Force-restore Method Research Articles

Evaluation of the snow cover in the Soil, Vegetation, and Snow (SVS) land surface model

AbstractThe Soil, Vegetation, and Snow (SVS) land surface model was recently developed at Environment and Climate Change Canada (ECCC) for operational numerical weather prediction and hydrological forecasting. This study examined the performance of the snow scheme in the SVS model over multiple years at ten well-instrumented sites from the Earth System Model-Snow Model Intercomparison Project (ESM-SnowMIP), which covers alpine, maritime and taiga climates. The SVS snow scheme is a simple single-layer snowpack scheme that uses the force-restore method. Stand-alone, point-scale verification tests showed that the model is able to realistically reproduce the main characteristics of the snow cover at these sites, namely snow water equivalent, density, snow depth, surface temperature, and albedo. SVS accurately simulated snow water equivalent, density and snow depth at open sites, but exhibited lower performance for subcanopy snowpacks (forested sites). The lower performance was attributed mainly to the limitations of the compaction scheme and the absence of a snow interception scheme. At open sites, the SVS snow surface temperatures were well represented but exhibited a cold bias, which was due to poor representation at night. SVS produced a reasonably accurate representation of snow albedo, but there was a tendency to overestimate late winter albedo. Sensitivity tests suggested improvements associated with the snow melting formulation in SVS.

Coupling of urban energy balance model with 3-D radiation model to derive human thermal (dis)comfort

While capabilities in urban climate modeling have substantially increased in recent decades, the interdependency of changes in environmental surface properties and human (dis)comfort have only recently received attention. The open-source solar long-wave environmental irradiance geometry (SOLWEIG) model is one of the state-of-the-art models frequently used for urban (micro-)climatic studies. Here, we present updated calculation schemes for SOLWEIG allowing the improved prediction of surface temperatures (wall and ground). We illustrate that parameterizations based on measurements of global radiation on a south-facing vertical plane obtain better results compared to those based on solar elevation. Due to the limited number of ground surface temperature parameterizations in SOLWEIG, we implement the two-layer force-restore method for calculating ground temperature for various soil conditions. To characterize changes in urban canyon air temperature (Tcan), we couple the calculation method as used in the Town Energy Balance (TEB) model. Comparison of model results and observations (obtained during field campaigns) indicates a good agreement between modeled and measured Tcan, with an explained variance of R2 = 0.99. Finally, we implement an energy balance model for vertically mounted PV modules to contrast different urban surface properties. Specifically, we consider (i) an environment comprising dark asphalt and a glass facade and (ii) an environment comprising bright concrete and a PV facade. The model results show a substantially decreased Tcan (by up to − 1.65°C) for the latter case, indicating the potential of partially reducing/mitigating urban heat island effects.

A New Model to Downscale Urban and Rural Surface and Air Temperatures Evaluated in Shanghai, China

AbstractA simple model, the Surface Temperature and Near-Surface Air Temperature (at 2 m) Model (TsT2m), is developed to downscale numerical model output (such as from ECMWF) to obtain higher-temporal- and higher-spatial-resolution surface and near-surface air temperature. It is evaluated in Shanghai, China. Surface temperature (Ts) and near-surface air temperature (Ta) submodels account for variations in land cover and their different thermal properties, resulting in spatial variations of surface and air temperature. The net all-wave radiation parameterization (NARP) scheme is used to compute net wave radiation for the surface temperature submodel, the objective hysteresis model (OHM) is used to calculate the net storage heat fluxes, and the surface temperature is obtained by the force-restore method. The near-surface air temperature submodel considers the horizontal and vertical energy changes for a column of well-mixed air above the surface. Modeled surface temperatures reproduce the general pattern of MODIS images well, while providing more detailed patterns of the surface urban heat island. However, the simulated surface temperatures capture the warmer urban land cover and are 10.3°C warmer on average than those derived from the coarser MODIS data. For other land-cover types, values are more similar. Downscaled, higher-temporal- and higher-spatial-resolution air temperatures are compared to observations at 110 automatic weather stations across Shanghai. After downscaling with TsT2m, the average forecast accuracy of near-surface air temperature is improved by about 20%. The scheme developed has considerable potential for prediction and mitigation of urban climate conditions, particularly for weather and climate services related to heat stress.

Using Earth’s Moon as a Testbed for Quantifying the Effect of the Terrestrial Atmosphere

In the past, the planetary radiation balance served to quantify the atmospheric greenhouse effect by the difference between the globally averaged near-surface temperature of and the respective effective radiation temperature of the Earth without atmosphere of resulting in . Since such a “thought experiment” prohibits any rigorous assessment of its results, this study considered the Moon as a testbed for the Earth in the absence of its atmosphere. Since the angular velocity of Moon’s rotation is 27.4 times slower than that of the Earth, the forcing method, the force-restore method, and a multilayer-force-restore method, used in climate modeling during the past four decades, were alternatively applied to address the influence of the angular velocity in determining the Moon’s globally averaged skin (or slab) temperature, . The multilayer-force-restore method always provides the highest values for , followed by the force-restore method and the forcing method, but the differences are marginal. Assuming a solar albedo of , a relative emissivity , and a solar constant of and applying the multilayer-force-restore method yielded and for the Moon. Using the same values for α, ε, and S, but assuming the Earth’s angular velocity for the Moon yielded and quantifying the effect of the terrestrial atmosphere by . A sensitivity study for a solar albedo of commonly assumed for the Earth in the absence of its atmosphere yielded , , and . This means that the atmospheric effect would be more than twice as large as the aforementioned difference of 33 K. To generalize the findings, twelve synodic months (i.e., 354 Earth days) and 365 Earth days, where , a Sun-zenith-distance dependent solar albedo, and the variation of the solar radiation in dependence of the actual orbit position and the tilt angle of the corresponding rotation axis to the ecliptic were considered. The case of Moon’s true angular velocity yielded and . Whereas Earth’s 27.4 times higher angular velocity yielded , and . In both cases, the effective radiation temperature is , because the computed global albedo is . Thus, the effective radiation temperature yields flawed results when used for quantifying the atmospheric greenhouse effect.

Evaluating the Utah Energy Balance (UEB) snow model in the Noah land-surface model

Abstract. Noah (version 2.7.1), the community land-surface model (LSM) of National Centers for Environmental Predictions-National Center for Atmospheric Research (NCEP-NCAR), which is widely used to describe the land-surface processes either in stand-alone or in coupled land-atmospheric model systems, is recognized to underestimate snow–water equivalent (SWE). Noah's SWE bias can be attributed to its simple snow sub-model, which does not effectively describe the physical processes during snow accumulation and melt period. To improve SWE simulation in the Noah LSM, the Utah Energy Balance (UEB) snow model is implemented in Noah to test alternate snow surface temperature and snowmelt outflow schemes. Snow surface temperature was estimated using the force-restore method and snowmelt event is regulated by accounting for the internal energy of the snowpack. The modified Noah's SWE simulations are compared with the SWE observed at California's NRCS SNOTEL stations for 7 water years: 2002–2008, while the model's snow surface temperature is verified with observed surface-temperature data at an observation site in Utah. The experiments show that modification in Noah's snow process substantially reduced SWE estimation bias while keeping the simplicity of the Noah LSM. The results suggest that the model did not benefit from the alternate temperature representation but primary improvement can be attributed to the substituted snowmelt process.

The sensitivity of ground surface temperature prediction to soil thermal properties Using the Simple Biosphere Model (SiB2)

Using the Simple Biosphere Model (SiB2), soil thermal properties (STP) were examined in a Tibetan prairie during the monsoon period to investigate ground surface temperature prediction. We improved the SiB2 model by incorporating a revised force-restore method (FRM) to take the vertical heterogeneity of soil thermal diffusivity (k) into account. The results indicate that (1) the revised FRM alleviates daytime overestimation and nighttime underestimation in modeled ground surface temperature (Tg), and (2) its role in little rainfall events is significant because the vertical gradient of k increases with increasing surface evaporation. Since the original formula of thermal conductivity (λ) in the SiB2 greatly underestimates soil thermal conductivity, we compared five algorithms of λ involving soil moisture to investigate the cause of overestimation during the day and underestimation at night on the basis of the revised FRM. The results show that (1) the five algorithms significantly improve Tg prediction, especially in daytime, and (2) taking one of these five algorithms as an example, the simulated Tg values in the daytime are closer to the field measurements than those in the nighttime. The differences between modeled Tg and field measurements are mostly within the margin of error of ±2 K during 3 August to 4 September 1998.

Air and biomass heat storage fluxes in a forest canopy: Calculation within a soil vegetation atmosphere transfer model

An analytical method for calculating the sub-diurnal change in heat storage in tree trunks is presented and incorporated in a soil vegetation atmosphere transfer (SVAT) model. The modelled change in biomass heat storage ( J tr) is driven by radial heat diffusion within the trunks and surface heat exchange by convection, insolation and longwave radiation. The calculation requires only variables from the previous and current time step and is independent of measured biomass temperature. The model was applied to a 40 m tall Australian temperate Eucalyptus forest at the Tumbarumba Ozflux site. A comparison between modelled and measured trunk temperatures showed agreement to within 1 °C, providing confidence in the model. Hourly values of J tr peaked at 61 W m −2 for this site. Similar values of J tr were obtained using an adaptation of the force-restore method. Additional calculations for a range of leaf area indices and trunk radii enable a quick estimate of the maximum hourly value of J tr for any forest with given leaf area index, quadratic mean trunk radius (at breast height) and biomass. Inclusion of heat storage fluxes in the hourly available energy budget for the forest improved agreement between available energy and measured heat fluxes above the canopy, with energy closure rising from 90 to 101%. Accounting for J tr in the SVAT model also improved agreement between measured and modelled fluxes of sensible and latent heat.

Evaluation of six parameterization approaches for the ground heat flux

There are numerous approaches to the parameterization of the ground heat flux that use different input data, are valid for different times of the day, and deliver results of different quality. Six of these approaches are tested in this study: three approaches calculating the ground heat flux from net radiation, one approach using the turbulent sensible heat flux, one simplified in situ measurement approach, and the force-restore method. On the basis of a data set recorded during the LITFASS-2003 experiment, the strengths and weaknesses of the approaches are assessed. The quality of the best approaches (simplified measurement and force-restore) approximates that of the measured data set. An approach calculating the ground heat flux from net radiation and the diurnal amplitude of the soil surface temperature also delivers satisfactory daytime results. The remaining approaches all have such serious drawbacks that they should only be applied with care. Altogether, this study demonstrates that ground heat flux parameterization has the potential to produce results matching measured ones very well, if all conditions and restrictions of the respective approaches are taken into account.

A Case Study on the Effects of Heterogeneous Soil Moisture on Mesoscale Boundary-Layer Structure in the Southern Great Plains, U.S.A. Part II: Mesoscale Modelling

The importance of soil moisture inputs and improved model physics in the prediction of the daytime boundary-layer structure during the Southern Great Plains Hydrology Experiment 1997 (SGP97) is investigated using the non-hydrostatic fifth-generation Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) Mesoscale Model MM5. This is Part II of a two-part study examining the relationship of surface heterogeneity to observed boundary-layer structure. Part I focuses on observations and utilizes a simple model while Part II uses observations and MM5 modelling. Soil moisture inputs tested include a lookup table based on soil type and season, output from an offline land-surface model (LSM) forced by atmospheric observations, and high-resolution (\(\approx\) 800 m) airborne microwave remotely sensed data. Model physics improvements are investigated by comparing an LSM directly coupled with the MM5 to a simpler force-restore method at the surface. The scale of land surface heterogeneities is compared to the scale of their effects on boundary-layer structure.

Impact Assessment of Urban Meteorology and the Atmospheric Environment Using Urban Sub-Domain Planning

For the purpose of (1) investigating the relationship between urban planning and the atmospheric environment, and (2) improving the atmospheric environment through rational and scientific planning, an urban sub-domain scale model is developed in the form of a three-dimensional non-hydrostatic model with k – ɛ closure. The distribution and azimuth of buildings, the screening of shortwave radiation by buildings, and the underlying surface type as characteristics of the urban environment are included, the ground temperature is calculated using the force-restore method, and the concentration equation is solved simultaneously. The model is evaluated using special field observations and wind-tunnel experiment data, showing that model results meet the observational and experimental data generally well. Based on the model, an index system and evaluation method is set up to assess the impact of urban meteorology and the atmospheric environment using urban sub-domain planning. As an example, two layouts of a specific sub-domain in Beijing are assessed. The impact assessment system of urban meteorology and the atmospheric environment using urban sub-domain planning, which includes the urban sub-domain scale numerical model, index system and evaluation method, provides an effective approach to improve the atmospheric environment through rational and scientific planning.

Determination of the Atmospheric Boundary-Layer within the Urban Environment

In this paper, novel mathematical methods are implemented. In particular a mesh refinement technique is developed that allows the larger scale topographical effects on the atmospheric boundary-layer to be taken into account, yet still enabling the fine resolution of the boundary-layer within the smaller scale of the urban environment, as well as a parameterisation for urban effects. In the latter, the surface roughness is included through additional drag terms within the Navier-Stokes equations. A surface energy budget equation is solved using a force-restore method to obtain a ground surface temperature. It is shown that this method allows the diurnal and yearly variation of the structure of the atmospheric boundary-layer to be accounted for within the model. The combined effects of all these features enable the resolution of the atmospheric boundary-layer within the urban canopy and also the surrounding area to be obtained.

Modelling snowpack surface temperature in the Canadian Prairies using simplified heat flow models

AbstractThree practical schemes for computing the snow surface temperature Ts, i.e. the force–restore method (FRM), the surface conductance method (SCM), and the Kondo and Yamazaki method (KYM), were assessed with respect to Ts retrieved from cloud‐free, NOAA‐AVHRR satellite data for three land‐cover types of the Paddle River basin of central Alberta. In terms of R2, the mean Ts, the t‐test and F‐test, the FRM generally simulated more accurate Ts than the SCM and KYM. The bias in simulated Ts is usually within several degrees Celsius of the NOAA‐AVHRR Ts for both the calibration and validation periods, but larger errors are encountered occasionally, especially when Ts is substantially above 0 °C. Results show that the simulated Ts of the FRM is more consistent than that of the SCM, which in turn was more consistent than that of the KYM. This is partly because the FRM considers two aspects of heat conduction into snow, a stationary‐mean diurnal (sinusoidal) temperature variation at the surface coupled to a near steady‐state ground heat flux, whereas the SCM assumes a near steady‐state, simple heat conduction, and other simplifying assumptions, and the KYM does not balance the snowpack heat fluxes by assuming the snowpack having a vertical temperature profile that is linear. Copyright © 2005 John Wiley & Sons, Ltd.

Reforming the force-restore method for predicting ground surface temperature

A reformed force-restore version that predicts exact values for ground surface temperature under a multifrequency surface forcing is developed. In developing such a version, the ground surface temperature is expanded into a Fourier series. A force-restore equation is proposed for each term in the series in terms of two unknown coefficients: forcing coefficient and restoring coefficient. Eliminating the errors in the predictions of each force-restore equation is employed in deriving explicit expressions for those coefficients. As an illustration for the applications of the reformed force-restore version, its predictions are used in evaluating the performance of a surface heat flux model and in investigating the validity range of a soil microwave radiometry model.

An extension of the force‐restore method to estimating soil temperature at depth and evaluation for frozen soils under snow

The force‐restore method (FRM) was originally developed for estimating diurnal fluctuations in the ground surface temperature. Because of its relatively simple parameterization, it is commonly applied in meteorological and other models for this purpose. Its application to the calculation of deeper soil temperatures, to frozen soils, and to soils under snow covers has heretofore not been possible. This study demonstrates an extension of the FRM that permits accurate estimates of seasonal variation in mean daily deep soil temperature. The extended FRM is shown to provide a lower boundary condition for the heat conduction method, permitting a combination of the two approaches that avoids some limitations of each. The combined approach provides representations of the mean daily soil temperature, soil temperature at depth in frozen soils, and ground surface temperature under a snow cover. Diurnal variations can also be calculated. The extended method and combined approaches are tested using field site measurements collected in cold weather periods in Saskatchewan, Canada, and are found to provide a reasonable representation of measurements.

An Intercomparison of Three Snow Schemes of Varying Complexity Coupled to the Same Land Surface Model: Local-Scale Evaluation at an Alpine Site

The Interactions between Soil, Biosphere, and Atmosphere land surface scheme is currently used coupled both to atmospheric models and to a distributed hydrological model. There are two snow-scheme options available for hydrological modeling: the baseline force-restore approach, which uses a composite snow-soil-vegetation energy budget and a single snow layer; and a multilayer detailed internal-process snow model. Only the force-restore method is routinely used in atmospheric modeling applications. Recent studies have shown that hydrological simulations for mountainous catchments within the Rhone basin, France, are significantly improved using the detailed snow scheme. The main drawback is that the scheme is computationally expensive, and it is not currently feasible for routine application in atmospheric models. For these reasons, a third new intermediate-complexity scheme has been developed that includes certain key physical processes from the complex model for improved snowpack realism and hydrological depiction while attemping to keep computational requirements similar to those of the simple default scheme. In the current study, the new scheme is described, evaluated, and compared with the results from the two other schemes at a local scale at an alpine site located within the Rhone basin for two contrasting (weather) years. All schemes are able to model the basic features of the snow cover with similar errors averaged over the 2-yr period; however, there are important differences on shorter timescales. When compared with the more complex scheme, it was found that differing surface energy budget parameter-izations (turbulent transfer, albedo) were the cause for the largest differences in total snowpack snow water equivalent (SWE) simulated by the models. When compared with the simple scheme, the ability for the intermediate model to simulate snow ripening resulted in the largest differences in simulated SWE and snow temperature during melt and runoff.

Estimation of Seasonal and Annual Evaporation using Agrometeorological Data from the Thai Meteorological Department by the Heat Budget Models

Seasonal evaporation on bare soil and lawn was estimated using only routine meteorological data at Bangkok and Chiang Mai in the Chao Phraya river basin in Thailand by using two methods. One method is that evaporation was estimated by the heat balance model using daily mean ground surface temperature (0 cm depth), (hereafter GST), The second is that it was estimated by using the Force-Restore Method for estimating daily mean soil temperature (hereafter FRM). Seasonal and annual evaporation were estimated by using agrometeorological station data of the Thai Meteorological Department in 1989 at Chiang Mai (lawn) and Bangkok (bare soil). At Chiang Mai, annual precipitation was 1000 mm, annual pan evaporation was 1540 mm and estimated value of annual evaporation (lawn) was 760 mm by the FRM (using soil temperature at 5 cm depth) and 815 mm by the GST method. At Bangkok, annual precipitation was 1320 mm, annual pan evaporation was 1560 mm and the estimated value of annual evaporation (bare soil) was 1080 mm by the FRM (using soil temperature at 5 cm depth) and 1140 mm by the GST method. The results of these two methods were comparatively close to each other, however the estimated evaporation by the GST method was slightly larger than that by the FRM. This difference was caused by the differences between the ground surface temperature and soil temperature at 5 cm depth. The reason considered was the difficulty of accurate ground surface temperature measurement by the stem thermometer. The estimated evaporation at Chiang Mai was comparatively close to the results of the complex area of vegetation obtained by Toda et al. (2000 b) and paddy field obtained by Toda et al. (2000 a).

Water temperature modelling in a small forested stream: implication of forest canopy and soil temperature

The demand for comprehensive environmental assessment of river ecosystem has increased for engineers and scientists. Accurate and versatile water temperature models are required to meet this demand. A number of hydrological models take vegetation and soil characteristics into account, but very few temperature models do. The objective of this paper is to incorporate soil temperature and vegetation as input variables in a deterministic heat budget model. The CEQUEAU hydrological and water temperature model was used to simulate water temperature in Catamaran Brook, a small catchment located in central New Brunswick. The model was modified by incorporating soil temperature as a parameter influencing the temperature of interflow, using the so-called force-restore method. Crown closure was also incorporated in the model as a factor influencing locally advected water using a negative exponential function. The modified model simulated daily water temperatures better than the original model. Root-mean-square error for a period of 5 years decreased from 2.10°C with the original model to 1.77°C with the modified model. Nash coefficient increased from 0.78 with the original model to 0.82 with the modified model. An analysis of residuals showed that the modified model is sensitive to additional parameters such as crown closure, especially for short time scales during periods of higher discharge and during extreme meteorological and hydrological events such as tropical storms.Key words: stream temperature, hydrology, deterministic model, CEQUEAU, forestry.

Inclusion of a Third Soil Layer in a Land Surface Scheme Using the Force–Restore Method

The inclusion of a third soil layer in the Interactions between Soil, Biosphere, and Atmosphere (ISBA) model is presented in this paper. The soil water content between the base of the root zone and the deep soil layer is described using a generalized form of the force-restore method. The new force-restore coefficient is calibrated using a detailed high-resolution soil water transfer model and then is related to the soil textural properties using simple regression relationships. It is shown that the use of a calibrated coefficient gives better results, in general, than a direct solution method when using similar model geometry with the same number of layers. In the initial two-layer version of ISBA, it was not possible to distinguish the root zone and subroot zone soil water reservoirs. With the three-layer version, the deep soil layer may provide water to the system through capillary rises only, and the available water content (for transpiration) is clearly defined. Three test cases are examined in which atmospheric forcing, a good description of the soil properties and vegetation cover, and measured soil moisture profile data are present for an annual cycle. Use of the three-layer version of ISBA gives general improvement in modeling results, and values for key parameters that relate evapotranspiration to soil moisture are more consistent with those inferred from observations, compared with the two-layer version.

The land-surface flux model PROGSURF

The land-surface flux model (PROGSURF) designed jointly at the Universities of Vienna and Budapest is reviewed; it belongs to the broad spectrum of PILPS 1 Project for Intercomparison of Land-surface Parameterization Schemes. 1 models. PROGSURF comprises one vegetation layer and three soil layers. Temperature prediction is made by the heat conduction equation in conjunction with the force-restore method. Turbulent heat fluxes are parameterized by gradient laws using the resistance concept. The formula for the canopy surface resistance involves both a parameter describing atmospheric demand and one describing moisture availability. Soil moisture prediction is made with Richards' equation. PROGSURF is tested in off-line mode for the Cabauw data set. The observed annual mean values of the state and flux quantities at the earth's surface are well reproduced. For example, the model yields latent and sensible heat fluxes of −35.3 and −2.4 W/m 2, respectively; evapotranspiration and runoff is −449 and 326 mm/yr; and root zone soil moisture content is 0.344 m 3/m 3. Further, the seasonal changes of water and energy balance components are well simulated. The sensitivity of PROGSURF to the canopy resistance formulation is analysed. We find that the atmospheric demand is largely represented by the saturation value of the evapotranspiration/soil moisture curve with maximum summer impact upon the annual value and further that the moisture availability is represented by the slope of the evapotranspiration curve. Both saturation value and slope control the amplitude of the seasonal fluctuation of the water balance components; at Cabauw site the saturation value is the governing parameter. These results fit satisfactorily into the other PILPS models. In particular, we are able to reproduce with PROGSURF the total variability of most other PILPS models by simply changing the atmospheric demand and soil moisture availability parameters. PROGSURF presently serves to simulate observed surface fluxes for an atmospheric diagnostic model.

Monthly Simulation of Surface Layer Fluxes and Soil Properties during FIFE

Abstract Global change and regional climate experiments with atmospheric numerical models rely on the parameterization of the surface boundary in order to evaluate impact on society and agriculture. In this paper, several surface modeling strategies have been examined in order to test their ability to simulate for a period of one month, and hence, their impact on short-term and regional climate modeling. The interaction between vegetation and soil models is also discussed. The resolution of a multiple-level soil model, the method of computing moisture availability, the Force–Restore Method, and vegetation parameterization were studied by comparing model-simulated soil temperature, soil moisture, and surface energy budget with observations and intercomparison of the simulations. The increase of model soil resolution improved both the simulation of daytime ground heat flux and latent heat. Evaporation from the soil surface with more coarse resolution soil was larger than the higher resolution simulation, bu...