一次沙尘暴过程中的地面感热通量分析

利用2016年3月3—5日的气象观测数据分析了一次沙尘暴过程中地面感热通量的变化特征。结果表明:在此次沙尘暴过程中,地面感热通量的日变化曲线呈现一波型。在通常情况下,白天地面感热通量是正值,夜间地面感热通量是负值。在出现沙尘暴的时段内,地面感热通量会发生很大变化。发生在夜间的沙尘暴阻碍地面辐射,减弱地面热量的损失,致使地面感热通量大于零;发生在白天的沙尘暴阻碍太阳辐射,显著消弱地面感热通量。     

Eddy-correlation measurements of sensible heat fluxes over a grass surface

Direct measurements of sensible heat fluxes were conducted over a grass surface at Ladner, British Columbia, using yaw-sphere-thermometer eddy-correlation systems. The results show that for half-hour averaging periods, there is no phase-lag between sensible heat and net radiation flux densities. Field comparison of two yaw-sphere-thermometer systems gave good and consistent agreement. At a height of 2 m above ground and a horizontal crosswind separation of 1.5 m, less than 5% variability was noted in the measured heat fluxes. For a 19-m horizontal separation, the variability was less than 20%. The aridity index (α) advanced by Priestley and Taylor (1972), is shown to be a potentially useful climatic indicator.     

A note on bulk aerodynamic coefficients for sensible heat and moisture fluxes

Values are presented for bulk aerodynamic coefficients which were calculated from two rather extensive sets of estimates of sensible heat and moisture fluxes based on profile measurements. These results are compared with a number of other results mainly based on fluxes estimated from eddy-correlation measurements.     

基于ＳＥＢＡＬ模型在城市地表通量反演的应用

利用ETM＋及少量地面观测数据,基于SEBAL模型,反演了武汉市2002年7月22日的显热通量和潜热通量。研究结果表明：显热通量和潜热通量的分布与下垫面类型分布相对应,其中城镇、工矿下垫面以显热交换为主,草地、林地、水体等下垫面以潜热交换为主;显热通量和潜热通量的分布能够清晰指示城市热岛分布状况,适当增加城区中绿地和水体,可增大潜热通量,减缓城市热岛效应。     

Comparison of three schemes for predicting surface sensible heat flux

This paper compares three schemes which use standard meteorological observations to estimate values of the surface sensible heat flux. All three schemes have been designed to be applicable to mid-latitude, grass covered surfaces. The estimates are compared with heat flux data measured by a sonic anemometer situated at Cardington in the UK. Consideration is also given to the problem of predicting the surface sensible heat flux when could information is not available, as is the case for automatic weather stations. Provided incoming solar radiation is available, the predictions are not substantially worse.     

Simultaneous determinations of the sensible and latent heat transfer coefficients for tree leaves

The heat and mass transfer coefficients for exchange across the fluid dynamic boundary layer over tree leaves were simultaneously determined in a controlled environment chamber. The mass transfer coefficients were calculated from measured values of evaporation, air specific humidity and a value of leaf specific humidity at leaf temperature. The heat transfer coefficients were calculated from measured values of air temperature, leaf temperature and an estimate of the sensible heat flux density calculated as the measured net radiation at the leaf surfaces minus the latent heat flux density. The experiments described in this paper indicate that the equations based on laminar boundary-layer theory can give reasonable estimates of the transfer coefficients of real tree leaves for the velocities most commonly experienced in plant canopies, if they are adjusted by a constant multiplier greater than one. Calculations of local mass transfer coefficients based on temperature measurements at three locations at different distances from the leading edge of the leaves, indicate that the deviation from theory is probably the result of transition to turbulent boundary-layer flow at some distance from the leading edge.     

Eddy correlation measurements of CO2, latent heat,and sensible heat fluxes over a crop surface

Eddy correlation equipment was used to measure mass and energy fluxes over a soybean crop. A rapid response CO₂ sensor, a drag anemometer, a Lyman-alpha hygrometer and a fine wire thermocouple were used to sense the fluctuating quantities.Diurnal fluxes of sensible heat, latent heat and CO₂ were calculated from these data. Energy budget closure was obtained by summing the sensible and latent heat fluxes determined by eddy correlation which balanced the sum of net radiation and soil heat flux. Peak daytime CO₂ fluxes were near 1.0 mg m^–2 (ground area) s^–1.The eddy correlation technique was also employed in this study to measure nocturnal CO₂ fluxes caused by respiration from plants, soil, and roots. These CO₂ fluxes ranged from - 0.1 to - 0.25 mg m^–2s^–1.From the data collected over mature soybeans, a relationship between CO₂ flux and photosynthetically active radiation (PAR) was developed. The crop did not appear to be light-saturated at PAR flux densities < 1800 Ei m^–2 s^–1. The light compensation point was found to be about 160 Ei m^–2 s^–1.Published as Paper No. 7402, Journal Series, Nebraska Agricultural Experiment Station. The work reported here was conducted under Nebraska Agricultural Experiment Station Project 27-003 and Regional Research Project 11–33.Post-doctoral Research Associate, Professor and Professor, respectively. Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0728.     

Estimation of the sensible heat flux of a semi-arid area using surface radiative temperature measurements

In the framework of an international field program for the study of semi-arid areas, observations were done in the region called La Crau in southern France. In this paper, the use of the surface radiative temperature for the determination of the sensible heat flux is addressed. We found that, once proper values of the roughness length of momentum (z ₀) and heat (z ₀h) are set, the sensible heat flux can be reliably predicted with a one-layer resistance model using standard observations of wind speed and air temperature, together with the surface temperature. The latter quantity has to be known with a precision better than ±2°C. From our observations, the value of the parameterB ^–1k ^–1 In (z ₀ z ₀h) was found to be 9.2, which falls between values quoted by Brutsaert (1982) for grass and bluff bodies.     

Regional differences in surface sensible and latent heat fluxes in China

This study documents the variability of surface sensible and latent heat fluxes in five regions of China (Northwest China, the Tibetan Plateau, Northeast China, North China, and Southeast China) using the ERA-40 reanalysis for the years 1960–2000. The surface sensible and latent heat flux variations are remarkably different in Northwest and Southeast China. The seasonal variation of the surface sensible heat fluxes is largest in Northwest China and smallest in Southeast China. In contrast, the seasonal variation in latent heat flux is largest in Southeast China and smallest in Northwest China. The interdecadal variation of surface sensible and surface latent heat fluxes strongly depends on both the region and season. The trends in surface sensible and latent heat fluxes in all four seasons are mainly caused by variations in both the land–air temperature difference and in the specific humidity. There is also a limited contribution of wind speed in some regions, depending on the season.     

Daily sensible heat flux estimation from a single measurement of surface temperature and maximum air temperature

Surface energy budget investigations of a range of agricultural surfaces in France and the African Sahel demonstrate consistent linear relationships between daily totals of sensible heat flux (H _d) and the difference between a once-a-day radiative measurement of surface temperature and the maximum air temperature at a height of 2 m. Surface temperature was measured with nadir-viewing radiothermometers near 1400 h (LST). The average residual standard error in the estimate ofH _d was 0.6 mm of equivalent evaporation.An equation for the daily sensible heat flux (H _d) having a form analogous to Dalton's evaporation formula was derived from surface energy budget considerations. This equation discriminates well between relatively homogeneous, low-cover surfaces where surface exchange characteristics can be assumed to be simple fractions of the height of the roughness elements. By contrast, data from two other crops with discontinuous plant cover suggest a much reduced sensitivity to canopy architecture. This result is not unreasonable if scalar transport were controlled by the thermal conductivity of a layer of still air close to ground level which is sheltered by the plant canopy. There is scope for further experimental and theoretical work on this matter.     

Turbulent transport processes of momentum and sensible heat in the surface layer over a paddy field

A sonic anemometer-thermometer was used to measure turbulent fluxes of momentum and sensible heat and related turbulence statistics just above plant canopies in unstable conditions. The stability dependence of transport processes is presented, using observational data in a wide range of instability. The analysis of joint probability distributions of w – u, w – T, w – wu, and w – wT confirmed that just above plant canopies, downdrafts were remarkably efficient for vertical transport of momentum and scalar quantities in near neutral conditions. Furthermore, it was shown that updrafts became more efficient than downdrafts for vertical transport, especially of scalar quantities, in very unstable conditions.     

Description and evaluation of a sensible heat flux detector

An eddy-correlation method is the basis of a newly-developed sensible heat-flux detector which collects air temperature information proportional to the vertical wind speed in two electronic counters, one for upflow and one for downflow. The current model uses fast-responding sensors for vertical velocity and air temperature, but the principle should be applicable to the measurement of other kinds of fluxes. Values of sensible heat transport above bare soil and above grass have been determined, from which a sampling duration of one hour has been found to be suitable. The system provides a relatively simple way to measure sensible heat fluxes and to determine the suitability of this flux technique for wider application.     

Time and height variability of the sensible heat flux in the surface layer

The energy-budget concept is used together with a high resolution spectral radiation model to study the time and height variation of the sensible heat flux and of the eddy thermal diffusivity for an actual case up to 50 m above ground. A data set of 32 h is chosen for this study. Time-height cross-sections of the local enthalpy changes, and the radiative and the sensible heat flux divergences are presented, which show the interaction of the two energy fluxes. It can be seen, for example, that during the transient hours from night to day the sensible heat flux divergence plays an outstanding role in the warming of the atmosphere, while during the clear night radiative cooling exceeds the cooling caused by the sensible heat flux. For the layer under consideration (0-50 m) a constancy of the sensible heat flux within 10% is obtained for seven hours only, namely for the time around noon and in the early afternoon. Selected night-time profiles of the thermal diffusivity are shown, which have their maximum below 48.3 m.The accuracy of the energy-budget method is studied in detail. The tests show that a high accuracy, with errors even less than 10% for some hours, can be expected, if special micrometeorological studies are made during the field phase and a layer depth of 50 cm or less is used in the radiation model.     

The exchange coefficients for latent and sensible heat flux over lakes: Dependence upon atmospheric stability

Components of the energy budget of a small lake were estimated over the autumnal cooling period. Measured values of the stored thermal energy and radiative heating were used to evaluate several bulk formulae for sensible and latent heat transfer. Over 50–100 day intervals, bulk formulae for latent and sensible heat flux without stability corrections were as good as formulae that incorporated such corrections; both satisfactorily reproduced the measured heat storage data. Over shorter (daily to weekly) time-scales, predictions incorporating stability corrections were superior to those without stability corrections. Over daily periods when the atmosphere was nearly neutral or was unstable, a formulation for sensible and latent heat transfer designed for small-scale systems (cooling ponds and reservoirs) agreed closely with the usual large-scale (oceanic) bulk formulations. The corrections for stability in the small-scale formulation are based on laboratory and theoretical studies of free convection; the stability correction in the large-scale formulation uses a bulk Richardson number in a manner consistent with flux-profile theory. Both agreed with the measured data for the unstable and near-neutral cases. Under stable atmospheric conditions (in a daily average sense), both formulations underestimated the measured fluxes     

Connections between surface sensible heat net flux and regional summer precipitation over China

Using the observed monthly precipitation and NCEP (National Centers for Environmental Prediction)reanalysis surface flux data from 1951-2000, the connections between the seasonal SSHNF (Surface Sensible Heat Net Flux) over the Asian continent and the regional summer precipitation of China were examined.The patterns of collective and individual correlations were identified. The results indicate that the responseof the regional summer precipitation of China to the seasonal SSHNF over the study area varies according to region and season. The interannual variability of summer precipitation anomalies over Xinjiang, the northernmost Northeast China, and the North China Plain are most sensitive to the anomaly of the seasonal SSHNF. There are significant collective correlations between the interannual anomalies of the seasonal SSHNF and summer precipitation over these regions. In contrast, the Southeast Tibetan Plateau,Huaihe River Valley, and surrounding areas exhibit the least significant correlation. Significant individual correlations exist between the summer precipitation over the southernmost Northeast China, East Inner Mongolia, South of the Yangtze River and South China and the seasonal SSHNF in certain seasons over the following areas: near Lake Baikal and Lake Balkhash, near Da Hinggan Mountains and Xiao Hinggan Mountains, as well as the Tibetan Plateau.     

Calculation of sensible and latent heat fluxes,and surface resistance from profile data

A set of semi-continuous measurements of temperature, wind and moisture gradients as well as of net radiation and ground heat flux covering a period of about one and a half years has been analysed to give a corresponding set of complete surface energy balance data on an hourly basis. An analysis of the evaporation data so obtained is given.It is shown that surface resistance r _S exhibits a diurnal trend: values are smallest (ca. 150 s m^-1) a few hours before noon and increase to as much as 800 s m^-1 towards dusk. The minimum values tend to be higher during dry periods when the soil moisture is low. There is also some indication that r _S decreases rapidly soon after rainfall.An exponential relation is found between the fraction of available energy used as evaporative flux, , and r _S for values of r _I/r_S <0.70, where r _I is the climatological resistance. On the other hand, the ratio of r _I to r _S is linearly correlated with , implying that an equilibrium state is established between the grass surface and the atmosphere, at least from mid-morning to mid-afternoon when the leaves are dry. Near-noon values calculated by Stewart and Thom for Thetford Forest also follow a linear trend.The above two regression results (In (r _S) versus r _I/r_S versus ) are combined to obtain an empirical relation of the form r _I=m exp (a-b) which is used to estimate evaporative flux. The estimates are found to be within 20% of calculated values.Guest Scientist from Department of Physics, University of Cape Coast, Cape Coast, Ghana.     

Estimating surface sensible heat flux using sodar and surface temperature measurements in the evolving convective boundary layer

A simple method is described for estimating the sensible heat flux by using a Doppler sodar system and a thermal probe. This method, which can be applied to a convective boundary layer in morning hours, is based on knowing the zero heat flux level from the reflectivity and the vertical wind speed.     

洋面动量、感热和潜热通量计算的研究

整体传输公式是一种常用的计算洋面海气通量的方法。在作气候平均计算时,存在两种平均方法:方法一F_1=AB及方法二F_2=AB。显然,方法一是合理的,而方法二是对方法一的近似。本文利用COADS资料针对不同的平均时间计算分析了方法二对方法一的近似程度,结果表明:利用方法二计算长期气候平均,平滑时间超过5天则对计算结果必须进行订正;对感热和潜热通量,月平均方法二在20％的精度内可代替方法一,而旬平均方法二则可在10％的精度内代替方法一;动量通量月平均和旬平均精度分别为40％和20％。因此方法二在计算月平均动量通量时必须作订正,或直接用方法一进行计算,本文同时计算比较了1972年(E1 Nino年)和1975年(非E1 Nino年)太平洋洋面的各项能量及总能量收支,发现1972年洋面能量收支年变化幅度比1975年小得多,其差别主要决定于感热和潜热的变化。     

Latent and sensible heat flux predictions from a uniform pine forest using surface renewal and flux variance methods

A surface renewal model that links organized eddy motion to the latent and sensible heat fluxes is tested with eddy correlation measurements carried out in a 13m tall uniform Loblolly pine plantation in Duke Forest, Durham, North Carolina. The surface renewal model is based on the occurance of ramp-like patterns in the scalar concentration measurements. To extract such ramp-like patterns from Eulerian scalar concentration measurements, a newly proposed time-frequency filtering scheme is developed and tested. The time-domain filtering is carried out using compactly-supported orthonormal wavelets in conjunction with the Universal Wavelet Thresholding approach of Donoho and Johnstone, while the frequency filtering is carried out by a band-pass sine filter centered around the ramp-occurrence frequency as proposed by other studies. The method was separately tested for heat and water vapour with good agreement between eddy correlation flux measurements and model predictions. The usefulness of the flux-variance method to predict sensible and latent heat fluxes is also considered. Our measurements suggest that the simple flux-variance method reproduces the measured heat and momentum fluxes despite the fact that the variances were measured within the roughness sublayer and not in the surface layer. Central to the predictions of water vapour fluxes using the flux-variance approach is the similarity between heat and water vapour transport by the turbulent air flow. This assumption is also investigated for this uniform forest terrain.     

Tests of a robust eddy correlation system for sensible heat flux

Summary Sensible heat flux estimates from a simple, one-propeller eddy correlation system (OPEC) were compared with those from a sonic anemometer eddy correlation system (SEC). In accordance with similarity theory, the performance of the OPEC system improved with increasing height of the sensor above the surface. Flux totals from the two systems at sites with adequate fetch were in excellent agreement after frequency response corrections were applied. The propeller system appears suitable for long periods of unattended measurement. The sensible heat flux measurements can be combined with net radiation and soil heat flux measurements to estimate latent heat as a residual in the surface energy balance.With 6 Figures