Sensible Heat Flux

Introduction

Accurate estimation of crop evapotranspiration (ETc) is fundamental for the development of efficient irrigation strategies in greenhouse systems, where environmental conditions differ significantly from open-field farming. In Iran, greenhouse agriculture, particularly for cucumbers (Cucumis sativus L.), has expanded considerably, making irrigation optimization a critical priority. The specific microclimate within greenhouses, including controlled humidity, temperature, and solar radiation levels, affects plant water needs, requiring tailored approaches to predict ETc. Traditional models, like the FAO 56 crop coefficient (Kc) method, provide a standardized way to estimate ETc but are generally suited to field crops under variable outdoor conditions. The limitations of fixed Kc values in capturing the complexity of greenhouse environments have prompted the exploration of alternative models. In recent years, machine learning (ML) techniques, especially ensemble methods like the Random Forest (RF) algorithm, have emerged as promising tools for ETc modeling due to their capacity to manage non-linear interactions among meteorological variables and enhance model flexibility. This study evaluates the performance of three ETc estimation approaches for greenhouse-grown cucumber: the conventional FAO 56 Kc method, a non-linear Kc model using a third-degree polynomial, and direct ETc prediction through the RF algorithm. These methods are assessed across two growth cycles, autumn-winter (A-W) and spring-summer (S-S), to capture seasonal differences in crop water requirements.

Materials and Methods

The study was conducted in a research greenhouse located at the College of Agriculture and Natural Recourses, University of Tehran, focusing on daily ETc of cucumber over two distinct growth periods. Environmental parameters were measured both inside and outside the greenhouse, including maximum, minimum, and average temperatures, relative humidity, and solar radiation. Reference evapotranspiration inside the greenhouse (EToG) was derived using a micro-lysimeter installed with a turfgrass surface, while daily ETc was measured using a soil water balance method, where soil moisture content was monitored daily across three experimental plots to ensure precision. ETc calculations were performed through three modeling approaches. In the first approach, the FAO 56 Kc model estimated ETc by applying fixed crop coefficients and multiplying them by EToG. Although this method has been widely applied in field conditions, its applicability to greenhouses is limited due to fixed Kc assumptions. In the second approach, a non-linear Kc model was developed using third-degree polynomial regression on Kc values calculated as the ratio of ETc to EToG, capturing growth-stage specific variations. In the final approach, the RF model directly predicted ETc based on a broad range of meteorological inputs. To optimize the RF model, hyperparameters were tuned using Python’s GridSearchCV tool, and data were split into training (70%) and testing (30%) sets to validate model performance. After initial RF modeling, a feature selection process using Permutation Feature Importance (PFI) was applied to identify the most influential variables, refining the RF model to the top four parameters.

Results and Discussion

The results highlighted seasonal variability in cumulative ETc, with the S-S period exhibiting nearly double the ETc of the A-W period due to higher ambient temperature and increased solar radiation. These findings underscore the necessity of dynamic ETc models that can accommodate seasonal and environmental variations. The FAO 56 Kc method produced a mean RMSE of 0.915 mm/day across both growth cycles, demonstrating limitations in fixed Kc approaches under greenhouse conditions. The non-linear Kc model, with an average RMSE of 0.64 mm/day, provided improved accuracy by adjusting Kc values across different growth stages, especially during mid-growth when water demand peaks. This improvement aligns with the premise that non-linear models can better capture the ETc variability within controlled environments. The RF algorithm demonstrated superior accuracy and flexibility, outperforming both Kc-based models with R² values of 0.96 for the A-W period and 0.94 for the S-S period in training datasets, and with respective RMSE values of 0.365 mm/day and 0.57 mm/day in testing datasets. These results illustrate the RF model’s capacity to accurately model ETc by capturing complex, non-linear interactions among variables such as maxTG (maximum temperature inside the greenhouse), meanRHG (average relative humidity inside the greenhouse), and RadiationG (solar radiation inside the greenhouse) during the A-W period, with RadiationG and EToG emerging as key variables during the S-S period. By emphasizing critical seasonal drivers of ETc, the RF model offers a robust alternative that adjusts to environmental changes without relying on static Kc values. This adaptability supports RF’s potential as a powerful tool for ETc estimation, accurately reflecting seasonal influences on greenhouse crop water needs.

Conclusion

The findings from this study demonstrate that the RF algorithm, when applied to ETc modeling in greenhouse conditions, provides a flexible, high-accuracy alternative to traditional Kc methods. Unlike the FAO 56 Kc and non-linear Kc models, which rely on predefined or growth-stage specific coefficients, the RF approach enables direct ETc prediction using real-time meteorological data. By optimizing input variables through feature selection, RF efficiently reduced the model complexity, focusing on the top four influential parameters while retaining high predictive accuracy. This reduction not only streamlines data collection requirements but also enhances the model's applicability in practical greenhouse operations. The results indicate that RF's capacity to model complex relationships among variables makes it especially suited for greenhouse environments, where precision irrigation is crucial for sustainable water management. Ultimately, this research underscores the importance of integrating machine learning techniques in ETc estimation, providing greenhouse operators with adaptive, resource-efficient tools for managing water use in controlled agricultural settings.

In the PILPS Phase 2a experiment, 23 land-surface schemes were compared in an off-line control experiment using observed meteorological data from Cabauw, the Netherlands. Two simple sensitivity experiments were also undertaken in which the observed surface air temperature was artificially increased or decreased by 2 K while all other factors remained as observed. On the annual timescale, all schemes show similar responses to these perturbations in latent, sensible heat flux, and other key variables. For the 2-K increase in temperature, surface temperatures and latent heat fluxes all increase while net radiation, sensible heat fluxes, and soil moistures all decrease. The results are reversed for a 2-K temperature decrease. The changes in sensible heat fluxes and, especially, the changes in the latent heat fluxes are not linearly related to the change of temperature. Theoretically, the nonlinear relationship between air temperature and the latent heat flux is evident and due to the convex relationship between air temperature and saturation vapor pressure. A simple test shows that, the effect of the change of air temperature on the atmospheric stratification aside, this nonlinear relationship is shown in the form that the increase of the latent heat flux for a 2-K temperature increase is larger than its decrease for a 2-K temperature decrease. However, the results from the Cabauw sensitivity experiments show that the increase of the latent heat flux in the ϩ2-K experiment is smaller than the decrease of the latent heat flux in the Ϫ2-K experiment (we refer to this as the asymmetry). The analysis in this paper shows that this inconsistency between the theoretical relationship and the Cabauw sensitivity experiments results (or the asymmetry) is due to (i) the involvement of the ␤ g formulation, which is a function of a series stress factors that limited the evaporation and whose values change in the Ϯ2-K experiments, leading to strong modifications of the latent heat flux; (ii) the change of the drag coefficient induced by the changes in stratification due to the imposed air temperature changes (Ϯ2 K) in parameterizations of latent heat flux common in current land-surface schemes. Among all stress factors involved in the ␤ g formulation, the soil moisture stress in the ϩ2-K experiment induced by the increased evaporation is the main factor that contributes to the asymmetry.

This paper addresses the effects of canopy physical processes on snow mass and energy balances in boreal ecosystems. We incorporate new parameterizations of radiation transfer through the vegetation canopy, interception of snow by the vegetation canopy, and under‐canopy sensible heat transfer processes into the Versatile Integrator of Surface and Atmosphere (VISA) and test the model results against the Boreal Ecosystem‐Atmosphere Study (BOREAS) data observed at South Study Area, Old Jack Pine. A modified two‐stream radiation transfer scheme that accounts for the three‐dimensional geometry of vegetation accurately simulates the transferring of solar radiation through the vegetation canopy when the leaf and stem area index is reduced to match the observed. VISA produces higher‐than‐observed surface albedo in wintertime. Implementation of a snow interception model that explicitly describes the loading and unloading of snow and the melting and refreezing of snow on the canopy into VISA ...

In the Project for Intercomparison of Land-Surface Parameterization Schemes phase 2a experiment, meteorological data for the year 1987 from Cabauw, the Netherlands, were used as inputs to 23 land-surface flux schemes designed for use in climate and weather models. Schemes were evaluated by comparing their outputs with long-term measurements of surface sensible heat fluxes into the atmosphere and the ground, and of upward longwave radiation and total net radiative fluxes, and also comparing them with latent heat fluxes derived from a surface energy balance. Tuning of schemes by use of the observed flux data was not permitted. On an annual basis, the predicted surface radiative temperature exhibits a range of 2 K across schemes, consistent with the range of about 10 W m Ϫ2 in predicted surface net radiation. Most modeled values of monthly net radiation differ from the observations by less than the estimated maximum monthly observational error (Ϯ10 W m Ϫ2 ). However, modeled radiative surface temperature appears to have a systematic positive bias in most schemes; this might be explained by an error in assumed emissivity and by models' neglect of canopy thermal heterogeneity. Annual means of sensible and latent heat fluxes, into which net radiation is partitioned, have ranges across schemes of

Land surface models (LSMs) need to be coupled with atmospheric general circulation models (GCMs) to adequately simulate the exchanges of energy, water, and carbon between the atmosphere and terrestrial surfaces. The heterogeneity of the land surface and its interaction with temporally and spatially varying meteorological conditions result in nonlinear effects on fluxes of energy, water, and carbon, making it challenging to scale these fluxes accurately. The issue of up-scaling remains one of the critical unsolved problems in the parameterization of subgrid-scale fluxes in coupled LSM and GCM models. A new distributed LSM, the Ecosystem–Atmosphere Simulation Scheme (EASS) was developed and coupled with the atmospheric Global Environmental Multiscale model (GEM) to simulate energy, water, and carbon fluxes over Canada’s landmass through the use of remote sensing and ancillary data. Two approaches (lumped case and distributed case) for handling subgrid heterogeneity were used to evalua...

A land surface model (a modified version of the Simple Biosphere Model, Version 2; SiB2) was parameterized and tested against two years of eddy covariance flux measurements made over un-grazed tallgrass prairie and a winter wheat field in Oklahoma, USA. The land surface model computed 30-min estimates of sensible and latent heat flux and carbon dioxide flux that agree well with the patterns observed in the field, simulating in particular the contrasting seasonal timing of fluxes in the wheat, where leaf area and physiological activity peak in the spring, and prairie, where leaf area and physiological activity peak in summer. However, systematic errors in flux estimates were also identified for particular times of day and season. These systematic errors are sometimes related to difficulty in correct definition of vegetation structure (LAI) and physiological activity. This was observed particularly in the wheat site towards the end of the growing season when senescence, which reduces both the amount and the physiological activity of leaves, is difficult to parameterize. Simulation errors are also attributed to problems in the mathematical description of water stress, soil respiration, and the leaf-to-canopy scaling methodology. SiB2 tends to predict too much photosynthetic activity at low solar angles, while developing soil moisture stress before it is seen in the field. Systematic errors in energy balance terms (heat and water fluxes) occur for bare soil and dormant vegetation, related to simulation of soil heat flux. Daytime errors in sensible and latent heat fluxes average 20 W m À2 , and can be more than 100 W m À2 at certain times. In regional and global climate models, the effect of land surface sub-model errors on atmospheric dynamics will depend in part on the magnitude of the systematic error, but also on the spatial extent and temporal duration over which the systematic error persists.

The El Niño-Southern Oscillation (ENSO) is a dominant source of global climate variability. The effects of this phenomenon alter the flow of heat from tropical to polar latitudes, resulting in weather and climate anomalies that are difficult to forecast. The current work quantified two components of the vertically integrated equation for the total energy content of an atmospheric column, to show the anomalous horizontal redistribution of surface heat flux anomalies. Symmetric and asymmetric components of the vertically integrated latent and sensible heat flux divergence were quantified using ERA-Interim atmospheric reanalysis output on 30 model layers between 1979 and 2016. Results indicate that asymmetry is a fundamental component of ENSO-induced weather and climate anomalies at the global scale, challenging the common assumption that each phase of ENSO is equal and opposite. In particular, a substantial asymmetric component was identified in the relationship between ENSO and patterns of extratropical climate variability that may be proportional to differences in sea surface temperature anomalies during each phase of ENSO. This work advances our understanding of the global distributions of source and sink regions, which may improve future predictions of ENSO-induced precipitation and surface temperature anomalies. Future studies should apply these methods to advance understanding and to validate predictions of ENSO-induced weather and climate anomalies.

Large-aperture scintillometers have been successfully used in a variety of ecosystems in New Mexico to measure sensible heat fluxes at the kilometer scale. ustainable management of water resources in arid and semiarid watersheds requires accurate information on consumptive water use over a range of space and time scales. Consumptive water use by grasses and shrubs, irrigated crops, and riparian vegetation in desert regions is highly variable in space and time. The spatial variability is caused by the heterogeneous nature of vegetation cover, hydraulic soil properties, groundwater table depths, and differences in water availability caused by hydrological

Accurate information on the distribution of sensible and latent heat fluxes as well as soil moisture is critical for evaluation of background characteristics. Since these fluxes are subject to rapid changes in time and space, it is nearly impossible to determine their spatial and temporal distributions over large areas from ground measurements alone. Therefore, prediction from remote sensing images is very attractive as it enables extensive area coverage and a high repetition rate. In this study, the Surface Energy Balance Algorithm for Land as implemented at New Mexico Tech (SEBAL NM ) is used to estimate sensible and latent heat fluxes in the White Volta Basin of Ghana, West Africa. The objectives are (i) to demonstrate a SEBAL NM application in a part of the world were ground measurements are very scarce and (ii) to compare evapotranspiration (ET) maps obtained from Landsat and MODIS imagery, respectively. The results of this study demonstrate that SEBAL NM can be applied for mapping sensible and latent heat fluxes as well as soil moisture over areas where few or no ground measurements are available using common satellite products (Landsat and MODIS).

A comparison study of water cycle parameters derived from ground-based remote-sensing instruments and from the regional model REMO is presented. Observational data sets were collected during three measuring campaigns in summer/autumn 2003 and 2004 at Richard Aßmann Observatory, Lindenberg, Germany. The remote sensing instruments which were used are differential absorption lidar, Doppler lidar, ceilometer, cloud radar, and micro rain radar for the derivation of humidity profiles, ABL height, water vapour flux profiles, cloud parameters, and rain rate. Additionally, surface latent and sensible heat flux and soil moisture were measured. Error ranges and representativity of the data are discussed. For comparisons the regional model REMO was run for all measuring periods with a horizontal resolution of 18 km and 33 vertical levels. Parameter output was every hour. The measured data were transformed to the vertical model grid and averaged in time in order to better match with gridbox model values. The comparisons show that the atmospheric boundary layer is not adequately simulated, on most days it is too shallow and too moist. This is found to be caused by a wrong partitioning of energy at the surface, particularly a too large latent heat flux. The reason is obviously an overestimation of soil moisture during drying periods by the one-layer scheme in the model. The profiles of water vapour transport within the ABL appear to be realistically simulated. The comparison of cloud cover reveals an underestimation of low-level and mid-level clouds by the model, whereas the comparison of high-level clouds is hampered by the inability of the cloud radar to see cirrus clouds above 10 km.

A comparison study of water cycle parameters derived from ground-based remote-sensing instruments and from the regional model REMO is presented. Observational data sets were collected during three measuring campaigns in summer/autumn 2003 and 2004 at Richard Aßmann Observatory, Lindenberg, Germany. The remote sensing instruments which were used are differential absorption lidar, Doppler lidar, ceilometer, cloud radar, and micro rain radar for the derivation of humidity profiles, ABL height, water vapour flux profiles, cloud parameters, and rain rate. Additionally, surface latent and sensible heat flux and soil moisture were measured. Error ranges and representativity of the data are discussed. For comparisons the regional model REMO was run for all measuring periods with a horizontal resolution of 18 km and 33 vertical levels. Parameter output was every hour. The measured data were transformed to the vertical model grid and averaged in time in order to better match with gridbox model values. The comparisons show that the atmospheric boundary layer is not adequately simulated, on most days it is too shallow and too moist. This is found to be caused by a wrong partitioning of energy at the surface, particularly a too large latent heat flux. The reason is obviously an overestimation of soil moisture during drying periods by the one-layer scheme in the model. The profiles of water vapour transport within the ABL appear to be realistically simulated. The comparison of cloud cover reveals an underestimation of low-level and mid-level clouds by the model, whereas the comparison of high-level clouds is hampered by the inability of the cloud radar to see cirrus clouds above 10 km.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The UBL/CLU (urban boundary layer/couche limite urbaine) observation and modelling campaign is a side-project of the regional photochemistry campaign ESCOMPTE. UBL/CLU focuses on the dynamics and thermodynamics of the urban boundary layer of Marseille, on the Mediterranean coast of France. The objective of UBL/CLU is to document the four-dimensional structure of the urban boundary layer and its relation to the heat and moisture exchanges between the urban canopy and the atmosphere during periods of low wind conditions, from June 4 to July 16, 2001. The project took advantage of the comprehensive observational set-up of the ESCOMPTE campaign over the Berre-Marseille area, especially the ground-based remote sensing, airborne measurements, and the intensive documentation of the regional meteorology. Additional instrumentation was installed as part of UBL/CLU. Analysis objectives focus on (i) validation of several energy balance computational schemes such as LUMPS, TEB and SM2-U, (ii) ground truth and urban canopy signatures suitable for the estimation of urban albedos and aerodynamic surface temperatures from satellite data, (iii) high resolution mapping of urban land cover, land-use and aerodynamic parameters used in UBL models, and (iv) testing the ability of high resolution atmospheric models to simulate the structure of the UBL during land and sea breezes, and the related transport and diffusion of pollutants over different districts of the city. This paper presents initial results from such analyses and details of the overall experimental set-up.

The performance of the general bulk formulation in estimating sensible heat flux at Nigerian Micrometeorological Experimental site was assessed. Reliable sensible heat flux was estimated with the use of accurate diurnal values of transfer coefficient of sensible heat. The performances of one α, two β and a modified α formulations in the estimation of latent heat flux were also assessed

A neural network inversion scheme including first guess information has been developed to retrieve surface temperature T s , along with atmospheric water vapor, cloud liquid water, and surface emissivities over land from a combined analysis of Special Sensor Microwave/Imager (SSM/I) and International Satellite Cloud Climatology Project (ISCCP) data. In the absence of routine in situ surface skin measurements, retrieved T s values are evaluated by comparison to the surface air temperature T air measured by the meteorological station network. The T s À T air difference shows all the expected variations with solar flux, soil characteristics, and cloudiness. During daytime the T s À T air difference is driven by the solar insulation, with positive differences that increase with increasing solar flux. With decreasing soil and vegetation moisture the evaporation rate decreases, increasing the sensible heat flux, thus requiring larger T s À T air differences. Nighttime T s À T air differences are governed by the longwave radiation balance, with T s usually closer or lower than T air . The presence of clouds dampens all the difference. After suppression of the variability associated to the diurnal solar flux variations, the T s and T air data sets show very good agreement in their synoptic variations, even for cloudy cases, with no bias and a global rms difference of $2.9 K. This value is an upper limit of the retrieval rms because it includes errors in the in situ data as well as errors related to imperfect time and space collocations between the satellite and in situ measurements.

To facilitate the study of flux heterogeneity within a region, the authors have designed, built, and field-tested a highly portable, rapidly deployable, eddy covariance CO 2 flux measurement system. The system is built from off-the-shelf parts and was assembled at a minimal cost. The unique combination of features of this system allow for a very rapid deployment with a minimal number of field personnel. The system is capable of making high precision, unattended measurements of turbulent CO 2 fluxes, latent heat (LE) fluxes, sensible heat fluxes (H), and momentum transfer fluxes. In addition, many of the meteorological and ecosystem variables necessary for quality control of the fluxes and for running ecosystem models are measured. A side-by-side field comparison of the system at a pair of established AmeriFlux sites has verified that, for single measurements, the system is capable of CO 2 flux accuracy of about ± 1.2 µmole/m 2 /sec, LE flux accuracy of about ± 15 Watts/m 2 , H flux accuracy of about ± 7 Watts/m 2 , and momentum transfer flux accuracy of about ± 11 gm-m/sec/sec. System deployment time is between 2 and 4 hours by a single person. The system was measured to draw between 30 and 35 Watts of power and may be run from available line power, storage batteries, or solar panels.

of Met Office, Exeter, were prepared as part of their official duties as employees of the UK Government. They are published with the permission of the Controller of Her Majesty's Stationary Office and the Queen's Printer for Scotland. Satellite data are used to quantify and examine the bias in the outgoing long-wave (LW) radiation over North Africa during May-July simulated by a range of climate models and the Met Office global numerical weather prediction (NWP) model. Simulations from an ensemble-mean of multiple climate models overestimate outgoing clear-sky long-wave radiation (LWc) by more than 20 W m -2 relative to observations from Clouds and the Earth's Radiant Energy System (CERES) for May-July 2000 over parts of the west Sahara, and by 9 W m -2 for the North Africa region (20 • W-30 • E, 10-40 • N). Experiments with the atmosphere-only version of the High-resolution Hadley Centre Global Environment Model (HiGEM), suggest that including mineral dust radiative effects removes this bias. Furthermore, only by reducing surface temperature and emissivity by unrealistic amounts is it possible to explain the magnitude of the bias. Comparing simulations from the Met Office NWP model with satellite observations from Geostationary Earth Radiation Budget (GERB) instruments suggests that the model overestimates the LW by 20-40 W m -2 during North African summer. The bias declines over the period 2003-2008, although this is likely to relate to improvements in the model and inhomogeneity in the satellite time series. The bias in LWc coincides with high aerosol dust loading estimated from the Ozone Monitoring Instrument (OMI), including during the GERBILS field campaign (18-28 June 2007) where model overestimates in LWc greater than 20 W m -2 and OMI-estimated aerosol optical depth (AOD) greater than 0.8 are concurrent around 20 • N, 0-20 • W. A model-minus-GERB LW bias of around 30 W m -2 coincides with high AOD during the period 18-21 June 2007, although differences in cloud cover also impact the model-GERB differences.

The Geostationary Earth Radiation Budget Intercomparison of Longwave and Shortwave radiation (GERBILS) was an observational field experiment over North Africa during June 2007. The campaign involved 10 flights by the FAAM BAe‐146 research aircraft over southwestern parts of the Sahara Desert and coastal stretches of the Atlantic Ocean. Objectives of the GERBILS campaign included characterisation of mineral dust geographic distribution and physical and optical properties, assessment of the impact upon radiation, validation of satellite remote sensing retrievals, and validation of numerical weather prediction model forecasts of aerosol optical depths (AODs) and size distributions. We provide the motivation behind GERBILS and the experimental design and report the progress made in each of the objectives. We show that mineral dust in the region is relatively non‐absorbing (mean single scattering albedo at 550 nm of 0.97) owing to the relatively small fraction of iron oxides present (1–3...

The Cloudnet project aims to provide a systematic evaluation of clouds in forecast and climate models by comparing the model output with continuous ground-based observations of the vertical profiles of cloud properties. In the models, the properties of clouds are simplified and expressed in terms of the fraction of the model grid box, which is filled with cloud, together with the liquid and ice water content of the clouds. These models must get the clouds right if they are to correctly represent both their radiative properties and their key role in the production of precipitation, but there are few observations of the vertical profiles of the cloud properties that show whether or not they are successful. Cloud profiles derived from cloud radars, ceilometers, and dual-frequency microwave radiometers operated at three sites in France, Netherlands, and the United Kingdom for several years have been compared with the clouds in seven European models. The advantage of this continuous appr...

Introduction
In determining the evapotranspiration (ET) of a crop species, factors such as type, crop density, growth stage, climate of the region, physicochemical characteristics and soil fertility, have a significant effect. Therefore, it has a significant complexity. In recent years, new technologies are used to estimate ET, such as surface energy balance algorithm for land (SEBAL), which estimates actual evapotranspiration, using satellite data and some ground data. The purpose of this research is to estimate the actual ET and water requirement of Rosa damascena using SEBAL during three crop growth years in a part of the Shahrekord high plain.

Materials and Methods
The studied farm with an area of 16.38 ha is located in the Shahrekord plain, Karoun watershed. The remote sensing data included 42 cloud-free images of Landsat 7 and Landsat 8 satellites (2017, 2018, and 2019). The growth period lasted from the beginning of April to the end of November of each crop year. Images were processed in ERDAS Imagine 2015 software for radiometric correction and subsequent calculations using SEBAL algorithm. In order to estimate the actual evapotranspiration, the energy balance equation is used. For this purpose, all energy fluxes such as, Rn: the net incoming radiation flux to the considered surface, H: the sensible heat flux, G0: the soil heat flux and lET: the latent heat flux of evapotranspiration should be taken into account. The first step in the SEBAL process is to calculate the net radiation flux of the Rn. The second, soil heat flux G0 that is the rate of heat capacity in the soil and vegetation resulting from heat conduction or heat energy used to heat or cools the volume of the soil mass. The third is to calculate sensible heat flux (H) is the rate of heat loss to the air by conduction and convection phenomena, which is caused by the thermal difference. In SEBAL process, two "anchor" pixels are used to create boundary conditions for energy balance. These include as "cold (wet)" and "warm (dry)" pixels that are determined in the study area. A cold pixel is selected at the surface of open water or the surface covered by a well-watered alfalfa crop. It is assumed that the temperature of the surface and the temperature of the air near the surface are the same in this pixel. The "warm" pixel is selected in dry agricultural lands and its ET is considered zero. It is necessary for SEBAL model to establishing a linear equation between the surface temperature (Ts) and the air-surface temperature difference (dT) for each pixel using hot (dry) and cold (wet) pixels.

Results and Discussion
Based on the results of three years of research in a 16.38 hectare Golmohammadi farm in the Shahrekord plain, using the Sabal algorithm and the number of 42 images on the days of Landsat 7 and Landsat 8 satellites passing, as well as using the modified Penman-Mantith-Fao mathematical relationship. It was found that the amount of evaporation and transpiration of hollyhocks in the studied area was on average 1043.8 mm during the growth period. According to the results of other researchers, which have been conducted using lysimeter data and field studies, it necessarily requires higher costs than remote sensing methods. In this research, the ability of the Sabal algorithm (as one of the best remote sensing algorithms) to estimate evaporation And the actual transpiration and determination of the water requirement of the chrysanthemum plant with a low cost and an easy method compared to the results of other researchers, which were done with difficult and expensive lysimetric methods, were proved and it is suitable to be used for other plant species and in other geographical areas. Results showed that actual evapotranspiration value of rose crop (ETC) obtained from the SEBAL during the three years of experiment were 1089.4, 1021.3, and 1020.6 mm per growth period. In the same period, reference crop evapotranspiration (ET0) values were 1214.8, 1100.5, and 1135.5 mm during the growth period, respectively. In other words, average value for ETC was 1043.8 mm in growth period.

Conclusion
Based on the results of three years of research in a 16.38 hectare Golmohammadi farm in the Shahrekord plain, using the Sabal algorithm and the number of 42 images on the days of Landsat 7 and Landsat 8 satellites passing, as well as using the modified Penman-Mantith-Fao mathematical relationship. It was found that the amount of evaporation and transpiration of hollyhocks in the studied area was on average 1043.8 mm during the growth period. According to the results of other researchers, which have been conducted using lysimeter data and field studies, it necessarily requires higher costs than remote sensing methods. In this research, the ability of the Sabal algorithm (as one of the best remote sensing algorithms) to estimate evaporation And the actual transpiration and determination of the water requirement of the chrysanthemum plant with a low cost and an easy method compared to the results of other researchers, which were done with difficult and expensive lysimetric methods, were proved and it is suitable to be used for other plant species and in other geographical areas.

Multilevel measurements of mean meteorological variables and turbulent fluxes of sensible and latent heat in the atmospheric surface layer (ASL) were undertaken at the experimental site located within the Teaching and Research Farm of Obafemi Awolowo University, Ile-Ife, Nigeria, between the 1st of June and 31st of July, 2016. Existing empirical flux-profile relationships under the framework of Monin-Obukhov similarity theory (MOST) were used to estimate the turbulent fluxes of sensible and latent heat. The performance of the flux-profile technique was then evaluated based on direct measurements of turbulent fluxes obtained from an eddy covariance system. The results showed that the sensible heat flux estimated from flux-profile relationships has a maximum value of 96.4 W/m2 (daytime mean value of 52.02 W/m2) in June while a peak value of 145.2 W/m2 (daytime mean value of 63.1 W/m2) was obtained from direct measurement. In July, a maximum value of 101.07 W/m2 was estimated as compar...

High-resolution computational fluid dynamics (CFD) simulations have been performed to assess the dispersion of air pollutants (CO 2 ) emanating from traffic in a busy street and in the vicinity of a complex configuration of buildings located in Salmiya, Kuwait City. New buildings are planned for this area, and the work here includes predictions for the dispersion of pollutants after the buildings' completion. The CFD simulations are based on calculated CO 2 concentration levels for traffic counts taken on location in Salmiya with the existing configuration of buildings. As the computer code used in this work has been evaluated previously, it will be applied here to predict with confidence any potential air pollution problem areas on the addition of the new buildings. It was found for very light wind, that the proposed new buildings help reduce pollution in the vicinity of residential buildings within the configuration of buildings, but as the wind becomes moderate to strong, there was a tendency for the pollutant to get trapped in the residential area. Results are given for both exceptionally high ambient temperatures and very light wind, which are not often reported in studies found in the literature.

An energy partitioning experiment was set-up within an experimental agroforest site at Cloich forest, near Edinburgh. Measurements of turbulent heat fluxes were made – during non stress conditions – both directly by eddy-covariance techniques and in the case of latent heat flux indirectly through closure of the energy budget equation. These measurements were made simultaneously in the thinned plots (one plot at a time) and a reference plot to eliminate differences due to external atmospheric conditions. Observed values of Bowen ratio ranged from 1 to 3.5, with significantly lower values in the thinned plots compared with those measured in the reference plot. On separation of the Bowen ratio into its two components, it was found that sensible heat flux remained constant between plots. The latent heat flux, however, increased as the tree density was reduced. A simple model of the evaporation from the forest plots based on the Penman-Monteith equation and incorporating an under-storey ...

The estimation of sensible heat flux, H, using large aperture scintillometer (LAS) under varying surface heterogeneity conditions was investigated. Surface roughness features characterized by variable topography and vegetation height were represented using data derived from the highly accurate light detection and range (lidar) techniques as well as from traditional vegetation survey and topographic map methods. The study was conducted at the Cibola National Wildlife Refuge, Southern California, over a riparian zone covered with natural vegetation dominated by tamarisk trees interspersed with bare soil in a region characterized by arid to semiarid climatic conditions. Estimates of H were obtained using different representations of surface roughness features derived from both traditional and lidar methods to estimate LAS beam height [z(u)] at each increment u along its path, vegetation height (h c ), displacement height (d), and roughness length (z 0 ) combined with the LAS weighing function, W(u), along the path. The effect of the LAS 3D footprint was examined to account for the contribution from the individual patches in the upwind direction, hence on the estimates of H. The results showed better agreement between LAS and Bowen ratio sensible heat fluxes when lidar-derived surface roughness was used, especially when considering the LAS 3D footprint effects. It was also found that, under certain conditions, the LAS path weighted h c and d obtained using the LAS weighting function W(u) is a good approximation of the 3D weighted footprint values.

The acceleration of ice mass loss observed since the 1970s in the tropical Andes is an alert on climate changes which can directly and indirectly impact most part of the populations living in the western Andes arid regions. In these regions, The glacier melting occurs throughout the year, contributing partially to the water supply to the rivers which provide water to the cities. It is estimated that during drought periods in the tropical Andes (Bolivia, Ecuador and Peru), 3.92 millions of people depend on the glacier melting water. The models currently used to predict the Andean glaciers behavior in response to climate change are based on energy balance which incorporate changes in meteorological conditions on glaciers. However, These models do not take into consideration the albedo reduction caused by Black Carbon (BC) aerosol deposition over the glaciers (BC-albedo effect), which has been pointed to be an important factor to glaciers retreat process in Greenland, West of China, and in the Hymalayas. In South America, the largest sources of BC emission are the wildfires in the Amazon basin and Brazilian savanna (cerrado), which release about 30 Gg/year of BC. The transport, deposition and impact of the BC from Amazon basin on the Central Andes Glacier is still unknown. In this work we modeled the emission, transport, deposition and impact of BC, from wildfires in Amazon basin, on central Andes Glaciers. We observed that seasonal changes in the atmospheric circulation which cause the transition between dry and wet periods in the Andean Mountains create favorable conditions for the transport of BC (and others aerosols) from the Amazon basin towards the central Andes. The BC deposition on the glaciers significantly reduces the snow/ice albedo on the surface, which contributes to the melting process. We estimate that changes in the Zongo glacier (located at Cordillera Blanca -Bolivia) albedo due to BC deposition have the potential to increase the glacier annual melting by 2.0-4.8%. In fact, it was possible to observe an equivalent increase on glacier melting in September, during the peak of the fire season at the Amazon basin. As a consequence, the annual melting period gets longer, and ice mass loss is higher than expected due to climate warming only.

On 15 January 2010, Thumba (8.5 • N, 76.9 • E) witnessed one of the longest noontime Annular Solar Eclipse (ASE) spanning a period of about 7 minutes centered at 13:14 Hrs Local Time. In this research article, we present a case study on the behaviour of the Atmospheric Boundary Layer characteristics and its vertical structure in response to this rare celestial event by making use of a suite of different in-situ instruments. During the peak period of the ASE, the incoming solar irradiance was dimmed by about 87% of its normal values, resulting in a significant reduction in the magnitudes of turbulent kinetic energy and surface-layer turbulent fluxes of heat and momentum. The intensity and vertical thickness of the sea/land breeze circulation cell over the study domain also weakened. However, the mixed layer heights determined from balloon-borne GPS Radiosonde did not show any appreciable changes. Analysis of vertical profiles of thermodynamic parameters in association with the wind direction during ASE indicated the formation of a double mixed layer between 700 m to 1500 m and is attributed to horizontal advection of a different airmass at those altitudes.

Background Fire danger indexes (FDIs) are used as proxies for fire potential and are often developed for specific locations. For practical purposes, the extrapolation of the underlying calculations into novel locations is common, but it is generally uncertain if the relationships between FDIs and fire potential observed in the environment in which the index was developed are equally relevant in others. For example, although a topographically, ecologically, and climatologically complex country, f ire danger forecasts in Peru use a standard set of nationwide thresholds applied to the Fire Weather Index. In this study, we validate the underlying assumption that weather-fire relationships are spatially uniform within Peru by (1) making cross-regional comparisons of the statistical distributions of four FDIs—Burning Index, Energy Release Component, Fire Weather Index, and Keetch-Byram Drought Index, and (2) making cross-regional comparisons of the expected daily MODIS hotspot count perce...

Many state-of-the-art coupled sea ice-ocean models use atmospheric and oceanic drag coefficients that are at best a function of the atmospheric stability but otherwise constant in time and space. Constant drag coefficients might lead to an incorrect representation of the ice-air and ice-ocean momentum exchange, since observations of turbulent fluxes imply high variability of drag coefficients. We compare three model runs, two with constant drag coefficients and one with drag coefficients varying as function of sea-ice characteristics. The computed drag coefficients range between 0.88 × - 10 3 and 4.68 × - 10 3 for the atmosphere, and between 1.28 × - 10 3 and 13.68 × - 10 3 for the ocean. They fall in the range of observed drag coefficients and illustrate the interplay of ice deformation and ice concentration in different seasons and regions. The introduction of variable drag coefficients improves the realism of the model simulation. In addition, using the average values of the variable drag coefficients improves simulations with constant drag coefficients. When drag coefficients depend on sea-ice characteristics, the average sea-ice drift speed in the Arctic basin increases from 6.22 cm s -1 to 6.64 cm s -1 . This leads to a reduction of ice thickness in the entire Arctic and particularly in the Lincoln Sea with a mean value decreasing from 7.86 m to 6.62 m. Variable drag coefficients lead also to a deeper mixed layer in summer and to changes in surface salinity. Surface temperatures in the ocean are also affected by variable drag coefficients with differences of up to 0.06 °C in the East Siberian Sea. Small effects are visible in the ocean interior

Playa systems are driven by evaporation processes, yet the mechanisms by which evaporation occurs through playa salt crusts are still poorly understood. In this study we examine playa evaporation as it relates to land surface energy fluxes, salt crust characteristics, groundwater and climate at the Salar de Atacama, a 3000 km 2 playa in northern Chile containing a uniquely broad range of salt crust types. Land surface energy budget measurements were taken at eight representative sites on this playa during winter (August 2001) and summer (January 2002) seasons. Measured values of net all-wave radiation were highest at vegetated and rough halite crust sites and lowest over smooth, highly reflective salt crusts. Over most of the Salar de Atacama, net radiation was dissipated by means of soil and sensible heat fluxes. Dry salt crusts tended to heat and cool very quickly, whereas soil heating and cooling occurred more gradually at wetter vegetated sites. Sensible heating was strongly linked to wind patterns, with highest sensible heat fluxes occurring on summer days with strong afternoon winds. Very little energy available at the land surface was used to evaporate water. Eddy covariance measurements could only constrain evaporation rates to within 0.1 mm d K1 , and some measured evaporation rates were less than this margin of uncertainty. Evaporation rates ranged from 0.1 to 1.1 mm d K1 in smooth salt crusts around the margin of the salar and from 0.4 to 2.8 mm d K1 in vegetated areas. No evaporation was detected from the rugged halite salt crust that covers the interior of the salar, though the depth to groundwater is less than 1 m in this area. These crusts therefore represent a previously unrecorded end member condition in which the salt crusts form a practically impermeable barrier to evaporation.

The purpose of the paper concerns remote sensing data assimilation in physically based models by the way off a multiobjective calibration procedure. Generally, the calibration of Soil Vegetation Atmosphere Transfer (SVAT) models consists in determining the best parameter set in terms of model performances. Due to model structural uncertainty and to errors on the observations, such a determination of a unique parameter set is generally impossible. This problem of non-uniqueness of the solution can be investigated by a multiobjective approach, in which different objective functions are optimised simultaneously. In this context, we developed a multiobjective approach allowing to combine sensitivity analyses and an iterative optimisation procedure of the model parameters in terms of uncertainty ranges. This paper investigates the potentialities of such a calibration approach in a remote sensing context, in order to drive SVAT models only by the way of remote sensing observations. The co...

Nighttime data collected at the bottom of a valley located in southern Brazil are studied. The analyzed quantities include momentum and sensible heat fluxes, turbulence statistics and intermittency factors, and their relationship to the stability parameter. The proper interval for averaging and flux calculations is found to be 20 min, based on the comparison of the fluxes and the random error associated in their determination. Each data series is classified as calm or windy, according to the mean wind speed. A much better dependency of the variables in terms of the stability parameter is found under windy conditions. Analysis of the wind direction and topographic scales indicates that distortion effects under calm conditions affect the flow, while the flow is in local equilibrium for windy conditions. In this case, the sensible heat flux shows a minimum for a value of z/L = 0.08, while the momentum flux and the normalized scales of the wind components and temperature decrease monotonically as the stability increases. An intermittency factor is proposed and shown to be larger (more intermittency) for more stable conditions.

Tropical glaciers are highly sensitive to climate change, with their mass balance influenced by temperature and precipitation, which affects the accumulation area. In this study, we developed an open-source tool to map the accumulation area of glaciers in the Cordillera Blanca, Peru (1988–2023), using Landsat images, spectral indices, and the Otsu method. We analyzed trends and correlations between snow accumulation area, meteorological patterns from ERA5 data, and oscillation modes. The results were validated using field data and manual mapping. Greater discrepancies were observed in glaciers with debris cover or small clean glaciers (<1 km2). The Amazonian and Pacific sectors showed a significant trend in decreasing accumulation areas, with reductions of 8.99% and 10.24%, respectively, from 1988–1999 to 2010–2023. El Niño events showed higher correlations with snow accumulation, snowfall, and temperature during the wet season, indicating a stronger influence on the Pacific sector. The accumulation area was strongly anti-correlated with temperature and correlated with snowfall in both sectors at a 95% confidence level (α = 0.05). The highest correlations with meteorological parameters were observed during the dry season, suggesting that even minor changes in temperature or precipitation could significantly impact the accumulation area.

This paper addresses the impact of roof-to-envelope ratio on overall energy savings of a green roof design over conventional roof designs. Simulations were performed using a modified version of the Environmental System Performance program simulator, developed at the University of Strathclyde. The modified design employed a model developed by Columbia University and the Goddard Institute of Space Science which models the evapotranspiritive effect of a green roof calculated using the Bowen ratio; that is, the ratio of sensible heat flux to the surrounding air to the latent heat flux resulting from evapourative energy losses. The resulting heat flux term is proportional to the external surface convection, but inversely proportional to the surface Bowen ratio, which is held constant and chosen to match experimental results obtained for a given roof design. The present study performed simulations for the month of July in a Toronto climate on square warehouse style one, two, and three-story buildings, with windows occupying 10% of the area of each wall. For the first set of simulations, the internal building load of each story was set to zero, and the roof-envelope ratio was increased by increasing the building width and length. For the final simulations, several roof-envelope ratios were chosen, and the internal load of each story was increased from 0 to 50,000 W. As the roof-envelope ratio increases, the cooling load of the upper floor for multi-story designs approaches the entire building cooling load. This indicates the importance of upper zone cooling in total building energy reductions. Furthermore, the total energy savings of a green-roofed building over a conventional roofed building were far more significant for single-story structures. A 250×250 m green-roof design with 50,000 W internal loading was found to have percentage energy savings of 73%, 29%, and 18%, for a one, two, and three-story design, respectively.

We present the main results from the second model intercomparison within the GEWEX (Global Energy and Water cycle EXperiment) Atmospheric Boundary Layer Study (GABLS). The target is to examine the diurnal cycle over land in today's numerical weather prediction and climate models for operational and research purposes. The set-up of the

Accurate estimates of surface energy exchange components are critical for understanding many physical processes of large lakes and their atmospheric environment. In this paper, the seasonal cycle of latent, sensible, and total heat flux from the surface of the Great Lakes is estimated. Lake surface temperatures derived from the NOAA/AVHRR satellite, along with meteorological data from surface station observations are incorporated in order to estimate spatial distributions of fluxes. Several well-known features are evident. Among these are the very high outgoing fluxes of latent and sensible heat during the late fall and early winter, which drive strong cooling of the lake surface and consequent convective mixing within the lake column. Another is greater seasonal variation of surface temperature and fluxes in shallower waters than in deeper waters. Due to strong static stability of the overlying atmospheric boundary layer during the spring, both the magnitude and the spatial variations of latent and sensible heat fluxes are small during the spring and, to a lesser degree, during the summer. The annual cycles of latent and sensible heat flux over the Great Lakes are roughly opposite in phase to the same fluxes over land, indicating a large exchange of energy via atmospheric advection between the lake and land surfaces. A major weakness of the method used here is that heat fluxes are calculated on the basis of an icefree surface, making the derived fluxes for January through March roughly estimated.

The Badain Jaran Desert is the second-largest area of shifting sands in China. Our first measurements of the energy components and water vapor fluxes on a megadune using eddy covariance technology were taken from April 2012 to April 2013. The results indicate that the longwave and shortwave radiative fluxes exhibited large fluctuations and seasonal dynamics. The total radiative energy loss by longwave and shortwave radiation was greater on the megadune than from other underlying surfaces. The radiation partitioning was different in different seasons. The land-atmosphere interaction was primarily represented by the sensible heat flux. The average sensible heat flux (40.1 W/m 2 ) was much larger than the average latent heat flux (14.5 W/m 2 ). Soil heat flux played an important role in the energy balance. The mean actual evaporation was 0.41 mm/d, and the cumulative actual evaporation was approximately 150 mm/a. The water vapor would transport downwardly and appear as dew condensation water. The amount of precipitation determined the actual evaporation. The actual evaporation was supposed to be equal to the precipitation on the megadune and the precipitation was difficult to recharge the groundwater. Our study can provide a foundation for further research on land-atmosphere interactions in this area.

One‐dimensional multilayer biosphere‐atmosphere models (e.g., CANVEG) describe ecosystem carbon dioxide (CO2) and water vapor (H2O) fluxes well when cold temperatures or the hydrologic state of the ecosystem do not induce stomatal closure. To investigate the CANVEG model framework under such conditions, CO2, H2O, and sensible heat fluxes were measured with eddy‐covariance methods together with xylem sap flux and leaf‐level gas exchange in a 16‐year‐old (in 1999) southeastern loblolly pine forest. Leaf‐level gas exchange measurements, collected over a 3‐year period, provided all the necessary biochemical and physiological parameters for the CANVEG model. Using temperature‐induced reductions of the biochemical kinetic rate constants, the CANVEG approach closely captures the diurnal patterns of the CO2 and H2O fluxes for two different formulations of the maximum Rubisco catalytic capacity (Vc max) ‐ temperature function, suggesting that the CANVEG approach is not sensitive to Vc max va...

Enclosed gas analyzer with short intake tube is a blend of a traditional long-tube closed-path design and a traditional open-path design. Analogous to closed-path, the enclosed design leads to minimal data loss during precipitation events and icing, and it does not have surface heating issues. Analogous to the open-path design, the enclosed design has good frequency response due to the short intake tube, does not require frequent calibration, needs minimal maintenance, and could be low power when used with short intake tube. In addition to these advantages, enclosed design could provide measurement of fast mixing ratio, or dry mole fraction, because native density measurements can be converted to mixing ratio units using fast measurements of temperature, water vapor and pressure inside the sampling cell. Fast mixing ratio implies that the thermal expansion and water dilution of the sampled air have been accounted for in such a conversion. Thus, no density corrections are required to compute fluxes when the fast mixing ratio is used. Such a way of calculating fluxes has been used frequently with traditional closed-path analyzers (e.g., LI-6262 and LI-7000), because fast fluctuations in the air temperature of the sample were attenuated in the long intake tube, and because water vapor was simultaneously measured and dry mole fraction was output from the instrument. In an enclosed design, such as the LI-7200 used with short tube, most but not all of the fast temperature fluctuations are attenuated, so calculating fluxes using the mixing ratio output of such an instrument requires validation. The CO 2 and H 2 O Eddy Covariance fluxes of from eight experiments with new LI-7200 enclosed analyzer were examined here: five deployments of the Ameriflux Roving Intercomparison Station in California, Arizona, New Mexico and Oregon; one deployment at a USDA flux site in Arizona; and two deployments at the LI-COR flux test facility in Nebraska. Fluxes were computed in two ways: (i) via the traditional way using the density corrections, and (ii) via a mixing ratio output from the instrument without applying the density corrections. The results of these comparisons have important implications for future gas flux measurements, because avoiding half-hourly or hourly density corrections could help to minimize at least two kinds of uncertainties: (i) the uncertainties associated with correcting the product of fast covariances of gas density using sensible and latent heat flux calculated over half-hour or an hour; and (ii) the uncertainties in the magnitudes of the sensible and latent heat fluxes used in correcting gas flux.

Precipitation from the West African Monsoon (WAM) provides food security and supports the economy in the region. As a consequence of the intrinsic complexities of the WAM's evolution, accurate simulations of the WAM and its precipitation regime, through the application of regional climate models (RCMs), are challenging. We used the coupled Weather Research and Forecasting (WRF) and Community Land Model (CLM) to explore impacts of radiation physics on the precipitation and dynamics of the WAM. Our results indicate that the radiation physics schemes produce not only biases in radiation fluxes and so radiative forcing which is expected but more importantly, result in large bias in precipitation of the WAM. Furthermore, the different radiation schemes led to variations in the meridional gradient of surface temperature between the north that is the Sahara desert and the south Guinean coastline. Climate diagnostics indicated that the changes in the meridional gradient of surface temperature affect the position and strength of the African Easterly Jet as well as the low-level monsoonal inflow from the Gulf of Guinea. The net result was that each radiation scheme produced differences in the WAM precipitation regime both spatially and in intensity. Such considerable variances in the WAM precipitation regime and dynamics, resulting from radiation representations, likely have strong feedbacks within the climate system and so have inferences when it comes to aspects of predicted climate change both for the region and globally.

Using atmospheric forcing data generated from a general circulation climate model, sixteen land surface schemes participating in the Project for the Intercomparison of Land-surface Parametrization Schemes (PILPS) were run o!-line to equilibrium using forcing data from a GCM representative of a tropical forest and a mid-latitude grassland grid point. The values for each land surface parameter (roughness length, minimum stomatal resistance, soil depth etc.) were provided. Results were quality controlled and analyzed, focusing on the scatter simulated amongst the models. There were large di!erences in how the models' partitioned available energy between sensible and latent heat. Annually averaged, simulations for the tropical forest ranged by 79 W m\ for the sensible heat #ux and 80 W m\ for the latent heat #ux. For the grassland, simulations ranged by 34 W m\ for the sensible heat #ux and 27 W m\ for the latent heat #ux. Similarly large di!erences were found for simulated runo! and soil moisture and at the monthly time scale. The models' simulation of annually averaged e!ective radiative temperature varied with a range, between all the models, of 1.4 K for tropical forest and 2.2 K for the grassland. The simulation of latent and sensible heat #uxes by a standard &bucket' models was anomalous although this could be corrected by an additional resistance term. These results imply that the current land surface models do not agree on the land surface climate

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Components of the surface water and energy balance are evaluated in the Met Office global Numerical Weather Prediction (NWP) 00-36 hour forecasts using (i) GEWEX Continental Scale Experiment (CSE) reference site data provided by the Coordinated Enhanced Observing Period (CEOP) project and (ii) other earth observing datasets from satellites and in-situ measurements. The global hydrological cycle in the model is in reasonable balance in recent model versions. However, comparison against available observations suggest that both precipitation and evaporation are overestimated over both land and ocean, with largest errors over the tropical oceans. Comparison of the model's seasonal and diurnal cycles of surface fluxes, temperature, precipitation, and moisture against the GEWEX /CEOP CSE sites during October 2002 to September 2003 reveals several issues concerning model parametrization performance. For the high latitude (Arctic) sites low cloud is overestimated during boreal winter leading to an enhanced greenhouse effect and too warm near surface temperatures in the model. Snow melt occurs too early in boreal spring in the model forecasts which currently have no snow analysis component. Possible reasons for early snow melt are discussed including the specification of albedo over heterogeneous terrain and excessive sublimation of snow in the model. The mid-latitude CEOP sites all show excessive evaporation and precipitation during boreal spring and early summer and comparison with the International Satellite Cloud Climatology (ISCCP) products show systematic under prediction of cloud cover over mid-latitude land in summer. Some of the largest biases in mid-latitude surface fluxes in summer are during daytime on non-precipitating cloudy days where the model overestimates the downward SW radiation, latent and sensible heat fluxes. Finally, over tropical land we see a tendency to underestimate precipitation which is in direct contrast to tropical oceans where precipitation accumulations are too large. We have also used the CEOP data to investigate structural errors in the vertical profiles of tropical humidity which suggest deficiencies in the convection scheme.