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1.
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   

2.
Air-sea bulk transfer coefficients in diabatic conditions   总被引：13，自引：0，他引：13  
On the basis of recent data for the roughness Reynolds number of the sea surface, and using the Owen-Thomson theory on the transfers of heat and mass between a rough surface and the flow above it, the bulk transfer coefficients of the sea surface have been estimated. For a reference height of 10 m, the neutral-lapse transfer coefficient for water vapor is larger by only a few percent than that for sensible heat. When the wind speed at the 10-m height is u 10>3 m s–1, the coefficient for sensible heat C H is larger by about 10% than that for momentum C D . For u 10<5 m s–1, however, the value of C D exceeds the value of C H , and for u 10=15 m s–1 it is shown that C H 0.8C D . It may be also proposed that 103 C D =1.11 to 1.70, 103 C E =1.18 to 1.30, and 103 C H =1.15 to 1.26 for a range of u 10=4 to 20 m s–1. A plot of diabatic transfer coefficients versus wind speed is obtained by using a parameter of the sea-air temperature difference. For practical purposes, the coefficients are approximated by empirical formulae.  相似文献   

3.
The deviation of the sea surface temperature from the water temperature below is calculated as a function of the heat flow through the air-sea interface, using wind tunnel determinations of the effective thermal diffusivity in a boundary layer. The influence ofQ, shortwave radiation, andH, latent and sensible heat transfer plus effective back radiation, and U, wind speed, can be described by:T 0 –T w =C 1 ·H/U +C 2 ·Q/U. The calculated coefficients vary slightly with reference depth, Tables II and III. They are in good agreement with independent observations.On leave at Department of Oceanography, Oregon State University, Corvallis, Oregon in 1969–70.  相似文献   

4.
Bulk transfer coefficients were evaluated from eddy correlation flux measurements on a fixed pier during onshore winds. The mean values are C D = 1.69 × 10-3, C H = 2.58 × 10-3 and C E = 1.51 × 10-3. The drag coefficient, C D, gradually increases with wind speed but C H and C E are independent of wind speed. According to theory and empirical formulas based on experimental results over flat grassland, the transfer coefficients should gradually increase with increasing instability. This is confirmed experimentally in the stable region in our case. However, the drag coefficient appears to decrease with increasing instability, which is against the theoretical result. A stability dependence is not clearly observed for C H or C E.  相似文献   

5.
The daytime boundary-layer heating process and the air-land heat budget were investigated over the coastal sea-breeze region by means of observations over the Sendai plain in Japan during the summer. In this area, the onset of the sea breeze begins at the coast around 0900 LST, intruding about 35 km inland by late afternoon. The cold sea breeze creates a temperature difference of over 10°C between the coastal and inland areas in the afternoon. On the other hand, warm air advection due to the combination of the counter-sea breeze and land-to-sea synoptic wind occurs in the layer above the cold sea breeze in the coastal region. Owing to this local warm air advection, there is no significant difference in the daytime heating rate over the entire atmospheric boundary layer between the coastal and inland areas. The sensible heat flux from the land surface gradually decreases as distance from the coastline increases, being mainly attributed to the cold sea breeze. The daytime mean cold air advection due to the sea breeze is estimated asQ adv local =–29 W m–2 averaged over the sea breeze region (035 km from the coastline). This value is 17% of the surface sensible heat fluxH over the same region. The results of a two-dimensional numerical model show that the value ofQ adv local /H is strongly affected by the upper-level synoptic wind direction. The absolute value ofQ adv local /H becomes smaller when the synoptic wind has the opposite direction of the sea breeze. This condition occurred during the observations used in the present study.  相似文献   

6.
The forcing mechanisms for Antarctic coastal polynyas and the thermodynamic effects of existing polynyas are studied by means of an air-sea-ice interaction experiment in the Weddell Sea in October and November 1986.Coastal polynyas develop in close relationship to the ice motion and form most rapidly with offshore ice motion. Narrow polynyas occur frequently on the lee side of headlands and with strong curvature of the coastline. From the momentum balance of drifting sea ice, a forcing diagram is constructed, which relates ice motion to the surface-layer wind vector v z and to the geostrophic ocean current vector c g . In agreement with the data, wind forcing dominates when the wind speed at a height of 3 m exceeds the geostrophic current velocity by a factor of at least 33. This condition within the ocean regime of the Antarctic coastal current usually is fulfilled for wind speeds above 5 m/s at a height of 3 m.Based on a nonlinear parameter estimation technique, optimum parameters for free ice drift are calculated. Including a drift dependent geostrophic current in the ice/water drag yields a maximum of explained variance (91%) of ice velocity.The turbulent heat exchange between sea ice and polynya surfaces is derived from surface-layer wind and temperature data, from temperature changes of the air mass along its trajectory and from an application of the resistance laws for the atmospheric PBL. The turbulent heat flux averaged over all randomly distributed observations in coastal polynyas is 143 W/m2. This value is significantly different over pack ice and shelf ice surfaces, where downward fluxes prevail. The large variances of turbulent fluxes can be explained by variable wind speeds and air temperatures. The heat fluxes are also affected by cloud feedback processes and vary in time due to the formation of new ice at the polynya surface.Maximum turbulent fluxes of more than 400 W/m2 result from strong winds and low air temperatures. The heat exchange is similarly intense in a narrow zone close to the ice front, when under weak wind conditions, a local circulation develops and cold air associated with strong surface inversions over the shelf ice is heated above the open water.  相似文献   

7.
Although the bulk aerodynamic transfer coefficients for sensible (C H ) and latent (C E ) heat over snow and sea ice surfaces are necessary for accurately modeling the surface energy budget, they have been measured rarely. This paper, therefore, presents a theoretical model that predicts neutral-stability values of C H and C E as functions of the wind speed and a surface roughness parameter. The crux of the model is establishing the interfacial sublayer profiles of the scalars, temperature and water vapor, over aerodynamically smooth and rough surfaces on the basis of a surface-renewal model in which turbulent eddies continually scour the surface, transferring scalar contaminants across the interface by molecular diffusion. Matching these interfacial sublayer profiles with the semi-logarithmic inertial sublayer profiles yields the roughness lengths for temperature and water vapor. When coupled with a model for the drag coefficient over snow and sea ice based on actual measurements, these roughness lengths lead to the transfer coefficients. C E is always a few percent larger than CH. Both decrease monotonically with increasing wind speed for speeds above 1 m s–1, and both increase at all wind speeds as the surface gets rougher. Both, nevertheless, are almost always between 1.0 × 10–3 and 1.5 × 10–3.  相似文献   

8.
近海海面油类漂流扩散的研究和预测实践   总被引：4，自引：0，他引：4  
根据珠江口气象站风速与潮汐站潮位资料，对1955－1998年12次El Nino过程的珠江口季风强度与海平面变化特点进行合成分析，结果表明，El Nino发生前一年冬季，珠江口冬季平均风速较常年值大0．4m/s,El Nino发生当年，月平均风速也普遍大于常年，而月平均海平面则普遍较常年偏低，其中10与11月份负距平为6cm左右。东亚地区的季风异常对珠江口海平面异常有着重大的影响。  相似文献   

9.
An attempt is made to apply the modern methods of surface wave simulation developed for oceanic conditions to the modeling of waves in medium-size inland reservoirs (10–100 km). The results of field measurements of wind speed and waves are described, and on their basis the parameterization C D (U 10) is proposed. WAVEWATCH III spectral wave model was adapted to the conditions of a medium-size inl and reservoir. The simulated data are compared with the field data. The use of the new parameterization C D (U 10) allowed reducing the values of the wind wave growth rate that improved consistency in data from the field experiment and numerical modeling concerning the height of significant waves. Further steps towards improving the quality of prediction of the adapted WAVEWATCH III model are discussed.  相似文献   

10.
Under growing wind-wave conditions the shear velocity,u *, over the water surface equalsg 2 H s 2 B a 2 C p 3 , whereg is the gravitational acceleration,H s is the significant wave height,B a is a constant, andC p is the wave celerity. From an independent field experiment in a lake environment which provided all three parameters (u *,H s , andC p ), the value ofB a is found to be 0.89, which is slightly lower than but consistent (within 20%) with the literature value between 0.90 and 1.06 obtained from an oceanic environment. Since thisu * equation does not include the wind speed,U 10, anotheru * formulation withU 10 in addition to the wave information is also evaluated. It is shown that the latter equation which includesU 10 is superior to the former withoutU 10.  相似文献   

11.
An attempt is made to construct a model, coupling land surface and atmospheric processes in the planetary boundary layer (PBL). A grassland strip in a semi-desert (hereinafter called desert) is presupposed, so as to simulate the case of heterogeneous vegetation cover.Modeling results indicate that every term in the equation of the surface energy balance changes as the air flows over the grassland. The striking contrast of water and energy conditions between the grassland and the desert means that the air over the grassland is cooler and wetter than that over the desert. Consequently, in the heating and dynamic forcing of the air by the underlying surface, heterogeneities arise and are then transferred upward by the turbulent motions. Horizontal differences thus develop in the PBL, resulting in a local circulation. Meanwhile, the horizontal differences affect the free atmosphere through vertical motion at the top of the PBL.List of symbols d 1,d 2,d 3 depths of surface, middle and lower layers of soil - T c ,T 1,T 2,T 3 temperatures of canopy, surface, middle and lower layers of soil - R nc net radiation of canopy layer - c shielding factor of vegetation - Ew, Etc evaporation from wet fraction of foliage and transpiration from dry fraction of foliage - Et 1,Et 2 transpiration of foliage water absorbed by the root in the upper and lower soil, respectively - H c sensible heat of canopy - P c ,D c precipitation rate and drainage of canopy - C s ,C c ,C w heat capacity of soil, canopy and water - w , s density of water and air near the surface - D hydraulic permeability of soil - s saturated value of the ratio of volumetric soil moisture - S g , g solar radiation and surface reflection - H g ,R L g turbulent heat flux and long wave radiation of surface - P g ,E g precipitation rate and evaporation of soil surface - K s soil thermal diffusivity - K (m),K (H),K (q) eddy coefficients of momentum, heat and moisture - u, v, w components of wind speed in three directions - air potential temperature - e turbulent kinetic energy - p atmospheric pressure - C p specific heat of air under constant pressure - R d gas constant - u * friction velocity - * feature temperature - h height of the PBL - f Coriolis parameter - L 0 Monin-Obukhov length - latent heat of vaporization - q specific humidity - M c ,M cm interception water storage of canopy and its maximum - 0 Exner number of largescale background field - perturbation Exner number - u g ,v g components of the geostrophic wind speed Sponsored by the National Natural Science Foundation of China.  相似文献   

12.
Wind-wave relationship from SEASAT radar altimeter data   总被引：2，自引：0，他引：2  
We present a nonlinear relationship between ocean surface wind at 10 m height (U 10 ) and significant wave height of wind-generated gravity waves, (H 1/3)gw, over the open oceans using SEASAT radar altimeter data. The data represent a variety of fetches, durations and strength of winds. Concurrent measurement of significant wave height, (H 1/3 ), which may contain a measure of swell and U 10 obtained from the processed geophysical data record (GDR) of the SEASAT radar altimeter were used in the analysis. The total wave energy, E alt, characterised by altimeter H 1/3 measurements was compared with the energy of a fully developed sea, E fd derived from U 10 measurements using the Pierson-Moskowitz model. The criteria E alt E fd was used in data selection to minimise the influence of swell. (H 1/3)gw thus obtained was used in a regression in terms of U 10 in a second-degree polynomial. Verification with independent radar altimeter data confirmed the validity of the proposed wind-wave model, which could be used for operational wave forecasting.  相似文献   

13.
Stably stratified flow in a marine atmospheric surface layer   总被引：3，自引：1，他引：2  
Data from the marine atmospheric surface layer have been analysed. The data set consists of about two weeks with tower measurements up to 31 m of mean profiles of wind, temperature, and humidity, together with 20 Hz turbulence data. Mean wind, temperature, and humidity profiles up to 2000 m are also available from pibal trackings and radio soundings. Wave height was measured at 2 Hz, using an inverted echo-sounder.It was found from pibal wind profiles that low level jets were present during 2/3 of the measurements, having their maxima in the height interval 40 to 300 m. Here only data from the remaining 1/3 of the measurements, without low level jets, have been analysed.Non-dimensional wind and temperature gradients agree with results over homogeneous land surfaces as regards stability dependence during stable conditions that prevailed during this experiment. Linear regression gave m = 1 + 6.8z/L and m = 1 + 8.3z/L. No significant sea wave influence was found. The same was vrue for me dimensionless standard deviations of the three wind components, except for the vertical component. The expected wind speed dependence was found for the neutral drag coefficient, givingC dN = 0.109U + 0.33 at 10 m, and a dependence on the wave parameter,C/u *, was confirmed. Note, however, that the data set was restricted to low and moderate wind speeds and that stratification was mainly stable.Power spectra, non-dimensionalized according to suface-layer theories, do not follow the expected stability dependence. It was shown that this may be a consequence of the presence of gravity waves in the stable marine boundary layer. Indicators of gravity waves were found in most runs. The TKE budget agrees with findings over homogeneous land areas. The pressure transport term was found to be a source of energy also for near neutral conditions.  相似文献   

14.
We report the spatio-temporal variability of surface-layer turbulent fluxes of heat, moisture and momentum over the Bay of Bengal (BoB) and the Arabian Sea (AS) during the Integrated Campaign for Aerosols, gases Radiation Budget (ICARB) field experiment. The meteorological component of ICARB conducted during March – May 2006 onboard the oceanic research vessel Sagar Kanya forms the database for the present study. The bulk transfer coefficients and the surface-layer fluxes are estimated using a modified bulk aerodynamic method, and then the spatio-temporal variability of these air-sea interface fluxes is discussed in detail. It is observed that the sensible and latent heat fluxes over the AS are marginally higher than those over the BoB, which we attribute to differences in the prevailing meteorological conditions over the two oceanic regions. The values of the wind stress, sensible and latent heat fluxes are compared with those obtained for the Indian Ocean Experiment (INDOEX) period. The variation of drag coefficient (C D ), exchange coefficients of sensible heat and moisture (C H = C E ) and neutral drag coefficient (C DN ) with wind speed is also discussed.
  相似文献   

15.
Bulk transfer coefficient over a snow surface   总被引：1，自引：0，他引：1  
The drag coefficient C D and the bulk transfer coefficient for sensible heat C H over a flat snow surface were determined experimentally. Theoretical considerations reveal that C D depends on the friction velocity u * as well as on the geometrical roughness h of the snow surface. It is found that C D increases with increasing u * and/or h. The dependency of C H on u * and h is so small that it is possible to consider C H as a constant for practical purposes: C H, 1 = 2.0 × 10–3 for a reference height of 1 m. The bulk transfer coefficient for water vapor is estimated at C E, 1 = 2.1 × 10–3 for a reference height of 1 m.  相似文献   

16.
利用布设在秦皇岛市抚宁地区的OTT Parsivel激光雨滴谱仪和卢龙地区S波段天气雷达,对2017—2019年4—9月共23次降水过程进行了观测,并分析了基于雨滴谱参数(滴谱粒子数N(D)和粒子直径大小D0)计算的雷达反射率因子ZD和雷达探测的雷达反射率因子ZR的差异ZC。结果表明,N(D)主要集中在130～530个范围内,ZC标准差随着N(D)的增大而逐渐减少;D0主要集中在0.8～1.6 mm范围内,ZC标准值在D0<1.2 mm范围内随着D0的增大而逐渐减少,D0在1.2～1.6 mm范围内趋于稳定;ZD主要集中在15～40 dBZ范围内,ZC标准差在15～35 dBZ范围内随着ZD值增大而减小。  相似文献   

17.
A logarithmic + polynomial approximation is proposed for the vertical temperature profile in a neutrally or stably stratified planetary boundary layer (PBL) in conditions of quasi-stationarity. Using this approximation with the asymptotic logarithmic + linear law of the Monin-Obukhov similarity theory for the near-surface layer and with the Zilitinkevich formula for the PBL thickness allows one to derive an analytical expression for the function C in the heat transfer law, which permits simple parameterization of the thermal interaction between the atmosphere and the underlying medium in terms of external parameters, such as the geostrophic wind velocity and the temperature difference across the PBL.  相似文献   

18.
利用珠海凤凰山陆气相互作用观测塔站2014年11月至2016年5月的观测数据,对比分析了干湿季森林下垫面能量通量和气象要素的变化特征,分析了在不同稳定度下3个风向范围（315°～45°、45°～135°和135°～225°）的动量和感热交换系数随冠层表面风速的变化特征,并对动量和感热交换系数进行了参数化研究。结果表明:干季感热和潜热通量值相当,湿季潜热远大于感热。干季和湿季的夜晚都出现负感热现象,感热从大气向森林输送。相对湿度的变化幅度大,与该地气象状况密切相关,相对湿度的垂直梯度夜晚较大,白天较小。干季的气温垂直梯度比湿季的明显。风速在冬季变化平缓,夏季变化剧烈,低层风速随高度变化梯度明显,高层较紊乱。各高度风向差异不大。中性和近中性状态下,在风向为315°～45°、45°～135°和135°～225°时,动量交换系数Cdn分别为0.05、0.0055和0.022,感热交换系数Chn分别为0.0055、0.003和0.004。在稳定和不稳定状态下,动量交换系数Cd、感热交换系数Ch随冠层表面风速v明显发生变化,稳定条件下,Cd、Ch随v的增大而增大;不稳定条件下,Cd、Ch随v的增大而减小。分不同风向对森林冠层Cd、Ch在稳定和不稳定条件下与v的关系进行了拟合,得到了参数化公式。  相似文献   

19.
Wintertime cold air outbreaks along a non-frozen sea channel or a long lake can become destructive if the related bands of heavy snowfall hit onto land. The forcing for such bands is studied with a 2D numerical model set across an east–west sea channel at 60oN (‘Gulf of Finland’), varying the basic geostrophic wind V g. Without any V g opposite coastal land breezes emerge with convergence. This results in a quasi-steady rising motion w max ~ 7.5 cm/s at 600 m in the middle of the gulf, which can force a snow band. During weak V g, the rising motion is reduced but least so for winds from 60o to 80o (~ENE), when modest alongshore bands could exist near the downstream (Estonian) coast. During V g of 4–6 m/s from any direction, the land breezes and rising motions are reduced more effectively, so snow bands are not expected during moderate basic flow. In contrast, during a strong V g of 20–25 m/s from 110o to 120o (~ESE) the land breeze perturbations are intense with w max up to 15–18 cm/s. The induced alongshore bands of heavy snowfall are located in these cases at the sea but quite close to the downstream (Finnish) coast. They can suddenly make a landfall if the basic wind turns clockwise.  相似文献   

20.
Summary The accuracy of evaporation estimates based on meteorological observations from selected coastal stations and various methods are tested in the area of the Aegean sea. The higher values of evaporation are predicted through Smith's approach and bulk aerodynamic formula withC E=1.85×103. Priestley-Taylor parameter and annual variation of evaporation in the are are presented analytically.With 5 Figures  相似文献   

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