I am Professor of Climate System Science at the University of Reading and Senior Scientist at the National Centre for Atmospheric Science (NCAS-Climate), leading and developing research on High-Resolution Global Climate Modelling and biosphere-atmosphere interactions.
Coupled photosynthesis-stomatal conductance (A-g s) models are commonly used in ecosystem models ... more Coupled photosynthesis-stomatal conductance (A-g s) models are commonly used in ecosystem models to represent the exchange rate of CO 2 and H 2 O between vegetation and the atmosphere. The ways these models account for water stress differ greatly among modelling schemes. This study provides insight into the impact of contrasting model configurations of water stress on the simulated leaf-level values of net photosynthesis (A), stomatal conductance (g s), the functional relationship among them and their ratio, the intrinsic water use efficiency (A/g s), as soil dries. A simple, yet versatile, normalized soil moisture dependent function was used to account for the effects of water stress on g s , on mesophyll conductance (g m) and on the biochemical capacity. Model output was compared to leaf-level values obtained from the literature. The sensitivity analyses emphasized the necessity to combine both stomatal and non-stomatal limitations of A in coupled A-g s models to accurately capture the observed functional relationships A vs. g s and A/g s vs. g s in response to drought. Accounting for water stress in coupled A-g s models by imposing either stomatal or biochemical limitations of A, as commonly practiced in most ecosystem models, failed to reproduce the observed functional relationship between key leaf gas exchange attributes. A quantitative limitation analysis revealed that the general pattern of C 3 photosynthetic response to water stress may be well represented in coupled A-g s models by imposing the highest limitation strength to g m , then to g s and finally to the biochemical capacity.
EGU General Assembly Conference Abstracts, Apr 1, 2012
ABSTRACT By 2020, the UK will need to generate 15% of its energy from renewables to meet our cont... more ABSTRACT By 2020, the UK will need to generate 15% of its energy from renewables to meet our contribution to the EU renewable energy target. Heating and cooling systems of buildings account for 30%-50% of the global energy consumption; thus, alternative low-carbon technologies such as horizontal Ground Couple Heat Pumps (GCHPs) can contribute to the reduction of anthropogenic CO2 emissions. Horizontal GCHPs currently represent a small fraction of the total energy generation in the UK. However, the fact that semi-detached and detached dwellings represent approximately 40% of the total housing stocks in the UK could make the widespread implementation of this technology particularly attractive in the UK and so could significantly increase its renewable energy generation potential. Using a simulation model, we analysed the dynamic interactions between the environment, the horizontal GCHP heat exchanger and typical UK dwellings, as well as their combined effect on heat pump performance and CO2 mitigation potential. For this purpose, a land surface model (JULES, Joint UK Land Environment Simulator), which calculates coupled soil heat and water fluxes, was combined with a heat extraction model. The analyses took into account the spatio-temporal variability of soil properties (thermal and hydraulic) and meteorological variables, as well as different horizontal GCHP configurations and a variety of building loads and heat demands. Sensitivity tests were performed for four sites in the UK with different climate and soil properties. Our results show that an installation depth of 1.0m would give us higher heat extractions rates, however it would be preferable to install the pipes slightly deeper to avoid the seasonal influence of variable meteorological conditions. A value of 1.5m for the spacing between coils (S) for a slinky configuration type is recommended to avoid thermal disturbances between neighbouring coils. We also found that for larger values of the spacing between the coils (S > 2), a slinky coil diameter (D) of 0.8m might be a better choice in terms of heat extraction rate. The fluid temperature of the pipe had a direct effect on the heat extraction rates of the system. The coefficient of performance of a heat pump did not remain constant and depended on the operating conditions and outdoor temperatures. The outcomes of this study will allow us to give recommendations to installers and relevant government bodies concerning the optimal configuration of future installations of horizontal GCHPs at UK developments. Finally, long-term simulations with the coupled JULES-GCHP model, using high resolution (1 km) meteorological (historical and projected data), soil physical and land cover data over the entire UK-domain, will allow us to explore the effect that global warming will have on future surface and soil temperatures, as well as soil moisture contents, and therefore its impact on the energy demand of the buildings and the CO2 mitigation potential of this type of renewable energy.
2050. We conclude that thermal acclimation of photosynthesis with the Farquhar photosynthesis sch... more 2050. We conclude that thermal acclimation of photosynthesis with the Farquhar photosynthesis scheme and the new optimality-based g s scheme together improve the simulation of carbon and water fluxes for the current day and have a large impact on modelled future carbon cycle dynamics in a warming world.
The PRIMAVERA project aimed to develop a new generation of advanced and well-evaluated high-resol... more The PRIMAVERA project aimed to develop a new generation of advanced and well-evaluated high-resolution global climate models. As part of PRIMAVERA, seven different climate models were run in both standard and higher resolution configurations, with common initial conditions and forcings to form a multi-model ensemble. The ensemble simulations were run on high performance computers across Europe and generated approximately 1.6 pebibytes of output. To allow the data from all models to be analysed at this scale, PRIMAVERA scientists were encouraged to bring their analysis to the data. All data was transferred to a Central Analysis Facility (CAF), in this case the JASMIN super-data-cluster, where it was catalogued and details made available to users using the PRIMAVERA Data Management Tool's (DMT's) web interface. Users from across the project were able to query the available data using the DMT and then access it at the CAF. Here we describe how the PRIMAVERA project used the CAF's facilities to enable users to analyse this multi-model data set. We believe that PRIMAVERA's experience using a CAF demonstrates how similar, multi institute, big-data projects can efficiently share, organise and analyse large volumes of data.
Journal Of Geophysical Research: Atmospheres, Sep 27, 2017
Western North Pacific tropical cyclone (TC) model tracks are analyzed in two large multimodel ens... more Western North Pacific tropical cyclone (TC) model tracks are analyzed in two large multimodel ensembles, spanning a large variety of models and multiple future climate scenarios. Two methodologies are used to synthesize the properties of TC tracks in this large data set: cluster analysis and mass moment ellipses. First, the models' TC tracks are compared to observed TC tracks' characteristics, and a subset of the models is chosen for analysis, based on the tracks' similarity to observations and sample size. Potential changes in track types in a warming climate are identified by comparing the kernel smoothed probability distributions of various track variables in historical and future scenarios using a Kolmogorov-Smirnov significance test. Two track changes are identified. The first is a statistically significant increase in the north-south expansion, which can also be viewed as a poleward shift, as TC tracks are prevented from expanding equatorward due to the weak Coriolis force near the equator. The second change is an eastward shift in the storm tracks that occur near the central Pacific in one of the multimodel ensembles, indicating a possible increase in the occurrence of storms near Hawaii in a warming climate. The dependence of the results on which model and future scenario are considered emphasizes the necessity of including multiple models and scenarios when considering future changes in TC characteristics. We focus here on TC tracks over the western North Pacific (WNP) basin. The WNP, climatologically, is the region with the largest number of TCs per year. Typhoons in the WNP can have large impacts in many Asian countries including the Philippines, China, Taiwan, Japan, Vietnam, and South Korea. A tragic example of the large
A multimodel, multiresolution set of simulations over the period 1950-2014 using a common forcing... more A multimodel, multiresolution set of simulations over the period 1950-2014 using a common forcing protocol from CMIP6 HighResMIP have been completed by six modeling groups. Analysis of tropical cyclone performance using two different tracking algorithms suggests that enhanced resolution toward 25 km typically leads to more frequent and stronger tropical cyclones, together with improvements in spatial distribution and storm structure. Both of these factors reduce typical GCM biases seen at lower resolution. Using single ensemble members of each model, there is little evidence of systematic improvement in interannual variability in either storm frequency or accumulated cyclone energy as compared with observations when resolution is increased. Changes in the relationships between large-scale drivers of climate variability and tropical cyclone variability in the Atlantic Ocean are also not robust to model resolution. However, using a larger ensemble of simulations (of up to 14 members) with one model at different resolutions does show evidence of increased skill at higher resolution. The ensemble mean correlation of Atlantic interannual tropical cyclone variability increases from ;0.5 to ;0.65 when resolution increases from 250 to 100 km. In the northwestern Pacific Ocean the skill keeps increasing with 50-km resolution to 0.7. These calculations also suggest that more than six members are required to adequately distinguish the impact of resolution within the forced signal from the weather noise. Denotes content that is immediately available upon publication as open access.
Previous studies have shown that the number, intensity, and structure of simulated tropical cyclo... more Previous studies have shown that the number, intensity, and structure of simulated tropical cyclones (TCs) in climate models get closer to the observations as the horizontal resolution is increased. However, the sensitivity of tropical cyclone precipitation and moisture budget to changes in resolution has received less attention. In this study, we use the five-model ensemble from project PRIMAVERA/HighResMIP to investigate the systematic changes of the water budget of tropical cyclones in a range of horizontal resolutions from 18 to 0.258. Our results show that, despite a large change in the distribution of TC intensity with resolution, the distribution of precipitation per TC (i.e., averaged in a 58 radial cap) does not change significantly. This result is explained by the fact that low-and high-resolution models represent equally well the large-scale balance that characterizes the moisture budget of TCs, with the radius of the moisture source extending to ;158 from the center of the TC (i.e. well beyond the TC edge). The wind profile is found to converge in the low and high resolutions for radii. 58, resulting in a moisture flux convergence into the TC of similar magnitude at low and high resolutions. In contrast to precipitation per TC, TC intensity does increase at higher resolution and this is explained by the larger surface latent heat flux near the center of the storm, which leads to an increase in equivalent potential temperature and warmer core anomalies, although this extra latent heat represents a negligible contribution to the overall moisture budget. We discuss the complication arising from the choice of the tracking algorithm when assessing the impact of model resolution.
Early Online Release: This preliminary version has been accepted for publication in Journal of Cl... more Early Online Release: This preliminary version has been accepted for publication in Journal of Climate, may be fully cited, and has been assigned DOI he final typeset copyedited article will replace the EOR at the above DOI when it is published.
Bomb cyclones are explosively intensifying extratropical cyclones that can cause severe damage to... more Bomb cyclones are explosively intensifying extratropical cyclones that can cause severe damage to life and property. However, the poor ability of coarse-resolution climate models to simulate bomb cyclones, including underestimation of the frequency of bomb cyclones, remains a problem. In this study, the dependence of bomb cyclone characteristics on horizontal resolution from 135 to 18 km is investigated by analyzing the outputs of HighResMIP historical simulations of atmospheric general circulation models and four reanalysis datasets. Robust resolution dependence of bomb cyclone characteristics is identified for both the models and the reanalyses. Finer horizontal resolution significantly increases the frequency of bomb cyclones and reduces their average horizontal size. A regression analysis indicates that bomb cyclone frequency is roughly doubled from 140 km to 25 km resolution. The overall increase in bomb cyclone number is associated with a large increase in small bomb cyclones and a moderate decrease in large ones. Bomb cyclones in higher-resolution models are also accompanied by a higher maximum wind speed and more extreme wind events, which is probably related to the increased pressure gradients due to the smaller size of the bomb cyclones. These results imply that high-resolution models should be used for evaluating the impacts of bomb cyclones.
Robust projections and predictions of climate variability and change, particularly at regional sc... more Robust projections and predictions of climate variability and change, particularly at regional scales, rely on the driving processes being represented with fidelity in model simulations. The role of enhanced horizontal resolution in improved process representation in all components of the climate system is of growing interest, particularly as some recent simulations suggest the possibility for significant changes in both large-scale aspects of circulation, as well as improvements in small-scale processes and extremes. However, such high resolution global simulations at climate time scales, with resolutions of at least 50 km in the atmosphere and 0.25° in the ocean, have been performed at relatively few research centers and generally without overall coordination, primarily due to their computational cost. Assessing the robustness of the response of simulated climate to model resolution requires a large multi-model ensemble using a coordinated set of experiments. The Coupled Model Intercomparison
Coupled photosynthesis-stomatal conductance (A-g s) models are commonly used in ecosystem models ... more Coupled photosynthesis-stomatal conductance (A-g s) models are commonly used in ecosystem models to represent the exchange rate of CO 2 and H 2 O between vegetation and the atmosphere. The ways these models account for water stress differ greatly among modelling schemes. This study provides insight into the impact of contrasting model configurations of water stress on the simulated leaf-level values of net photosynthesis (A), stomatal conductance (g s), the functional relationship among them and their ratio, the intrinsic water use efficiency (A/g s), as soil dries. A simple, yet versatile, normalized soil moisture dependent function was used to account for the effects of water stress on g s , on mesophyll conductance (g m) and on the biochemical capacity. Model output was compared to leaf-level values obtained from the literature. The sensitivity analyses emphasized the necessity to combine both stomatal and non-stomatal limitations of A in coupled A-g s models to accurately capture the observed functional relationships A vs. g s and A/g s vs. g s in response to drought. Accounting for water stress in coupled A-g s models by imposing either stomatal or biochemical limitations of A, as commonly practiced in most ecosystem models, failed to reproduce the observed functional relationship between key leaf gas exchange attributes. A quantitative limitation analysis revealed that the general pattern of C 3 photosynthetic response to water stress may be well represented in coupled A-g s models by imposing the highest limitation strength to g m , then to g s and finally to the biochemical capacity.
EGU General Assembly Conference Abstracts, Apr 1, 2012
ABSTRACT By 2020, the UK will need to generate 15% of its energy from renewables to meet our cont... more ABSTRACT By 2020, the UK will need to generate 15% of its energy from renewables to meet our contribution to the EU renewable energy target. Heating and cooling systems of buildings account for 30%-50% of the global energy consumption; thus, alternative low-carbon technologies such as horizontal Ground Couple Heat Pumps (GCHPs) can contribute to the reduction of anthropogenic CO2 emissions. Horizontal GCHPs currently represent a small fraction of the total energy generation in the UK. However, the fact that semi-detached and detached dwellings represent approximately 40% of the total housing stocks in the UK could make the widespread implementation of this technology particularly attractive in the UK and so could significantly increase its renewable energy generation potential. Using a simulation model, we analysed the dynamic interactions between the environment, the horizontal GCHP heat exchanger and typical UK dwellings, as well as their combined effect on heat pump performance and CO2 mitigation potential. For this purpose, a land surface model (JULES, Joint UK Land Environment Simulator), which calculates coupled soil heat and water fluxes, was combined with a heat extraction model. The analyses took into account the spatio-temporal variability of soil properties (thermal and hydraulic) and meteorological variables, as well as different horizontal GCHP configurations and a variety of building loads and heat demands. Sensitivity tests were performed for four sites in the UK with different climate and soil properties. Our results show that an installation depth of 1.0m would give us higher heat extractions rates, however it would be preferable to install the pipes slightly deeper to avoid the seasonal influence of variable meteorological conditions. A value of 1.5m for the spacing between coils (S) for a slinky configuration type is recommended to avoid thermal disturbances between neighbouring coils. We also found that for larger values of the spacing between the coils (S > 2), a slinky coil diameter (D) of 0.8m might be a better choice in terms of heat extraction rate. The fluid temperature of the pipe had a direct effect on the heat extraction rates of the system. The coefficient of performance of a heat pump did not remain constant and depended on the operating conditions and outdoor temperatures. The outcomes of this study will allow us to give recommendations to installers and relevant government bodies concerning the optimal configuration of future installations of horizontal GCHPs at UK developments. Finally, long-term simulations with the coupled JULES-GCHP model, using high resolution (1 km) meteorological (historical and projected data), soil physical and land cover data over the entire UK-domain, will allow us to explore the effect that global warming will have on future surface and soil temperatures, as well as soil moisture contents, and therefore its impact on the energy demand of the buildings and the CO2 mitigation potential of this type of renewable energy.
2050. We conclude that thermal acclimation of photosynthesis with the Farquhar photosynthesis sch... more 2050. We conclude that thermal acclimation of photosynthesis with the Farquhar photosynthesis scheme and the new optimality-based g s scheme together improve the simulation of carbon and water fluxes for the current day and have a large impact on modelled future carbon cycle dynamics in a warming world.
The PRIMAVERA project aimed to develop a new generation of advanced and well-evaluated high-resol... more The PRIMAVERA project aimed to develop a new generation of advanced and well-evaluated high-resolution global climate models. As part of PRIMAVERA, seven different climate models were run in both standard and higher resolution configurations, with common initial conditions and forcings to form a multi-model ensemble. The ensemble simulations were run on high performance computers across Europe and generated approximately 1.6 pebibytes of output. To allow the data from all models to be analysed at this scale, PRIMAVERA scientists were encouraged to bring their analysis to the data. All data was transferred to a Central Analysis Facility (CAF), in this case the JASMIN super-data-cluster, where it was catalogued and details made available to users using the PRIMAVERA Data Management Tool's (DMT's) web interface. Users from across the project were able to query the available data using the DMT and then access it at the CAF. Here we describe how the PRIMAVERA project used the CAF's facilities to enable users to analyse this multi-model data set. We believe that PRIMAVERA's experience using a CAF demonstrates how similar, multi institute, big-data projects can efficiently share, organise and analyse large volumes of data.
Journal Of Geophysical Research: Atmospheres, Sep 27, 2017
Western North Pacific tropical cyclone (TC) model tracks are analyzed in two large multimodel ens... more Western North Pacific tropical cyclone (TC) model tracks are analyzed in two large multimodel ensembles, spanning a large variety of models and multiple future climate scenarios. Two methodologies are used to synthesize the properties of TC tracks in this large data set: cluster analysis and mass moment ellipses. First, the models' TC tracks are compared to observed TC tracks' characteristics, and a subset of the models is chosen for analysis, based on the tracks' similarity to observations and sample size. Potential changes in track types in a warming climate are identified by comparing the kernel smoothed probability distributions of various track variables in historical and future scenarios using a Kolmogorov-Smirnov significance test. Two track changes are identified. The first is a statistically significant increase in the north-south expansion, which can also be viewed as a poleward shift, as TC tracks are prevented from expanding equatorward due to the weak Coriolis force near the equator. The second change is an eastward shift in the storm tracks that occur near the central Pacific in one of the multimodel ensembles, indicating a possible increase in the occurrence of storms near Hawaii in a warming climate. The dependence of the results on which model and future scenario are considered emphasizes the necessity of including multiple models and scenarios when considering future changes in TC characteristics. We focus here on TC tracks over the western North Pacific (WNP) basin. The WNP, climatologically, is the region with the largest number of TCs per year. Typhoons in the WNP can have large impacts in many Asian countries including the Philippines, China, Taiwan, Japan, Vietnam, and South Korea. A tragic example of the large
A multimodel, multiresolution set of simulations over the period 1950-2014 using a common forcing... more A multimodel, multiresolution set of simulations over the period 1950-2014 using a common forcing protocol from CMIP6 HighResMIP have been completed by six modeling groups. Analysis of tropical cyclone performance using two different tracking algorithms suggests that enhanced resolution toward 25 km typically leads to more frequent and stronger tropical cyclones, together with improvements in spatial distribution and storm structure. Both of these factors reduce typical GCM biases seen at lower resolution. Using single ensemble members of each model, there is little evidence of systematic improvement in interannual variability in either storm frequency or accumulated cyclone energy as compared with observations when resolution is increased. Changes in the relationships between large-scale drivers of climate variability and tropical cyclone variability in the Atlantic Ocean are also not robust to model resolution. However, using a larger ensemble of simulations (of up to 14 members) with one model at different resolutions does show evidence of increased skill at higher resolution. The ensemble mean correlation of Atlantic interannual tropical cyclone variability increases from ;0.5 to ;0.65 when resolution increases from 250 to 100 km. In the northwestern Pacific Ocean the skill keeps increasing with 50-km resolution to 0.7. These calculations also suggest that more than six members are required to adequately distinguish the impact of resolution within the forced signal from the weather noise. Denotes content that is immediately available upon publication as open access.
Previous studies have shown that the number, intensity, and structure of simulated tropical cyclo... more Previous studies have shown that the number, intensity, and structure of simulated tropical cyclones (TCs) in climate models get closer to the observations as the horizontal resolution is increased. However, the sensitivity of tropical cyclone precipitation and moisture budget to changes in resolution has received less attention. In this study, we use the five-model ensemble from project PRIMAVERA/HighResMIP to investigate the systematic changes of the water budget of tropical cyclones in a range of horizontal resolutions from 18 to 0.258. Our results show that, despite a large change in the distribution of TC intensity with resolution, the distribution of precipitation per TC (i.e., averaged in a 58 radial cap) does not change significantly. This result is explained by the fact that low-and high-resolution models represent equally well the large-scale balance that characterizes the moisture budget of TCs, with the radius of the moisture source extending to ;158 from the center of the TC (i.e. well beyond the TC edge). The wind profile is found to converge in the low and high resolutions for radii. 58, resulting in a moisture flux convergence into the TC of similar magnitude at low and high resolutions. In contrast to precipitation per TC, TC intensity does increase at higher resolution and this is explained by the larger surface latent heat flux near the center of the storm, which leads to an increase in equivalent potential temperature and warmer core anomalies, although this extra latent heat represents a negligible contribution to the overall moisture budget. We discuss the complication arising from the choice of the tracking algorithm when assessing the impact of model resolution.
Early Online Release: This preliminary version has been accepted for publication in Journal of Cl... more Early Online Release: This preliminary version has been accepted for publication in Journal of Climate, may be fully cited, and has been assigned DOI he final typeset copyedited article will replace the EOR at the above DOI when it is published.
Bomb cyclones are explosively intensifying extratropical cyclones that can cause severe damage to... more Bomb cyclones are explosively intensifying extratropical cyclones that can cause severe damage to life and property. However, the poor ability of coarse-resolution climate models to simulate bomb cyclones, including underestimation of the frequency of bomb cyclones, remains a problem. In this study, the dependence of bomb cyclone characteristics on horizontal resolution from 135 to 18 km is investigated by analyzing the outputs of HighResMIP historical simulations of atmospheric general circulation models and four reanalysis datasets. Robust resolution dependence of bomb cyclone characteristics is identified for both the models and the reanalyses. Finer horizontal resolution significantly increases the frequency of bomb cyclones and reduces their average horizontal size. A regression analysis indicates that bomb cyclone frequency is roughly doubled from 140 km to 25 km resolution. The overall increase in bomb cyclone number is associated with a large increase in small bomb cyclones and a moderate decrease in large ones. Bomb cyclones in higher-resolution models are also accompanied by a higher maximum wind speed and more extreme wind events, which is probably related to the increased pressure gradients due to the smaller size of the bomb cyclones. These results imply that high-resolution models should be used for evaluating the impacts of bomb cyclones.
Robust projections and predictions of climate variability and change, particularly at regional sc... more Robust projections and predictions of climate variability and change, particularly at regional scales, rely on the driving processes being represented with fidelity in model simulations. The role of enhanced horizontal resolution in improved process representation in all components of the climate system is of growing interest, particularly as some recent simulations suggest the possibility for significant changes in both large-scale aspects of circulation, as well as improvements in small-scale processes and extremes. However, such high resolution global simulations at climate time scales, with resolutions of at least 50 km in the atmosphere and 0.25° in the ocean, have been performed at relatively few research centers and generally without overall coordination, primarily due to their computational cost. Assessing the robustness of the response of simulated climate to model resolution requires a large multi-model ensemble using a coordinated set of experiments. The Coupled Model Intercomparison
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Papers by Pier Luigi Vidale