Observations Of Net Radiation Research Articles

The urban energy balance of a lightweight low-rise neighborhood in Andacollo, Chile

Worldwide, the majority of rapidly growing neighborhoods are found in the Global South. They often exhibit different building construction and development patterns than the Global North, and urban climate research in many such neighborhoods has to date been sparse. This study presents local-scale observations of net radiation (Q*) and sensible heat flux (QH) from a lightweight low-rise neighborhood in the desert climate of Andacollo, Chile, and compares observations with results from a process-based urban energy-balance model (TUF3D) and a local-scale empirical model (LUMPS) for a 14-day period in autumn 2009. This is a unique neighborhood-climate combination in the urban energy-balance literature, and results show good agreement between observations and models for Q* and QH. The unmeasured latent heat flux (QE) is modeled with an updated version of TUF3D and two versions of LUMPS (a forward and inverse application). Both LUMPS implementations predict slightly higher QE than TUF3D, which may indicate a bias in LUMPS parameters towards mid-latitude, non-desert climates. Overall, the energy balance is dominated by sensible and storage heat fluxes with mean daytime Bowen ratios of 2.57 (observed QH/LUMPS QE)–3.46 (TUF3D). Storage heat flux (ΔQS) is modeled with TUF3D, the empirical objective hysteresis model (OHM), and the inverse LUMPS implementation. Agreement between models is generally good; the OHM-predicted diurnal cycle deviates somewhat relative to the other two models, likely because OHM coefficients are not specified for the roof and wall construction materials found in this neighborhood. New facet-scale and local-scale OHM coefficients are developed based on modeled ΔQS and observed Q*. Coefficients in the empirical models OHM and LUMPS are derived from observations in primarily non-desert climates in European/North American neighborhoods and must be updated as measurements in lightweight low-rise (and other) neighborhoods in various climates become available.

Evaluation of leaf wetness duration models for operational use in strawberry disease-warning systems in four US states.

Leaf wetness duration (LWD) plays a key role in disease development and is often used as an input in disease-warning systems. LWD is often estimated using mathematical models, since measurement by sensors is rarely available and/or reliable. A strawberry disease-warning system called "Strawberry Advisory System" (SAS) is used by growers in Florida, USA, in deciding when to spray their strawberry fields to control anthracnose and Botrytis fruit rot. Currently, SAS is implemented at six locations, where reliable LWD sensors are deployed. A robust LWD model would facilitate SAS expansion from Florida to other regions where reliable LW sensors are not available. The objective of this study was to evaluate the use of mathematical models to estimate LWD and time of spray recommendations in comparison to on site LWD measurements. Specific objectives were to (i) compare model estimated and observed LWD and resulting differences in timing and number of fungicide spray recommendations, (ii) evaluate the effects of weather station sensors precision on LWD models performance, and (iii) compare LWD models performance across four states in the USA. The LWD models evaluated were the classification and regression tree (CART), dew point depression (DPD), number of hours with relative humidity equal or greater than 90% (NHRH ≥90%), and Penman-Monteith (P-M). P-M model was expected to have the lowest errors, since it is a physically based and thus portable model. Indeed, the P-M model estimated LWD most accurately (MAE <2h) at a weather station with high precision sensors but was the least accurate when lower precision sensors of relative humidity and estimated net radiation (based on solar radiation and temperature) were used (MAE = 3.7h). The CART model was the most robust for estimating LWD and for advising growers on fungicide-spray timing for anthracnose and Botrytis fruit rot control and is therefore the model we recommend for expanding the strawberry disease warning beyond Florida, to other locations where weather stations may be deployed with lower precision sensors, and net radiation observations are not available.

Energy and water balance response of a vegetated wetland to herbicide treatment of invasive Phragmites australis

Summary The energy and water balance of a Phragmites australis dominated wetland in south central Nebraska was analyzed to assess consumptive water use and the potential for “water savings” as a result of vegetation eradication via herbicide treatment. Energy balance measurements were made at the field site for two growing seasons (treated and untreated), including observations of net radiation, heat storage, and sensible heat flux, which was measured using a large-aperture scintillometer. Latent heat flux was calculated as a residual of the energy balance, and comparisons were made between the two growing seasons and with model simulations to examine the relative impacts of vegetation removal and climate variability. Observed ET rates dropped by roughly 32% between the two growing seasons, from a mean of 4.4 ± 0.7 mm day−1 in 2009 (with live vegetation) to 3.0 ± 0.8 mm day−1 in 2010 (with dead P. australis). These results are corroborated by the Agro-IBIS model simulations, and the reduction in ET implies a total “water savings” of 245 mm over the course of the growing season. The significant decreases in ET were accompanied by a more-than-doubling of sensible heat flux, as well as a ∼60% increase in heat storage due to decreased LAI. Removal of P. australis was also found to cause measurable changes in the local micrometeorology at the wetland. Consistent with the observed increase in sensible heat flux during 2010, warmer, drier, windier conditions were observed in the dead, P. australis section of the wetland, compared to an undisturbed section of live, native vegetation. Modeling results suggest that the elimination of transpiration in 2010 was partially offset by an increase in surface evaporation, thereby reducing the subsequent water savings by roughly 60%. Thus, the impact of vegetation removal depends on the local climate, depth to groundwater, and management decisions related to regrowth of vegetation.

Sensible and Latent Heat Flux Variability and Response to Dry–Wet Soil Moisture Zones Across China

Our understanding of the spatio-temporal variability of sensible and latent heat fluxes over land has advanced slowly due to the absence of long-term measurements. To help address this, we produced a long-term heat flux dataset by using a land-surface model driven using observation-based atmospheric forcing. We then corrected the dataset using net radiation observations, and validated the corrected dataset using multiple-source measurements. The results indicate that the corrected dataset represents the variability of these two heat fluxes well on various time scales. Based on the dataset, analyses show that, during 1951–2008, sensible heat flux decreased significantly over China, with a linear trend of $$-$$ 0.04 W m $$^{-2}$$ year $$^{-1}$$ , while latent heat flux increased at 0.02 W m $$^{-2}$$ year $$^{-1}$$ . Regionally, the trends appeared more significant in north-east China, south-west China, and the Tibetan Plateau. On average, the Tibetan Plateau showed the maximum sensible heat flux, especially over the south-west region, with averages $$>$$ 100 W m $$^{-2}$$ . Meanwhile, higher latent heat fluxes mainly covered the Yangtze-Huaihe river basin and southward, with averages $$>$$ 70 W m $$^{-2}$$ . Regarding the response of heat fluxes to soil moisture, the variations of sensible and latent fluxes were more sensitive to soil moisture over dry regions (arid and semi-arid soil moisture zones), while the stronger anomalies for both fluxes occurred over wet regions (semi-humid and humid soil moisture zones).

Assessing the impacts of vegetation heterogeneity on energy fluxes and snowmelt in boreal forests

Aims In the mid- and high-latitude regions, three quarters of the land surface is covered by boreal conifer forests, and snow lasts for 6–8 months of the year. Correctly modeling surface energy balance and snowmelt at mid- and high-latitudes has a significant influence on climate and hydrological processes. However, the heterogeneous and clumped forest structure exerts important control over the radiative energy at the forest floor, which results in large variations of underneath snow cover and snowmelt rate. The goal of this study is to investigate the impact of hierarchically clumped vegetation structure in boreal forest on snowmelt and exchanges of energy and water. Methods We used a simple Clumped Canopy Scheme (CCS) for canopy radiation transfer to characterize the impact of the clumped forest structure on net radiation at the snow surface underneath forests. The CCS was integrated with the Variable Infiltration Capacity macroscale hydrological model (herein referred to as VIC-CCS) to characterize the impact of clumped vegetation structure on surface energy balance and snowmelt during the snow season. A twin simulation, VICCCS and the standard VIC model, was performed to isolate the impact of CCS on the energy and water fluxes and snowmelt rates. The simulation results were compared to in situ measurements at four different forest stands: old aspen forest in the Southern Study Area (SOA), black spruce forests in the Southern and Northern Study Areas (SOBS and NOBS) and fen wetland in the Northern Study Area (NFEN) within the Boreal Ecosystem–Atmosphere Study (BOREAS) region in central Canada during 1994 to1996. Important Findings Simulations showed that the implementation of CCS has reduced incoming long-wave radiation at the underlying snow surface and, thereby, lowered the snowmelt rate. Comparison against ground observations of net radiation and surface flux rates showed a reasonable agreement while demonstrating implementation of CCS can markedly improve model surface energy budget and energy inputs computation for snowmelt. The modeled snowmelt matches reasonably well with observations with root mean square error (RMSE) ranging from 16.51 to 19.81 mm using VIC-CCS versus 29.86 to 32.61 mm for VIC only in the four forest sites. The improvement is the most significant for the deciduous forest (old aspen) site, reducing RMSE by16 mm. This study demonstrates that taking into account the effect of the clumped forest structure in land surface parameterization schemes is critical for snowmelt prediction in the boreal regions.

Method Development for Estimating Sensible Heat Flux over the Tibetan Plateau from CMA Data

Abstract To clarify the thermal forcing of the Tibetan Plateau, long-term coarse-temporal-resolution data from the China Meteorological Administration have been widely used to estimate surface sensible heat flux by bulk methods in many previous studies; however, these estimates have seldom been evaluated against observations. This study at first evaluates three widely used bulk schemes against Tibet instrumental flux data. The evaluation shows that large uncertainties exist in the heat flux estimated by these schemes; in particular, upward heat fluxes in winter may be significantly underestimated, because diurnal variations of atmospheric stability were not taken into account. To improve the estimate, a new method is developed to disaggregate coarse-resolution meteorological data to hourly according to statistical relationships derived from high-resolution experimental data, and then sensible heat flux is estimated from the hourly data by a well-validated flux scheme. Evaluations against heat flux observations in summer and against net radiation observations in winter indicate that the new method performs much better than previous schemes, and therefore it provides a robust basis for quantifying the Tibetan surface energy budget.

Calibration of a water and energy balance model: Recursive parameter estimation versus particle swarm optimization

It is well known that one of the major problems in the application of land surface models is the determination of the various model parameters. In most cases, only one or a limited number of variables are used to estimate these parameters. This study evaluates the use of two fundamentally different global optimization methods, multistart weight‐adaptive recursive parameter estimation (MWARPE) and particle swarm optimization (PSO), for the estimation of hydrologic model parameters on the basis of data for multiple variables. MWARPE iteratively uses the linear recursive filter equations in a Monte Carlo setting and therefore does not rely on the explicit minimization of an objective function. However, a major drawback of the MWARPE method is the high dimensionality, determined by the number of observations, of the matrix to be inverted. On the other hand, PSO is a stochastic optimization method based on the collective strength of a population of individuals with flocking or herding behavior, as observed in a wide number of biological systems. In situ observations of net radiation; latent, sensible, and ground heat fluxes; and the soil moisture profile are used to determine the parameters of a simplified water and energy balance model. Both optimization methods are analyzed in terms of model performance and computational efficiency. Comparable results, expressed in terms of the root mean square error values, were obtained for both methods. However, it was found that MWARPE tends to slightly overfit the data.

Avaliação de modelos de estimativa do saldo de radiação e do método de Priestley-Taylor para a região de Dourados, MS

Este trabalho foi realizado com o objetivo de avaliar modelos de estimativa da radiação líquida e o método de Priestley-Taylor para a região de Dourados. O ajuste dos parâmetros dos modelos foi realizado com base em uma série de 1.421 dados diários de radiação líquida, radiação solar global, radiação extraterrestre, temperaturas máxima e mínima. Uma segunda série de dados com 360 observações diárias foi utilizada para validar as equações geradas. A evapotranspiração de referência (ET0) foi estimada pela equação de Priestley-Taylor, como função da radiação solar global. Os valores de ET0 foram comparados com 218 medidas lisimétricas. As estimativas de radiação líquida geradas com base apenas nas temperaturas máximas e mínimas não foram satisfatórias, mas o modelo que utilizou radiação extraterrestre, além dessas duas variáveis, apresentou performance mediana. Os modelos que utilizaram a radiação solar global como variável independente tiveram desempenho classificados como ótimos. O método de Prietley-Taylor apresentou desempenho muito bom, possibilitando estimar a evapotranspiração de referência diária da região de Dourados com base na radiação solar global e na temperatura média do ar.

A mobile platform to constrain regional estimates of evapotranspiration

Regional estimates of evapotranspiration (ET) are needed for environmental analysis and management purposes, yet can be difficult to obtain. Current methods for determining regional ET have spatial, temporal, methodological, and/or logistical limitations that affect their usefulness. To address these gaps, we developed a surface mobile measurement technique, the Regional Evaporative Fraction Energy Balance platform (REFEB), which measures evaporative fraction (EF) and water use efficiency (WUE) using a truck operating on a public right of way. REFEB can measure EF and WUE at 25 or more locations per day, which allows for rapid, dense, and spatially distributed sampling of fields across a region. We assessed the accuracy of the field measurements of EF and WUE with REFEB by comparing them to an Eddy covariance (EC) and Bowen ratio energy balance (BREB) tower. This site validation showed that REFEB has error and uncertainty similar to previous BREB approaches. We then used empirical relationships between field measurements and remote sensing vegetation indices to derive regional maps of EF. We combined these EF maps with satellite observations of net radiation to derive monthly and annual calculations of ET at a 250 m resolution during calendar year 2004 in the Imperial Valley, California, a major agricultural region that is dependent upon irrigation and which has a well constrained water budget. We then summed ET for the Imperial Valley and compared the result to a surface water budget based on irrigation and drainage measurements, which showed good annual and seasonal agreement. These results indicate REFEB produces accurate field measurements of EF and WUE, which can be scaled to estimate regional ET at time scales ranging from less than a week to annual sums.

Estimation of surface longwave radiation components from ground‐based historical net radiation and weather data

A methodology for estimating ground upwelling, clear‐sky and cloud downwelling longwave radiations (L↑, Lsky↓, and Lcld↓) and net shortwave radiation (Sn) at 30‐min temporal scales based on long‐term ground‐based net radiations and meteorological observations is described. Components of surface radiation can be estimated from empirical models, cloud radiation models, and remote sensing observations. The proposed method combines the local calibration of empirical models and the radiative energy balance method to obtain the dual‐directional, dual‐spectral components of the surface radiation for the offline land surface process modeling and ecosystem study. By extracting information of radiation components from long‐term net radiation and concurrent weather data, the utility of tower net radiation observations is maximized. Four test sites with multiyears' radiation records were used to evaluate the method. The results show that when compared with the results of empirical models using default parameters the proposed method is able to produce more accurate estimates of longwave surface components (Lg↑, Lsky↓, Lcld↓) and net shortwave radiation (Sn). Overall, the estimated and observed surface radiation components show high correlations (&gt;0.90), high index of agreement (&gt;0.89), and low errors (root mean square error &lt;30 W m−2 and bias &lt;11 W m−2) at all of the test sites. The advantage of this scheme is that the refinement is achieved using the information from the historical net radiation and weather data at each observation site without additional measurements. This method is applicable for many existing observation sites worldwide which have long‐term (at least 1 year) continuous net radiation records.

Heat balance of an asphalt surface: observations and physically‐based simulations

AbstractA physically‐based 1‐D heat and mass transfer model was tested to estimate the heat fluxes of an asphalt surface. The model was run for two summer months for a road test site in southwest Sweden. Parameters for thermal properties, surface runoff, radiation and turbulent transfer were obtained from a description of the road stratification and from the literature. Coefficients of determination (r2) 0.94, 0.93 and 0.97 were obtained when simulated results were compared with observations of net radiation, heat flow below the surface and surface temperature respectively, all with slope coefficients close to unity. In addition, simulation results elucidated the role of water vapour transport through the asphalt‐soil profile and its effect on the latent heat flow from the surface. Problems were identified with closure of the heat balance in measurements based on discrepancy between simulated and observed sensible heat flux. Copyright © 2006 Royal Meteorological Society.

Estimating the surface water and radiation balance in an upland area from space

The Synthetic Aperture Radar (SAR) carried aboard ERS-1 and-2 has been used to estimate soil moisture in a naturally vegetated area of upland moor in Lancashire, north-west England. This holds promise for the determination of catchment-scale evapotranspiration rates using direct measurements of changes in soil moisture content. Combining such measurements as these with observations of net radiation from the NOAA AVHRR passive radiometer has led to the development of a method, based upon the techniques of Price (IEEE Transactions on Geoscience and Remote Sensing, 28, 940-948, 1990) combined with some new methodologies, whereby the sensible heat flux can be found by the closure of the energy balance equation. A review of the methodology developed is presented together with the potential for refining the system using further instruments. There are limitations of the procedure due to the restricted temporal coverage of the sensors concerned, and their inability to penetrate the surface to investigate soil-water-vegetation processes within the root zone. It is believed, however, that models can be constructed to account for these deficiencies to enable retrieval of an entire surface energy and water budget. These would have a plethora of applications, both direct and as inputs to atmospheric and hydrological models.

Inconsistencies in net radiation estimates from use of several models of instruments in a desert environment

Studies of surface energy and water balance generally require an accurate estimate of net radiation and its spatial distribution. A project quantifying both short term and seasonal water use of shrub and grass vegetation in the Jornada Experimental Range in New Mexico prompted a study to compare net radiation observations using two types of net radiometers currently being used in research. A set of 12 REBS net radiometers were compared with each other and one Swissteco, over wet and dry surfaces in an arid landscape under clear skies. The set of REBS exhibited significant differences in output over both surfaces. However, they could be cross calibrated to yield values within 10 W m −2, on average. There was also a significant bias between the REBS and Swissteco over a dry surface, but not over a wet one. The two makes of instrument could be made to agree under the dry conditions by using regression or autoregression techniques. However, the resulting equations would induce bias for the wet surface condition. Thus, it is not possible to cross calibrate these two makes of radiometer over the range of environmental conditions observed. This result indicates that determination of spatial distribution of net radiation over a variable surface should be made with identical instruments which have been cross calibrated. The need still exists for development of a radiometer and calibration procedures which will produce accurate and consistent measurements over a range of surface conditions.

Sensitivity of regional climate to deforestation in the Amazon basin

Deforestation results in several adverse effects on the natural environment. The focus of this paper is on the effects of deforestation on land-surface processes and regional climate of the Amazon basin. In general, the effects of deforestation on climate are likely to depend on the scale of the deforested area. In this study, we are interested in the effects due to deforestation of areas with a scale of about 250 km. Hence, a meso-scale climate model is used in performing numerical experiments on the sensitivity of regional climate to deforestation of areas with that size. It is found that deforestation results in less net surface radiation, less evaporation, less rainfall, and warmer surface temperature. The magnitude of the change in temperature is of the order of 0·5°C, the magnitudes of the changes in the other variables are of the order of 10%. In order to verify some of the results of the numerical experiments, the model simulations of net surface radiation are compared to recent observations of net radiation over cleared and undisturbed forest in the Amazon. The results of the model and the observations agree in the following conclusion: the difference in net surface radiation between cleared and undisturbed forest is, almost, equally partitioned between net solar radiation and net long-wave radiation. This finding contributes to our understanding of the basic physics in the deforestation problem.

Calibration, comparison, and correction of net radiation instruments used during FIFE

Net all‐wave radiation was observed at 22 surface sites during the 1987 observation year of the First ISLSCP Field Experiment (FIFE). Eight groups of investigators employed seven different designs of net radiometer by five different manufacturers. To establish true differences in received net radiation among sites requires knowledge of differences due to instrument performance. After careful Sun/shade calibration, side‐by‐side comparison revealed daytime differences as large as 5 to 7% for instruments of the same manufacture and 10 to 15% between manufacturer. The largest differences are between instruments with so‐called “thin windows” and “thick windows” and between instruments of “double‐dome” and “single‐dome” design. Comparisons with four‐component reference net radiation observations reveal that the double‐dome and thick window instruments have substantially lower sensitivity to longwave (thermal) net radiation than to shortwave (solar) net radiation. The magnitude of the sensitivity difference is greater when the sky is clear than when cloudy. Observations with thin window instruments agreed more closely with the reference component net radiation. Field observations made with double‐dome radiometers can be corrected when net shortwave radiation is separately measured. Such a correction is shown to reduce the systematic root‐mean‐square differences among instruments to between one half and one quarter of those shown by uncorrected measurements. When net shortwave radiation is not available, correction according to a regression comparison against a “standard” net radiometer may be used. This reduced the systematic root‐mean‐square differences by up to one half of their uncorrected values. From this analysis it is estimated that the regression corrected daytime net radiation observations reported to the FIFE Information System include systematic‐root‐mean‐square instrumental differences of 15 to 35 W m−2.

Analysis of an empirical model for soil heat flux under a growing wheat crop for estimating evaporation by an infrared-temperature based energy balance equation

A net-radiation-based empirical model for soil heat flux ( G) is analyzed for inclusion in a canopy-temperature-based energy balance equation to estimate evaporation from a growing wheat crop. The observed direct correlation between net radiation and soil heat flux for bare soils is extended to include the effect of growing vegetation by considering the canopy attenuation of net radiation. The parameters of the soil heat flux model are determined using observations of net radiation, evaporation and estimated sensible heat flux over Pavon wheat, while the empirical model is used to calculate and compare against the latent heat flux observations over Ciano wheat. Comparisons are done for 9 days of diurnal observations, which included clear and partially cloudy skies and the leaf area index varying from 0 (i.e., bare soil) to 4.7. The performance of the empirical model was not very satisfactory for 2 days of data over bare soil, primarily because of the phase difference in the diurnal variations of soil heat flux and net radiation. A linear regression analysis using the estimated and the observed latent heat fluxes for all 9 days gave a correlation coefficient of 0.97 and a standard error of 39 W m −2. The results of a sensitivity analysis show that errors in estimating G translate directly into a bias in estimating the latent heat flux, and the magnitude of this bias decreases as the vegetation leaf area index increases.

An analysis of infrared temperature observations over wheat and calculation of latent heat flux

From half-hourly averaged observations of net radiation, latent and soil heat fluxes over wheat, the sensible heat flux is calculated as the residual component of the surface energy balance. Then, the aerodynamic surface temperature is obtained by solving iteratively the aerodynamic equation for sensible heat flux, taking into consideration the bluffbody (differences in roughness height for heat and momentum exchange) and the stability (differences in surface and air temperatures) corrections to the aerodynamic resistance. The aerodynamic temperatures are found to be lower (higher) than the infrared thermometric observations under stable (unstable) atmospheric conditions. However, when the infrared temperatures were used in a resistance-energy balance equation to estimate the latent heat flux, then the estimated fluxes showed a high linear correlation ( r = 0.96) and a moderate standard error (47 W m −2) under regression analysis with the observed fluxes.

Some Results of Actual Observations of Net Radiation and Soil Heat Transfer in Unheated Greenhouses

The net radiation and soil heat transfer have been measured day and night in multi-span greenhouses.(1) The heat storage ratio: The ratio of the soil heat transfer to the net radiation in the daytime became larger under the shade and the high value of larger than 0.5 was obtained in the case with high soil moisture.(2) The radiant heat ratio: The ratio of the net radiation to the soil heat transfer in the night-time was about 0.8, therefore the ratio of heat convection was estimated so small as about 0.2.(3) The good proportional relation was found between the soil heat transfer and the soil temperature difference from the floor surface to the depth of 1cm. The thermal conductivity of 0.4-0.5kcal/m·hr·°C was obtained for the wet volcanic ash floor.(4) The convection heat transfer coefficient of floor surface in the night-time was calculated from the temperature difference between soil surface and room air, and the convective heat flux which was obtained from the difference between net radiation and soil heat transfer.The typical value of 1.7kcal/m2·hr·°C was obtained for the double-roofed multi-span greenhouse.(5) The design values of soil heat transfer should be modified a little larger than the present values, in reference to the temperature difference between inside and outside as shown in the figure.

Micrometeorological observations of a soil surface during the partial phases of the total solar eclipse of March 7, 1970

Summary Simultaneous observations of net radiation and temperature for the entire partiaI eclipse were obtained at a site with maximum obscuration of 92 0/0 of the direct solar radiation. A strongly negative net radiation of --96 mly/min comparable to nocturnal conditions (--110 mly/min) was found at minimum light. Since lowlight levels under normal daytime conditions (thick clouds) coincide with weak temperature gradients, organisms with both optical and thermal sensors may show a confused behavior under eclipse conditions. The contribution of direct solar radiation to the net radiation was computed using limb-darkened solar eclipse functions (included in an appendix) which show considerable departures from the uniform disk approximation.

The exponential wind profile

AbstractFrom a definition and a hypothesis the form of the wind profile in the turbulent boundary layer when the air is thermally stratified is derived as magnified image.This solution is expected to be applicable in all stabilities and to all heights below which the shearing stress and the vertical heat flux remain constant.A critical examination of the experimental procedure necessary to test the validity of this, or of any, formulation for the steady‐state wind profile leads to a specification which the observational site and the weather conditions should meet.The results of a series of experiments are presented and analysed. These comprise measurements of wind speed and temperature at a number of levels up to 16 metres, supplemented by observations of net radiation, heat flux into the air and into the ground, and shearing stress. the analysis affords good verification of the form proposed for the wind profile.A variety of evidence is adduced to show that buoyancy modifies the transfer of heat more strongly than that of momentum, and that the discrimination increases with height above the surface.