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Chandran directed the BAO operation until 1982 when he moved to head the Atmospheric Studies Program at WPL. Graph Jagadish Chandran Kaimal, a prominent atmospheric scientist who made pivotal contributions to the study of turbulence in the Earth's boundary layer, died peacefully of natural causes at his home in Hamilton, New York, on 25 January 2021. Later, after Jim's return as a post-doctoral researcher, further work that Chandran strongly supported revealed the important influence that topographically-generated mesoscale flows had on the boundary-layer structure at the BAO. [Extracted from the article]

We review developments in the field of boundary-layer flow over complex topography, focussing on the period from 1970 to the present day. The review follows two parallel strands: the impact of hills on flow in the atmospheric boundary layer and gravity-driven flows on hill slopes initiated by heating or cooling of the surface. For each strand we consider the understanding that has resulted from analytic theory before moving to more realistic numerical computation, initially using turbulence closure models and, more recently, eddy-resolving schemes. Next we review the field experiments and the physical models that have contributed to present understanding in both strands. For the period 1970–2000 with hindsight we can link major advances in theory and modelling to the key papers that announced them, but for the last two decades we have cast the net wider to ensure that we have not missed steps that eventually will be seen as critical. Two important new themes are given prominence in the 2000–2020 period. The first is flow over hills covered with tall plant canopies. The presence of a canopy changes the flow in important ways both when the flow is nearly neutral and also when it is stably stratified, forming a link between our two main strands. The second is the use of eddy-resolving models as vehicles to bring together hill flows and gravity-driven flows in a unified description of complex terrain meteorology. [ABSTRACT FROM AUTHOR]

Summary: Limitations and utility of three measures of water use characteristics were evaluated: water use efficiency (WUE), intrinsic WUE and marginal water cost of carbon gain (∂E/∂A) estimated, respectively, as ratios of assimilation (A) to transpiration (E), of A to stomatal conductance (gs) and of sensitivities of E and A with variation in gs. Only the measure ∂E/∂A estimates water use strategy in a way that integrates carbon gain relative to water use under varying environmental conditions across scales from leaves to communities. This insight provides updated and simplified ways of estimating ∂E/∂A and adds depth to understanding ways that plants balance water expenditure against carbon gain, uniquely providing a mechanistic means of predicting water use characteristics under changing environmental scenarios. [ABSTRACT FROM AUTHOR]

Simple first-order closure remains an attractive way of formulating equations for complex canopy flows when the aim is to find analytic or simple numerical solutions to illustrate fundamental physical processes. Nevertheless, the limitations of such closures must be understood if the resulting models are to illuminate rather than mislead. We propose five conditions that first-order closures must satisfy, then test two widely used closures against them. The first is the eddy diffusivity based on a mixing length. We discuss the origins of this approach, its use in simple canopy flows and extensions to more complex flows. We find that it satisfies most of the conditions and, because the reasons for its failures are well understood, it is a reliable methodology. The second is the velocity-squared closure that relates shear stress to the square of mean velocity. Again we discuss the origins of this closure and show that it is based on incorrect physical principles and fails to satisfy any of the five conditions in complex canopy flows; consequently its use can lead to actively misleading conclusions. [ABSTRACT FROM AUTHOR]

We revisit the analytical model for atmospheric boundary-layer flow over a hill covered with a canopy of Finnigan and Belcher (Q J R Meteorol Soc 130:1-29, ). Remaining within the overall scope of that analysis we extend in two ways. First we include the impacts of the advection terms within the upper canopy in a simple, but approximate, manner. Second we establish a modification for the associated pressure perturbation. Both extensions allow us to extend the parameter range wherein the analytical framework can be expected to reasonably hold. The within-canopy advection terms act to provide a downstream shift, and decreased magnitude, to the flow perturbations within the canopy as compared to the predictions from the original analysis. Through continuity, similar, but smaller, impacts are seen above the canopy. Together these act to reduce the differences in the streamwise positions of the topographic speed-up seen above and within the canopy. The modified pressure perturbation also acts to decrease the magnitude of the flow perturbations. The predicted topographic influence on the flow is reduced from that given in the original analysis but, importantly, the positions where the topographic influences most strongly affect the flow, and by extension the scalar concentration fields, are also changed. Predictions from the revised analysis are shown to be in good agreement with wind-tunnel data for flow over an isolated narrow ridge covered by a partially dense canopy. [ABSTRACT FROM AUTHOR]

Measurements of turbulence structure in a wind-tunnel model canopy of bluff elements show many of the features associated with vegetation canopies and roughness sublayers but also display features more characteristic of the inertial sublayer (ISL). Points of similarity include the existence of an inflexion point in the space-time averaged streamwise velocity at the canopy top, the variation with height of turbulent second moments and the departure of the turbulent kinetic energy budget from local equilibrium in and just above the canopy. Quadrant analysis shows characteristic dominance of sweep over ejection events within the canopy although sweeps are more frequent than usually seen in vegetation canopies. Points of difference are a u′, w′ correlation coefficient that is closer to the ISL value than to most canopy data, and a turbulent Prandtl number midway between canopy and ISL values. Within the canopy there is distinct spatial partitioning into two flow regimes, the wake and non-wake regions. Both time-mean and conditional statistics take different values in these different regions of the canopy flow. We explain many of these features by appealing to a modified version of the mixing-layer hypothesis that links the dominant turbulent eddies to the instability of the inflexion point at canopy top. However, it is evident that these eddies are perturbed by the quasi-coherent wakes of the bluff canopy elements. Based upon an equation for the instantaneous velocity perturbation, we propose a criterion for deciding when the eddies linked to the inflexion point will dominate flow structure and when that structure will be replaced by an array of superimposed element wakes. In particular, we show that the resemblance of some features of the flow to the ISL does not mean that ISL dynamics operate within bluff-body canopies in any sense. [ABSTRACT FROM AUTHOR]

An understanding of how topography, including that covered by a plant canopy, influences the flow and turbulence is important in many meteorological and micrometeorological applications. We revisit the framework of Finnigan and Belcher (Q J Roy Meteorol Soc 130:1–29, 2004) for neutral flow over sinusoidal two-dimensional topography covered by a canopy and present a minor modification that enables a formal match between the forms for the flow within and above the canopy, including within the deep canopy. The modification then allows the easy extension of the framework to generalised two-dimensional topography. The revised framework affirms the conclusions of Finnigan and Belcher (op.cit.); above the canopy the flow perturbations are maximised near to where the perturbation pressure is a minimum, whereas deep within the canopy the flow perturbations are maximised when the streamwise gradient of the perturbation pressure is largest. However, the extension to general topography strongly illustrates that it is the pressure perturbation, not the hill shape directly, that controls the magnitude and location of the topographic impacts on the flow. For isolated ridges with a plateau, the flow perturbations above the canopy maximise, not at the ridge crest, but where the hill curvature is largest. Multiple recirculation regions can also exist within the canopy, as determined by the streamwise gradient of the pressure perturbation. These results indicate that knowledge of the terrain over a larger area than hither-to-thought is required to assess whether the use of micrometeorological techniques is appropriate at individual sites. [ABSTRACT FROM AUTHOR]

The mean flow and scalar concentration profiles within and above a tall canopy are well known to violate the standard boundary-layer flux-gradient relationships. We present a theory for the scalar concentration profile that is comprised of a canopy exchange model coupled to a modified surface-layer model. The coupling between the two components and the modifications to the surface-layer profiles are formulated through the mixing-layer analogy for the flow at canopy top. This analogy provides an additional length scale—the vorticity thickness—upon which the profiles depend and a set of criteria that allows a reduction in the empiricism associated with earlier forms in the literature. Predictions of the mean scalar concentration profiles are shown to match observations over a wide range of diabatic stabilities for both potential temperature and water vapour. [ABSTRACT FROM AUTHOR]

The mean flow profile within and above a tall canopy is well known to violate the standard boundary-layer flux–gradient relationships. Here we present a theory for the flow profile that is comprised of a canopy model coupled to a modified surface-layer model. The coupling between the two components and the modifications to the surface-layer profiles are formulated through the mixing layer analogy for the flow at a canopy top. This analogy provides an additional length scale—the vorticity thickness—upon which the flow just above the canopy, within the so-called roughness sublayer, depends. A natural form for the vertical profiles within the roughness sublayer follows that overcomes problems with many earlier forms in the literature. Predictions of the mean flow profiles are shown to match observations over a range of canopy types and stabilities. The unified theory predicts that key parameters, such as the displacement height and roughness length, have a significant dependence on the boundary-layer stability. Assuming one of these parameters a priori leads to the incorrect variation with stability of the others and incorrect predictions of the mean wind speed profile. The roughness sublayer has a greater impact on the mean wind speed in stable than unstable conditions. The presence of a roughness sublayer also allows the surface to exert a greater drag on the boundary layer for an equivalent value of the near-surface wind speed than would otherwise occur. This characteristic would alter predictions of the evolution of the boundary layer and surface states if included within numerical weather prediction models. [ABSTRACT FROM AUTHOR]

Abstract: Formal derivation of the storage term in eddy flux estimates of surface exchange shows that it is just the difference between instantaneous concentration profiles at the tower measured at the beginning and end of the averaging period, T, divided by T. As such, the storage term is likely to be a poorer estimate of the true concentration change in a representative volume around the tower than the time-averaged eddy flux is of exchange from the surface patch. This is because instantaneous profiles are easily biased by a single gust. To avoid this, many workers compute the storage from time-averaged concentration profiles centered on the beginning and the end of the averaging period. Here we show that this procedure underestimates the storage by at least 50% in most conditions with larger errors occurring when the integral time scale of the turbulence is much smaller than the averaging time T. Reducing the averaging time to the minimum required to smooth out the influence of individual gusts does not improve things significantly. [Copyright &y& Elsevier]

Abstract: The use of footprint functions in complex flows has been questioned because of anomalous behaviour reported in recent model studies. We show that the concentration footprint can be identified with the Green''s function of the scalar concentration equation or the transition probability of a Lagrangian formulation of the same equation and so is well behaved and bounded by 0 and 1 in both simple and complex flows. The flux footprint in contrast is not a Green''s function but a functional of the concentration footprint and is not guaranteed to be similarly well behaved. We show that in simple, homogeneous shear flows, the flux footprint, defined as the vertical eddy flux induced by a unit point source, is bounded by 0 and 1 but that this is not true in more general flow fields. Analysis of recent model studies also shows that the negative flux footprints reported in homogeneous plant canopy flows are an artefact of reducing a canopy with a complex source–sink distribution in the vertical to a single layer but that in canopies on hilly topography, the problems are more fundamental. Finally we compare footprint inversion with the direct mass-balance method of measuring surface exchange. We conclude first that the flux footprint is an appropriate measure of the area influencing both eddy and advective fluxes on a tower but that the concentration footprint is the correct measure when the storage term is important. Second, we deduce that there are serious obstacles to inverting flux footprints in complex terrain. [Copyright &y& Elsevier]

To assess annual budgets of CO2 exchange between the biosphere and atmosphere over representative ecosystems, long-term measurements must be made over ecosystems that do not exist on ideal terrain. How to interpret eddy covariance measurements correctly remains a major task. At present, net ecosystem CO2 exchange is assessed, by members of the micrometeorological community, as the sum of eddy covariance measurements and the storage of CO2 in the underlying air. This approach, however, seems unsatisfactory as numerous investigators are reporting that it may be causing nocturnal respiration flux densities to be underestimated. A new theory was recently published by Lee (1998, Agricultural and Forest Meteorology 91: 39–50) for assessing net ecosystem-atmosphere CO2 exchange (Ne) over non-ideal terrain. It includes a vertical advection term. We apply this equation over a temperate broadleaved forest growing in undulating terrain. Inclusion of the vertical advection term yields hourly, daily and annual sums of net ecosystem CO2 exchange that are more ecologically correct during the growing season. During the winter dormant period, on the other hand, corrected CO2 flux density measurements of an actively respiring forest were near zero. This observation is unrealistic compared to chamber measurements and model calculations. Only during midday, when the atmosphere is well-mixed, do measurements of Ne match estimates based on model calculations and chamber measurements. On an annual basis, sums of Ne without the advection correction were 40% too large, as compared with computations derived from a validated and process-based model. With the inclusion of the advection correction term, we observe convergence between measured and calculated values of Ne on hourly, daily and yearly time scales. We cannot, however, conclude that inclusion of a one-dimensional, vertical advection term into the continuity equation is sufficient for evaluating CO2 exchange over tall forests in complex terrain. There is an indication that the neglected term, ū}(∂ c/∂ x), is non-zero and that CO2 may be leaking from the sides of the control volume during the winter. In this circumstance, forest floor CO2 efflux densities exceed effluxes measured above the canopy. [ABSTRACT FROM AUTHOR]

Describes a study which investigated the single-point statistics of turbulence in the roughness sub-layer occupied by a plant canopy. Analysis framework and flow equations; Description of coherent structures that dominate turbulence in the canopy; Details of a heuristic model for canopy flow.

• Eastern Amazon rainforest canopy is partially to wholly wet for 66% of the time. • Dew accounts for 50% of canopy wetness in the dry season and 40% in the wet season. • The upper canopy is wet for a longer duration than the lower canopy. • A meteorological data-based physical model captures 48% of the variance in canopy wetness. • A beta regression captures 55% of the variance in canopy wetness. Canopy wetness is a common condition that influences photosynthesis, the leaching or uptake of solutes, the water status and energy balance of canopies, and the interpretation of eddy covariance and remote sensing data. While often treated as a binary variable, 'wet' or 'dry', forest canopies are often partially wet, requiring the use of a continuous description of wetness. Minor precipitation events such as dew, that wet a fraction of the canopy, have been found to contribute to dry season foliar water uptake in the Eastern Amazon, and are fundamentally important to the canopy energy balance. However, few studies have reported the spatial and temporal distribution of canopy wetness, or the relative contribution of dew to leaf wetness, for forest ecosystems. In this study, we use two canopy profiles of leaf wetness sensors, coupled with meteorological data, to address fundamental questions about spatial and temporal variation of leaf wetness in an Eastern Amazonian rainforest. We also investigate how well meteorological tower data can predict canopy wetness using two models, one empirical and one that is physically-based. The results show that the canopy is 100% dry only for 34% of the time, otherwise being between 5% and 100% wet. Dew accounts for 20% or 43% of total annual leaf wetness, and 36% or 50% of canopy wetness in dry season, excluding or including dew events that co-occur with rain, respectively. Wetness duration was higher at the top than bottom of the canopy, mainly because of rain events, whilst dew formation was strongly dependent on the local canopy structure and varied horizontally through the canopy. The best empirical model accounted for 55% of the variance in canopy wetness, while the physical model accounted for 48% of the variance. We discuss future modelling improvements of the physical model to increase its predictive capacity. [ABSTRACT FROM AUTHOR]

Success in scaling the very stable boundary layer has been mixed. One possible reason for this is that wave-turbulence interaction can result in significant energy coupling between turbulence within the planetary boundary layer and the mean flow outside the PBL. Three regimes are described where wave-turbulence interaction forms a significant part of the dynamics. In the first, energy and momentum flows are confined within the PBL and do not preclude local scaling. In the other two, which involve topographically forced waves and propagating waves respectively, energy/momentum transfers across the PBL make success in local scaling unlikely. [ABSTRACT FROM AUTHOR]

An existing second-order closure model is modified to include the effects on mean and turbulent motions of form and viscous drag in vegetative canopies. The additional physical mechanisms represented by the closure are viscous and pressure drag on canopy elements, their role in momentum absorption, in the creation of fine scale turbulent eddies and in enhancing the total viscous dissipation in the canopy airspace. Viscous dissipation is split into a standard ’isotropic‘ contribution associated with the spectral eddy cascade and a foliage contribution associated with work against pressure and viscous drag on the foliage. Changes in the turbulent time scale that result from these mechanisms are included in the standard parameterisations of third moments and of the eddy cascade contribution to dissipation. The model is tested against a wind- tunnel ’wheat‘ canopy, a corn canopy and a eucalypt canopy, a height range from 50 mm to 12.6 m. Model results show that the parameterisations of foliage interaction used in the closure are sufficiently robust to reproduce second-moment profiles within and above vegetative canopies to a high degree of accuracy without resorting to ’tuning‘ of the model constants. The model also shows the natural emergence of two length scales, one associated with the familiar eddy cascade isotropic contribution to total dissipation and the other associated with the length scales of the canopy elements. [ABSTRACT FROM AUTHOR]

Turbulent flow over urban-like roughness has been numerically studied for various purposes, such as the clarification of turbulent characteristics over rough walls, visualization of turbulent structures around block arrays, and evaluation of urban ventilation and pedestrian winds. In such simulations, a portion of the developing boundary layer is extracted as a numerical domain, assuming periodic boundary conditions in the horizontal direction to reproduce laterally homogeneous rough surfaces. However, the conditions required to drive the airflow by an artificial momentum source uniquely determine the turbulent statistics, which are different from those in developing boundary layers. Therefore, this study presents a new approach for driving the airflow over urban-like block arrays. The new method is based on spatially averaged Navier–Stokes equations to prove the necessity of height-dependent momentum provision. The turbulent flow over a cubical-block array is determined using large-eddy simulations driven by four different momentum sources. Regardless of the driving force, the vertical profiles of the streamwise velocity components are identical. In contrast, slight differences in the vertical Reynolds stress, variances in the velocity components, and turbulence kinetic energy are appropriately reproduced in the new approach. In addition, the budget equations of the turbulent statistics reveal that a change in the vertical Reynolds stress affects the energy production and its redistribution into variance components. The proposed method can contribute to the reproduction of a realistic turbulent flow and provide a theoretical understanding of the momentum provision. [ABSTRACT FROM AUTHOR]

The spatial variability of the mean flow and turbulence in and above a model canopy is investigated using three-dimensional laser Doppler velocimetry. The mean flow and turbulence are shown to be highly variable in space within the canopy but rapidly converge above the canopy. The coherent variations in the mean flow generate dispersive fluxes contributing almost a fifth to the total flux of momentum, and a greater contribution to the divergence of the flux, within the canopy. The higher-order turbulent statistics are more variable than the mean flow and often strongly correlated in space to variations in the mean flow. The implications of this microscale spatial variability for both field experiments and other laboratory experiments into canopy flow are discussed. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article regarding the relationship of food security to effective distribution and production.

This paper introduces the design of the CSIRO variant of the Global Trade and Environment model (GTEM-C). GTEM-C is a hybrid model that combines the top-down macroeconomic representation of a computable general equilibrium model with the bottom-up engineering details of energy production. The model features detailed accounting for global energy flows that are embedded in traded energy goods, and it offers a unified framework to analyse the energy-carbon-environment nexus. As an illustrative example, we present simulation results on global energy transformation under the Intergovernmental Panel on Climate Change’s representative carbon pathways 4.5 and 8.5. By testing the model’s sensitivity to the relevant parameter, we find that the pace of electrification will significantly contain the spiking of carbon prices because electricity can be produced from carbon-free or less carbon-intensive technologies. The decoupling of energy use and carbon footprint, due to the uptake of clean electricity technologies, such as nuclear, wind, solar, and carbon capture and storage, allows the world to maintain high level of energy consumption, which is essential to economic growth. [ABSTRACT FROM AUTHOR]

Forest canopies are important components of the terrestrial carbon budget, which has motivated a worldwide effort, FLUXNET, to measure CO2 exchange between forests and the atmosphere. These measurements are difficult to interpret and to scale up to estimate exchange across a landscape. Here we review the effects of complex terrain on the mean flow, turbulence, and scalar exchange in canopy flows, as exemplified by adjustment to forest edges and hills, including the effects of stable stratification. We focus on the fundamental fluid mechanics, in which developments in theory, measurements, and modeling, particularly through large-eddy simulation, are identifying important processes and providing scaling arguments. These developments set the stage for the development of predictive models that can be used in combination with measurements to estimate exchange at the landscape scale. [ABSTRACT FROM AUTHOR]

Abstract: Turbulence within open canopies is shown to undergo a dramatic change in character during the transition from convective to stable conditions. In convective conditions the flow within the canopy is coupled through turbulent exchange to the flow aloft. As the transition proceeds, the within- and above-canopy flows decouple and vertically coherent waves form within the canopy. The intensity of above-canopy turbulence is not a good indicator of flow decoupling. Within-canopy waves can lead to large random error in the measurement of the change of storage and the advection terms in the mass balance equation. More importantly, errors associated with sampling over incomplete wave cycles will inevitably be combined with true advective flux divergences at non-ideal sites. Quantitative estimates of likely errors on storage of heat and CO2 within the canopy are presented. [Copyright &y& Elsevier]

No Abstract available. [ABSTRACT FROM AUTHOR]

• Single-layer canopy parameterizations in land surface models may be insufficient. • Simulations with a one-layer canopy are degraded compared to a multilayer model. • Results differ because of within-canopy temperature and wind speed profiles. • Single-layer canopies cannot capture gradients of leaf water potential. • Additional resolution over 5–10 layers gives little change in model performance. The land surface models that provide surface fluxes of energy and mass to the atmosphere in weather forecast and climate models typically represent plant canopies as a homogenous single layer of phytomass without vertical structure (commonly referred to as a big leaf). This modeling paradigm harkens back to a 30–40-year-old debate about whether big-leaf models adequately simulate fluxes for vegetated surfaces compared to more complex and computationally costly multilayer canopy models. This article revisits that scientific debate. We review the early literature to place our findings in context and discuss recent advancements in roughness sublayer theory, observations of canopy structure and leaf traits, and computational methods that facilitate the use of multilayer models. Using a model with variable vertical resolution, we compare a multilayer canopy representation with the equivalent one-layer canopy to ask how well the one-layer canopy replicates the multilayer benchmark and to identify why differences occur. Comparisons with flux tower measurements at several forest sites spanning multiple years show that sensible heat flux, latent heat flux, gross primary production, and friction velocity for the one-layer canopy degrade in comparison to the benchmark multilayer canopy. For the forest sites considered, 5–10 canopy layers sufficiently reproduce the observed fluxes. Vertical variation of within-canopy air temperature, specific humidity, and wind speed in the multilayer canopy alters fluxes compared with the one-layer canopy. The vertical profile of leaf water potential, in which the upper canopy is water-stressed on dry soils, also causes differences between the one-layer and multilayer canopies. The differences between one-layer and multilayer canopies suggest that the land surface modeling community should revisit the big-leaf surface flux parameterizations used in models. [ABSTRACT FROM AUTHOR]

Highlights • The agent-based model was created using the basic knowledge of gust, wind, and tree. • The Agent-based model demonstrated wind damage similar to the observed damage in forests. • The model described damage propagation and forest edge effects. • The model showed some phenomena, which were similar to the previous research. • Possibilities of improving the agent-based model were discusses. Abstract Powerful storms, consisting of strong gusts and winds, damage forests. Therefore, foresters need forest management strategies to reduce the damage risk. This paper focused on the damage patterns within the forest as the final results of multiple tree-wind dynamic interactions in time and space during a storm. Recent developments in computer technology allow for the possibility of simulating the complex and dynamic phenomena of damage during a storm but are extremely time consuming. To simplify the simulations without losing the crucial aspects of wind damage in forests, we introduced a computer simulation model using the agent-based modelling (ABM) technique, which capture the phenomena and interactions of individuals called 'agents'. We created an ABM for forest wind damage simulation, coupling together an accepted understanding of wind gusts in forests, tree bending moments, and damage propagation. The model was tested with variations in three conditions: trees acclimated and unacclimated to their wind environment; three levels of gust strength; and three tree planting densities. The ABM was able to replicate damage patterns and demonstrate damage propagation within the forest and the effects of forest edges. The difference in the rate of damage in the forest between acclimated and unacclimated edges became similar with an increase in the gust intensity, and a decrease in tree density through a reduction in the shelter effect of the forest. The ABM could be improved in the future by parametrizing the variation in individual tree resistance, and the variation in gust and wind strength, as well as adding more information on local environmental conditions such as topography and soil variation, and storm characteristics such as duration and intensity. [ABSTRACT FROM AUTHOR]

Land surface models used in climate models neglect the roughness sublayer and parameterize within-canopy turbulence in an ad hoc manner. We implemented a roughness sublayer turbulence parameterization in a multilayer canopy model (CLM-ml v0) to test if this theory provides a tractable parameterization extending from the ground through the canopy and the roughness sublayer. We compared the canopy model with the Community Land Model (CLM4.5) at seven forest, two grassland, and three cropland AmeriFlux sites over a range of canopy heights, leaf area indexes, and climates. CLM4.5 has pronounced biases during summer months at forest sites in midday latent heat flux, sensible heat flux, gross primary production, nighttime friction velocity, and the radiative temperature diurnal range. The new canopy model reduces these biases by introducing new physics. Advances in modeling stomatal conductance and canopy physiology beyond what is in CLM4.5 substantially improve model performance at the forest sites. The signature of the roughness sublayer is most evident in nighttime friction velocity and the diurnal cycle of radiative temperature, but is also seen in sensible heat flux. Withincanopy temperature profiles are markedly different compared with profiles obtained using Monin-Obukhov similarity theory, and the roughness sublayer produces cooler daytime and warmer nighttime temperatures. The herbaceous sites also show model improvements, but the improvements are related less systematically to the roughness sublayer parameterization in these canopies. The multilayer canopy with the roughness sublayer turbulence improves simulations compared with CLM4.5 while also advancing the theoretical basis for surface flux parameterizations. [ABSTRACT FROM AUTHOR]

Land surface models used in climate models neglect the roughness sublayer and parameterize within-canopy turbulence in an ad hoc manner. We implemented a roughness sublayer turbulence parameterization in a multi-layer canopy model (CLM-ml v0) test if this theory provides a tractable parameterization extending from the ground through the canopy and the roughness sublayer. We compared the canopy model with the Community Land Model (CLM4.5) at 7 forest, 2 grassland, and 3 cropland AmeriFlux sites over a range of canopy height, leaf area index, and climate. The CLM4.5 has pronounced biases during summer months at forest sites in mid-day latent heat flux, sensible heat flux, and gross primary production, nighttime friction velocity, and the radiative temperature diurnal range. The new canopy model reduces these biases by introducing new physics. The signature of the roughness sublayer is most evident in sensible heat flux, friction velocity, and the diurnal cycle of radiative temperature. Within-canopy temperature profiles are markedly different compared with profiles obtained using Monin-Obukhov similarity theory, and the roughness sublayer produces cooler daytime and warmer nighttime temperatures. The herbaceous sites also show model improvements, but the improvements are related less systematically to the roughness sublayer parameterization in these short canopies. The multi-layer canopy with the roughness sublayer turbulence improves simulations compared with the CLM4.5 while also advancing the theoretical basis for surface flux parameterizations. [ABSTRACT FROM AUTHOR]

Landscape discontinuities such as forest edges play an important role in determining the characteristics of the atmospheric flow by generating increased turbulence and triggering the formation of coherent tree-scale structures. In a fragmented landscape, consisting of surfaces of different heights and roughness, the multiplicity of edges may lead to complex patterns of flow and turbulence that are potentially difficult to predict. Here, we investigate the effects of different levels of forest fragmentation on the airflow. Five gap spacings (of length approximately 5 h, 10 h, 15 h, 20 h, 30 h, where h is the canopy height) between forest blocks of length 8.7 h, as well as a reference case consisting of a continuous forest after a single edge, were investigated in a wind tunnel. The results reveal a consistent pattern downstream from the first edge of each simulated case, with the streamwise velocity component at tree top increasing and turbulent kinetic energy decreasing as gap size increases, but with overshoots in shear stress and turbulent kinetic energy observed at the forest edges. As the gap spacing increases, the flow appears to change monotonically from a flow over a single edge to a flow over isolated forest blocks. The apparent roughness of the different fragmented configurations also decreases with increasing gap size. No overall enhancement of turbulence is observed at any particular level of fragmentation. [ABSTRACT FROM AUTHOR]

Losses at every stage in the food system influence the extent to which nutritional requirements of a growing global population can be sustainably met. Inefficiencies and losses in agricultural production and consumer behaviour all play a role. This paper aims to understand better the magnitude of different losses and to provide insights into how these influence overall food system efficiency. We take a systems view from primary production of agricultural biomass through to human food requirements and consumption. Quantities and losses over ten stages are calculated and compared in terms of dry mass, wet mass, protein and energy. The comparison reveals significant differences between these measurements, and the potential for wet mass figures used in previous studies to be misleading. The results suggest that due to cumulative losses, the proportion of global agricultural dry biomass consumed as food is just 6% (9.0% for energy and 7.6% for protein), and 24.8% of harvest biomass (31.9% for energy and 27.8% for protein). The highest rates of loss are associated with livestock production, although the largest absolute losses of biomass occur prior to harvest. Losses of harvested crops were also found to be substantial, with 44.0% of crop dry matter (36.9% of energy and 50.1% of protein) lost prior to human consumption. If human over-consumption, defined as food consumption in excess of nutritional requirements, is included as an additional inefficiency, 48.4% of harvested crops were found to be lost (53.2% of energy and 42.3% of protein). Over-eating was found to be at least as large a contributor to food system losses as consumer food waste. The findings suggest that influencing consumer behaviour, e.g. to eat less animal products, or to reduce per capita consumption closer to nutrient requirements, offer substantial potential to improve food security for the rising global population in a sustainable manner. [ABSTRACT FROM AUTHOR]

We study changes in crop cover under future climate and socio-economic projections. This study is not only organised around the global and regional adaptation or vulnerability to climate change but also includes the influence of projected changes in socio-economic, technological and biophysical drivers, especially regional gross domestic product. The climatic data are obtained from simulations of RCP4.5 and 8.5 by four global circulation models/earth system models from 2000 to 2100. We use Random Forest, an empirical statistical model, to project the future crop cover. Our results show that, at the global scale, increases and decreases in crop cover cancel each other out. Crop cover in the Northern Hemisphere is projected to be impacted more by future climate than the in Southern Hemisphere because of the disparity in the warming rate and precipitation patterns between the two Hemispheres. We found that crop cover in temperate regions is projected to decrease more than in tropical regions. We identified regions of concern and opportunities for climate change adaptation and investment. [ABSTRACT FROM AUTHOR]

Large-eddy simulation of atmospheric boundary layers interacting with a coupled and resolved plant canopy reveals the influence of atmospheric stability variations from neutral to free convection on canopy turbulence. The design and implementation of a new multilevel canopy model is presented. Instantaneous fields from the simulations show that organized motions on the scale of the atmospheric boundary layer (ABL) depth bring high momentum down to canopy top, locally modulating the vertical shear of the horizontal wind. The evolution of these ABL-scale structures with increasing instability and their impact on vertical profiles of turbulence moments and integral length scales within and above the canopy are discussed. Linkages between atmospheric turbulence and biological control impact horizontal scalar source distributions. Decreasing spatial correlation between momentum and scalar fluxes with increasing instability results from ABL-scale structures spatially segregating momentum and scalar exchange at canopy top. In combination, these results suggest the need for roughness sublayer parameterizations to incorporate an additional length or time scale reflecting the influence of ABL-scale organized motions. [ABSTRACT FROM AUTHOR]

Only a minority of those exposed to human papillomavirus (HPV) develop HPV-related cervical and oropharyngeal cancer. Because host immunity affects infection and progression to cancer, we tested the hypothesis that genetic variation in immune-related genes is a determinant of susceptibility to oropharyngeal cancer and other HPV-associated cancers by performing a multitier integrative computational analysis with oropharyngeal cancer data from a head and neck cancer genome-wide association study (GWAS). Independent analyses, including single-gene, gene-interconnectivity, protein-protein interaction, gene expression, and pathway analysis, identified immune genes and pathways significantly associated with oropharyngeal cancer. TGFβR1, which intersected all tiers of analysis and thus selected for validation, replicated significantly in the head and neck cancer GWAS limited to HPV-seropositive cases and an independent cervical cancer GWAS. The TGFβR1 containing p38-MAPK pathway was significantly associated with oropharyngeal cancer and cervical cancer, and TGFβR1 was overexpressed in oropharyngeal cancer, cervical cancer, and HPV+ head and neck cancer tumors. These concordant analyses implicate TGFβR1 signaling as a process dysregulated across HPV-related cancers. This study demonstrates that genetic variation in immune-related genes is associated with susceptibility to oropharyngeal cancer and implicates TGFβR1/TGFβ signaling in the development of both oropharyngeal cancer and cervical cancer. Better understanding of the immunogenetic basis of susceptibility to HPV-associated cancers may provide insight into host/virus interactions and immune processes dysregulated in the minority of HPV-exposed individuals who progress to cancer. [ABSTRACT FROM AUTHOR]

Using an incomplete third-order cumulant expansion method (ICEM) and standard second-order closure principles, we show that the imbalance in the stress contribution of sweeps and ejections to momentum transfer (Δ S o ) can be predicted from measured profiles of the Reynolds stress and the longitudinal velocity standard deviation for different boundary-layer regions. The ICEM approximation is independently verified using flume data, atmospheric surface layer measurements above grass and ice-sheet surfaces, and within the canopy sublayer of maturing Loblolly pine and alpine hardwood forests. The model skill for discriminating whether sweeps or ejections dominate momentum transfer (e.g. the sign of Δ S o ) agrees well with wind-tunnel measurements in the outer and surface layers, and flume measurements within the canopy sublayer for both sparse and dense vegetation. The broader impact of this work is that the “genesis” of the imbalance in Δ S o is primarily governed by how boundary conditions impact first and second moments. [ABSTRACT FROM AUTHOR]