Surface Energy Balance Components Research Articles

Long-term estimation of soil heat flux by single layer soil temperature

Soil heat flux is one of the important components of surface energy balance. In this study, long-term estimation of soil heat flux from single layer soil temperature was carried out by the traditional sinusoidal analytical method and the half-order time derivative method of Wang and Bras [Wang and Bras (1999) J Hydrol 216:214-226]. In order to understand the characteristics of soil heat flux and to examine the performances of the two methods, a field experiment was conducted at a temperate and humid grassland in Cork, Ireland. Our results show that the soil heat flux had the same magnitude as the sensible heat flux at this grassland site. It was also demonstrated that the analytical method did not predict the soil heat flux well because the sinusoidal assumption for the temporal variation in soil heat flux was invalid. In contrast, good agreement was found between the soil heat flux measurements and predictions made by the half-order time derivative method. This success suggests that this method could be used to estimate soil heat flux from long-term remotely sensed surface temperature.

Diurnal-to-seasonal characteristics of surface energy balance and temperature in East Asian summer monsoon simulations

We used regional climate model simulations of the East Asian Summer Monsoon (EASM) to study diurnal-to-seasonal characteristics of the surface energy balance and temperature, and their relationships to clouds and surface soil moisture. Simulations were performed for the period May through September 1988 and 1989, 2 years with significant differences in observed surface air temperature, radiation, and clouds over the Yangtze-Huai River Valley (YHRV), which are realistically reproduced by the model. Differences in daytime evolutions of the YHRV surface net radiation, heat fluxes, and surface air temperature between 2-year summers result mainly from fluctuation of shortwave cloud radiative forcing. Clouds dominate daily variability of the YHRV surface net solar radiation, surface net radiation, and latent heat, generally accounting for above 80% of the total variances. Consequently, they are more effective in damping the diurnal temperature range by reducing daytime maximum temperature as compared to surface soil moisture. Both clouds and soil moisture exhibit small effects on nighttime minimum temperature, which is largely controlled by the greenhouse effect of the atmospheric water vapor. Surface energy balance components and temperature evolve with the march of EASM, which is quite different between 2 years. The comparative analyses of observations and other available data can generally validate the major conclusions from the simulations.

A Semiempirical Microscale Model of the Surface Energy Balance and Its Application to Two Urban Rooftops

Abstract Individual structures within the same local-scale (102–104 m) environment may experience different microscale (<103 m) climates. Urban microclimate variations are often a result of site-specific features, including spatial and material characteristics of surfaces and surrounding structures. A semiempirical surface energy balance model is presented that incorporates radiative and meteorological measurements to statistically parameterize energy fluxes that are not measured directly, including sensible heat transport, storage heat flux through conduction, and evaporation (assumed to be negligible under dry conditions). Two Chicago rooftops were chosen for detailed study. The City Hall site was located in an intensely developed urban area characterized by close-set high-rise buildings. The University rooftop was in a highly developed area characterized by three- to seven-story buildings of stone, concrete, and brick construction. Two identical sets of instruments recorded measurements contemporaneously from these rooftops during summer 2005, and results from the week of 29 July to 5 August are presented here. The model explains 83.7% and 96% of the variance for the City Hall and University sites, respectively. Results apply to a surface area of approximately 1260 m2, at length scales similar to the dimensions of built structures and other urban elements. A site intercomparison revealed variations in surface energy balance components caused by site-specific features and demonstrated the relevance of the model to urban applications.

Mapping evapotranspiration in the Indus Basin using ASTER data

Conventional methods that use point measurements to estimate evapotranspiration are representative only of local areas and cannot be extended to large areas because of heterogeneity of landscape. To overcome this difficulty, remote sensing has proven to be the most suitable approach for large area estimation of evapotranspiration because remote sensing data can provide representative parameters such as radiometric surface temperature, albedo and vegetation index. The heterogeneity is more prominent in the Indus Basin as more than 80% of farmers have land holdings less than 4 ha, and within these holdings, two or three different crops are usually grown. The limitation of most remote sensing based procedures to estimate evapotranspiration is the measurements of large number of crop‐specific and climatic parameters, which are not only difficult to obtain but also require considerable field work, equipment and therefore involve much expenditure. The purpose of this study was to present a simple methodology that requires minimum ground observations for estimation of evapotranspiration to test the reliability of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for estimation of evapotranspiration in the Indus Basin. The methodology is based on surface energy balance to estimate sensible and latent heat fluxes by combining remotely sensed data from ASTER with common meteorological data. The various components of surface energy balance were computed during satellite overpass and 24‐h integrated fluxes were derived for the full ASTER scene acquired over the lower Rechna doab region of the Indus Basin. The surface brightness temperatures were derived from thermal band 13 and NDVI from two VNIR bands of the ASTER. Evapotranspiration values from the maize field in the Indus Basin, as estimated using ASTER data at Shahkot, Jaranwala and Satiana locations, were estimated as 2.05, 2.77 and 2.32 mm day−1, respectively. The estimated evapotranspiration was compared with evapotranspiration computed at three different locations using CROPWAT software and was found to be in close agreement.

Surface energy balance measurements at a tropical site in West Africa during the transition from dry to wet season

In one of the first micrometeorological experiments at a tropical site in West Africa, direct measurements of all surface energy balance components were carried out. The experiment NIMEX-1 in Ile-Ife, Nigeria (7°33′ N, 4°33′ E), was conducted from February 19, 2004 to March 9, 2004, during the transition from the dry to the wet season. Three typical weather situations could be observed: firstly, monsoonal winds from the southwest blew over desiccated soils. Almost 100% of the available energy at the surface was transformed into sensible heat flux. Secondly, after several thundershowers, monsoonal winds swept over soils of increased water content, which led to a partitioning of the available energy corresponding to Bowen ratios between 0.3 and 0.5. Thirdly, harmattan winds advected dry dusty air from northern directions, which reduced the incoming shortwave radiation. Again, Bowen ratios range from 0.3 to 0.5 during daytime, whereas latent heat fluxes are still high during the night due to the advection of very dry air. No systematic non-closure of the surface energy balance could be found for the NIMEX-1 dataset. Unlike other experiments in Europe, most of the ogives for the sensible and latent heat flux were found to be convergent during NIMEX-1 in Ile-Ife. This can be attributed to the homogeneity of the surrounding bush, which lacks the defined borders found in agriculturally cultivated landscapes.

Comparison of Four Methods to Estimate Urban Heat Storage

Abstract The relative performance of four independent methods to estimate the magnitude and diurnal behavior of net heat storage fluxes (ΔQS) in a city center is assessed. This heat flux is a significant but understudied component of the urban surface energy balance (SEB). Direct measurement of this SEB term at the local scale (horizontal length scale ∼102–104 m) is practically unattainable primarily because of the complex array of materials and the three-dimensionality of urban systems. Results of an 8-day summertime observational study at a site in the center of Marseille, France, are presented. This locale is an ideal environment for such research because of the warm, dry climate (hence the SEB is dominated by sensible heat exchanges) and the high density of tall buildings with thick walls (hence it has a large thermal mass that favors heat storage as a component of the SEB). Estimates of ΔQS derived as residuals in the SEB, after the remaining terms are measured directly, (termed RES) are compared with those calculated from a parameterization scheme [objective hysteresis model (OHM)], a local-scale numerical model [Town Energy Balance model (TEB)], and a bulk heat transfer method [thermal mass scheme (TMS)]. Inputs to the methods include observed meteorological data and morphometric properties of the urban site. All approaches yield a similar diurnal course. The OHM and TEB methods tend to slightly overestimate storage uptake by day when compared with the RES, whereas TMS slightly underestimates it. All methods underestimate heat storage release at night when compared with RES and show some sensitivity to wind speed, especially above about 5 m s−1. OHM estimates perform satisfactorily in the mean but miss short-term variability and are poor at night. TEB simulations show the best agreement with RES results, particularly at night. TMS values are comparable to those from the other methods, but its extensive input requirements render it almost impractical. Overall, the convergence of results is reassuring but the lack of a standard for quantifying heat storage and the spread of results mean this term remains a source of imprecision in urban energy balance measurement and modeling.

Effect of spatial variation on areal evapotranspiration simulation in Haibei, Tibet plateau, China

Quantification of areal evapotranspiration from remote sensing data requires the determination of surface energy balance components with support of field observations. Much attention should be given to spatial resolution sensitivity to the physics of surface heterogeneity. Using the Priestley–Taylor model, we generated evapotranspiration maps at several spatial resolutions for a heterogeneous area at Haibei, and validated the evapotranspiration maps with the flux tower data. The results suggested that the mean values for all evapotranspiration maps were quite similar but their standard deviations decreased with the coarsening of spatial resolution. When the resolution transcended about 480 m, the standard deviations drastically decreased, indicating a loss of spatial structure information of the original resolution evapotranspiration map. The absolute values of relative errors of the points for evapotranspiration maps showed a fluctuant trend as spatial resolution of input parameter data layers coarsening, and the absolute value of relative errors reached minimum when pixel size of map matched up to measuring scale of eddy covariance system. Finally, based on the analyses of the semi‐variogram of the original resolution evapotranspiration map and the shapes of spatial autocorrelation indices of Moran and Geary for evapotranspiration maps at different resolutions, an appropriate resolution was suggested for the areal evapotranspiration simulation in this study area.

Transitions in the surface energy balance during the life cycle of a monsoon season

In this observational/diagnostic study, we illustrate the time history of some important parameters of the surface energy balance during the life cycle of a single monsoon season. This chronology of the surface energy balance portrays the differential equilibrium state from the preonset phase to the withdrawal phase. This includes an analysis of the time history of base variables such as soil moisture, ground temperature, cloud cover, precipitation and humidity. This is followed by an analysis of the components of the surface energy balance where we note subtle changes in the overall balances as we proceed from one epoch of the monsoon to the next. Of interest here is the transition sequence: preonset, onset, break, revival, break, revival and withdrawal during the year 2001. Computations are all illustrated for a box over central India where the coastal effects were small, data coverage was not sparse and where the semi-arid land mass changes drastically to a lush green area. This region exhibited large changes in the components of surface energy balance. The principal results pertain to what balances the difference among the incoming short wave radiation (at the earth’s surface) and the long wave radiation exhibited by the ground. That difference is balanced by a dominant sensible heat flux and the reflected short wave radiation in the preonset stage. A sudden change in the Bowen ratio going from>1 to <1 is noted soon after the onset of monsoon. Thereafter the latent heat flux from the land surface takes an important role and the sensible heat flux acquires a diminishing role. We also examine the subtle changes that occur in the components of surface energy balance between the break and the active phases. The break phases are seen to be quite different from the preonset phases. This study is aimed to illustrate the major importance of moisture and clouds in the radiative transfer computations that are central to the surface energy balance during each epoch. These sensitivities (of moisture and clouds) have major consequences for weather and climate forecasts

Surface energy balance calculations for small northern lakes

An energy balance model is used to determine diurnal surface energy balance components for three different sized high-latitude Canadian lakes in the Mackenzie River Basin (MRB) during the open water seasons of 2000, 2001, and 2002. Surface net radiation is derived from the component fluxes of the radiation balance. Turbulent heat fluxes are calculated using the aerodynamic method with input from local meteorological stations and experimentally derived drag coefficients. Lake heat storage, determined as a residual of the surface energy balance, is used together with measured water temperature profiles to calculate the daily mixing layer depth. The model uses readily available meteorological inputs for radiation calculations. Verification results for surface energy balance components show mean bias error (MBE) generally less than 5% of the mean measured daily fluxes and root mean square error (RMSE) less than 38%, which decreases to less than 16% for 10-day averaging periods. The model tends to overestimate net radiation by 7% and latent and sensible heat fluxes by about 4% and 1%, respectively, on average. Inferred slab layer depths indicate that the shallowest lake was isothermal while the deeper lakes showed temporal variations as expected. Copyright © 2006 Royal Meteorological Society.

PROJECTION OF THE IMPACT OF CLIMATE CHANGE ON THE SURFACE ENERGY AND WATER BALANCE IN THE SEYHAN RIVER BASIN TURKEY

In this study, the surface energy and water balance components and related hydrological variables of the Seyhan River basin Turkey are estimated through off-line simulation of the land surface model. The simulation domain is 2.75 degree × 2.75 degree area (E34.25-37.0, N36.5-N39.25) with 5 min resolution (33 × 33 grids). As for the atmospheric forcing data, the products from RCM (Regional Climate Model) for both present and future (warm-up) condition are used. Based on the field survey and NDVI time series analysis, landcover dataset of this target basin is improved and utilized in the numerical simulation. In terms of basin average annual water balance, precipitation is projected to decrease about 210mm, while evapotranspiration increases about 30mm by the higher evaporation demand. This means that the reduction in runoff is about 240mm. Furthermore, irrigation water demand will increase about 10mm. Considering the amount of present water balance, these impacts are thought to be significantly large.

Investigating the Sensitivity of Glacier Mass-Balance/Elevation Profiles to Changing Meteorological Conditions: Model Experiments for Haut Glacier D'Arolla, Valais, Switzerland

This paper presents the results of a distributed surface energy balance model which is used to calculate season-long patterns of melt on a small valley glacier, Haut Glacier d’Arolla, Valais, Switzerland, under different summer meteorological conditions and winter snow depth distributions. The model uses a Digital Elevation Model of the glacier and the surrounding topography, together with meteorological data collected at a site in front of the glacier to determine hourly totals of the surface energy balance components, and hence melt, over the entire glacier surface throughout a melt season, with a spatial resolution of 20 m. From these results, the spatially averaged mass-balance/elevation profile for the glacier can be calculated. A cubic relationship with elevation gives the best fit to the calculated mass-balance curve. The shape of this profile varies with the imposed change in meteorological conditions, however, becoming increasingly “S” shaped for warmer or less snowy conditions. These mass-balance profile changes are due to the complex interplay between albedo variations due to different snow depths over the glacier surface (and eventual removal of the snow cover), the variations in solar energy receipts caused by slope and aspect variation over the glacier and the changing patterns of shading by the surrounding topography. The changes in mass-balance profile lead to maximum calculated mass-balance sensitivity to imposed change occurring at intermediate elevations on the glacier; the calculated equilibrium-line altitude (ELA) occurs at the upper end of this zone, resulting in very large calculated changes in the ELA for different climatic conditions.

Cloud Parameterizations in SUNYA Regional Climate Model for the East Asia Summer Monsoon Simulations

East Asia summer monsoon (EASM) simulations are conducted to evaluate three schemes which determine cloud properties used in the radiation calculation of the State University of New York at Albany (SUNYA) regional climate model (RCM). Scheme-Ⅰ uses diagnostic cloud cover and cloud water while Scheme-Ⅱ uses prognostic cloud water along with overcast sky; both schemes are commonly employed in RCMs. In Scheme-Ⅲ, cloud cover is determined by diagnostic formula, but the cloud water is calculated by the weighted means of its diagnosed and prognosed values. Therefore, Scheme-Ⅲ considers the subgrid-scale clouds as Scheme-Ⅰ and maintains consistent cloud properties in radiation calculation and microphysical processes as Scheme-Ⅱ. Cloud radiative forcing (CRF) which provides a quantification of the cloud-radiation-climate interaction is adopted to compare the three schemes in simulating the 1991 EASM, characterized by large amounts of cloud and persistent rainfall over Yangtze-Huai River valley. With these three cloud schemes, the SUNYA RCM is capable of simulating the intra-seasonal variations of observed cloud cover and longwave CRF. The transition of shortwave CRF is not properly simulated due to the constantly presented low-level clouds. Mostly the magnitude of CRF is overestimated by 13-22 W m^(-2) for shortwave CRF and by 12-16 W m^(-2) for longwave CRF. It is also found that the surface temperature biases are highly correlated (with correlation coefficient greater than 0.8) to the shortwave CRF biases. Therefore, Scheme-Ⅲ resulting in less low-level cloud water and the least shortwave CRF biases simulates surface temperatures in better agreement with observations. Analyses of surface energy balance components indicate that the CRF changes dominate the surface temperature responses and the consequent surface latent heat and sensible heat flux feedbacks significantly offset them. Finally, comparisons of the diurnal variations of simulated cloud water among the three schemes show that Scheme-Ⅲ provides consistency between cloud microphysics and radiation.

A model of the production and transport of CO 2 in soil: predicting soil CO 2 concentrations and CO 2 efflux from a forest floor

A process-based model of the transport of heat and water in the soil and surface energy balance components is extended to include production of CO 2 from heterotrophic (microbial decomposition) and autotrophic (root) respiration, and transport of the resulting CO 2 in both the gaseous and liquid phases. The production of CO 2 is determined by the amount and type as well as distribution in the soil profile of organic matter and roots, and their respective first-order rate constants. Influences of soil water and temperature are considered through their effects on respiration, CO 2 diffusivities and chemical equilibria among various C species in the soil–solution–air continuum. Also included is CO 2 uptake by plant roots associated with root water uptake. Model calculations, using independently determined parameters, are compared with measurements of soil CO 2 concentrations and chamber-measured forest floor fluxes in a second-growth 54-year-old Douglas-fir forest located on the east coast of Vancouver Island, Canada. Measured and modeled forest floor CO 2 effluxes and soil CO 2 concentration profiles, as well as soil water contents and temperatures showed good agreement. The efflux was most sensitive to soil temperature, and the influence of soil water content was relatively small. In this rapidly draining soil, the CO 2 efflux, at time scales as small as half-hour, was very well approximated by the total production of CO 2 in the soil profile, even during and after rainfall, which significantly increases soil water content. This is because CO 2 diffusion in this forest soil is relatively rapid compared to changes in the rates of CO 2 production. In this podzolic soil ecosystem with low soil pH, liquid-phase diffusion appears to play a minor role in CO 2 transport. High soil CO 2 concentrations, up to 10,000 μmol mol −1 in summer and 6000 μmol mol −1 in winter, and a positive downward gradient at the 1 m depth indicate some CO 2 sources associated with very low CO 2 diffusivity at deeper depths.

Estimating Land Surface Energy Budgets From Space: Review and Current Efforts at the University of Wisconsin—Madison and USDA–ARS

Since the advent of the meteorological satellite, a large research effort within the community of earth scientists has been directed at assessing the components of the land surface energy balance from space. The development of these techniques from first efforts to the present time are reviewed, and the integrated system used to estimate the radiative and turbulent land surface fluxes is described. This system is now running in real time over the continental United States at a resolution of 10 km, producing daily and time-integrated flux components.

Effect of surface layer thickness on simultaneous transport of heat and water in a bare soil and its implications for land surface schemes

A physically‐based multi‐layer numerical model is developed to determine the coupled transport of heat and water in the soil and in the soil‐atmosphere boundary layer. Using inputs of standard weather data and initial soil conditions the model is capable of predicting the surface energy balance components as well as water content and temperature profiles in the soil. It is used to predict these variables for a bare silt loam soil under two tillage treatments, viz. culti‐packed and left loose after disc‐harrowing, and the predicted results are compared with measurements. Very good agreement between the model predictions and measured evaporation and heat fluxes and soil water and temperatures for a ten‐day period shows that the model is capable of simulating the coupled transport of soil heat and soil water and their transfer across the soil surface‐atmosphere interface adequately. Model predictions were compared with those of CLASS (Canadian Land Surface Scheme). It is shown that CLASS, version 2.6, provides good estimates of evaporation and hence the latent heat flux density, QE, under wetter soil conditions, but overestimates QE at moderately wet soil conditions and underestimates it under dry soil conditions. Under dry to moderately wet soil conditions the calculation of evaporation from bare soil is very sensitive to the thickness of the top layer particularly as the thickness approaches 10 cm.

Evapotranspiration estimation using thematic mapper spectral satellite data in the Ethiopian rift and adjacent highlands

Quantification of actual evapotranspiration from spectral satellite data requires determination of the surface energy balance components with the support of field observations. In this paper an approach called Surface Energy Balance Algorithm for Land (SEBAL) is presented to calculate daily evaporation of some of the Ethiopian rift lakes and the surrounding landscape from the Thematic Mapper spectral satellite data on the basis of the energy balance approach. The result has been used in part to support long-term evapotranspiration estimation made using conventional methods. Conventional open-water evaporation estimation methods usually assume that the surface temperatures of lakes remain uniform and that evaporation proceeds more or less at the same rate over the total lake surface. However, this study clearly demonstrated that evaporation from a single lake varies depending upon surface temperature, albedo and on the incoming fluxes from groundwater and surface waters. The daily evaporation of the rift lakes is highly variable, ranging from 4.9 to 5.9 mm/day. On the land surface, actual evapotranspiration increases with altitude following the availability of moisture in the soil instead of the temperature gradient. On average it ranges from 0.2 mm/day in rift lacustrine soils and salty lake shores to around 4.5 mm/day in the highland mountain peaks covered with afro-alpine vegetation. The relative spatial differences of the SEBAL result from the land surface is in good agreement with the conventional evapotranspiration estimates.

A numerical model for surface energy balance and thermal regime of the active layer and permafrost containing unfrozen water

This paper describes a surface energy balance approach-based one-dimensional heat transfer model for estimating surface energy balance components and the thermal regime of soil. The surface energy balance equation was used to estimate the upper boundary temperature conditions for thermal conduction calculations and to calculate surface heat fluxes. The influence of unfrozen water on the thermal properties of soils was accounted for in the heat transfer model. The effect of snow was included in the model by extending the heat conduction solution into the snow layer and computing the surface heat balance components and the snow surface temperature. The model was driven by meteorological data collected at Barrow, AK, and was validated against the observed ground temperatures at Barrow. The results show good agreement between the simulated and the measured soil temperatures at depths of 0.01, 0.29, 0.50, and 1.0 m. When snow cover was present, snow surface temperatures were colder than ground surface temperatures and air temperatures, with mean temperature differences of −5.36 and −1.55 °C, respectively. We conclude that the model presented in this study can be used to calculate the surface energy balance components, simulate the ground temperatures, and investigate the impact of seasonal snow cover on the thermal regime of the active layer and permafrost containing unfrozen water with a quite reasonable accuracy. Snow density, which determines the snow thermal conductivity, volumetric heat capacity, and albedo in this model, can strongly affect the performance of this model.

Simulating the Greenland atmospheric boundary layer Part II: Energy balance and climate sensitivity

A three-dimensional dynamic downscaling model of the Greenland atmospheric boundary layer is usedto investigate the surface energy balance of the Greenland ice sheet for the summer ablation season of1998. The model is forced by ECMWF analysis data and has a horizontal resolution of 20 km. Theresults show that the turbulent heat fluxes contribute significantly (32%) to the total surface energy fluxin the ablation region. A climate sensitivity experiment is carried out with the model by increasing thefree atmospheric forcing temperature by 1 K. The resulting change, known as climate sensitivity, in2 m temperature, 2 m wind speed and the surface energy balance components are discussed. The 2 mtemperature is shown to have a climate sensitivity significantly less than unity, as low as 0.3, in regionswhere melt prevails for most of the ablation season. The surface energy flux in the ablation region isfound to increase by 21% for a 1 K increase in atmospheric temperature. Wind speeds also increase, particularly near the margin of the ice sheet, as a result of enhanced katabatic forcing. Enhanced windspeeds are shown to account for roughly 12% of the climate sensitivity of the sensible heat flux whenaveraged over the ablation region. Albedo feedback is also shown to play an important role in the totalclimate sensitivity of the surface energy balance.

Parametrization schemes of incident radiation in the North Water polynya

Surface incident radiation is a critical component of the Arctic surface energy balance making it important for sea‐ice model parametrizations to properly account for these fluxes. In this article, we test the performance of various incident short‐wave (K?) and long‐wave (L?) flux parametrizations using unique observations from the 1998 International North Water (NOW) Polynya Project between March and July. The dataset includes hourly observations over terrestrial, fast‐ice and full marine polynya environments allowing for parametrization comparisons between each environment and determination of any seasonal biases. Performance testing is highly dependent on observed input parameters that contain relative errors, however, significant differences between the marine and fast‐ice fluxes are evident. Results are very similar between the terrestrial and fast‐ice sites. The best K? clear‐sky schemes underestimate fluxes in the colder season and overestimate them in the warm season, with greater biases in the marine setting. The K? cloudy‐sky results suggest a similar cold and warm season bias but with greater magnitudes, especially in the marine environment. The K? cloudy‐sky schemes require seasonal improvements, especially in the marine atmosphere. The L? clear‐sky fluxes were generally overestimated during the colder season. Accounting for a less emissive atmosphere resulted in better flux approximations in all environments. L? cloudy‐sky fluxes were generally underestimated. Adjusting the cloudy‐sky emissivity improved the estimated fluxes, however, results were very different in the marine setting. The L? cloudy‐sky parametrizations may require re‐evaluation due to a consistent negative bias as the observed flux increases.

Land data assimilation with satellite measurements for the estimation of surface energy balance components and surface control on evaporation

A variational land data assimilation system is used to estimate latent heat flux and surface control on evaporation. The dynamic equation for surface temperature with energy balance is used as a constraint on the estimation using the adjoint technique. Measurements of land surface temperature from satellite remote sensing are assimilated over two subregions within the Southern Great Plains 1997 hydrology field experiment. The performance of the estimation is linked to the timing of the satellite overpass. During days when the measurements close to the time of peak ground temperature are available, the estimation is adequate. The approach shows that satellite remote sensing of land temperature may be used to provide estimates of components of the surface energy balance and land surface control on evaporation. The latter parameter is related to surface soil moisture, and here they are compared with independent values derived from ground measurements.