increasing wind speed and wave height, and decreases with wave age. However, scatter in the data limits the use of these parameters and other wave dependent parameterizations for modelling efforts. Upon close inspection, it is found that during the onset of three wind events analyzed separately, each of these parameters correlate well with the drag coefficient. However, the dependence of the drag coefficient on each of these parameters varies markedly from event to event. The disparity appears most closely linked to the turning rate of the wind, indicating that temporal and directional effects may play an important role. A temporal lag of O(4) hours between the rise of the wind and subsequent rise in the drag coefficient is also noticed, further pointing out the complexity of the wind-stress system. 相似文献
11.
Determination of the Drag Coefficient over the Tibetan Plateau 总被引：7，自引：0，他引：7
Li Guoping Duan Tingyang Wan Jun Gong Yuanf Shigenori Haginoy Chen Longxun Li Weiliang 《大气科学进展》1996,13(4):511-518
In this paper,a preliminary study is given on the drag (i.e.bulk transfer for momentum) coefficient,on the basis of data from four sets of AWS in Tibet during the first observational year from July 1993 to July 1994 according to China Japan Asian Monsoon Cooperative Research Program.The results show that the drag coefficient over the Tibetan Plateau is 3.3 to 4.4×103.In addition,monthly and diurnal variations of drag coefficient and the relationship among the drag coefficients and the bulk Richardson number,surface roughness length and wind speed at 10 m height are discussed in detail. 相似文献
12.
利用辽宁省风能资源专业观测网2009年6月至2010年5月26座测风塔10—70 m(部分塔为100 m)高度的逐10 min梯度风观测数据,采用线性相关分析的方法,研究了近地层最大风速和极大风速的关系。结果表明:年内最大风速与极大风速多数出现在同一大风天气过程中,但极大风速并非主要发生在出现最大风速的20 min内;最大风速和极大风速易出现在午后和傍晚;极大风速与最大风速普遍具有较好的线性相关关系,日时距、10 min时距和大风条件下,日时距的相关性最好,平均相关系数达到0.970;不同时距和大风条件下,极大风速与最大风速的比值系数相差不大,但从相关性看可以考虑优先使用日时距样本的最大风速推算极大风速;随着高度的增加,极大风速与最大风速的比值系数减小,10 m高度日极大风速是日最大风速的1.42倍左右,70 m高度则是1.24倍左右,利用最大风速推算不同高度极大风速时不宜采用统一的比值系数。 相似文献
13.
The horizontal and vertical wind velocity fluctuations were measured using two sonic anemometers at a height of 135 cm above
a snow surface under a transverse snow wave-forming condition. A snow-wave was formed when the wind at a height of 1 m blew
at a speed of more than 7 m s−1 after an approximate accumulation of from 10 to 20 cm of new snow on a snowfield. For example, when a snow-wave had a wavelength
of 10 m and a wave height of 15 to 20 cm, the measured horizontal and vertical velocity components showed that they had a
frequency peak of 0.7 Hz in coherence and co-spectrum corresponding to this wavelength. The results suggest that wind turbulence
and snow-wave formation interact with each other. 相似文献
14.
The horizontal and vertical wind velocity fluctuations were measured using two sonic anemometers at a height of 135 cm above a snow surface under a transverse snow wave-forming condition. A snow-wave was formed when the wind at a height of 1 m blew at a speed of more than 7 m s–1 after an approximate accumulation of from 10 to 20 cm of new snow on a snowfield. For example, when a snow-wave had a wavelength of 10 m and a wave height of 15 to 20 cm, the measured horizontal and vertical velocity components showed that they had a frequency peak of 0.7 Hz in coherence and co-spectrum corresponding to this wavelength. The results suggest that wind turbulence and snow-wave formation interact with each other. 相似文献
15.
GRAPES中地形重力波拖曳物理过程的引进和应用试验 总被引：6，自引：2，他引：4
在中国新一代全球中期/区域中尺度同化与预报系统(GRAPES)模式中引进了ECMWF地形重力波拖曳物理过程,填补了GRAPES全球中期数值预报系统中物理过程的空白。重新计算了地形重力波过程需要的地形静态资料数据,并与原ECMWF模式的地形静态参数进行了对比分析,验证了模式地形参数的正确性。利用GRAPES模式,进行了地形重力波拖曳物理过程影响的敏感性数值试验;结果表明:引进地形重力波拖曳过程以后,在存在大地形的区域,风场会发生变化,当纬向风遇到青藏高原时,一部分气流会产生爬坡效应而越过高原,使高原上空的西风气流减弱;另一部分气流会绕过高原,在高原的南侧产生绕流;随着模式积分时间的延长,风场变化会越来越明显,地形越复杂,风场的变化也越复杂;连续的模式积分试验结果显示,引进地形重力波过程,可以延长GRAPES模式的可用预报时效,提高了全球形势预报的准确率。通过对一次降水过程的模拟,对地形重力波过程影响降水预报的原因进行了简单分析。结果显示:引进地形重力波拖曳过程后,改变了大气流场的分布,使预报的流场更接近于大气真实状态,从而提高了降水预报的准确率。 相似文献
16.
Fetch Limited Drag Coefficients 总被引：5，自引：1，他引：5
Measurements made at a tower located 2 km off the coast of Denmark inshallow water during the Risø Air Sea Experiment (RASEX) are analyzedto investigate the behaviour of the drag coefficient in the coastal zone.For a given wind speed, the drag coefficient is larger during conditions ofshort fetch (2-5 km) off-shore flow with younger growing waves than it isfor longer fetch (15-25 km) on-shore flow. For the strongest on-shorewinds, wave breaking enhances the drag coefficient. Variation of the neutral drag coefficient in RASEX is dominated byvariation of wave age, frequency bandwidth of the wave spectra and windspeed. The frequency bandwidth is proportional to the broadness of the waveheight spectra and is largest during conditions of light wind speeds. Usingthe RASEX data, simple models of the drag coefficient and roughness length are developed in terms of wind speed, wave age and bandwidth. An off-shoreflow model of the drag coefficient in terms of nondimensional fetch isdeveloped for situations when the wave state is not known. 相似文献
17.
18.
Aerodynamic roughness of the sea surface at high winds 总被引：2，自引：0，他引：2
The role of the surface roughness in the formation of the aerodynamic friction of the water surface at high wind speeds is
investigated. The study is based on a wind-over-waves coupling theory. In this theory waves provide the surface friction velocity
through the form drag, while the energy input from the wind to waves depends on the friction velocity and the wind speed.
The wind-over-waves coupling model is extended to high wind speeds taking into account the effect of sheltering of the short
wind waves by the air-flow separation from breaking crests of longer waves. It is suggested that the momentum and energy flux
from the wind to short waves locally vanishes if they are trapped into the separation bubble of breaking longer waves. At
short fetches, typical for laboratory conditions, and strong winds the steep dominant wind waves break frequently and provide
the major part of the total form drag through the air-flow separation from breaking crests, and the effect of short waves
on the sea drag is suppressed. In this case the dependence of the drag coefficient on the wind speed is much weaker than would
be expected from the standard parameterization of the roughness parameter through the Charnock relation. At long fetches,
typical for the field, waves in the spectral peak break rarely and their contribution to the air-flow separation is weak.
In this case the surface form drag is determined predominantly by the air-flow separation from breaking of the equilibrium
range waves. As found at high wind speeds up to 60 m s−1 the modelled aerodynamic roughness is consistent with the Charnock relation, i.e. there is no saturation of the sea drag.
Unlike the aerodynamic roughness, the geometrical surface roughness (height of short waves) could be saturated or even suppressed
when the wind speed exceeds 30 m s−1. 相似文献
19.
E. L. Deacon 《Boundary-Layer Meteorology》1973,5(3):321-340
Data on the relationship of the surface wind to the geostrophic wind at Porton Down, Salisbury Plain, are presented for various
stability conditions and analysed in the light of the Rossbynumber similarity theory. For near-neutral conditions, the geostrophic
drag coefficients for geostrophic wind speeds 5 to 15 m s-1 are close to those found by other workers but at higher speeds the values are low. Comparisons of geostrophic and radar wind
speeds for ⋍900-m height, suggest that undetectably small mean cyclonic curvatures of the trajectories of the air are responsible
for this departure.
A value of the geostrophic drag coefficient for the open sea at wind speeds around 8 m s-1 (neutral conditions) is deduced from recent observations of the drag in relation to the surface wind, combined with the ratios
of 900-mb radar wind to surface wind obtained from the North Atlantic weather ship data tabulations of Findlater et al. (1966). 相似文献
20.
The air–water exchange of momentum and scalars (temperature and water vapour) is investigated using the Lake-Atmosphere Turbulent EXchange (LATEX) dataset. The wind waves and swell are found to affect the coupling between the water surface and the air differently. The surface-stress vector aligns with the wind velocity in the presence of wind waves, but a wide range of stress–wind misalignment angles is observed during swell. The momentum transport efficiency decreases when significant stress–wind misalignment is present, suggesting a strong influence of surface wave properties on surface drag. Based on this improved understanding of the role of wave–wind misalignment, a new relative wind speed for surface-layer similarity formulations is proposed and tested using the data. The new expression yields a value of the von Kármán constant (\(\kappa \)) of 0.38, compared to 0.36 when using the absolute wind speed, as well as reduced data fitting errors. Finally, the ratios of aerodynamic to scalar roughness lengths are computed and various existing models in the literature are tested using least-square fitting to the observed ratios. The tests are able to discriminate between the performance of various models; however, they also indicate that more investigations are required to understand the physics of scalar exchanges over waves. 相似文献