Gabriel Katul
Duke University, Nicholas School of the Environment, Faculty Member
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Causality and Persistence in Ecological Systems: A Nonparametric Spectral Granger Causality Approach,
Research Interests: Environmental Engineering, Civil Engineering, Stochastic Process, Water resources, Applied Economics, and 11 moreWater Cycle, Seasonality, Probability Distribution & Applications, Eddy Covariance, Soil moisture, Evapotranspiration, Tropical rainforest, Tropical rain forest, Probability Density Function, Global Climate Model, and Soil moisture content
The existence of a "-1" power-law scaling at low wavenumbers in the longitudinal velocity spectrum of wall-bounded turbulence was explained by multiple mechanisms; however, experimental support has not been uniform across... more
The existence of a "-1" power-law scaling at low wavenumbers in the longitudinal velocity spectrum of wall-bounded turbulence was explained by multiple mechanisms; however, experimental support has not been uniform across laboratory studies. This letter shows that Heisenberg's eddy viscosity approach can provide a theoretical framework that bridges these multiple mechanisms and explains the elusiveness of the "-1" power law in some experiments. Novel theoretical outcomes are conjectured about the role of intermittency and very-large scale motions in modifying the k⁻¹ scaling.
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Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying underlying frequencies in nonstationary and gap-infested time series, such as eddy-covariance-measured net ecosystem exchange of CO2 (NEE).... more
Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying underlying frequencies in nonstationary and gap-infested time series, such as eddy-covariance-measured net ecosystem exchange of CO2 (NEE). We employed OWT to analyze the frequency characteristics of synchronously measured and modeled NEE at adjacent pine (PP) and hardwood (HW) ecosystems. Wavelet cospectral analysis showed that NEE at PP was more correlated to light and vapor pressure deficit at the daily time scale, and NEE at HW was more correlated to leaf area index (LAI) and temperature, especially soil temperature, at seasonal time scales. Models were required to disentangle the impacts of environmental drivers on the components of NEE, ecosystem carbon assimilation (Ac) and ecosystem respiration (RE). Sensitivity analyses revealed that using air temperature rather than soil temperature in RE models improved the modeled wavelet spectral frequency response on time scales longer tha...
Research Interests: Soil, Water, Time Series, Carbon Dioxide, Plant Biology, and 24 moreEcology, Wavelet Analysis, Seasonality, Tree Physiology, Eddy Covariance, Soil moisture, Wavelet Transform, Temperature, Net Ecosystem Exchange, Tree, Trees, Leaf Area Index, Water Use, Soil Temperature, Forestry Sciences, Ecosystem, Air Temperature, Spectrum analysis, Pinus Taeda, Frequency Response, Vapor Pressure Deficit, Plant Leaves, Light Attenuation, and Model Simplification
Research Interests: Environmental Engineering, Civil Engineering, Atmospheric Science, Turbulence, Boundary Layer Meteorology, and 11 moreTime Series, Water resources, Carbon Dioxide, Applied Economics, Atmospheric sciences, Sampling methods, Evapotranspiration, Greenhouse gases, Ozone, Southern California, and Water Vapor
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A scanning water Raman-lidar, designed and constructed to study surface-atmosphere processes with high spatial and temporal resolution is described. It is shown that the lidar is able to measure the absolute water content and then... more
A scanning water Raman-lidar, designed and constructed to study surface-atmosphere processes with high spatial and temporal resolution is described. It is shown that the lidar is able to measure the absolute water content and then calculate evaporative fluxes and other atmospheric parameters quickly over relatively large areas. This capability provides new opportunities for the study of microscale atmospheric processes. Examples
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Over the past three decades, a number of field experiments have suggested that land-cover heterogeneity (LCH) impacts Monin and Obukhov (M–O) scaling, when applied to second-order statistics of temperature (T), water vapor (q), and CO2... more
Over the past three decades, a number of field experiments have suggested that land-cover heterogeneity (LCH) impacts Monin and Obukhov (M–O) scaling, when applied to second-order statistics of temperature (T), water vapor (q), and CO2 (c) fluctuations. To further explore how LCH modifies M–O scaling for second-order statistics, 2 years of atmospheric surface layer (ASL) measurements, conducted above a Mediterranean
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The space-time statistical structure of soil water uptake by oak trees was investigated in a 3.1-m-diameter closed top chamber using a three-dimensional measurement grid of soil moisture and pressure, and measurements of tree... more
The space-time statistical structure of soil water uptake by oak trees was investigated in a 3.1-m-diameter closed top chamber using a three-dimensional measurement grid of soil moisture and pressure, and measurements of tree transpiration. Using the time domain reflectometry (TDR) measured moisture content, resistance block measured soil water pressure, and a compact constant head permeameter measured saturated hydraulic conductivity, the
Research Interests: Environmental Engineering, Civil Engineering, Stochastic Process, Plant Ecology, Monte Carlo Simulation, and 18 moreWater resources, Spatial Statistics, Applied Economics, Soil moisture, Field Experiment, Space Time, First-Order Logic, Coefficient of Variation, Oak, Spatial Variability, Soil Hydraulic Properties, Taylor Series, Statistical Properties, Moisture Content, Three Dimensional, Time Domain Reflectometry, Soil Water, and Unsaturated Zone
Among the fundamental problems in canopy turbulence, particularly near the forest floor, remain the local diabatic effects and linkages between turbulent length scales and the canopy morphology. To progress on these problems, mean and... more
Among the fundamental problems in canopy turbulence, particularly near the forest floor, remain the local diabatic effects and linkages between turbulent length scales and the canopy morphology. To progress on these problems, mean and higher order turbulence statistics are collected in a uniform pine forest across a wide range of atmospheric stability conditions using five 3-D anemometers in the subcanopy.
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The linkages between soil moisture dynamics and convection triggers, defined here as the first crossing between the boundary layer height (hBL) and lifting condensation level (hLCL), are complicated by a large number of interacting... more
The linkages between soil moisture dynamics and convection triggers, defined here as the first crossing between the boundary layer height (hBL) and lifting condensation level (hLCL), are complicated by a large number of interacting processes occurring over a wide range of space and time scales. To progress on this problem, a soil-plant hydrodynamics model was coupled to a simplified ABL
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High elevation snow-melt runoff represents one of the main sources of freshwater in many different regions of the world, e.g. Western North America, where as much as 75% of water supplies are delivered from snowmelt. This resource is... more
High elevation snow-melt runoff represents one of the main sources of freshwater in many different regions of the world, e.g. Western North America, where as much as 75% of water supplies are delivered from snowmelt. This resource is sensitive to climatic fluctuations, as changes in the precipitation regime have been proven to affect both the total runoff volume and the
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A central topic in rainfall research is to determine whether rainfall variability at a given space-time scale is caused by dynamics acting at some other scales. Random multiplicative cascades (RMCs) are standard approaches for describing... more
A central topic in rainfall research is to determine whether rainfall variability at a given space-time scale is caused by dynamics acting at some other scales. Random multiplicative cascades (RMCs) are standard approaches for describing rainfall variability across a wide range of time scales. Their popularity stems from their ability to reproduce rainfall self-similarity and long-range correlations as well as
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Rainfall variability occurs over a wide range of time scales owing to processes initiated by cloud microphysics and sustained by atmospheric circulation. A central topic in rainfall research is to determine whether rainfall variability at... more
Rainfall variability occurs over a wide range of time scales owing to processes initiated by cloud microphysics and sustained by atmospheric circulation. A central topic in rainfall research is to determine whether rainfall variability at a given scale is caused by dynamics acting at some other scales. Random multiplicative cascades (RMCs) are standard approaches for describing rainfall variability across such
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Long-distance seed dispersal is an important topic in ecology, but notoriously difficult to quantify. Previous modeling approaches have failed to simulate long-distance dispersal, and it has remained unclear which mechanisms determine... more
Long-distance seed dispersal is an important topic in ecology, but notoriously difficult to quantify. Previous modeling approaches have failed to simulate long-distance dispersal, and it has remained unclear which mechanisms determine long-distance dispersal and what their relative importance is. We simulated wind dispersal of grassland plant seeds with four mechanistic models of increasing complexity and realism to assess which pro-
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Predicted changes in precipitation and air temperature patterns can lead to major alterations in timing and volume of mountain snowmelt runoff with a possible increased incidence of catastrophic events such as flooding and summer... more
Predicted changes in precipitation and air temperature patterns can lead to major alterations in timing and volume of mountain snowmelt runoff with a possible increased incidence of catastrophic events such as flooding and summer droughts. Here, the role of the temperature seasonal cycle and the relative duration of cold and warm seasons on the partitioning of precipitation into snow and
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Global climate models predict decreases in leaf stomatal conductance and transpiration due to increases in atmospheric CO2. The consequences of these reductions are increases in soil moisture availability and continental scale run-off at... more
Global climate models predict decreases in leaf stomatal conductance and transpiration due to increases in atmospheric CO2. The consequences of these reductions are increases in soil moisture availability and continental scale run-off at decadal time-scales. Thus, a theory explaining the differential sensitivity of stomata to changing atmospheric CO2 and other environmental conditions must be identified. Here, these responses are investigated using optimality theory applied to stomatal conductance. An analytical model for stomatal conductance is proposed based on: (a) Fickian mass transfer of CO2 and H2O through stomata; (b) a biochemical photosynthesis model that relates intercellular CO2 to net photosynthesis; and (c) a stomatal model based on optimization for maximizing carbon gains when water losses represent a cost. Comparisons between the optimization-based model and empirical relationships widely used in climate models were made using an extensive gas exchange dataset collect...
Research Interests: Mass Transfer, Carbon Dioxide, Photosynthesis, Plant Biology, Ecology, and 15 moreOptimality Theory, Atmosphere, Water use efficiency, Soil moisture, Climate Model, Water Loss, Theoretical Models, Pinus, Environmental Conditions, Analytical Model, Pinus Taeda, Global Climate Model, Gas Exchange, Plant Leaves, and Stomatal Conductance
C4 photosynthesis evolved independently numerous times, probably in response to declining atmospheric CO2 concentrations, but also to high temperatures and aridity, which enhance water losses through transpiration. Here, the environmental... more
C4 photosynthesis evolved independently numerous times, probably in response to declining atmospheric CO2 concentrations, but also to high temperatures and aridity, which enhance water losses through transpiration. Here, the environmental factors controlling stomatal behaviour of leaf-level carbon and water exchange were examined across the evolutionary continuum from C3 to C4 photosynthesis at current (400 μmol mol(-1)) and low (280 μmol mol(-1)) atmospheric CO2 conditions. To this aim, a stomatal optimization model was further developed to describe the evolutionary continuum from C3 to C4 species within a unified framework. Data on C3, three categories of C3-C4 intermediates, and C4 Flaveria species were used to parameterize the stomatal model, including parameters for the marginal water use efficiency and the efficiency of the CO2-concentrating mechanism (or C4 pump); these two parameters are interpreted as traits reflecting the stomatal and photosynthetic adjustments during the ...
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Possible linkages between climatic fluctuations in rainfall at low frequencies and local intensity fluctuations within single storms is now receiving significant attention in climate change research. To progress on a narrower scope of... more
Possible linkages between climatic fluctuations in rainfall at low frequencies and local intensity fluctuations within single storms is now receiving significant attention in climate change research. To progress on a narrower scope of this problem, the cross-scale probabilistic structure of rainfall intensity records collected over time scales ranging from hours to decades at sites dominated by either convective or frontal
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Nocturnal evapotranspiration (ETN) is often assumed to be negligible in terrestrial ecosystems, reflecting the common assumption that plant stomata close at night to prevent water loss from transpiration. However, recent evidence across a... more
Nocturnal evapotranspiration (ETN) is often assumed to be negligible in terrestrial ecosystems, reflecting the common assumption that plant stomata close at night to prevent water loss from transpiration. However, recent evidence across a wide range of species and climate conditions suggests that significant transpiration occurs at night, frustrating efforts to estimate total annual evapotranspiration (ET) from conventional methods such as
Research Interests: Applied Mathematics, Earth Sciences, Modeling, Biometeorology, Biological Sciences, and 20 moreModels, Eddy Covariance, Evapotranspiration, Missing Data, Measurement Error, Transpiration, Nocturnal, Water Use, Qualitative Analysis, Water Loss, Forest ecosystem, Ecosystem, Multiple Imputation, Flux, Night, Early Terrestrial Ecosystems, Wind Speed, Southeast, Vapor Pressure Deficit, and Non linear regression
Orthonormal wavelet expansions are applied to atmospheric surface layer velocity measurements. The effect of intermittent events on the energy spectrum of the inertial subrange is investigated through analysis of wavelet coefficients. The... more
Orthonormal wavelet expansions are applied to atmospheric surface layer velocity measurements. The effect of intermittent events on the energy spectrum of the inertial subrange is investigated through analysis of wavelet coefficients. The local nature of the orthonormal wavelet transform in physical space makes it possible to identify a relationship between the inertial subrange slope of the local wavelet spectrum and
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A new, parameter-free method, based on orthonormal wavelet expansions is proposed for calculating the principal time scale of coherent structures in atmospheric surface layer measurements. These organized events play an important role in... more
A new, parameter-free method, based on orthonormal wavelet expansions is proposed for calculating the principal time scale of coherent structures in atmospheric surface layer measurements. These organized events play an important role in the exchange of heat, mass, and momentum between the land and the atmosphere. This global technique decomposes the energy contribution at each scale into organized and random
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Research Interests: Pharmacology, Biochemistry, Bioinformatics, Evolutionary Biology, Genetics, and 57 moreMarine Biology, Neuroscience, Environmental Science, Geophysics, Physics, Materials Science, Quantum Physics, Developmental Biology, Immunology, Climate Change, Water, Molecular Biology, Structural Biology, Genomics, RNA, Computational Biology, Transcriptomics, Carbon Dioxide, Carbon, Biotechnology, Systems Biology, Biomass, Cancer, Biology, Metabolomics, Cell Cycle, Proteomics, Ecology, Drug Discovery, Evolution, Carbon Sequestration, Nanotechnology, Astrophysics, Neurobiology, Medicine, Multidisciplinary, Palaeobiology, Functional Genomics, Nature, Signal Transduction, Astronomy, DNA, Atmosphere, Cell Signalling, Medical Research, Nitrogen deposition, Nitrogen, Nutrient Limitation, Trees, Gymnosperms, Soil Fertility, Tree growth, Forest ecosystem, Ecosystem, Transient Stability, Earth Science, and Carbon Sink
The conceptual framework for modeling the inertial subrange is strongly influenced by the Kolmogorov cascade phenomena, which is nowadays the subject of significant reinterpretation. It has been argued that the effects of boundary... more
The conceptual framework for modeling the inertial subrange is strongly influenced by the Kolmogorov cascade phenomena, which is nowadays the subject of significant reinterpretation. It has been argued that the effects of boundary conditions influence large-scale motion and direct interaction between large and small scales is possible by means other than passing sequentially through the full cascade. Using longitudinal (u)
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In stably stratified turbulent flows, the mixing efficiency associated with eddy diffusivity for heat, or equivalently the turbulent Prandtl number (Pr(t)), is fraught with complex dynamics originating from the scalewise interplay between... more
In stably stratified turbulent flows, the mixing efficiency associated with eddy diffusivity for heat, or equivalently the turbulent Prandtl number (Pr(t)), is fraught with complex dynamics originating from the scalewise interplay between shear generation of turbulence and its dissipation by density gradients. A large corpus of data and numerical simulations agree on a near-universal relation between Pr(t) and the Richardson number (R(i)), which encodes the relative importance of buoyancy dissipation to mechanical production of turbulent kinetic energy. The Pr(t)-R(i) relation is shown to be derivable solely from the cospectral budgets for momentum and heat fluxes if a Rotta-like return to isotropy closure for the pressure-strain effects and Kolmogorov's theory for turbulent cascade are invoked. The ratio of the Kolmogorov to the Kolmogorov-Obukhov-Corrsin phenomenological constants, and a constant associated with isotropization of the production whose value (= 3/5) has been pre...
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Missing data is a ubiquitous problem in evaluating long-term experimental measurements, such as those associated with the FluxNet project, due to the equipment failures, system maintenance, power-failure, and lightning strikes among other... more
Missing data is a ubiquitous problem in evaluating long-term experimental measurements, such as those associated with the FluxNet project, due to the equipment failures, system maintenance, power-failure, and lightning strikes among other things. To estimate annual values of net ecosystem carbon exchange (NEE), latent heat flux (LE) and sensible heat flux (H), such gaps in the measured data must be
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Microtopography, consisting of small-scale excursions in the elevation of the land surface on millimeter to centimeter scales, is ubiquitous on hillslopes, but its effects are rarely incorporated into hydrological analyses of... more
Microtopography, consisting of small-scale excursions in the elevation of the land surface on millimeter to centimeter scales, is ubiquitous on hillslopes, but its effects are rarely incorporated into hydrological analyses of rainfall-runoff partitioning. To progress toward a hydrological theory that accounts for microtopography, two research questions are considered: (1) Does microtopography change the partitioning of rainfall into runoff and infiltration
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Page 1. Role of biomass spread in vegetation pattern formation within arid ecosystems Sally Thompson,1 Gabriel Katul,1 and Sean M. McMahon1 Received 12 February 2008; revised 10 June 2008; accepted 6 August 2008; published 29 October... more
Page 1. Role of biomass spread in vegetation pattern formation within arid ecosystems Sally Thompson,1 Gabriel Katul,1 and Sean M. McMahon1 Received 12 February 2008; revised 10 June 2008; accepted 6 August 2008; published 29 October 2008. ...
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Using long-term (1948-1996) pan evaporation measurements, a 6% increase in warm-season (May-October) actual evapotranspiration (ET) is computed over the conterminous United States between 1949 and 1996 via the complementary hypothesis.... more
Using long-term (1948-1996) pan evaporation measurements, a 6% increase in warm-season (May-October) actual evapotranspiration (ET) is computed over the conterminous United States between 1949 and 1996 via the complementary hypothesis. This predicted increase in ET is in agreement with the measured precipitation increase for the same period if long-term wet-surface ET is assumed to be constant. Long-term relative humidity and
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Longitudinal velocity and temperature measurements above a uniform dry lakebed were used to investigate sources of eddy-motion anisotropy within the inertial subrange. Rather than simply test the adequacy of locally isotropic relations,... more
Longitudinal velocity and temperature measurements above a uniform dry lakebed were used to investigate sources of eddy-motion anisotropy within the inertial subrange. Rather than simply test the adequacy of locally isotropic relations, we investigated directly the sources of anisotropy. These sources, in a daytime desert-like climate, include: (1) direct interaction between the large-scale and small-scale eddy motion, and (2) thermal
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The existence of universal power laws at low wavenumbers (K) in the energy spectrum (Eu) of the turbulent longitudinal velocity (u) is examined theoretically and experimentally for the near-neutral atmospheric surface layer. Newly derived... more
The existence of universal power laws at low wavenumbers (K) in the energy spectrum (Eu) of the turbulent longitudinal velocity (u) is examined theoretically and experimentally for the near-neutral atmospheric surface layer. Newly derived power-law solutions to Tchen's approximate integral spectral budget equation are tested for strong- and weak-interaction cases between the mean flow and turbulent vorticity fields. To verify
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The Janzen–Connell (JC) effect, which hypothesizes that recruitment and growth of seedlings is positively correlated to the distance from the parent tree, is shown to generate highly organized vegetation biomass spatial patterns when... more
The Janzen–Connell (JC) effect, which hypothesizes that recruitment and growth of seedlings is positively correlated to the distance from the parent tree, is shown to generate highly organized vegetation biomass spatial patterns when coupled to a revised Fisher–Kolmogorov (FK) equation. Spatial organization arises through a novel mechanism of non-local activation and local inhibition. Over a single generation, the revised FK model calculations predict a “hen and chicks” dynamic pattern with mature trees surrounded by new seedlings growing at characteristic spatial distances in agreement with field data. Over longer timescales, the importance of stochastic dynamics, such as those associated with randomly occurring light gaps, increase thereby causing a substantial deviation between predictions from the deterministic FK model and its stochastic counterpart derived to account for such random disturbances. At still longer timescales, however, statistical measures of the spatial organiza...
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Research Interests: Environmental Engineering, Civil Engineering, Atmospheric Science, Turbulence, Boundary Layer Meteorology, and 11 moreTime Series, Water resources, Carbon Dioxide, Applied Economics, Atmospheric sciences, Sampling methods, Evapotranspiration, Greenhouse gases, Ozone, Southern California, and Water Vapor
Research Interests: Environmental Engineering, Civil Engineering, Atmospheric Science, Boundary Layer Meteorology, Water resources, and 11 moreDesertification, Applied Economics, Atmospheric Turbulence, Shear Stress, Heat Flux, Atmospheric Boundary Layer, Arid Region, Free Convection, Atmospheric Turbulence at ABL, Sensible Heat Flux, and Atmsopheric Sciences
Heat fluxes under unstable atmospheric conditions are measured and analyzed using orthonormal wavelet expansions. Both wavelet and Fourier power spectra display a -1 power law that can be derived from dimensional arguments for latent and... more
Heat fluxes under unstable atmospheric conditions are measured and analyzed using orthonormal wavelet expansions. Both wavelet and Fourier power spectra display a -1 power law that can be derived from dimensional arguments for latent and sensible heat flux in the turbulent production subrange. The wavelet expansion is used to investigate the spatial structure of the heat fluxes for those scales
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Research Interests: Environmental Engineering, Civil Engineering, Atmospheric Science, Turbulence, Water resources, and 12 moreTurbulent Flows, Applied Economics, Multidisciplinary, Global change, Atmospheric sciences, Numerical Simulation, Atmospheric Turbulence, Laboratory experiment, Second Order, Geophysical, Probability Density Function, and Sensible Heat Flux
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Research Interests: Environmental Engineering, Civil Engineering, Water resources, Applied Economics, Very Low Frequency Electromagnetics, and 13 moreLow Frequency, Seasonality, Soil moisture, Evapotranspiration, Power Law, Data Collection, Spectrum, Analytical Model, Loblolly Pine, Southeastern United States, Diurnal Cycle, Frequency Domain, and Soil moisture content
... 2 Marc Aubinet,3 Paul Berbigier,4 Christian Bernhofer,5 Han Dolman,6 Eva Falge,7 Chris Field,8 ... during nocturnal periods [Lavigne et al., 1997; Law et al., 2001; Aubinet et al., 2000; Wilson et al ... Howland Maine/USA 1996 1997... more
... 2 Marc Aubinet,3 Paul Berbigier,4 Christian Bernhofer,5 Han Dolman,6 Eva Falge,7 Chris Field,8 ... during nocturnal periods [Lavigne et al., 1997; Law et al., 2001; Aubinet et al., 2000; Wilson et al ... Howland Maine/USA 1996 1997 5.5 K 45°150 N 68°450 W Spruce-Hemlock ...
Research Interests: Environmental Engineering, Civil Engineering, Plant Ecology, Water resources, Applied Economics, and 12 moreSeasonality, Eddy Covariance, Evapotranspiration, Vapor Pressure, Heat Flux, Mediterranean Climate, Boundary Layer, Deciduous Forest, Soil Water Content, Water Vapor, Sensible Heat Flux, and Vapor Pressure Deficit
Research Interests: Environmental Engineering, Civil Engineering, Stochastic Process, Water resources, Applied Economics, and 11 moreWater Cycle, Seasonality, Probability Distribution & Applications, Eddy Covariance, Soil moisture, Evapotranspiration, Tropical rainforest, Tropical rain forest, Probability Density Function, Global Climate Model, and Soil moisture content
Abstract The use of stem sap flow data to estimate diurnal whole-tree transpiration and canopy stomatal conductance depends critically upon knowledge of the time lag between transpiration and water flux through the stem. In this study,... more
Abstract The use of stem sap flow data to estimate diurnal whole-tree transpiration and canopy stomatal conductance depends critically upon knowledge of the time lag between transpiration and water flux through the stem. In this study, the time constant for water ...
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Scale separation crossing many orders of magnitude is a consistent challenge in the ecological sciences. Wind dispersal of seed that generates plant propagation fronts is a typical case where timescales range from less than a second for... more
Scale separation crossing many orders of magnitude is a consistent challenge in the ecological sciences. Wind dispersal of seed that generates plant propagation fronts is a typical case where timescales range from less than a second for fast turbulent processes to interannual timescales governing plant growth and climatic forcing. We show that the scale separation can be overcome by developing mechanistic and statistical links between processes at the different timescales. A mechanistic model is used to scale up from the turbulent regime to hourly timescales, while a superstatistical approach is used to relate the half-hourly timescales to annual vegetation migration speeds. We derive a semianalytical model to predict vegetation front movement as a function of wind-forcing statistics and characteristics of the species being dispersed. This model achieves better than order-of-magnitude agreement in a case study of tree dispersal from the early Holocene, a marked improvement over diffusion models. Plant migration is shown to depend nonlinearly on the wind environment forcing the movement but linearly on most physiological parameters. Applications of these analytical results to parameterizing models of plant dispersion and the implications of the superstatistical approach for addressing other ecological problems plagued by similar "dimensionality curses" are outlined.
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Research Interests: Remote Sensing, Climate Change, Carbon, Environmental Monitoring, Climate, and 16 moreCarbon Cycle, Nitrogen Cycle, Multidisciplinary, Temperature, Feedback, Nitrogen, Trees, Boreal Forest, Climate Model, Ecosystem, Spatial Variation, Woody Plants, Early Terrestrial Ecosystems, Surface Energy, Spacecraft, and Plant Leaves
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Research Interests: Economics, Plant Ecology, Carbon Dioxide, Photosynthesis, Optimality Theory, and 16 moreBiological Sciences, Atmosphere, Vapor Pressure, Stomata, Transpiration, Relative Humidity, Water Loss, Theoretical Models, Greenhouse gases, Vapour pressure deficit, Plant cell, Water Vapor, Vapor Pressure Deficit, Gas Exchange, Plant Transpiration, and Stomatal Conductance
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A stability correction function φ(m)(ζ) that accounts for distortions to the logarithmic mean velocity profile (MVP) in the lower atmosphere caused by thermal stratification was proposed by Monin and Obukhov in the 1950s using dimensional... more
A stability correction function φ(m)(ζ) that accounts for distortions to the logarithmic mean velocity profile (MVP) in the lower atmosphere caused by thermal stratification was proposed by Monin and Obukhov in the 1950s using dimensional analysis. Its universal character was established from many field experiments. However, theories that describe the canonical shape of φ(m)(ζ) are still lacking. A previous link between the spectrum of turbulence and the MVP is expanded here to include the effects of thermal stratification on the turbulent kinetic energy dissipation rate and eddy-size anisotropy. The resulting theory provides a novel explanation for the power-law exponents and coefficients already reported for φ(m)(ζ) from numerous field experiments.
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Research Interests: Mathematical Physics, Quantum Physics, Water Availability, Case Study, Power Law, and 10 moreBrownian Motion, FOkker Planck Equation, SURFACE RUNOFF PREDICTION, Diffusion Coefficient, First Passage Time, Time Dependent, Stochastic Model, Temperature Effect, Resource Availability, and Functional Form
Research Interests: Water, Carbon Dioxide, Ecology, Environmental Monitoring, Eddy Covariance, and 13 moreSoil moisture, Evapotranspiration, Net Ecosystem Exchange, Leaf Area Index, Poaceae, Oecologia, Ecosystem, Radiative Transfer, Southeastern United States, Water Vapor, Carbon Sink, Volatilization, and Stomatal Conductance
Research Interests: Plant Ecology, Soil, Atmospheric Science, Carbon Dioxide, Ecology, and 20 moreClimate, Carbon Isotopes, Stable Isotope, North Carolina, Trees, Oecologia, Spatial Variability, Inverse Modeling, Carbon Isotope, Theoretical Models, Time Factors, Gas Chromatography/mass Spectrometry, Soil Type, Forest Floor, Loblolly Pine, Deciduous Forest, Temporal Variability, Vapor Pressure Deficit, Vegetation Structure, and Growing Season
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... One of the main difficulties with the application of Fourier transforms to study the ... u. Muliiresolutionanalysis In this section, multiresolution analysis as developed by Mallat ( 1989a,b) is ... contained in the wavenumber... more
... One of the main difficulties with the application of Fourier transforms to study the ... u. Muliiresolutionanalysis In this section, multiresolution analysis as developed by Mallat ( 1989a,b) is ... contained in the wavenumber bandwidth dk (Tennekes and Lumley 1972; Monin and Yaglom ...
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... i) and pressure ( - ( Ui ) Ip ) are of order 10 z. These eddy-size estimates are consistent withBradshaw's (1967) arguments that the vertical exchange processes scale with z, while the horizontal... more
... i) and pressure ( - ( Ui ) Ip ) are of order 10 z. These eddy-size estimates are consistent withBradshaw's (1967) arguments that the vertical exchange processes scale with z, while the horizontal exchange processes are influenced by the in-active eddy motion in the outer layer. ...
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Research Interests: Remote Sensing, Radiation, Carbon, Photosynthesis, Energy, and 26 moreModeling, Heat Transfer, Sensitivity Analysis, Multidisciplinary, Models, Eddy Covariance, North Carolina, Lead, Forests, Direction, Regional scale, Heat Flux, Vortex, Geophysical, Coupling, Data Processing, Pinus Taeda, Nonlinearity, Forest Floor, Loblolly Pine, Energy Distribution, High Spatial Resolution, Radiation Balance, Forest Canopy, Growing Season, and Radiation absorption
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Research Interests: Carbon Dioxide, Kinetics, Atmospheric Modeling, Sensitivity Analysis, Multidisciplinary, and 12 moreEddy Covariance, Soil moisture, Geophysical, Low Temperature, Boundary Layer, Loblolly Pine, Water Vapor, Sensible Heat Flux, Vapor Pressure Deficit, Forest Canopy, Gas Exchange, and Dynamic Properties
Research Interests: Combustion, Heat Transfer, Large Eddy Simulation, Direct Numerical Simulation, Fluid Dynamics, and 13 moreMultidisciplinary, Multiphase flows, Transport Phenomena in Porous Media, Turbulence modeling, Dimensional Analysis, Turbulent boundary layer, Gradient, Power Law, Field Study, Temperature measurement, Geophysical, Reynolds Number, and Numerical and Experimental Methods in Fluid Dynamics
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Research Interests: Hydrology, Carbon Dioxide, Multidisciplinary, Eddy Covariance, Evapotranspiration, and 14 moreBoreal Forest, Heat Flux, North America, Geophysical, Mediterranean Climate, Surface Energy, Energy Flux, Soil Water Content, Water Vapor, J, Sensible Heat Flux, Vapor Pressure Deficit, Temperate Forest, and Climate Sensitivity
Research Interests: Seed Dispersal, Ecology, Large Eddy Simulation, Biological Sciences, Environmental Sciences, and 14 moreStandard Deviation, Spatial Heterogeneity, Power Law, Dispersal Kernel, Spatial Scale, Species Composition, Atmospheric Boundary Layer, Plant population ecology, Long Distance Dispersal, Analytical Model, Numerical Model, Wind Speed, Tree Height, and Developing Regions
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... Modelling night-time ecosystem respiration by a constrained source optimization method.Chun-Ta Lai 1,* ,; Gabriel Katul 2 ,; John Butnor 3 ,; David Ellsworth 4 ,; Ram Oren 2. ... Correspondence: Chun-Ta Lai,. *Correspondence: Chun-Ta... more
... Modelling night-time ecosystem respiration by a constrained source optimization method.Chun-Ta Lai 1,* ,; Gabriel Katul 2 ,; John Butnor 3 ,; David Ellsworth 4 ,; Ram Oren 2. ... Correspondence: Chun-Ta Lai,. *Correspondence: Chun-Ta Lai, tel. ...
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Research Interests: Biological Sciences, Global change, Environmental Sciences, Eddy Covariance, Soil moisture, and 15 moreNorth Carolina, Vapor Pressure, Electron Transport, Leaf Area Index, Leaf Nitrogen, Pinus Taeda, Vertical Distribution, Loblolly Pine, Ecological Applications, Quantum Yield, Leaf Area, Carbon Sink, Model coupling, gross Primary Production, and Stomatal Conductance
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Predicting forest-tree seed dispersal across a landscape is useful for estimating gene flow from genetically engineered (GE) or transgenic trees. The question of biocontainment has yet to be resolved, although field-trial permits for... more
Predicting forest-tree seed dispersal across a landscape is useful for estimating gene flow from genetically engineered (GE) or transgenic trees. The question of biocontainment has yet to be resolved, although field-trial permits for transgenic forest trees are on the rise. Most current field trials in the United States occur in the Southeast where Pinus taeda L., an indigenous species, is the major timber commodity. Seed dispersal distances were simulated using a model where the major determinants were: (1) forest canopy height at seed release, (2) terminal velocity of the seeds, (3) absolute seed release, and (4) turbulent-flow statistics, all of which were measured or determined within a P. taeda plantation established from seeds collected from wild forest-tree stands at the Duke Forest near Durham, North Carolina, USA. In plantations aged 16 and 25 years our model results showed that most of the seeds fell within local-neighborhood dispersal distances, with estimates ranging from 0.05 to 0.14 km from the source. A fraction of seeds was uplifted above the forest canopy and moved via the long-distance dispersal (LDD) process as far as 11.9-33.7 km. Out of 10(5) seeds produced per hectare per year, roughly 440 seeds were predicted to be uplifted by vertical eddies above the forest canopy and transported via LDD. Of these, 70 seeds/ha traveled distances in excess of 1 km from the source, a distance too great to serve as a biocontainment zone. The probability of LDD occurrence of transgenic conifer seeds at distances exceeding 1 km approached 100%.
Research Interests: Gene Flow, Seed Dispersal, Ecology, Genetic Engineering, Biological Sciences, and 17 moreEnvironmental Sciences, North Carolina, United States, Ecological, Turbulent Flow, Trees, Germination, Field Trial, Genetically Modified, Ecosystem, Seeds, Long Distance Dispersal, Time Factors, Pinus Taeda, Seasons, Ecological Applications, and Forest Canopy
Research Interests: Diversity, Atmospheric Modeling, Seed Dispersal, Fluid Dynamics, Biological Sciences, and 13 moreEnvironmental Sciences, Computation Fluid Dynamics, Atmospheric Turbulence, Bird Migration, High Resolution, Biological systems, Long Distance Dispersal, Landscape Structure, In Silico, Large Eddy Simulation(LES), Landscape Heterogeneity, Wind Flow, and Long Distance
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Eddy-correlation measurements above an uneven-aged forest, a uniform-irrigated bare soil field, and within a grass-covered forest clearing were used to investigate the usefulness of the fluxvariance method above uniform and non-uniform... more
Eddy-correlation measurements above an uneven-aged forest, a uniform-irrigated bare soil field, and within a grass-covered forest clearing were used to investigate the usefulness of the fluxvariance method above uniform and non-uniform terrain. For this purpose, the Monin and Obukhov (1954) variance similarity functions were compared with direct measurements. Such comparisons were in close agreement for momentum and heat but not
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Research Interests: Boundary Layer Meteorology, Large Eddy Simulation, Seasonality, Atmospheric sciences, Spatial Heterogeneity, and 13 moreNorth Carolina, Case Study, Atmospheric Boundary Layer, Spatial Variability, Drag Force, Statistical Properties, Length scale, Three Dimensional, Spatial Correlation, Boundary Layer, Penetration Depth, Forest Canopy, and Momentum Transfer
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Research Interests: Environmental Engineering, Geology, Hydrogeology, Computational Fluid Dynamics, Atmospheric Science, and 17 moreHydrology, Turbulence, Turbulence Modelling, Boundary Layer Meteorology, Water resources, Environmental Management, Ecology, Micrometeorology, Forest Ecology, Planning, Environmental Fluid Mechanics, Geophysical Fluid Dynamics, Turbulence modeling, Atmospheric sciences, Biosphere - atmosphere interactions, Forest Meteorology, and Geographic Information Systems (GIS)
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The state-of-the-art biosphere-atmosphere models used to compute heat, water vapor, and CO2 fluxes from canopies do not explicitly resolve local atmospheric stability. However, efforts to measure and model nighttime CO2 fluxes from... more
The state-of-the-art biosphere-atmosphere models used to compute heat, water vapor, and CO2 fluxes from canopies do not explicitly resolve local atmospheric stability. However, efforts to measure and model nighttime CO2 fluxes from ecosystems suggest that local atmospheric stability within the deeper canopy layers may be crucial towards accurate representation of nighttime CO2 fluxes. In order to assess the relative importance
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The nocturnal canopy Sublayer (CSL) at the top of a 15 m tall even-aged pine forest has been studied. We quantified the role of organised motion on scalar and momentum transport close to the canopy-atmosphere interface using time series... more
The nocturnal canopy Sublayer (CSL) at the top of a 15 m tall even-aged pine forest has been studied. We quantified the role of organised motion on scalar and momentum transport close to the canopy-atmosphere interface using time series measurements of velocity, temperature, carbon dioxide and water vapour concentration. Our analysis highlights that the nocturnal CSL has 2 end-members --
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The complex vertical structure of the canopy plays a critical role in controlling the local scalar source-sink (Sc) distribution and net ecosystem exchange (NEE) from forested ecosystems. To quantify the interplay between Sc and NEE,... more
The complex vertical structure of the canopy plays a critical role in controlling the local scalar source-sink (Sc) distribution and net ecosystem exchange (NEE) from forested ecosystems. To quantify the interplay between Sc and NEE, multiple approaches have been developed and are broadly classified as forward or inverse. The first is based on a one-dimensional ecophysiological-radiative transfer and turbulent transport
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Daytime respiration from tall-forested ecosystems remains among the least understood components in the total carbon balance. These forests pose unique challenges to respiration measurements because of the large number of respiring organs,... more
Daytime respiration from tall-forested ecosystems remains among the least understood components in the total carbon balance. These forests pose unique challenges to respiration measurements because of the large number of respiring organs, their complex vertical distribution and their high spatial variability in forest floor carbon dioxide efflux. The definition of the net vertical flux (FN) as covariance between fluctuations of
Research Interests: Time Series, Carbon Dioxide, Carbon Cycle, High Frequency, Sampling methods, and 16 moreEddy Covariance, Conceptual Framework, Soil Carbon, Spatial Variability, North America, Forest ecosystem, Total Organic Carbon, Social Network Analysis Big Data, Vertical Distribution, Boundary Layer, Drag Coefficient, Forest Floor, Relaxed Eddy Accumulation, Leaf Area, Water Vapor, and Respiration Rate
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Triaxial sonic anemometer velocity and temperature measurements were used to investigate the local structure of the velocity and temperature fluctuations in the unstable atmospheric surface layer above a grass-covered forest clearing.... more
Triaxial sonic anemometer velocity and temperature measurements were used to investigate the local structure of the velocity and temperature fluctuations in the unstable atmospheric surface layer above a grass-covered forest clearing. Despite the existence of a 2/3 power law in the longitudinal velocity (2 decades) and temperature (1 decade) structure functions, local isotropy within the inertial subrange was not attained
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Random multiplicative cascades (RMCs) represent a common tool in modeling both the energy dissipation in fully developed turbulence and rainfall intermittency build-up from large to fine time scales. The popularity of RMCs stems from... more
Random multiplicative cascades (RMCs) represent a common tool in modeling both the energy dissipation in fully developed turbulence and rainfall intermittency build-up from large to fine time scales. The popularity of RMCs stems from their inherent multi-fractality and their ability to reproduce self-similar and long-term correlation characteristics of these two processes. However, causality in the flow of information from large-to-fine
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Rainfall variability across diverse time scales is often represented by a random multiplicative cascade (RMC). Whether `large scale' variability influences `finer scale' dynamics at later times... more
Rainfall variability across diverse time scales is often represented by a random multiplicative cascade (RMC). Whether `large scale' variability influences `finer scale' dynamics at later times (forward causal cascade) or conversely (inverse causal cascade) are usually not accounted for in classical RMC representations. We investigate this causal structure in rainfall cascades using the continuous wavelet transform (CWT), cross-scale correlations, and
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Research Interests: Earth Sciences, Carbon Dioxide, Climate variability, Water Availability, Biological Sciences, and 17 moreWater Cycle, Seasonality, Eddy Covariance, Evapotranspiration, Environmental Control, Water balance, Net Ecosystem Exchange, Environmental Variables, Carbon balance, Leaf Area Index, Water Loss, Spectrum, Forest ecosystem, Mean Annual Temperature, Leaf Area, Water Vapor, and Vapor Pressure Deficit
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Research Interests: Environmental Engineering, Civil Engineering, Stochastic Process, Water resources, Water Cycle, and 10 moreProbability Distribution & Applications, Soil moisture, Water balance, Air Temperature, Tropical rainforest, Carbon Sink, Global Climate Model, Empirical Model, Vapor Pressure Deficit, and Stomatal Conductance
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Research Interests: Environmental Engineering, Civil Engineering, Water, Water resources, Climate variability, and 11 moreIntelligent Transport System, Evapotranspiration, Water Use, Early Terrestrial Ecosystems, Hydraulic Architecture, Large Scale, Vascular Plants, Tropical Climate, Leaf Area, Temperate Forest, and Stomatal Conductance
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Research Interests: Environmental Engineering, Civil Engineering, Water resources, Heat Exchanger, Water use efficiency, and 11 moreSoil moisture, Case Study, Energy Balance, Leaf Area Index, Water Loss, Dynamic Response, Energy Flux, Large Eddy Simulation(LES), Simulation Model, Forest Canopy, and Stomatal Conductance
Lateral redistribution of surface water in patchy arid ecosystems has been hypothesized to contribute to the maintenance of vegetation patches through the provision of a water subsidy from bare sites to vegetated sites. Such runon–runoff... more
Lateral redistribution of surface water in patchy arid ecosystems has been hypothesized to contribute to the maintenance of vegetation patches through the provision of a water subsidy from bare sites to vegetated sites. Such runon–runoff processes occur during Hortonian runoff events on topographically sloping ground. Surface flow redistribution may also occur on topographically flat ground if the presence of the vegetation patch creates a contrast in infiltration rate, leading to a free-surface gradient in ponded water. The precise dynamics ...
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This study proposes a two-dimensional Lagrangian stochastic dispersion model forestimating spatial and temporal variation of scalar sources, sinks, and fluxes withina forest canopy. Carbon dioxide and heat dispersion experiments were... more
This study proposes a two-dimensional Lagrangian stochastic dispersion model forestimating spatial and temporal variation of scalar sources, sinks, and fluxes withina forest canopy. Carbon dioxide and heat dispersion experiments were conducted forfield testing the model. These experiments also provided data for field testing a newlydeveloped one-dimensional Lagrangian analytical dispersion model. It was found that these two models produce similar scalar source-sinkand flux distribution patterns. Comparing with CO 2 flux ...