Land Surface Heat Fluxes Research Articles

Evaluating CEOP model performance with the observational data from Tongyu reference site, semi-arid region of China

Using data archived in the Coordinated Enhanced Observing Period (CEOP) project, comparisons between field observations undertaken at Tongyu CEOP reference site in China and model output from year 2003 to 2004 have been implemented, and in particular, the time series and diurnal cycles of precipitation, near-surface temperature, air temperature, and latent and sensible heat fluxes are presented. The results show that the ability of the model simulations on the temperatures, such as air temperature and the surface temperature, is satisfactory compared with the simulations on the land surface heat fluxes and the precipitation at Tongyu site. In addition, the multi-model ensemble exhibits better results over all items in comparison with the observations. The differences of the precipitation at the interannual and the seasonal time scales between the model results and observations indicate that some of the models are able to reproduce the larger amount of precipitation in 2003 than that in 2004, which is consistent with the trend of the observations at Tongyu site even though the mean square errors of models output calculated from daily precipitation during year 2003 and 2004 are even greater than the daily amount of the precipitation. The poor skill in the quantitative simulation of the precipitation indicates that the deficiency of the models in simulating the surface heat fluxes may be closely related to the biases of the precipitation simulations. In terms of the seasonal time series of the precipitation, there is an increase during summer, accompanied by the same increased trend of the latent heat flux and the decreased trend of the sensible heat flux from the insitu observations.

An assessment of urban heat island of Lokoja Town and surroundings using LandSat ETM data.

The urban centre and its suburban environment are largely influenced by changes driven by people as a result of urbanization and other anthropogenic activities. Urbanization impacts on air and water quality, local climate and biodiversity. This study assesses the Urban Heat Island (UHI) of Lokoja town and surroundings from LandSat ETM satellite imagery of 2001 using remote sensing techniques. Band 3, 4 and 6 of the imagery were use in the estimation of NDVI, land surface emissivity and surface temperature. The results show that urban heat island in Lokoja town is significant, with average Land surface temperature values range from 301.13K to 336.14K., and maximum urban/suburban temperature difference reaching 10.9oC. This suggests that vegetation is the principal determinant controlling the spatial distribution of land surface heat flux. This approach was found to be more effective in assessing urban heat island than using the conventional “in situ” temperature estimation.

Recent advances on the study of atmosphere-land interaction observations on the Tibetan Plateau

Abstract. As a unique geological and geographical unit, the Tibetan Plateau dramatically impacts the world's environment and especially controls climatic and environmental changes in China, Asia and even in the Northern Hemisphere. Tibetan Plateau, therefore, provides a field laboratory for studying global change. With support from various agencies in the People's Republic of China, a Tibetan Observation and Research Platform (TORP) is now implementing. Firstly the background of the establishment of the TORP, the establishing and monitoring plan of long-term scale (5–10 years) of the TORP has been introduced. Then the preliminary observational analysis results, such as the characteristics of land surface heat fluxes and CO2 flux partitioning (diurnal variation and inter-monthly variation etc.), the characteristics of atmospheric and soil variables, the structure of the Atmospheric Boundary Layer (ABL) and the turbulent characteristics have also been shown in this paper.

Toward an estimation of global land surface heat fluxes from multisatellite observations

The sensitivity of a suite of satellite observations to land surface heat fluxes and the estimation of satellite‐derived fluxes using a statistical model are investigated. The satellite data include visible and near‐infrared reflectances (Advanced Very High Resolution Radiometer [AVHRR]), thermal infrared surface skin temperature and its diurnal cycle (International Satellite Cloud Climatology Project [ISCCP]), active microwave backscatter (European Remote‐sensing Satellite [ERS] scatterometer), and passive microwave emissivities (Special Sensor Microwave/Imager [SSM/I]). Fluxes at the global scale are taken from Land Surface Models (LSM): the GSWP‐2 multimodel analysis, the ISBA, and ORCHIDEE participating models, along with the National Centers for Environmental Prediction/the National Center for Atmospheric Research (NCEP/NCAR) reanalysis, on a monthly timescale from 1993 to 1995. The simulated LSM fluxes and the satellite observations are linked through a statistical model. Once calibrated, the statistical model reproduces the LSM latent and sensible fluxes for all types of snow‐free environments, with global RMS errors <25 W/m2, proving that the satellite data contain relevant information for flux estimation. The estimated fluxes have realistic spatial and seasonal patterns, although some local differences between the original and estimated fluxes are found. These differences are used to reveal potential problems in the LSMs, for instance, an anomaly in the GSWP‐2 radiative forcings. Comparisons between the original and estimated fluxes and 76 tower fluxes over North America are carried out, and the differences show similar statistics. However, the largest differences between the original and estimated fluxes do not occur in these regions. Demonstrating the superiority of the proposed technique outside of these regions remains difficult in the absence of validation data sets.

Estimating surface fluxes over the north Tibetan Plateau area with ASTER imagery

Abstract. Surface fluxes are important boundary conditions for climatological modeling and Asian monsoon system. The recent availability of high-resolution, multi-band imagery from the ASTER (Advanced Space-borne Thermal Emission and Reflection radiometer) sensor has enabled us to estimate surface fluxes to bridge the gap between local scale flux measurements using micrometeorological instruments and regional scale land-atmosphere exchanges of water and heat fluxes that are fundamental for the understanding of the water cycle in the Asian monsoon system. A parameterization method based on ASTER data and field observations has been proposed and tested for deriving surface albedo, surface temperature, Normalized Difference Vegetation Index (NDVI), Modified Soil Adjusted Vegetation Index (MSAVI), vegetation coverage, Leaf Area Index (LAI), net radiation flux, soil heat flux, sensible heat flux and latent heat flux over heterogeneous land surface in this paper. As a case study, the methodology was applied to the experimental area of the Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau (CAMP/Tibet), located at the north Tibetan Plateau. The ASTER data of 24 July 2001, 29 November 2001 and 12 March 2002 was used in this paper for the case of summer, winter and spring. To validate the proposed methodology, the ground-measured surface variables (surface albedo and surface temperature) and land surface heat fluxes (net radiation flux, soil heat flux, sensible heat flux and latent heat flux) were compared to the ASTER derived values. The results show that the derived surface variables and land surface heat fluxes in three different months over the study area are in good accordance with the land surface status. Also, the estimated land surface variables and land surface heat fluxes are in good accordance with ground measurements, and all their absolute percentage difference (APD) is less than 10% in the validation sites. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface variables and land surface heat fluxes using the ASTER data and filed observation over the study area.

Two Improvements of an Operational Two-Layer Model for Terrestrial Surface Heat Flux Retrieval.

In order to make the prediction of land surface heat fluxes more robust, two improvements were made to an operational two-layer model proposed previously by Zhang. These improvements are: 1) a surface energy balance method is used to determine the theoretical boundary lines (namely ‘true wet/cool edge’ and ‘true dry/warm edge’ in the trapezoid) in the scatter plot for the surface temperature versus the fractional vegetation cover in mixed pixels; 2) a new assumption that the slope of the Tm – f curves is mainly controlled by soil water content is introduced. The variables required by the improved method include near surface vapor pressure, air temperature, surface resistance, aerodynamic resistance, fractional vegetation cover, surface temperature and net radiation. The model predictions from the improved model were assessed in this study by in situ measurements, which show that the total latent heat flux from the soil and vegetation are in close agreement with the in situ measurement with an RMSE (Root Mean Square Error) ranging from 30 w/m2∼50 w/m2, which is consistent with the site scale measurement of latent heat flux. Because soil evaporation and vegetation transpiration are not measured separately from the field site, in situ measured CO2 flux is used to examine the modeled λEveg. Similar trends of seasonal variations of vegetation were found for the canopy transpiration retrievals and in situ CO2 flux measurements. The above differences are mainly caused by 1) the scale disparity between the field measurement and the MODIS observation; 2) the non-closure problem of the surface energy balance from the surface fluxes observations themselves. The improved method was successfully used to predict the component surface heat fluxes from the soil and vegetation and it provides a promising approach to study the canopy transpiration and the soil evaporation quantitatively during the rapid growing season of winter wheat in northern China.

Determination of regional land surface heat fluxes over a heterogeneous landscape of the Jiddah area of Saudi Arabia by using Landsat‐7 ETM data

AbstractIn this study, a parameterization method based on Landsat‐7 Enhanced Thematic Mapper (ETM) data and field observations is presented and tested for deriving the regional land surface variables, vegetation variables and land surface heat fluxes over a heterogeneous landscape. As a case study, the method and two Landsat‐7 ETM images are applied to the Jiddah area of Saudi Arabia. The regional distribution maps of surface reflectance, normalized difference vegetation index, modified soil adjusted vegetation index (MSAVI), vegetation coverage, leaf area index, surface temperature, net radiation flux, soil heat flux, sensible heat flux and latent heat flux have been determined over the Jiddah area. The derived results have been validated by using the ‘ground truth’. The results show that the more reasonable regional distributions of land surface variables (surface reflectance, surface temperature), vegetation variables (MSAVI and vegetation coverage), net radiation, soil heat flux and sensible heat flux can be obtained by using the method proposed in this study. Further improvement of the method is also discussed. Copyright © 2006 John Wiley & Sons, Ltd.

Determination of regional distributions and seasonal variations of land surface heat fluxes from Landsat‐7 Enhanced Thematic Mapper data over the central Tibetan Plateau area

In this study, a parameterization method based on Landsat‐7 ETM data and field observations has been proposed and tested for deriving surface reflectance, surface temperature, NDVI, MSAVI, vegetation coverage, LAI, net radiation flux, soil heat flux, sensible heat flux and latent heat flux over heterogeneous landscape. As a case study, the methodology was applied to the experimental area of the CAMP/Tibet, which located at the central Tibetan Plateau. Two scenes of Landsat‐7 ETM data were used in this study. The scene of 9 June 2002 was selected as a case of summer, and the scene of 2 December 2002 was selected as a case of winter. To validate the proposed methodology, the ground‐measured surface reflectance, surface temperature, net radiation flux, soil heat flux, sensible heat flux and latent heat flux are compared to Landsat‐7 ETM derived values. The results show that the derived surface variables and land surface heat fluxes in two different months over the study area are in good accordance with the land surface status. These parameters show a wide range due to the strong contrast of surface features. Also, the estimated land surface variables and land surface heat fluxes are in good agreement with ground measurements, and all their absolute percent difference is less than 9.9% in the validation sites. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface variables and land surface heat fluxes using the Landsat‐7 ETM data and filed observations over the study area.

Impact of Spatial Heterogeneity of Soil Moisture on Mesoscale Fluctuations and Mesoscale Fluxes

AbstractLand surface heat fluxes and atmospheric boundary layer (ABL) are simulated using the Regional Atmospheric Modeling System (RAMS). Eight experiments on land‐surface wetness discontinuities with heterogeneous length scales from 40km to 2km are carried out without large‐scale background wind. The two‐dimensional amplitude spectra of land surface heat fluxes, mesoscale fluctuations and mesoscale heat fluxes are analyzed by two‐dimensional fast Fourier transform algorithm (FFT). Then ABL parameterization for large‐scale models, such as GCM (General Circulation Model) is discussed. The results show that amplitude spectra of the land surface heat fluxes and the mesoscale fluctuations in each experiment reach maximum, when wave number is corresponding to heterogeneous length scale, and when different length scales coexist, the largest scale is dominant. Differently, amplitude spectra of the mesoscale heat fluxes, besides wave number corresponding to heterogeneous length scale, still have several peaks at other wave numbers. It appears that the relationships between the land surface heat fluxes and the heterogeneous length scale are significant, but the mesoscale heat fluxes don't indicate similar relationships with heterogeneous length scale. The representability of grid‐cell averaged surface fluxes is good but that of mesoscale fluxes is not so good.

Study on the Regional Land Surface Heat Fluxes over Heterogeneous Landscape of the Tibetan Plateau Area

Study on the Regional Land Surface Heat Fluxes over Heterogeneous Landscape of the Tibetan Plateau Area

Impact of land use changes on surface warming in China

Land use changes such as urbanization, agriculture, pasturing, deforestation, desertification and irrigation can change the land surface heat flux directly, and also change the atmospheric circulation indirectly, and therefore affect the local temperature. But it is difficult to separate their effects from climate trends such as greenhouse-gas effects. Comparing the decadal trends of the observation station data with those of the NCEP/NCAR Reanalysis (NNR) data provides a good method to separate the effects because the NNR is insensitive to land surface changes. The effects of urbanization and other land use changes over China are estimated by using the difference between the station and the NNR surface temperature trends. Our results show that urbanization and other land use changes may contribute to the observed 0.12°C (10yr)−1 increase for daily mean surface temperature, and the 0.20°C (10yr)−1 and 0.03°C (10 yr)−1 increases for the daily minimum and maximum surface temperatures, respectively. The urban heat island effect and the effects of other land-use changes may also play an important role in the diurnal temperature range change. The spatial pattern of the differences in trends shows a marked heterogeneity. The land surface degradation such as deforestation and desertification due to human activities over northern China, and rapidly-developed urbanization over southern China, may have mostly contributed to the increases at stations north of about 38°N and in Southeast China, respectively. Furthermore, the vegetation cover increase due to irrigation and fertilization may have contributed to the decreasing trend of surface temperature over the lower Yellow River Basin. The study illustrates the possible impacts of land use changes on surface temperature over China.

Estimating surface evapotranspiration using combined MODIS and CBERS-02 data

Spatial scale error is one of the most serious problems in the estimates of land surface heat fluxes of sensible and latent from satellite-borne data such as MODIS 1km resolution reflectance and emissive data. One of the feasible and economic ways to decrease the spatial scale error is to use high resolution land use class data together with the MODIS data. CBERS-02 data were used to produce land use class of Baiyangdian area, Hebei Province, China in the autumn of 2004. The area ratio of each class in MODIS pixel was calculated, and used to derive the heat fluxes of the mixed pixel. The results showed that the estimated heat fluxes of soil, sensible and latent have been changed remarkably after using the high resolution land class data. It could be concluded from the comparison between simulated and ground-measured fluxes as well as the theoretical analysis that high resolution land class data are useful to diminishing the scale error of heat fluxes estimated from low resolution satellite data.

Diurnal and inter-monthly variation of land surface heat fluxes over the central Tibetan Plateau area

The energy and water cycle over the Tibetan Plateau play an important role in the Asian monsoon system, which in turn is a major component of both the energy and water cycles of the global climate system. Using field observational data observed from the GAME/Tibet (GEWEX (Global Energy and Water cycle Experiment) Asian Monsoon Experiment on the Tibetan Plateau) and the CAMP/Tibet (CEOP (Coordinated Enhanced Observing Period) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau), some results on the local surface energy partitioning (diurnal variation, inter-monthly variation and vertical variation etc.) are presented in this study. The study on the regional surface energy partitioning is of paramount importance over heterogeneous landscape of the Tibetan Plateau and it is also one of the main scientific objectives of the GAME/Tibet and the CAMP/Tibet. Therefore, the regional distributions and their inter-monthly variations of surface heat fluxes (net radiation flux, soil heat flux, sensible heat flux and latent heat flux) are also derived by combining NOAA-14/AVHRR data with field observations. The derived results were validated by using the ground truth, and it shows that the derived regional distributions and their inter-monthly variations of land surface heat fluxes are reasonable by using the method proposed in this study. Further improvement of the method and its applying field were also discussed.

Remote sensing parameterization of regional land surface heat fluxes over arid area in northwestern China

Distributions of regional land surface variables, vegetation variables and land surface heat fluxes over the AECMP’95 area were analyzed using a new parameterized method of combining satellite remote sensing with field observations. The results show that reasonable regional distribution of surface reflectance, surface temperature, modified soil adjusted vegetation index, vegetation coverage, net radiation, soil heat flux and sensible heat flux over heterogeneous arid area in northwestern China can be obtained by using this method. This technique is still in the development stage, the derived latent heat flux shows a bit higher trend than the observed values over the whole study area. The recommendations of improving the scheme are also presented.

Remote sensing parameterization of land surface heat fluxes over arid and semi-arid areas

Dealing with the regional land surfaces heat fluxes over inhomogeneous land surfaces in arid and semi-arid areas is an important but not an easy issue. In this study, one parameterization method based on satellite remote sensing and field observations is proposed and tested for deriving the regional land surface heat fluxes over inhomogeneous landscapes. As a case study, the method is applied to the Dunhuang experimental area and the HEIFE (Heihe River Field Experiment, 1988–1994) area. The Dunhuang area is selected as a basic experimental area for the Chinese National Key Programme for Developing Basic Sciences: Research on the Formation Mechanism and Prediction Theory of Severe Climate Disaster in China (G1998040900, 1999–2003). The four scenes of Landsat TM data used in this study are 3 June 2000, 22 August 2000, and 29 January 2001 for the Dunhuang area and 9 July 1991 for the HEIFE area. The regional distributions of land surface variables, vegetation variables, and heat fluxes over inhomogeneous landscapes in arid and semi-arid areas are obtained in this study.

Regionalization of Surface Fluxes over Heterogeneous Landscape of the Tibetan Plateau by Using Satellite Remote Sensing Data

In this study, a parameterization method based on NOAA-14/AVHRR data and field observations is described and tested for deriving the regional land surface variables, vegetation variables and land surface heat fluxes over a heterogeneous landscape. As a case study, the method was applied to the Tibetan Plateau area. The regional distribution maps of surface reflectance, MSAVI, vegetation coverage, surface temperature, net radiation, soil heat flux, sensible heat flux and latent heat flux were determined over the Tibetan Plateau area. The derived results were validated by using the “ground truth”. The results show that the more reasonable regional distributions and their seasonal variations of land surface variables (surface reflectance, surface temperature), vegetation variables (MSAVI and vegetation coverage), net radiation, soil heat flux and sensible heat flux can be obtained by using the method proposed in this study. However, the approach of deriving regional latent heat flux, and their seasonal variation as the residual of the energy budget, may not be a good method due to the unbalance of energy and the strong advection over the study area. Further improvement of the method was also discussed.

Determination of Regional Land Surface Heat Flux Densities over Heterogeneous Landscape of HEIFE Integrating Satellite Remote Sensing with Field Observations.

In this study, a parameterization method based on satellite remote sensing and field observations is described and tested for deriving the regional land surface variables, vegetation variables and land surface heat flux densities over heterogeneous landscape. As a case study, the method is applied to the HEIFE area in northwestern China. The regional distribution maps of the NDVI, the MSAVI, vegetation coverage, leaf area index (LAI), surface reflectance, surface temperature, net radiation density, soil heat flux, sensible heat flux and latent heat flux have been determined over the HEIFE area. The derived results have been validated by using the “ground truth”. Comparisons between the results derived from the method proposed in this study, and the previous results (in which the land surface variables and surface heat fluxes were directly derived from the Surface Energy Balance Algorithm for Land—SEBAL) have also been given in this paper. The results show that the more reasonable regional distributions of land surface variables (surface reflectance, surface temperature), vegetation variables (the NDVI, the MSAVI, vegetation coverage and the LAI), net radiation, soil heat flux, sensible heat flux and latent heat flux can be obtained by using the method proposed in this study. Further improvement of this method is also discussed.

IRSUTE: A Minisatellite Project for Land Surface Heat Flux Estimation from Field to Regional Scale

Thermal infrared remote sensing has proved its usefulness in various environmental applications, including the evaluation of surface heat fluxes exchanged between the continental biosphere and the lower atmosphere. The concept of a minisatellite, IRSUTE, has been evaluated. It is designed to allow the derivation of accurate (±50 W m −2 or ±0.8 mm/d water evaporation) estimates of surface heat flux at the field scale (near 40 m). Such estimates will be useful for meteorological, hydrological, and agricultural studies. The instrument will also be useful for environmental monitoring, for example, frost mapping, forest fires, volcano activity, thermal pollution, etc. The IRSUTE concept has been further elaborated by conducting scientific studies (modeling canopy radiative temperature, method for flux estimation, ergodicity problem, emissivity of natural surfaces, correction of atmospheric effect), by analyzing methodological aspects (definition of pixel size, overpass time, time repeat cycle, analysis of angular effects) and system specification (superposition error and MTF effects assessment). These studies have resulted in the definition of a feasible instrument corresponding to the minisatellite category (95 kg), with a high spatial resolution (40 m), four bands in the thermal infrared domain (3.5–4.0 μm and three bands between 8.2 μm and 11.0 μm, with two options), a 1-day revisit, corresponding to an orbite altitude of 540 km. The narrow ground swath (40 km) precludes a global coverage; as a result IRSUTE will focus on a set of test-sites. The phase A study is now complete. The main elements of IRSUTE are defined. This article describes the IRSUTE mission characteristics and the main experimental results which led to the chosen specifications.

Effective parameters for surface heat fluxes in heterogeneous terrain

The relations between most land-surface characteristics and surface heat fluxes are typicallynon-linear. Because the ground surface is heterogeneous at all scales, it is important to accountfor these non-linear relations. Effective parameters are often applied for that purpose. Steadystatesimulations were used in this paper to thoroughly analyse the effective parameters impactunder a broad range of atmospheric conditions. The effect of different types of aggregatingfunctions on the accuracy of various effective parameters is also examined. The authors foundthat linear averaging of leaf area index and soil water content gives higher latent and lowersensible heat fluxes than the corresponding flux averaging over all surface types existing in onesquare grid. Linear averaging of roughness length under unstable conditions provides higherlatent and lower sensible heat fluxes than flux averaging, whereas under stable conditions giveshigher sensible and lower latent heat fluxes. Non-linear functions result to be more useful thanlinear functions to compute the effective value of those parameters which affect the surface heatfluxes independently of the atmospheric stability (e.g., leaf area index and soil water content,and unlike roughness length).

Sensitivity of shallow convective precipitation induced by land surface heterogeneities to dynamical and cloud microphysical parameters

To parameterize shallow convective clouds and precipitation induced by land surface processes in large‐scale atmospheric models (e.g., global climate models and weather forecast models), it is primordial to identify the atmospheric variables and cloud microphysical parameters which have a predominant impact on the development and formation of this type of clouds. For this purpose a sensitivity analysis of the various parameters and processes involved in the development and formation of this type of clouds and precipitation was performed with the Fourier amplitude sensitivity test (FAST). This test determines the relative contribution of the distribution of individual input parameters, assuming that their exact value is unknown, to the variance of the model output. By simultaneously varying all parameters according to their individual probability density function (PDF), the number of computations needed is very much reduced. Assuming various PDFs of cloud microphysical characteristics under a broad range of atmospheric conditions, this analysis demonstrated that given an appropriate atmospheric water content, vertical velocity and air temperature are the dominant atmospheric factor in shallow convective precipitation. This emphasizes the need to correctly calculate the spatial distribution of land surface heat fluxes, which affect the development of microscale and mesoscale turbulence in the atmospheric planetary boundary layer. The uncertainty in estimating cloud droplet concentration, pristine ice concentration, mass coefficient, collision efficiency, terminal velocity, snow crystals diameter, and aggregates diameter can affect quite significantly, one way or the other, the mixing ratio of the various water particles simulated with the cloud microphysics scheme. The relative importance of some of these parameters is very much dependent upon temperature and vertical velocity.