Momentum Roughness Length Research Articles

Variation in Zero Plane Displacement and Roughness Length for Momentum Revisited

Zero plane displacement height (d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document}) and momentum roughness length (z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document}), describe the aerodynamic characteristics of a vegetated surface. Usually, d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document} are assumed to be constant functions of the physical characteristics of the surface. Prior evidence collected from the literature and our examination of flux tower data show that d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document} vary in time at sites with tree and shrub canopies, but not grasslands. The conventional explanations of these variations are based on linear functions of wind velocity and friction velocity, with little theoretical basis. This study explains the variation in aerodynamic parameters by matching four analytical canopy velocity models to a logarithmic above-canopy velocity profile at canopy height. d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document} come out as functions of 2 non-dimensional terms, the canopy momentum absorption capacity (parameter) and a (measurable) Péclet number. To test the theories of variation, we analysed the velocity profiles from Ozflux and Ameriflux sites. None of the theories could recreate d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document} at half-hourly intervals. However, the canopy velocity models were able better to recreate the distribution of the variations in d0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d_0$$\\end{document} and z0m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z_{0m}$$\\end{document}. Additionally, the estimates of canopy momentum absorption capacity varied consistently with phenological changes in the canopies, whereas, the fitting parameters of the linear regression of using wind speed and friction velocity did not exhibit physically interpretable variations. The canopy velocity models may offer better predictions with an accurate estimation of the canopy height, a horizontally homogeneous and rigid canopy, and incorporation of the roughness sublayer.

Effect of Small-Scale Topographical Variations and Fetch from Roughness Elements on the Stable Boundary Layer Turbulence Statistics

Understanding the influence of roughness and terrain slope on stable boundary layer turbulence is challenging. This is investigated using observations collected from October to November of 2018 during the Stable Atmospheric Variability ANd Transport (SAVANT) field campaign conducted in a shallow sloping Midwestern field. We analyze the turbulence velocity scale and its variation with the mean wind speed using observations up to 10–20 m on four meteorological towers located along a shallow gully. The roughness length for momentum over this complex terrain varied with wind direction from 0.0049 m to a maximum of 0.12 m for winds coming through deciduous trees present in the field. The variation of the turbulence velocity with wind speed shows a transition from a weak wind regime to a stronger wind regime, as reported by past studies. This transition is not observed for winds coming from the tree area, where turbulence is enhanced even for weak wind speeds. For weak stratification and stronger winds, the turbulent velocity scale increased with an increase in roughness while the terrain slope is seen to have a weak influence. The sizes of the dominant turbulent eddies seen from the vertical velocity power spectra are observed to be larger for winds coming through the tree area. The turbulence enhancement by the trees is found to be strong within a fetch distance of 7 times the tree height and not observable at 16 times of the tree height.

Spatiotemporal scale-dependent effects of urban morphology on meteorology: A case study in Beijing using observations and simulations

Urban morphology has a great impact on urban meteorology, but the scaling effects in the underlying relationships have seen little research. In this work, the controls of building and vegetation morphology on urban meteorology at different spatial (30 m, 90 m, 300 m, 500 m, 1 km) and temporal (diurnal, seasonal) scales are explored, using in-situ observations and WRF (Weather Research and Forecast) modeling. The random forest method is employed to derive the importance of morphological indicators for meteorology, based on in-situ observations from weather stations. This work reaches the following conclusions. (1) Morphological factors have the largest impacts at 30-m scale, and are the strongest influences on air temperature (Ta), wind speed (WS) and relative humidity (RH). The sky view factor (SVF) is the most important of these factors at the 30-m scale. Vegetation strongly affects Ta and RH in summer at scales of >90 m. (2) The main indicators during daytime and night-time are different: vegetation has a more impact on Ta during the night than during the day in summer, while SVF is the main factor controlling Ta at night during winter. Morphology has greater influence on diurnal variations in Ta at scales of <100 m. (3) The WRF simulation is consistent with observations and reveals that building height is the most important indicator for WS. This is because building height affects the roughness length for momentum (Z0m), which is the main factor influencing WS. This work can help in urban planning, to improve the urban thermal and wind environment.

The Impacts of Adjusting Momentum Roughness Length on Strong and Weak Hurricane Forecasts: A Comprehensive Analysis of Weather Simulations and Observations

Abstract The momentum roughness length (z0) significantly impacts wind predictions in weather and climate models. Nevertheless, the impacts of z0 parameterizations in different wind regimes and various model configurations on the hurricane size, intensity, and track simulations have not been thoroughly established. To bridge this knowledge gap, a comprehensive analysis of 310 simulations of 10 real hurricanes using the Weather Research and Forecasting (WRF) Model is conducted in comparison with observations. Our results show that the default z0 parameterizations in WRF perform well for weak (category 1–2) hurricanes; however, they underestimate the intensities of strong (category 3–5) hurricanes. This finding is independent of model resolution or boundary layer schemes. The default values of z0 in WRF agree with the observational estimates from dropsonde data in weak hurricanes while they are much larger than observations in strong hurricanes regime. Decreasing z0 close to the values of observational estimates and theoretical hurricane intensity models in high wind regimes (≳45 m s−1) led to significant improvements in the intensity forecasts of strong hurricanes. A momentum budget analysis dynamically explained why the reduction of z0 (decreased surface turbulent stresses) leads to stronger simulated storms.

Observed and Parameterized Roughness Lengths for Momentum and Heat Over Rough Ice Surfaces

AbstractTurbulent heat fluxes, that is, the sensible heat flux and latent heat flux, are important sources/sinks of energy for surface melt over glaciers and ice sheets. Therefore, credible simulations of for example, future Greenland Ice Sheet mass loss need an accurate description of these fluxes. However, the parameterization of surface turbulent heat fluxes in climate models requires knowledge about the surface roughness lengths for momentum, heat and moisture, which are currently either unknown or tuned to indirect observations. In this study we take advantage of a large data set of eddy covariance observations acquired during multiple years and at multiple sites over the Greenland Ice Sheet. These in‐situ observations are used to develop an improved parameterization for the roughness length for momentum, and update the parameterization for the roughness lengths for heat and moisture over rough ice surfaces. The newly derived parameterizations are implemented in a surface energy balance model that is used to compute surface melt. Sensitivity experiments confirm the high sensitivity of surface melt to the chosen roughness length models. The new parameterization models the sensible heat flux to within 10 W m−2, and the cumulative ice ablation within 10% at three out of four sites. Two case studies demonstrate the important contribution of the turbulent heat fluxes to surface ablation. The presented roughness parameterizations can be implemented in climate models to improve the physical representation of surface roughness over rough snow and ice surfaces, which is expected to improve the modeled turbulent heat fluxes and thus surface melt.

Reconstruction of the hourly fine-resolution apparent temperature (Humidex) with the aerodynamic parameters

Apparent temperature is the preferred measure of hotness or coldness expressed to depict the human sense. Spatially explicit measurement of the hourly apparent temperature is essential for capturing the threats to bioclimatic comfort and preventing potential mortality/morbidity risk from heat or cold. However, existing apparent temperature products only provide daily observations at the spatial resolution of several dozen kilometers, resulting in some substantial underestimations for some life-threatening thermal stresses highly localized in space and time. Furthermore, some data-driven models lack mechanical constraints on the turbulent exchange between the surface and the atmosphere, making some unsatisfactory accuracy. Here, we propose Humidex reconstruction model incorporating atmospheric dynamics theory and aerodynamic parameters (i.e., heat and momentum roughness lengths for natural surfaces and three urban canopy geometry parameters for artificial surfaces), capable of developing an hourly dataset at fine-grained spatial resolution (0.01° × 0.01°). In this study, a total of 2952 h in four seasons were selected to test the seasonal performance of this model, taking the Yangtze River Delta as an example. The results show that the Humidex products from this model generally outperform the existing comparable products, with the hourly population root mean square error (RMSE) ranging from 1 to 2 °C in winter and autumn and 2–3 °C in spring and summer. Moreover, the constraint of aerodynamic parameters can reduce RMSE with a significant margin for each season, up to 2 °C, especially in areas with dense woodlands or buildings. In addition, the results demonstrate the excellent performance of this model in capturing short-lived thermal health threats, which are easily overlooked when observed data only provides a daily variation. This indicates that the model can allow researchers and practitioners investigate the fine-grained spatial and temporal evolution of thermal stress and its impact on public health, tourism, learning, and work performance.

Flux–Gradient Relationships Below 2 m Over a Flat Site in Complex Terrain

The surface–atmosphere turbulent exchange fluxes are experimentally determined using the eddy-covariance method. Their estimation using profiles of the variables of interest is a less costly alternative, although restricted to certain ranges of stability and assumed to hold for relatively flat and homogeneous terrain. It relays usually on the prescription of the roughness lengths for momentum, heat and matter, the latter two being adjustable parameters with unclear physical significance. The relations are derived with data from screen level to a few tens of metres upward. The application of these expressions using data only at one level in the surface layer implies assuming zero wind speed and the land surface temperature at their respective roughness lengths. The latter is a quantity that experimentally can only be determined radiatively with a substantial uncertainty. In this work the flux-profile relationships for momentum and sensible heat are assessed over a flat site in moderately inhomogeneous complex terrain in the southern pre-Pyrenees, using data between 2 m and the surface. The main findings are that (i) the classical expressions hold in the daytime for most of the dataset, (ii) the iterative estimations using the Obukhov length and the direct ones using the bulk Richardson number provide very similar results, (iii) using a second observation of temperature avoids a radiometric measure of land surface temperature and the prescription of a thermal roughness length value, (iv) the estimations over wet terrain with high irradiance depart largely from observations.

The effects of ocean surface waves on global intraseasonal prediction: case studies with a coupled CFSv2.0–WW3 system

Abstract. This article describes the implementation of a coupling between a global forecast model (CFSv2.0) and a wave model (WW3) and investigates the effects of ocean surface waves on the air–sea interface in the new framework. Several major wave-related processes, including the Langmuir mixing, the Stokes–Coriolis force with entrainment, air–sea fluxes modified by the Stokes drift, and momentum roughness length, are evaluated in two groups of 56 d experiments, one for boreal winter and the other for boreal summer. Comparisons are made against in situ buoys, satellite measurements, and reanalysis data to evaluate the influence of waves on intraseasonal prediction of sea surface temperature (SST), 2 m air temperature (T02), mixed layer depth (MLD), 10 m wind speed (WSP10), and significant wave height (SWH). The wave-coupled experiments show that overestimated SSTs and T02s, as well as underestimated MLDs at mid-to-high latitudes in summer from original CFSv2.0, are significantly improved due to enhanced vertical mixing generated by the Stokes drift. For WSP10s and SWHs, the wave-related processes generally reduce biases in regions where WSP10s and SWHs are overestimated. On the one hand, the decreased SSTs stabilize the marine atmospheric boundary layer and weaken WSP10s and then SWHs. On the other hand, the increased roughness length due to waves reduces the originally overestimated WSP10s and SWHs. In addition, the effects of the Stokes drift and current on air–sea fluxes also rectify WSP10s and SWHs. These cases are helpful for the future development of the two-way CFSv2.0–wave coupled system.

Sensible Heat and Latent Heat Flux Estimates in a Tall and Dense Forest Canopy under Unstable Conditions

A method to estimate the sensible heat flux (H) for unstable atmospheric condition requiring measurements taken in half-hourly basis as input and involving the land surface temperature (LST), HLST, was tested over a tall and dense aspen stand. The method avoids the need to estimate the zero-plane displacement and the roughness length for momentum. The net radiation (Rn) and the latent heat flux (λE) dominated the surface energy balance (SEB). Therefore, λE was estimated applying the residual method using HLST as input, λER-LST. The sum of H and λE determined with the eddy covariance (EC) method led to a surface energy imbalance of 20% Rn. Thus, the reference taken for the comparisons were determined forcing the SEB using the EC Bowen ratio (BREB method). For clear sky days, HLST performed close to HBREB. Therefore, it showed potential in the framework of remote sensing because the input requirements are similar to current methods widely used. For cloudy days, HLST scattered HBREB and nearly matched the accumulated sensible hear flux. Regardless of the time basis and cloudiness, λER-LST was close to λEBREB. For all the data, both HLST and λER-LST were not biased and showed, respectively, a mean absolute relative error of 24.5% and 12.5% and an index of agreement of 68.5% and 80%.

Constant flux layers with gravitational settling: links to aerosols, fog and deposition velocities

Abstract. Turbulent boundary layer concepts of constant flux layers and surface roughness lengths are extended to include aerosols and the effects of gravitational settling. Interactions between aerosols and the Earth's surface are represented via a roughness length for aerosol which will generally be different from the roughness lengths for momentum, heat or water vapour. Gravitational settling will impact vertical profiles and the surface deposition of aerosols, including fog droplets. Simple profile solutions are possible in neutral and stably stratified atmospheric surface boundary layers. These profiles can be used to predict deposition velocities and to illustrate the dependence of deposition velocity on reference height, friction velocity and gravitational settling velocity.

Modelling the effect of BIPV window in the built environment: Uncertainty and sensitivity

BIPV (building-integrated photovoltaic) window has been proven as a promising technology to increase renewable energy and reduce environmental effects of the building. The effect of BIPV window in the built environment could change significantly with the window configuration, building materials, and urban landscape, which have a large variability within cities. In this study, we adopted a newly developed building energy model coupled with a single-layer urban canopy model (BEM-SLUCM) to characterize the uncertainties of BIPV window effect at the neighbourhood scale in a hot desert climate city, Phoenix, USA. Using an advanced Markov chain Monte Carlo algorithm, extensive simulations were conducted to quantify the sensitivity of extreme outdoor microclimate, building cooling load and renewable energy generation to various input parameters. Results show that the canyon aspect ratio, window coverage, and power generation efficiency are pivotal to maximize the electricity generation by BIPV window. Canyon air temperature and building cooling load are highly sensitive to momentum roughness length above canyon, thickness of building envelope, air conditioning setpoint temperature, and canyon aspect ratio. This indicates a strong dynamic interaction between building's indoor space and the surrounding canyon environment. In contrast, thermal and optical properties of BIPV window have negligible effects on the urban thermal environment. Findings in this study reveal key mechanisms that regulate the urban microclimate and building energy consumption, provide guidance for BIPV applications in the built environment, and shed new lights on the sustainable design of urban neighbourhoods.

Seasonality in aerodynamic resistance across a range of North American ecosystems

Surface roughness – a key control on land-atmosphere exchanges of heat and momentum – differs between dormant and growing seasons. However, how surface roughness shifts seasonally at fine time scales (e.g., days) in response to changing canopy conditions is not well understood. This study: (1) explores how aerodynamic resistance changes seasonally; (2) investigates what drives these seasonal shifts, including the role of vegetation phenology; and (3) quantifies the importance of including seasonal changes of aerodynamic resistance in “big leaf” models of sensible heat flux (H). We evaluated aerodynamic resistance and surface roughness lengths for momentum (z0m) and heat (z0h) using the kB−1 parameter (ln(z0m/z0h)). We used AmeriFlux data to obtain surface-roughness estimates, and PhenoCam greenness data for phenology. This analysis included 23 sites and ∼190 site years from deciduous broadleaf, evergreen needleleaf, woody savanna, cropland, grassland, and shrubland plant-functional types (PFTs). Results indicated clear seasonal patterns in aerodynamic resistance to sensible heat transfer (Rah). This seasonality tracked PhenoCam-derived start-of-season green-up transitions in PFTs displaying the most significant seasonal changes in canopy structure, with Rah decreasing near green-up transitions. Conversely, in woody savanna sites and evergreen needleleaf forests, patterns in Rah were not linked to green-up. Our findings highlight that decreases in kB−1 are an important control over Rah, explaining > 50% of seasonal variation in Rah across most sites. Decreases in kB−1 during green-up are likely caused by increasing z0h in response to higher leaf area index. Accounting for seasonal variation in kB−1 is key for predicting H as well; assuming kB−1 to be constant resulted in significant biases that also exhibited strong seasonal patterns. Overall, we found that aerodynamic resistance can be sensitive to phenology in ecosystems having strong seasonality in leaf area, and this linkage is critical for understanding land-atmosphere interactions at seasonal time scales.

Surface Heat and Moisture Exchange in the Marginal Ice Zone: Observations and a New Parameterization Scheme for Weather and Climate Models

AbstractAircraft observations from two Arctic field campaigns are used to characterize and model surface heat and moisture exchange over the marginal ice zone (MIZ). We show that the surface roughness lengths for heat and moisture over uninterrupted sea ice vary with roughness Reynolds number (; itself a function of the roughness length for momentum, , and surface wind stress), with a peak at the transition between aerodynamically smooth (&lt;0.135) and aerodynamically rough (&gt;2.5) regimes. A pre‐existing theoretical model based on surface‐renewal theory accurately reproduces this peak, in contrast to the simple parameterizations currently employed in two state‐of‐the‐art numerical weather prediction models, which are insensitive to . We propose a new, simple parameterization for surface exchange over the MIZ that blends this theoretical model for sea ice with surface exchange over water as a function of sea ice concentration. In offline tests, this new scheme performs much better than the existing schemes for the rough conditions observed during the ‘Iceland Greenland Seas Project’ field campaign. The bias in total turbulent heat flux across the MIZ is reduced to only 13 W m−2 for the new scheme, from 48 and 80 W m−2 for the Met Office Unified Model and ECMWF Integrated Forecast System schemes, respectively. It also performs marginally better for the comparatively smooth conditions observed during the ‘Aerosol‐Cloud Coupling and Climate Interactions in the Arctic’ field campaign. The new surface exchange scheme has the benefit of being physically‐motivated, comparatively accurate and straightforward to implement, although to reap the full benefits an improvement to the representation of sea ice topography via is required.

A Graphical Interpretation of the Rescaled Complementary Relationship for Evapotranspiration

AbstractWet‐surface evaporation equations related to the Penman equation can be represented graphically on vapor pressure (e) versus temperature (T) graphs (Qualls &amp; Crago, 2020, https://doi.org/10.1029/2019wr026766). Here, actual regional evaporation is represented graphically on (e, T) graphs using the Complementary Relationship (CR) between actual and apparent potential evaporation. The CR proposed by the authors can be represented in a simple and intuitive geometric form, in which lines representing the regional latent heat flux, LE, and the wet surface (Priestley &amp; Taylor, 1972, https://doi.org/10.1175/1520-0493(1972)100&lt;0081:otaosh&gt;2.3.co;2) evaporation rate, LEPT, intersect at e = 0. This approach allows a graphical estimate of LE (or the corresponding mathematical formulation), provided available energy, wind speed, air temperature and humidity, and roughness lengths for momentum and sensible heat are available. The wet surface temperature is needed, and a calculation method for it is provided. The formulation works well using monthly data from seven sites in Australia, even when the same value of the Priestley &amp; Taylor parameter α is used for all sites. Overall, compared to eddy covariance measurements, root mean square difference averaged 19 W m−2; this compares favorably with the CR formulation proposed by Brutsaert (2015, https://doi.org/10.1002/2015wr017720).

Determination of Vapor and Momentum Roughness Lengths Above an Undulating Soil Surface Based on PIV‐Measured Velocity Profiles

AbstractAccurately predicting bare‐soil evaporation requires the proper characterization of the near‐surface atmospheric conditions. These conditions, dependent on factors such as surface microtopography and wind velocity, vary greatly and therefore require high‐resolution datasets to be fully incorporated into evaporation models. These factors are oftentimes parameterized in models through the aerodynamic resistance (ra), in which the vapor roughness length (z0v) and the momentum roughness length (z0m) are two crucial parameters that describe the transport near the soil‐atmosphere interface. Typically, when evaluating bare‐soil evaporation, these two characteristic lengths are assumed equal, although differences are likely to occur especially in turbulent flows over undulating surfaces. Thus, this study aims to investigate the relationship between z0v and z0m above undulating surfaces to ultimately improve accuracy in estimating evaporation rate. To achieve this goal, four uniquely designed wind tunnel—soil tank experiments were conducted considering different wind speeds and undulation spacings. Particle image velocimetry (PIV) was used to measure the velocity field above the undulating surface in high resolution. Using the high‐fidelity data set, the logarithmic ratio of z0v to z0m is determined and used to estimate ra. Results confirm that these lengths differ significantly, with the logarithmic ratio roughly ranging from −15 to −5 under the conditions tested. PIV‐measured results demonstrate this ratio is closely tied to the mass and momentum transport behaviors influenced by surface undulations. Using the data‐integrated formulation of ra, predictions of evaporation rate were prepared for both the laboratory and lysimeter experiments, demonstrating the efficacy of the proposed approach in this study.

Replication Data for: Determination of vapor and momentum roughness lengths above an undulating soil surface based on PIV-measured velocity profiles

Replication Data for: Determination of vapor and momentum roughness lengths above an undulating soil surface based on PIV-measured velocity profiles

Estimation of evapotranspiration fluxes from Sal (Shorea robusta Gaertn.f) forest using METRIC model: case study of Doon Valley, India

The present study focusses on the estimation of ET using Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) model over the Sal (Shorea robusta Gaertn.f) forest in the subtropical Doon Valley, India for the dry periods of 2016–18. Parameterization of METRIC model was done for surface temperature (Ts), momentum roughness length (zom), and surface albedo (α) estimations to make it suitable for Forest ET assessment. Results showed good agreement between the daily ET derived from the METRIC model and observed ET by eddy covariance method at Barkot Flux Tower (BFT) site. Results of parameterized METRIC model showed improvement over non-parameterized model with higher coefficient of determination (0.81), Nash Sutcliffe Efficiency (0.71) and lower Root Mean Square Error (0.48 mm). Average ET for the Sal forest ranged from 1.18-4.78 mm/day. Monthly and seasonal ET was derived using cubic spline interpolation-based time integration of reference ET fraction (ETrF).

Comparison of momentum roughness lengths of the WRF-SWAN online coupling and WRF model in simulation of tropical cyclone Gonu

The surface enthalpy fluxes (latent and sensible heat fluxes) provide the necessary energy to intensify tropical cyclones (TCs). The surface momentum fluxes modify the intensity of TCs. Various parameters affect the surface fluxes. Drag and enthalpy exchange coefficients are known as parameters that lead to ambiguity in the surface fluxes. Thus, for simulating a TC, various drag and enthalpy exchange coefficients are tested in numerical simulations. Exchange coefficients directly relate to roughness lengths. The main goal of this study was comparing derived roughness lengths of the COAWST (WRF-SWAN online coupling) and WRF models with one another. The TC Gonu formed over the Arabian Sea in 2007 was selected for this study. Employing self-reliant WRF, it is found that track and intensity of the TC Gonu can be best simulated when Donelan parameterization is applied for momentum roughness length and Large-Pond parameterization for enthalpy roughness length. In the second section, simulations were conducted in the coupled mode using the COAWST model with the Large-Pond parameterization (for the enthalpy roughness length). Results cleared that the use of Oost parameterization leads to a high overestimation of simulated momentum roughness length compared with other parameterizations while both the Drennan and Taylor parameterizations were somewhat close to reality. Differences of simulated maximum 10-m wind speed between the Oost parameterization and other parameterizations were more than differences of their simulated minimum central pressure. These results proved that the momentum roughness length affects the maximum 10-m wind speed more significantly than the minimum central pressure. In the last section, a simulation was performed using the COAWST model with the Donelan–Large-Pond parameterization. In this simulation, only 10-m wind speed from the WRF model transferred to the SWAN model. The results showed that simulated wave heights in the open ocean were in good agreement with the results of other researchers. In general, the SWAN model performance is evaluated satisfactorily while the parameterizations using the wave information need to be more investigated.

The Effects of Ocean Surface Waves on Global Forecast in CFS Modeling System v2.0

Abstract. It has been well known that ocean surface gravity waves have enormous effects on physical processes at the atmosphere–ocean interface. However, the effects of surface waves on global forecast in several days are less studied. To investigate this, we incorporated the WAVEWATCH III model into the Climate Forecast System Model version 2.0 (CFS2.0), with the Chinese Community Coupler version 2.0 (C-Coupler2). Two major wave-related processes, the Langmuir mixing and the sea surface momentum roughness, were considered. Extensive comparisons were performed against in-situ buoys, satellite measurements and reanalysis data, to evaluate the influence of the two processes on the forecast of sea surface temperature, mixed layer depth, significant wave height, and 10-m wind speed. A series of 7-day simulations demonstrate that the newly developed atmosphere-ocean-wave coupling system could improve the CFS global forecast. The Langmuir mixing parameterization could increase the vertical movement of water and effectively reduce the warm bias of sea surface temperature and shallow bias of mixed layer depth in the Antarctic circumpolar current in austral summer, whereas the significant wave height and 10-m wind speed are insensitive to it. On the other hand, the modified momentum roughness length could significantly reduce the overestimated 10-m wind speed and significant wave height in mid-high latitudes. This is because the enhanced frictional dissipation at high wind speed could reduce 10-m wind speed and consequently decrease the significant wave height. But its effect on the temperature structure in upper ocean is less obvious.

Avaliação de alternativas para a parametrização dos comprimentos de rugosidade de quantidade de movimento e vapor d'água em lagos

An assessment of the performance of various parameterization alternatives for roughness lengths of momentum and water vapour was performed. The micrometereological data used in this work was measured in the Itaipu reservoir, Brazil. Four models was tested for momentum roughness length, and four for water vapour. The parameterization for horizontal momentum flux are based on the Charnock equation and generalizations while the water vapour model are based on equations proposed by Brutsaert. The four models for momentum flux produced very similar results, in terms of goodness of fit and errors, and turned out only weakly dependent on friction velocity. Already the parameterizations for water vapor produced more dispersed results, and the best parameterizations found very poorly depend on the Reynolds roughness number, or are independent of it. Both in the case of momentum and water vapour, the optimal parameter values? of each parameterization found for Itaipu are significantly larger than those reported in the literature.