The Experts below are selected from a list of 16116 Experts worldwide ranked by ideXlab platform

Thomas L Frolicher - One of the best experts on this subject based on the ideXlab platform.

  • sensitivity of radiative forcing ocean heat uptake and climate feedback to changes in anthropogenic greenhouse gases and aerosols
    Journal of Geophysical Research, 2015
    Co-Authors: David Paynter, Thomas L Frolicher
    Abstract:

    We use both prescribed sea surface temperature and fully coupled versions of the Geophysical Fluid Dynamics Laboratory coupled climate model (CM3) to analyze the sensitivity of radiative forcing, ocean heat uptake, and climate feedback to changes in anthropogenic greenhouse gases and aerosols considered separately over the 1870 to 2005 period. The global anthropogenic aerosol climate feedback parameter (− α) of −1.13 ± 0.33 Wm−2 K−1 is indistinguishable from the greenhouse gas − α of −1.28 ± 0.23 Wm−2 K−1. However, this greenhouse gas climate feedback parameter is about 50% larger than that obtained for CM3 from a widely used Linear Extrapolation method of regressing Earth's top of atmosphere imbalance against surface air temperature change in idealized CO2 radiative forcing experiments. This implies that the global mean surface temperature change due to forcing over the 1870–2005 period is 50% smaller than that predicted using the climate feedback parameter obtained from idealized experiments. This difference results from time dependence in α, which makes the radiative forcing obtained by the fixed sea surface temperature method incompatible with that obtained by the Linear Extrapolation method fitted over the first 150 years after CO2 is quadrupled. On a regional scale, α varies greatly between the greenhouse gas and aerosol case. This suggests that the relationship between transient and equilibrium climate sensitivities obtained from idealized CO2 simulations, using techniques such as regional feedback analysis and heat uptake efficacy, may not hold for other forcing scenarios.

  • Sensitivity of radiative forcing, ocean heat uptake, and climate feedback to changes in anthropogenic greenhouse gases and aerosols
    Journal of Geophysical Research: Atmospheres, 2015
    Co-Authors: David Paynter, Thomas L Frolicher
    Abstract:

    We use both prescribed sea surface temperature and fully coupled versions of the Geophysical Fluid Dynamics Laboratory coupled climate model (CM3) to analyze the sensitivity of radiative forcing, ocean heat uptake, and climate feedback to changes in anthropogenic greenhouse gases and aerosols considered separately over the 1870 to 2005 period. The global anthropogenic aerosol climate feedback parameter (− α) of −1.13 ± 0.33 Wm−2 K−1 is indistinguishable from the greenhouse gas − α of −1.28 ± 0.23 Wm−2 K−1. However, this greenhouse gas climate feedback parameter is about 50% larger than that obtained for CM3 from a widely used Linear Extrapolation method of regressing Earth's top of atmosphere imbalance against surface air temperature change in idealized CO2 radiative forcing experiments. This implies that the global mean surface temperature change due to forcing over the 1870–2005 period is 50% smaller than that predicted using the climate feedback parameter obtained from idealized experiments. This difference results from time dependence in α, which makes the radiative forcing obtained by the fixed sea surface temperature method incompatible with that obtained by the Linear Extrapolation method fitted over the first 150 years after CO2 is quadrupled. On a regional scale, α varies greatly between the greenhouse gas and aerosol case. This suggests that the relationship between transient and equilibrium climate sensitivities obtained from idealized CO2 simulations, using techniques such as regional feedback analysis and heat uptake efficacy, may not hold for other forcing scenarios.

David Paynter - One of the best experts on this subject based on the ideXlab platform.

  • sensitivity of radiative forcing ocean heat uptake and climate feedback to changes in anthropogenic greenhouse gases and aerosols
    Journal of Geophysical Research, 2015
    Co-Authors: David Paynter, Thomas L Frolicher
    Abstract:

    We use both prescribed sea surface temperature and fully coupled versions of the Geophysical Fluid Dynamics Laboratory coupled climate model (CM3) to analyze the sensitivity of radiative forcing, ocean heat uptake, and climate feedback to changes in anthropogenic greenhouse gases and aerosols considered separately over the 1870 to 2005 period. The global anthropogenic aerosol climate feedback parameter (− α) of −1.13 ± 0.33 Wm−2 K−1 is indistinguishable from the greenhouse gas − α of −1.28 ± 0.23 Wm−2 K−1. However, this greenhouse gas climate feedback parameter is about 50% larger than that obtained for CM3 from a widely used Linear Extrapolation method of regressing Earth's top of atmosphere imbalance against surface air temperature change in idealized CO2 radiative forcing experiments. This implies that the global mean surface temperature change due to forcing over the 1870–2005 period is 50% smaller than that predicted using the climate feedback parameter obtained from idealized experiments. This difference results from time dependence in α, which makes the radiative forcing obtained by the fixed sea surface temperature method incompatible with that obtained by the Linear Extrapolation method fitted over the first 150 years after CO2 is quadrupled. On a regional scale, α varies greatly between the greenhouse gas and aerosol case. This suggests that the relationship between transient and equilibrium climate sensitivities obtained from idealized CO2 simulations, using techniques such as regional feedback analysis and heat uptake efficacy, may not hold for other forcing scenarios.

  • Sensitivity of radiative forcing, ocean heat uptake, and climate feedback to changes in anthropogenic greenhouse gases and aerosols
    Journal of Geophysical Research: Atmospheres, 2015
    Co-Authors: David Paynter, Thomas L Frolicher
    Abstract:

    We use both prescribed sea surface temperature and fully coupled versions of the Geophysical Fluid Dynamics Laboratory coupled climate model (CM3) to analyze the sensitivity of radiative forcing, ocean heat uptake, and climate feedback to changes in anthropogenic greenhouse gases and aerosols considered separately over the 1870 to 2005 period. The global anthropogenic aerosol climate feedback parameter (− α) of −1.13 ± 0.33 Wm−2 K−1 is indistinguishable from the greenhouse gas − α of −1.28 ± 0.23 Wm−2 K−1. However, this greenhouse gas climate feedback parameter is about 50% larger than that obtained for CM3 from a widely used Linear Extrapolation method of regressing Earth's top of atmosphere imbalance against surface air temperature change in idealized CO2 radiative forcing experiments. This implies that the global mean surface temperature change due to forcing over the 1870–2005 period is 50% smaller than that predicted using the climate feedback parameter obtained from idealized experiments. This difference results from time dependence in α, which makes the radiative forcing obtained by the fixed sea surface temperature method incompatible with that obtained by the Linear Extrapolation method fitted over the first 150 years after CO2 is quadrupled. On a regional scale, α varies greatly between the greenhouse gas and aerosol case. This suggests that the relationship between transient and equilibrium climate sensitivities obtained from idealized CO2 simulations, using techniques such as regional feedback analysis and heat uptake efficacy, may not hold for other forcing scenarios.

Junliang Zhang - One of the best experts on this subject based on the ideXlab platform.

  • the experimental measurement of local and bulk oxygen transport resistances in the catalyst layer of proton exchange membrane fuel cells
    Journal of Physical Chemistry Letters, 2017
    Co-Authors: Chao Wang, Xiaojing Cheng, Shuiyun Shen, Xiaohui Yan, Jiewei Yin, Guanghua Wei, Jiabin Lu, Junliang Zhang
    Abstract:

    Remarkable progress has been made in reducing the cathodic Pt loading of PEMFCs; however, a huge performance loss appears at high current densities, indicating the existence of a large oxygen transport resistance associated with the ultralow Pt loading catalyst layer. To reduce the Pt loading without sacrificing cell performance, it is essential to illuminate the oxygen transport mechanism in the catalyst layer. Toward this goal, an experimental approach to measure the oxygen transport resistance in catalyst layers is proposed and realized for the first time in this study. The measuring approach involves a dual-layer catalyst layer design, which consists of a dummy catalyst layer and a practical catalyst layer, followed by changing the thickness of dummy layer to respectively quantify the local and bulk resistances via limiting current measurements combined with Linear Extrapolation. The experimental results clearly reveal that the local resistance dominates the total resistance in the catalyst layer.

  • The Experimental Measurement of Local and Bulk Oxygen Transport Resistances in the Catalyst Layer of Proton Exchange Membrane Fuel Cells
    2017
    Co-Authors: Chao Wang, Xiaojing Cheng, Shuiyun Shen, Xiaohui Yan, Jiewei Yin, Guanghua Wei, Junliang Zhang
    Abstract:

    Remarkable progress has been made in reducing the cathodic Pt loading of PEMFCs; however, a huge performance loss appears at high current densities, indicating the existence of a large oxygen transport resistance associated with the ultralow Pt loading catalyst layer. To reduce the Pt loading without sacrificing cell performance, it is essential to illuminate the oxygen transport mechanism in the catalyst layer. Toward this goal, an experimental approach to measure the oxygen transport resistance in catalyst layers is proposed and realized for the first time in this study. The measuring approach involves a dual-layer catalyst layer design, which consists of a dummy catalyst layer and a practical catalyst layer, followed by changing the thickness of dummy layer to respectively quantify the local and bulk resistances via limiting current measurements combined with Linear Extrapolation. The experimental results clearly reveal that the local resistance dominates the total resistance in the catalyst layer

Andrew K Skidmore - One of the best experts on this subject based on the ideXlab platform.

  • towards red edge positions less sensitive to canopy biophysical parameters for leaf chlorophyll estimation using properties optique spectrales des feuilles prospect and scattering by arbitrarily inclined leaves sailh simulated data
    Journal of remote sensing, 2008
    Co-Authors: Andrew K Skidmore, Clement Atzberger
    Abstract:

    Several methods for extracting the chlorophyll sensitive red-edge position (REP) from hyperspectral data are reported in literature. This study is a continuation of a recent paper published as 'A new technique for extracting the red edge position from hyperspectral data: the Linear Extrapolation method'. The method was validated experimentally for estimation of foliar nitrogen concentrations of rye, maize and mixed grass/herb. The objective of this study was to test the utility of the Linear Extrapolation method under different conditions including variable canopy biophysical parameters, solar zenith angle, sensor noise and spectral bandwidth. REPs were extracted from synthetic canopy spectra that were simulated using properties optique spectrales des feuilles (PROSPECT) and scattering by arbitrarily inclined leaves (SAILH) radiative transfer models. REPs extracted by the Linear Extrapolation method involving wavebands at 680, 694, 724 and 760 nm produced the highest correlation (R 2 = 0.75) with leaf chlorophyll content with minimal effects of leaf and canopy biophysical confounders (leaf area index, leaf inclination distribution and leaf dry matter content) compared to traditional techniques including the Linear interpolation, inverted Gaussian modelling and polynomial fitting techniques. In addition, the new technique is insensitive to changes in solar zenith angle. However, the advantage of using the Linear Extrapolation method compared to the various alternative methods diminishes with increasing sensor noise and decreasing spectral resolution. In summary, the Linear Extrapolation technique confirms its high potential for leaf chlorophyll estimation. The efficacy of the technique under field conditions needs to be established.

  • a new technique for extracting the red edge position from hyperspectral data the Linear Extrapolation method
    Remote Sensing of Environment, 2006
    Co-Authors: Andrew K Skidmore
    Abstract:

    Abstract The position of the inflexion point in the red edge region (680 to 780 nm) of the spectral reflectance signature, termed the red edge position (REP), is affected by biochemical and biophysical parameters and has been used as a means to estimate foliar chlorophyll or nitrogen content. In this paper, we report on a new technique for extracting the REP from hyperspectral data that aims to mitigate the discontinuity in the relationship between the REP and the nitrogen content caused by the existence of a double-peak feature on the derivative spectrum. It is based on a Linear Extrapolation of straight lines on the far-red (680 to 700 nm) and NIR (725 to 760 nm) flanks of the first derivative reflectance spectrum. The REP is then defined by the wavelength value at the intersection of the two lines. The output is a REP equation, REP = − ( c 1  −  c 2 ) / ( m 1  −  m 2 ), where c 1 and c 2 , and m 1 and m 2 represent the intercepts and slopes of the far-red and NIR lines, respectively. Far-red wavebands at 679.65 and 694.30 nm in combination with NIR wavebands at 732.46 and 760.41 nm or at 723.64 and 760.41 nm were identified as the optimal combinations for calculating nitrogen-sensitive REPs for three spectral data sets (rye canopy, and maize leaf and mixed grass/herb leaf stack spectra). REPs extracted using this new technique (Linear Extrapolation method) showed high correlations with a wide range of foliar nitrogen concentrations for both narrow and wider bandwidth spectra, being comparable with results obtained using the traditional Linear interpolation, polynomial and inverted Gaussian fitting techniques. In addition, the new technique is simple as is the case with the Linear interpolation method, but performed better than the latter method in the case of maize leaves at different developmental stages and mixed grass/herb leaves with a low nitrogen concentration.

  • a new technique for extracting the red edge position from hyperspectral data the Linear Extrapolation method
    Remote Sensing of Environment, 2006
    Co-Authors: Moses Azong Cho, Andrew K Skidmore
    Abstract:

    Abstract The position of the inflexion point in the red edge region (680 to 780 nm) of the spectral reflectance signature, termed the red edge position (REP), is affected by biochemical and biophysical parameters and has been used as a means to estimate foliar chlorophyll or nitrogen content. In this paper, we report on a new technique for extracting the REP from hyperspectral data that aims to mitigate the discontinuity in the relationship between the REP and the nitrogen content caused by the existence of a double-peak feature on the derivative spectrum. It is based on a Linear Extrapolation of straight lines on the far-red (680 to 700 nm) and NIR (725 to 760 nm) flanks of the first derivative reflectance spectrum. The REP is then defined by the wavelength value at the intersection of the two lines. The output is a REP equation, REP = − ( c 1  −  c 2 ) / ( m 1  −  m 2 ), where c 1 and c 2 , and m 1 and m 2 represent the intercepts and slopes of the far-red and NIR lines, respectively. Far-red wavebands at 679.65 and 694.30 nm in combination with NIR wavebands at 732.46 and 760.41 nm or at 723.64 and 760.41 nm were identified as the optimal combinations for calculating nitrogen-sensitive REPs for three spectral data sets (rye canopy, and maize leaf and mixed grass/herb leaf stack spectra). REPs extracted using this new technique (Linear Extrapolation method) showed high correlations with a wide range of foliar nitrogen concentrations for both narrow and wider bandwidth spectra, being comparable with results obtained using the traditional Linear interpolation, polynomial and inverted Gaussian fitting techniques. In addition, the new technique is simple as is the case with the Linear interpolation method, but performed better than the latter method in the case of maize leaves at different developmental stages and mixed grass/herb leaves with a low nitrogen concentration.

Chao Wang - One of the best experts on this subject based on the ideXlab platform.

  • the experimental measurement of local and bulk oxygen transport resistances in the catalyst layer of proton exchange membrane fuel cells
    Journal of Physical Chemistry Letters, 2017
    Co-Authors: Chao Wang, Xiaojing Cheng, Shuiyun Shen, Xiaohui Yan, Jiewei Yin, Guanghua Wei, Jiabin Lu, Junliang Zhang
    Abstract:

    Remarkable progress has been made in reducing the cathodic Pt loading of PEMFCs; however, a huge performance loss appears at high current densities, indicating the existence of a large oxygen transport resistance associated with the ultralow Pt loading catalyst layer. To reduce the Pt loading without sacrificing cell performance, it is essential to illuminate the oxygen transport mechanism in the catalyst layer. Toward this goal, an experimental approach to measure the oxygen transport resistance in catalyst layers is proposed and realized for the first time in this study. The measuring approach involves a dual-layer catalyst layer design, which consists of a dummy catalyst layer and a practical catalyst layer, followed by changing the thickness of dummy layer to respectively quantify the local and bulk resistances via limiting current measurements combined with Linear Extrapolation. The experimental results clearly reveal that the local resistance dominates the total resistance in the catalyst layer.

  • The Experimental Measurement of Local and Bulk Oxygen Transport Resistances in the Catalyst Layer of Proton Exchange Membrane Fuel Cells
    2017
    Co-Authors: Chao Wang, Xiaojing Cheng, Shuiyun Shen, Xiaohui Yan, Jiewei Yin, Guanghua Wei, Junliang Zhang
    Abstract:

    Remarkable progress has been made in reducing the cathodic Pt loading of PEMFCs; however, a huge performance loss appears at high current densities, indicating the existence of a large oxygen transport resistance associated with the ultralow Pt loading catalyst layer. To reduce the Pt loading without sacrificing cell performance, it is essential to illuminate the oxygen transport mechanism in the catalyst layer. Toward this goal, an experimental approach to measure the oxygen transport resistance in catalyst layers is proposed and realized for the first time in this study. The measuring approach involves a dual-layer catalyst layer design, which consists of a dummy catalyst layer and a practical catalyst layer, followed by changing the thickness of dummy layer to respectively quantify the local and bulk resistances via limiting current measurements combined with Linear Extrapolation. The experimental results clearly reveal that the local resistance dominates the total resistance in the catalyst layer