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Alan K. Betts - One of the best experts on this subject based on the ideXlab platform.

  • Estimates of net CO2 flux by application of Equilibrium Boundary Layer concepts to CO2 and water vapor measurements from a tall tower
    Journal of Geophysical Research, 2004
    Co-Authors: Brent R. Helliker, Alan K. Betts, Joseph A. Berry, Peter S. Bakwin, Kenneth J. Davis, A. Scott Denning, James R. Ehleringer, John B. Miller, Martha P. Butler, Daniel M. Ricciuto
    Abstract:

    fluxes that affects the CO2 and water vapor mixing ratios. We apply quasi-Equilibrium concepts for the terrestrial ABL to measurements of CO2 and water vapor made within the ABL from a tall tower (396 m) in Wisconsin. We suppose that CO2 and water vapor mixing ratios in the ABL approach an Equilibrium on timescales longer than a day: a balance between the surface fluxes and the exchange with the free troposphere above. By using monthly averaged ABL-to-free-tropospheric water vapor differences and surface water vapor flux, realistic estimates of vertical velocity exchange with the free troposphere can be obtained. We then estimated the net surface flux of CO2 on a monthly basis for the year of 2000, using ABL-to-free-tropospheric CO2 differences, and our flux difference estimate of the vertical exchange. These ABL-scale estimates of net CO2 flux gave close agreement with eddy covariance measurements. Considering the large surface area which affects scalars in the ABL over synoptic timescales, the flux difference approach presented here could potentially provide regional-scale estimates of net CO2 flux. INDEX TERMS: 1615 Global Change: Biogeochemical processes (4805); 1818 Hydrology: Evapotranspiration; 3307 Meteorology and Atmospheric Dynamics: Boundary Layer processes; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; KEYWORDS: Boundary Layer, CO2 exchange, evapotranspiration

  • Coupling between CO2, water vapor, temperature, and radon and their fluxes in an idealized Equilibrium Boundary Layer over land
    Journal of Geophysical Research, 2004
    Co-Authors: Alan K. Betts, Brent R. Helliker, Joseph A. Berry
    Abstract:

    on the growth of the daytime dry Boundary Layer. We show Equilibrium solutions for the diurnally averaged properties of the Boundary Layer that link the mixed Layer Equilibrium (on timescales longer than a day) of potential temperature, water vapor, CO2 (and other trace gases such as radon) with an interactive cloud Layer and with the surface energy, water, and carbon balance. We examine these processes as a function of a set of external parameters: soil water content, which directly impacts respiration and photosynthesis, and hence transpiration; the surface net shortwave, directly linked to net radiation, which is also coupled to photosynthesis and transpiration; and the radiative cooling of the mixed Layer (ML), which in the Equilibrium model directly affects the surface sensible heat. We also show solutions where the net shortwave and radiative cooling are coupled to the cloud field. Our other variable model parameters are the properties of air entrained into the CBL, the midtropospheric values of vapor mixing ratio, CO2 and radon, and the lapse rate above cloud base. We considered two idealized ecosystems: forest (based on observations in Wisconsin) and grassland (using parameter estimates from the literature) to show how the vegetation model affects the ML Equilibrium. We show how the mass transport out of the subcloud Layer and the mass exchange with the free troposphere couples the mixed Layer Equilibrium of water vapor, CO2, and radon with the corresponding surface fluxes. We suggest that regional ML budgets may give useful constraints on regional carbon budgets, and that the coupling with the cloud field is a fundamental part of the ML Equilibrium. INDEX TERMS: 1818 Hydrology: Evapotranspiration; 1615 Global Change: Biogeochemical processes (4805); 3307 Meteorology and Atmospheric Dynamics: Boundary Layer processes; 3322 Meteorology and Atmospheric Dynamics: Land/ atmosphere interactions; KEYWORDS: Boundary Layer, CO2 fluxes, energy and water fluxes

  • Idealized Model for Equilibrium Boundary Layer over Land
    Journal of Hydrometeorology, 2000
    Co-Authors: Alan K. Betts
    Abstract:

    An idealized Equilibrium mixed Layer (ML) model is used to explore the coupling between the surface, the ML, and the atmosphere above. It shows that ML depth increases as vegetative resistance to evaporation increases. The surface radiative forcing also increases ML depth; the ML radiative and evaporative cooling processes reduce ML depth. The model largely uncouples mean ML structure from the mean ML fluxes. The upper Boundary condition controls ML potential temperature and mixing ratio but does not affect the fluxes; it is the surface radiative forcing and the radiative and evaporative cooling terms within the ML (together with the vegetative resistance Ry ) that control the surface fluxes and evaporative fraction. Furthermore, for a given Ry , the radiative and evaporative cooling terms in the ML control the surface sensible heat flux, and the surface radiative forcing then controls the surface latent heat flux. The solutions show that, except for extreme high values of vegetative resistance and very dry air above the ML, this idealized Equilibrium ML is capped by shallow cumulus clouds, as over the ocean. At the same time as Ry increases, the ML structure and depth shift from the oceanic limit toward a warmer, drier Boundary Layer. It is shown that surface evaporation controls Equilibrium near-surface relative humidity and not vice versa. The Equilibrium solutions also give insight into how the gradient of mean mixing ratio across the Mississippi River basin is linked to changes in surface pressure as well as vegetative resistance to evaporation. The Equilibrium model is oversimplified, and the nonlinearities introduced by the diurnal cycle have not been addressed, but nonetheless the solutions are a plausible zero-order fit to daily mean model data for the Missouri and Arkansas‐Red River basins and to summer composites from the First International Land-Surface Climatology Project Field Experiment.

  • Integration of satellite and surface data using a radiative-convective oceanic Boundary-Layer model
    Journal of Applied Meteorology, 1992
    Co-Authors: Alan K. Betts, Patrick Minnis, W. Ridgway, David F. Young
    Abstract:

    Abstract A mixing-line Boundary-Layer model is used to retrieve cloud-top height from satellite-derived cloud-top temperature using 700-hPa National Meteorological Center (NMC) analyses and the Comprehensive Ocean and Atmosphere Data Set (COADS) surface data as supporting datasets. Results are compared with the fixed-lapse-rate method of retrieving Boundary-Layer depth from sea surface temperatures (SST) and cloud-top temperatures. A radiative-convective Equilibrium Boundary-Layer model is used to retrieve Boundary-Layer structure given SST and surface wind, satellite cloud-top temperatures and cloud fraction, and the 700-hPa NMC thermodynamic analyses. Good agreement is found between the COADS data and the model solutions for low-level temperature and moisture. This suggests that Equilibrium Boundary-Layer models may be of use over remote oceans in the retrieval of Boundary-Layer structure.

Joseph A. Berry - One of the best experts on this subject based on the ideXlab platform.

  • Estimates of net CO2 flux by application of Equilibrium Boundary Layer concepts to CO2 and water vapor measurements from a tall tower
    Journal of Geophysical Research, 2004
    Co-Authors: Brent R. Helliker, Alan K. Betts, Joseph A. Berry, Peter S. Bakwin, Kenneth J. Davis, A. Scott Denning, James R. Ehleringer, John B. Miller, Martha P. Butler, Daniel M. Ricciuto
    Abstract:

    fluxes that affects the CO2 and water vapor mixing ratios. We apply quasi-Equilibrium concepts for the terrestrial ABL to measurements of CO2 and water vapor made within the ABL from a tall tower (396 m) in Wisconsin. We suppose that CO2 and water vapor mixing ratios in the ABL approach an Equilibrium on timescales longer than a day: a balance between the surface fluxes and the exchange with the free troposphere above. By using monthly averaged ABL-to-free-tropospheric water vapor differences and surface water vapor flux, realistic estimates of vertical velocity exchange with the free troposphere can be obtained. We then estimated the net surface flux of CO2 on a monthly basis for the year of 2000, using ABL-to-free-tropospheric CO2 differences, and our flux difference estimate of the vertical exchange. These ABL-scale estimates of net CO2 flux gave close agreement with eddy covariance measurements. Considering the large surface area which affects scalars in the ABL over synoptic timescales, the flux difference approach presented here could potentially provide regional-scale estimates of net CO2 flux. INDEX TERMS: 1615 Global Change: Biogeochemical processes (4805); 1818 Hydrology: Evapotranspiration; 3307 Meteorology and Atmospheric Dynamics: Boundary Layer processes; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; KEYWORDS: Boundary Layer, CO2 exchange, evapotranspiration

  • Coupling between CO2, water vapor, temperature, and radon and their fluxes in an idealized Equilibrium Boundary Layer over land
    Journal of Geophysical Research, 2004
    Co-Authors: Alan K. Betts, Brent R. Helliker, Joseph A. Berry
    Abstract:

    on the growth of the daytime dry Boundary Layer. We show Equilibrium solutions for the diurnally averaged properties of the Boundary Layer that link the mixed Layer Equilibrium (on timescales longer than a day) of potential temperature, water vapor, CO2 (and other trace gases such as radon) with an interactive cloud Layer and with the surface energy, water, and carbon balance. We examine these processes as a function of a set of external parameters: soil water content, which directly impacts respiration and photosynthesis, and hence transpiration; the surface net shortwave, directly linked to net radiation, which is also coupled to photosynthesis and transpiration; and the radiative cooling of the mixed Layer (ML), which in the Equilibrium model directly affects the surface sensible heat. We also show solutions where the net shortwave and radiative cooling are coupled to the cloud field. Our other variable model parameters are the properties of air entrained into the CBL, the midtropospheric values of vapor mixing ratio, CO2 and radon, and the lapse rate above cloud base. We considered two idealized ecosystems: forest (based on observations in Wisconsin) and grassland (using parameter estimates from the literature) to show how the vegetation model affects the ML Equilibrium. We show how the mass transport out of the subcloud Layer and the mass exchange with the free troposphere couples the mixed Layer Equilibrium of water vapor, CO2, and radon with the corresponding surface fluxes. We suggest that regional ML budgets may give useful constraints on regional carbon budgets, and that the coupling with the cloud field is a fundamental part of the ML Equilibrium. INDEX TERMS: 1818 Hydrology: Evapotranspiration; 1615 Global Change: Biogeochemical processes (4805); 3307 Meteorology and Atmospheric Dynamics: Boundary Layer processes; 3322 Meteorology and Atmospheric Dynamics: Land/ atmosphere interactions; KEYWORDS: Boundary Layer, CO2 fluxes, energy and water fluxes

Brent R. Helliker - One of the best experts on this subject based on the ideXlab platform.

  • Estimates of net CO2 flux by application of Equilibrium Boundary Layer concepts to CO2 and water vapor measurements from a tall tower
    Journal of Geophysical Research, 2004
    Co-Authors: Brent R. Helliker, Alan K. Betts, Joseph A. Berry, Peter S. Bakwin, Kenneth J. Davis, A. Scott Denning, James R. Ehleringer, John B. Miller, Martha P. Butler, Daniel M. Ricciuto
    Abstract:

    fluxes that affects the CO2 and water vapor mixing ratios. We apply quasi-Equilibrium concepts for the terrestrial ABL to measurements of CO2 and water vapor made within the ABL from a tall tower (396 m) in Wisconsin. We suppose that CO2 and water vapor mixing ratios in the ABL approach an Equilibrium on timescales longer than a day: a balance between the surface fluxes and the exchange with the free troposphere above. By using monthly averaged ABL-to-free-tropospheric water vapor differences and surface water vapor flux, realistic estimates of vertical velocity exchange with the free troposphere can be obtained. We then estimated the net surface flux of CO2 on a monthly basis for the year of 2000, using ABL-to-free-tropospheric CO2 differences, and our flux difference estimate of the vertical exchange. These ABL-scale estimates of net CO2 flux gave close agreement with eddy covariance measurements. Considering the large surface area which affects scalars in the ABL over synoptic timescales, the flux difference approach presented here could potentially provide regional-scale estimates of net CO2 flux. INDEX TERMS: 1615 Global Change: Biogeochemical processes (4805); 1818 Hydrology: Evapotranspiration; 3307 Meteorology and Atmospheric Dynamics: Boundary Layer processes; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; KEYWORDS: Boundary Layer, CO2 exchange, evapotranspiration

  • Coupling between CO2, water vapor, temperature, and radon and their fluxes in an idealized Equilibrium Boundary Layer over land
    Journal of Geophysical Research, 2004
    Co-Authors: Alan K. Betts, Brent R. Helliker, Joseph A. Berry
    Abstract:

    on the growth of the daytime dry Boundary Layer. We show Equilibrium solutions for the diurnally averaged properties of the Boundary Layer that link the mixed Layer Equilibrium (on timescales longer than a day) of potential temperature, water vapor, CO2 (and other trace gases such as radon) with an interactive cloud Layer and with the surface energy, water, and carbon balance. We examine these processes as a function of a set of external parameters: soil water content, which directly impacts respiration and photosynthesis, and hence transpiration; the surface net shortwave, directly linked to net radiation, which is also coupled to photosynthesis and transpiration; and the radiative cooling of the mixed Layer (ML), which in the Equilibrium model directly affects the surface sensible heat. We also show solutions where the net shortwave and radiative cooling are coupled to the cloud field. Our other variable model parameters are the properties of air entrained into the CBL, the midtropospheric values of vapor mixing ratio, CO2 and radon, and the lapse rate above cloud base. We considered two idealized ecosystems: forest (based on observations in Wisconsin) and grassland (using parameter estimates from the literature) to show how the vegetation model affects the ML Equilibrium. We show how the mass transport out of the subcloud Layer and the mass exchange with the free troposphere couples the mixed Layer Equilibrium of water vapor, CO2, and radon with the corresponding surface fluxes. We suggest that regional ML budgets may give useful constraints on regional carbon budgets, and that the coupling with the cloud field is a fundamental part of the ML Equilibrium. INDEX TERMS: 1818 Hydrology: Evapotranspiration; 1615 Global Change: Biogeochemical processes (4805); 3307 Meteorology and Atmospheric Dynamics: Boundary Layer processes; 3322 Meteorology and Atmospheric Dynamics: Land/ atmosphere interactions; KEYWORDS: Boundary Layer, CO2 fluxes, energy and water fluxes

V. Couaillier - One of the best experts on this subject based on the ideXlab platform.

  • Multiple scale modeling of turbulent nonEquilibrium Boundary Layer flows
    Physics of Fluids, 1996
    Co-Authors: Vincent Gleize, Roland Schiestel, V. Couaillier
    Abstract:

    Multiple scale models are investigated in order to improve modeling of turbulent nonEquilibrium Boundary Layers. The model is first calibrated on the standard Equilibrium Boundary Layer and then applied to several nonEquilibrium flows. Applications include the flow around an airfoil, the shock–Boundary Layer interaction, the transonic bump flow, and a three‐dimensional bump. The multiple scale model predictions are compared with experimental results and with standard one‐scale models. Several improvements are obtained that make the multiple scale model an interesting tool for tackling the prediction of nonEquilibrium turbulent flows.

Johan Larsson - One of the best experts on this subject based on the ideXlab platform.

  • A non-Equilibrium wall-model for LES of shock/Boundary Layer interaction at high Reynolds number
    42nd AIAA Fluid Dynamics Conference and Exhibit, 2012
    Co-Authors: Soshi Kawai, Johan Larsson
    Abstract:

    A dynamic non-Equilibrium wall-model for large-eddy simulation at arbitrarily high Reynolds numbers is proposed and validated on a Equilibrium Boundary Layer and a shock /Boundary-Layer interaction problem. The proposed method stems directly from reasoning about how the turbulence length scale changes with wall distance in the inertial subLayer and the resolution-characteristics of numerical methods. The model approximately dynamically matches the total stresses and heat uxes at the matching location and also accounts for the physics that the unresolved stresses and heat uxes are increased in the wall-normal direction toward the wall in the inner-Layer wall-model. The resulting method is shown to accurately predict both Equilibrium and non-Equilibrium (separated) Boundary Layers at a very high Reynolds number, with both realistic instantaneous elds and accurate statistics (both skin friction and turbulence quantities), something that existing non-Equilibrium wall-models fail to do robustly.

  • a non Equilibrium wall model for les of shock Boundary Layer interaction at high reynolds number
    42nd AIAA Fluid Dynamics Conference and Exhibit, 2012
    Co-Authors: Soshi Kawai, Johan Larsson
    Abstract:

    A dynamic non-Equilibrium wall-model for large-eddy simulation at arbitrarily high Reynolds numbers is proposed and validated on a Equilibrium Boundary Layer and a shock /Boundary-Layer interaction problem. The proposed method stems directly from reasoning about how the turbulence length scale changes with wall distance in the inertial subLayer and the resolution-characteristics of numerical methods. The model approximately dynamically matches the total stresses and heat uxes at the matching location and also accounts for the physics that the unresolved stresses and heat uxes are increased in the wall-normal direction toward the wall in the inner-Layer wall-model. The resulting method is shown to accurately predict both Equilibrium and non-Equilibrium (separated) Boundary Layers at a very high Reynolds number, with both realistic instantaneous elds and accurate statistics (both skin friction and turbulence quantities), something that existing non-Equilibrium wall-models fail to do robustly.

  • A Dynamic Wall-Model for Large-Eddy Simulation of High Reynolds Number Shock-Induced Separated Flows
    2012
    Co-Authors: Soshi Kawai, Johan Larsson
    Abstract:

    Weproposea simple yetefficientdynamic wall-modelfor large-eddysimulation (LES) that accurately predicts the turbulent statistics (most importantly, the predicted skin friction) and makes the LES applicable at realistic high Reynolds numbers. The proposed wall model stems directly from considerations of how turbulence length scales behave in the logarithmic Layer, and thus in other words the method is based solidly on physical reasoning. To be applicable to separated flows, the non-Equilibrium effects are involved in the model, thus the model does not assume Equilibrium Boundary Layer. Supersonic turbulent Boundary Layer on a flat plate at high Reynolds numbers are first used to verify the proposed model, and then the wall-modeled LES is applied to the shock-wave/turbulent Boundary Layer interacting separated flow at the higher Reynolds number (freestream Mach number of 1.69 and Reynolds number of Re� = 50,000). The resulting method is shown to accurately predict Equilibrium Boundary Layer at very high Reynolds numbers, with both realistic instantaneous fields (without overly elongated unphysical near-wall structures) and accurate statistics (both skin friction and turbulence quantities). Careful validations on the non-Equilibrium separated flows will be discussed at the presentation.