Sebastien Biraud - Academia.edu (original) (raw)

Papers by Sebastien Biraud

As part of the In-Situ Aerosol Profiles (IAP) campaign, non-aerosol instruments which have been i... more As part of the In-Situ Aerosol Profiles (IAP) campaign, non-aerosol instruments which have been incorporated into the aerosol package include a programmable flask package for obtaining samples of carbon dioxide and other trace gases at each flight level.

Carbon Dioxide Flux Wind Data: 4m samples

Carbon Dioxide Flux Gas Data: 4m samples

Precision Gas System Coefficients

Atmospheric Environment, 2021

Abstract Northern high latitudes are likely to be heavily impacted by climate change, changes tha... more Abstract Northern high latitudes are likely to be heavily impacted by climate change, changes that will undoubtedly alter carbon cycling across these regions. An understanding of both the magnitude and drivers of current CO2 and CH4 fluxes are a prerequisite for making robust projections of future changes. In this study, we use observations from the recent Airborne Carbon Measurements (ACME-V) aircraft campaign to estimate the magnitude and environmental predictors CO2 and CH4 fluxes in Alaska. ACME-V consisted of 38 flights across the North Slope between late May and mid-September 2015, making it the most detailed airborne survey of northern Alaska to date. These data, combined with a geostatistical inverse model, provide a unique lens into fluxes across the region. Using this approach, we estimate a large CO2 flux to the atmosphere from the North Slope of Alaska in early summer that is counterbalanced by CO2 uptake in late summer; this balance between early season respiration and late-summer photosynthesis drives the total summer CO2 flux across northern Alaska during the study period. We further compare our results to process-based flux estimates (the Terrestrial Model Intercomparison Project, MsTMIP and the Wetland and Wetland CH4 Inter-comparison of Models Project, WETCHIMP) and several recent studies of the same spatial domain. We observe a similarity in CO2 flux totals between MsTMIP suite of models and our study (June 2015–0.86 – 0.57 vs 0.96, July 2015 MsTMIP −1.01 – 0.00 vs −0.14 and August 2915 MsTMIP −0.73 – 0.29 vs −0.50 μmol m−2 s−1, MsTMIP and our study, respectively, averaged across the North Slope). However, we find significantly higher CH4 fluxes from the North Slope than any of the WETCHIMP models. Specifically, we estimate total CH4 fluxes from the North Slope of Alaska of +0.64 ± 0.13 Tg (95% confidence), during June through August 2015 while the WETCHIMP model estimates range from 0.004 to 0.1 Tg, depending upon the model. Furthermore, the contribution of the North Slope tundra to the overall Alaskan CH4 fluxes during the entire period was ~27%, compared to 3% in state-of-the-art process-based models.

Carbon Monoxide Mixing Ratio System

Scientific Data, 2021

A Correction to this paper has been published: https://doi.org/10.1038/s41597-021-00851-9.

Data from flasks are sampled at the Atmospheric Radiation Measurement Program ARM, Southern Great... more Data from flasks are sampled at the Atmospheric Radiation Measurement Program ARM, Southern Great Plains Site and analyzed by the National Oceanic and Atmospheric Administration NOAA, Earth System Research Laboratory ESRL. The SGP site is included in the NOAA Cooperative Global Air Sampling Network. The surface samples are collected from a 60 m tower at the ARM SGP Central Facility, usually once per week in the afternoon. The aircraft samples are collected approximately weekly from a chartered aircraft, and the collection flight path is centered over the tower where the surface samples are collected. The samples are collected by the ARM and LBNL Carbon Project.

Journal of Geophysical Research, 2009

Characterizing net ecosystem exchanges of CO 2 (NEE) and sensible and latent heat fluxes in heter... more Characterizing net ecosystem exchanges of CO 2 (NEE) and sensible and latent heat fluxes in heterogeneous landscapes is difficult, yet critical given expected changes in climate and land use. We report here a measurement and modeling study designed to improve our understanding of surface to atmosphere gas exchanges under very heterogeneous land cover in the mostly agricultural U.S. Southern Great Plains (SGP). We combined three years of site-level, eddycovariance measurements in several of the dominant land-cover types with regional-scale climate data from the distributed Mesonet sampling stations and NEXRAD precipitation measurements to calibrate a land-surface model of trace-gas and energy exchanges (ISOLSM). Yearly variations in vegetation cover distributions were estimated from MODIS NDVI and compared to regional and sub-regional vegetation cover type estimates from the USDA census. We first applied ISOLSM at a 250 m spatial scale to account for vegetation cover type and leaf area variations that occur on hundred meter scales. Because of computational constraints, we developed a sub-sampling scheme within 10 km 'macrocells' to perform these high-resolution simulations. We estimate that the Atmospheric Radiation Measurement Climate Research Facility (ACRF) SGP region net CO 2 exchange with the local atmosphere was-240,-340, and-270 gC m-2 y-1 (positive toward the atmosphere) in 2003, 2004, and 2005, respectively, with large seasonal variations. We also performed simulations using two scaling approaches at resolutions of 10, 30, 60, and 90 km. The scaling approach applied in current land-surface models led to regional NEE biases of up to 50 and 20% in weekly and annual estimates, respectively. An important factor in causing these biases was the complex LAI distribution 1 within cover types. Biases in predicted weekly-average regional latent heat fluxes were smaller than for NEE, but larger than for either ecosystem respiration or assimilation alone. However, spatial and diurnal variations of hundreds of W m-2 in LH fluxes were common. We conclud that, in this heterogeneous system, characterizing vegetation cover type and LAI at the scale of spatial variation are necessary for accurate estimates of bottom-up, regional NEE and surface energy fluxes.

Journal of Geophysical Research, 2009

This study evaluates the potential impact of clouds on ecosystem CO 2 and CO 2 isotope fluxes (''... more This study evaluates the potential impact of clouds on ecosystem CO 2 and CO 2 isotope fluxes (''isofluxes'') in two contrasting ecosystems (a broadleaf deciduous forest and a C 4 grassland) in a region for which cloud cover, meteorological, and isotope data are available for driving the isotope-enabled land surface model (ISOLSM). Our model results indicate a large impact of clouds on ecosystem CO 2 fluxes and isofluxes. Despite lower irradiance on partly cloudy and cloudy days, predicted forest canopy photosynthesis was substantially higher than on clear, sunny days, and the highest carbon uptake was achieved on the cloudiest day. This effect was driven by a large increase in light-limited shade leaf photosynthesis following an increase in the diffuse fraction of irradiance. Photosynthetic isofluxes, by contrast, were largest on partly cloudy days, as leaf water isotopic composition was only slightly depleted and photosynthesis was enhanced, as compared to adjacent clear-sky days. On the cloudiest day, the forest exhibited intermediate isofluxes: although photosynthesis was highest on this day, leaf-to-atmosphere isofluxes were reduced from a feedback of transpiration on canopy relative humidity and leaf water. Photosynthesis and isofluxes were both reduced in the C 4 grass canopy with increasing cloud cover and diffuse fraction as a result of near-constant light limitation of photosynthesis. These results suggest that some of the unexplained variation in global mean d 18 O of CO 2 may be driven by large-scale changes in clouds and aerosols and their impacts on diffuse radiation, photosynthesis, and relative humidity.

Geophysical Research Letters, 2005

In this study, we demonstrate that mid-latitude surface measurements of diurnal temperature range... more In this study, we demonstrate that mid-latitude surface measurements of diurnal temperature range (DTR) can be used to reconstruct decadal variability of regional-scale terrestrial photosynthetic activity 1) during and prior to the period with satellite retrievals of land greenness and 2) without the need for moisture data. While the two relative maxima present in the seasonal evolution of DTR can determine the beginning and the end of the growing season, the summertime average DTR can be used as a proxy of summertime terrestrial photosynthesis. In a case study in the eastern United States (1966-1997), the DTR reconstructions indicate significant natural decadal variability in photosynthetic activity, but no secular, long-term trend. The summertime photosynthesis was found to be controlled primarily by moisture availability. Also, contrary to existing model parameterizations, the timing of spring onset was found to depend on both temperature and moisture.

Agricultural and Forest Meteorology, 2012

We use the radon tracer method to estimate monthly average net ecosystem exchange (NEE) of carbon... more We use the radon tracer method to estimate monthly average net ecosystem exchange (NEE) of carbon dioxide in the Southern Great Plains of the USA for the year 2007. These estimates are compared with optimized flux estimates of NEE from NOAA CarbonTracker, sampled with a Lagrangian particle dispersion model to identify the upwind area influencing each measurement. The radon-tracer equation is very simple: F(CO2) = F(Rn) x delta(CO2)/delta(Rn), where F(CO2) is NEE, F(Rn) is the flux of radon out of the soil, and delta(X) is the discrepancy between a measured concentration and "background" levels, caused by near-field terrestrial fluxes. The F(Rn) term presents a challenge in applying the radon-tracer method, since neither its mean value nor seasonality are well known. We present two lines of evidence to help constrain the seasonal cycle of radon flux in the Southern Great Plains during 2007 (a year with record high early-summer soil moisture), increasing our confidence in applying the radon-tracer method. The first line of evidence comes from a comparison between the observed seasonal cycle of radon at ARM-CART SGP and simulations made by 14 global transport models as part of the "Transcom4" experiment which assumed constant radon emissions. The second line of evidence uses the radon-tracer approach in reverse, using measured eddy covariance CO2 fluxes and nighttime accumulation of CO2 and radon to calculate radon fluxes.

Prepared for the Environmental Protection AgencybyAtmospheric Research Group, Department of Exper... more Prepared for the Environmental Protection AgencybyAtmospheric Research Group, Department of Experimental Physics, National University of Ireland, GalwayandLaboratoire des Sciences du Climat et de l'Environnement, Bat 709 – Orme des Merisiers, 91191 Gif-sur-Yvette, FranceAuthors:S. Gerard Jennings, Philippe Ciais, Sebastien Biraud and Michel RamonetENVIRONMENTAL PROTECTION AGENCYAn Ghniomhaireacht um Chaomhnu ComhshaoilPO Box 3000, Johnstown Castle, Co. Wexford, IrelandTelephone: +353 5391 60600 Fax: +353 5391 60699E-mail: info@epa.ie Website: www.epa.ie

As part of the In-Situ Aerosol Profiles (IAP) campaign, non-aerosol instruments which have been i... more As part of the In-Situ Aerosol Profiles (IAP) campaign, non-aerosol instruments which have been incorporated into the aerosol package include a programmable flask package for obtaining samples of carbon dioxide and other trace gases at each flight level.

Carbon Dioxide Flux Wind Data: 4m samples

Carbon Dioxide Flux Gas Data: 4m samples

Precision Gas System Coefficients

Atmospheric Environment, 2021

Abstract Northern high latitudes are likely to be heavily impacted by climate change, changes tha... more Abstract Northern high latitudes are likely to be heavily impacted by climate change, changes that will undoubtedly alter carbon cycling across these regions. An understanding of both the magnitude and drivers of current CO2 and CH4 fluxes are a prerequisite for making robust projections of future changes. In this study, we use observations from the recent Airborne Carbon Measurements (ACME-V) aircraft campaign to estimate the magnitude and environmental predictors CO2 and CH4 fluxes in Alaska. ACME-V consisted of 38 flights across the North Slope between late May and mid-September 2015, making it the most detailed airborne survey of northern Alaska to date. These data, combined with a geostatistical inverse model, provide a unique lens into fluxes across the region. Using this approach, we estimate a large CO2 flux to the atmosphere from the North Slope of Alaska in early summer that is counterbalanced by CO2 uptake in late summer; this balance between early season respiration and late-summer photosynthesis drives the total summer CO2 flux across northern Alaska during the study period. We further compare our results to process-based flux estimates (the Terrestrial Model Intercomparison Project, MsTMIP and the Wetland and Wetland CH4 Inter-comparison of Models Project, WETCHIMP) and several recent studies of the same spatial domain. We observe a similarity in CO2 flux totals between MsTMIP suite of models and our study (June 2015–0.86 – 0.57 vs 0.96, July 2015 MsTMIP −1.01 – 0.00 vs −0.14 and August 2915 MsTMIP −0.73 – 0.29 vs −0.50 μmol m−2 s−1, MsTMIP and our study, respectively, averaged across the North Slope). However, we find significantly higher CH4 fluxes from the North Slope than any of the WETCHIMP models. Specifically, we estimate total CH4 fluxes from the North Slope of Alaska of +0.64 ± 0.13 Tg (95% confidence), during June through August 2015 while the WETCHIMP model estimates range from 0.004 to 0.1 Tg, depending upon the model. Furthermore, the contribution of the North Slope tundra to the overall Alaskan CH4 fluxes during the entire period was ~27%, compared to 3% in state-of-the-art process-based models.

Carbon Monoxide Mixing Ratio System

Scientific Data, 2021

A Correction to this paper has been published: https://doi.org/10.1038/s41597-021-00851-9.

Data from flasks are sampled at the Atmospheric Radiation Measurement Program ARM, Southern Great... more Data from flasks are sampled at the Atmospheric Radiation Measurement Program ARM, Southern Great Plains Site and analyzed by the National Oceanic and Atmospheric Administration NOAA, Earth System Research Laboratory ESRL. The SGP site is included in the NOAA Cooperative Global Air Sampling Network. The surface samples are collected from a 60 m tower at the ARM SGP Central Facility, usually once per week in the afternoon. The aircraft samples are collected approximately weekly from a chartered aircraft, and the collection flight path is centered over the tower where the surface samples are collected. The samples are collected by the ARM and LBNL Carbon Project.

Journal of Geophysical Research, 2009

Characterizing net ecosystem exchanges of CO 2 (NEE) and sensible and latent heat fluxes in heter... more Characterizing net ecosystem exchanges of CO 2 (NEE) and sensible and latent heat fluxes in heterogeneous landscapes is difficult, yet critical given expected changes in climate and land use. We report here a measurement and modeling study designed to improve our understanding of surface to atmosphere gas exchanges under very heterogeneous land cover in the mostly agricultural U.S. Southern Great Plains (SGP). We combined three years of site-level, eddycovariance measurements in several of the dominant land-cover types with regional-scale climate data from the distributed Mesonet sampling stations and NEXRAD precipitation measurements to calibrate a land-surface model of trace-gas and energy exchanges (ISOLSM). Yearly variations in vegetation cover distributions were estimated from MODIS NDVI and compared to regional and sub-regional vegetation cover type estimates from the USDA census. We first applied ISOLSM at a 250 m spatial scale to account for vegetation cover type and leaf area variations that occur on hundred meter scales. Because of computational constraints, we developed a sub-sampling scheme within 10 km 'macrocells' to perform these high-resolution simulations. We estimate that the Atmospheric Radiation Measurement Climate Research Facility (ACRF) SGP region net CO 2 exchange with the local atmosphere was-240,-340, and-270 gC m-2 y-1 (positive toward the atmosphere) in 2003, 2004, and 2005, respectively, with large seasonal variations. We also performed simulations using two scaling approaches at resolutions of 10, 30, 60, and 90 km. The scaling approach applied in current land-surface models led to regional NEE biases of up to 50 and 20% in weekly and annual estimates, respectively. An important factor in causing these biases was the complex LAI distribution 1 within cover types. Biases in predicted weekly-average regional latent heat fluxes were smaller than for NEE, but larger than for either ecosystem respiration or assimilation alone. However, spatial and diurnal variations of hundreds of W m-2 in LH fluxes were common. We conclud that, in this heterogeneous system, characterizing vegetation cover type and LAI at the scale of spatial variation are necessary for accurate estimates of bottom-up, regional NEE and surface energy fluxes.

Journal of Geophysical Research, 2009

This study evaluates the potential impact of clouds on ecosystem CO 2 and CO 2 isotope fluxes (''... more This study evaluates the potential impact of clouds on ecosystem CO 2 and CO 2 isotope fluxes (''isofluxes'') in two contrasting ecosystems (a broadleaf deciduous forest and a C 4 grassland) in a region for which cloud cover, meteorological, and isotope data are available for driving the isotope-enabled land surface model (ISOLSM). Our model results indicate a large impact of clouds on ecosystem CO 2 fluxes and isofluxes. Despite lower irradiance on partly cloudy and cloudy days, predicted forest canopy photosynthesis was substantially higher than on clear, sunny days, and the highest carbon uptake was achieved on the cloudiest day. This effect was driven by a large increase in light-limited shade leaf photosynthesis following an increase in the diffuse fraction of irradiance. Photosynthetic isofluxes, by contrast, were largest on partly cloudy days, as leaf water isotopic composition was only slightly depleted and photosynthesis was enhanced, as compared to adjacent clear-sky days. On the cloudiest day, the forest exhibited intermediate isofluxes: although photosynthesis was highest on this day, leaf-to-atmosphere isofluxes were reduced from a feedback of transpiration on canopy relative humidity and leaf water. Photosynthesis and isofluxes were both reduced in the C 4 grass canopy with increasing cloud cover and diffuse fraction as a result of near-constant light limitation of photosynthesis. These results suggest that some of the unexplained variation in global mean d 18 O of CO 2 may be driven by large-scale changes in clouds and aerosols and their impacts on diffuse radiation, photosynthesis, and relative humidity.

Geophysical Research Letters, 2005

In this study, we demonstrate that mid-latitude surface measurements of diurnal temperature range... more In this study, we demonstrate that mid-latitude surface measurements of diurnal temperature range (DTR) can be used to reconstruct decadal variability of regional-scale terrestrial photosynthetic activity 1) during and prior to the period with satellite retrievals of land greenness and 2) without the need for moisture data. While the two relative maxima present in the seasonal evolution of DTR can determine the beginning and the end of the growing season, the summertime average DTR can be used as a proxy of summertime terrestrial photosynthesis. In a case study in the eastern United States (1966-1997), the DTR reconstructions indicate significant natural decadal variability in photosynthetic activity, but no secular, long-term trend. The summertime photosynthesis was found to be controlled primarily by moisture availability. Also, contrary to existing model parameterizations, the timing of spring onset was found to depend on both temperature and moisture.

Agricultural and Forest Meteorology, 2012

We use the radon tracer method to estimate monthly average net ecosystem exchange (NEE) of carbon... more We use the radon tracer method to estimate monthly average net ecosystem exchange (NEE) of carbon dioxide in the Southern Great Plains of the USA for the year 2007. These estimates are compared with optimized flux estimates of NEE from NOAA CarbonTracker, sampled with a Lagrangian particle dispersion model to identify the upwind area influencing each measurement. The radon-tracer equation is very simple: F(CO2) = F(Rn) x delta(CO2)/delta(Rn), where F(CO2) is NEE, F(Rn) is the flux of radon out of the soil, and delta(X) is the discrepancy between a measured concentration and "background" levels, caused by near-field terrestrial fluxes. The F(Rn) term presents a challenge in applying the radon-tracer method, since neither its mean value nor seasonality are well known. We present two lines of evidence to help constrain the seasonal cycle of radon flux in the Southern Great Plains during 2007 (a year with record high early-summer soil moisture), increasing our confidence in applying the radon-tracer method. The first line of evidence comes from a comparison between the observed seasonal cycle of radon at ARM-CART SGP and simulations made by 14 global transport models as part of the "Transcom4" experiment which assumed constant radon emissions. The second line of evidence uses the radon-tracer approach in reverse, using measured eddy covariance CO2 fluxes and nighttime accumulation of CO2 and radon to calculate radon fluxes.

Prepared for the Environmental Protection AgencybyAtmospheric Research Group, Department of Exper... more Prepared for the Environmental Protection AgencybyAtmospheric Research Group, Department of Experimental Physics, National University of Ireland, GalwayandLaboratoire des Sciences du Climat et de l'Environnement, Bat 709 – Orme des Merisiers, 91191 Gif-sur-Yvette, FranceAuthors:S. Gerard Jennings, Philippe Ciais, Sebastien Biraud and Michel RamonetENVIRONMENTAL PROTECTION AGENCYAn Ghniomhaireacht um Chaomhnu ComhshaoilPO Box 3000, Johnstown Castle, Co. Wexford, IrelandTelephone: +353 5391 60600 Fax: +353 5391 60699E-mail: info@epa.ie Website: www.epa.ie