Search results for "FluxNet"
showing 10 items of 12 documents
Environment-sensitivity functions for gross primary productivity in light use efficiency models
2022
International audience; The sensitivity of photosynthesis to environmental changes is essential for understanding carbon cycle responses to global climate change and for the development of modeling approaches that explains its spatial and temporal variability. We collected a large variety of published sensitivity functions of gross primary productivity (GPP) to different forcing variables to assess the response of GPP to environmental factors. These include the responses of GPP to temperature; vapor pressure deficit, some of which include the response to atmospheric CO2 concentrations; soil water availability (W); light intensity; and cloudiness. These functions were combined in a full fact…
The FLUXCOM ensemble of global land-atmosphere energy fluxes
2019
Although a key driver of Earth’s climate system, global land-atmosphere energy fluxes are poorly constrained. Here we use machine learning to merge energy flux measurements from FLUXNET eddy covariance towers with remote sensing and meteorological data to estimate global gridded net radiation, latent and sensible heat and their uncertainties. The resulting FLUXCOM database comprises 147 products in two setups: (1) 0.0833° resolution using MODIS remote sensing data (RS) and (2) 0.5° resolution using remote sensing and meteorological data (RS + METEO). Within each setup we use a full factorial design across machine learning methods, forcing datasets and energy balance closure corrections. For…
Monitoring tropical forests under a functional perspective with satellite-based vegetation optical depth.
2020
Monitoring ecosystem functions in forests is a priority in a climate change scenario, as climate-induced events may initially alter the functions more than slow-changing attributes, such as biomass. The ecosystem functional properties (EFPs) are quantities that characterize key ecosystem processes. They can be derived by point observations of gas and energy exchanges between the ecosystems and the atmosphere that are collected globally at FLUXNET flux tower sites and upscaled at ecosystem level. The properties here considered describe the ability of ecosystems to optimize the use of resources for carbon uptake. They represent functional forest information, are dependent on environmental dri…
Simulation of surface energy fluxes and meteorological variables using the Regional Atmospheric Modeling System (RAMS): Evaluating the impact of land…
2018
Atmospheric mesoscale numerical models are commonly used not only for research and air quality studies, but also for other related applications, such as short-term weather forecasting for atmospheric, hydrological, agricultural and ecological modelling. A key element to produce faithful simulations is the proper representation of the soil parameters used in the initialization of the corresponding mesoscale numerical model. The Regional Atmospheric Modeling System (RAMS) is used in the current study. The model code has been updated in order to permit the model to be initialized using a heterogeneous soil moisture and temperature distribution derived from land surface models. Particularly, RA…
Partitioning net carbon dioxide fluxes into photosynthesis and respiration using neural networks
2020
Abstract The eddy covariance (EC) technique is used to measure the net ecosystem exchange (NEE) of CO2 between ecosystems and the atmosphere, offering a unique opportunity to study ecosystem responses to climate change. NEE is the difference between the total CO2 release due to all respiration processes (RECO), and the gross carbon uptake by photosynthesis (GPP). These two gross CO2 fluxes are derived from EC measurements by applying partitioning methods that rely on physiologically based functional relationships with a limited number of environmental drivers. However, the partitioning methods applied in the global FLUXNET network of EC observations do not account for the multiple co‐acting…
A satellite stand-alone procedure for deriving net radiation by using SEVIRI and MODIS products
2018
Abstract In this study, a new stand-alone satellite approach for the estimation of net surface radiation (Rn) has been implemented and validated for the Italian territory. The method uses the MODIS and MSG-SEVIRI time series products and it is independent of the use of ancillary data (i.e. ground measurements). A database of daily measurements of Rn, provided by 9 stations of the FLUXNET network, was used to validate the method in different ecological scenarios in the period 2010-12. The Rn modelled by the proposed approach and the corresponding FLUXNET measurements were in good agreement, with RMSE and R2 of 19.8 Wm−2 and 0.87, respectively, at 8-days scale, and 23.3 Wm−2 and 0.92, respect…
Analysis of the energy balance closure over a FLUXNET boreal forest in Finland
2010
Abstract. The imbalance in the surface energy budget, when using eddy-covariance techniques to measure turbulent fluxes, is still an unresolved problem. Important progresses have been reported in recent years identifying potential reasons for this lack of energy balance closure. In this paper we focus on the data collected in a FLUXNET boreal forest site in Sodankylä, Finland. Using one month half-hourly data, an average Energy Balance Ratio (EBR) of 0.72 is obtained. The inclusion of the heat storage terms in the energy budget yields an improvement of about 6% in the total closure. The sensitivity of the energy balance closure to the turbulence intensity is analysed in terms of the frictio…
Time-domain based feature space at FLUXNET sites for vegetation patterns identification
2019
Monitoring the flux transfer of mass and energy occurring within the soil-plant-atmosphere continuum is a pivotal key for understanding hydrological and vegetation relationships. Average daily values of the Priestley - Taylor (PT) parameter were calculated for 4 eddy covariance (EC) flux tower sites from FLUXNET network, characterized by different vegetation features, over the 2010-12 reference period. Site-by-site feature spaces (built by difference in diurnal and night-time land surface temperature versus enhanced vegetation index, ΔLST-EVI) were obtained by combining satellite data (MODIS) and observed PT parameter (ϕ) retrieved by FLUXNET surface energy balance (SEB) fluxes. The results…
Scaling carbon fluxes from eddy covariance sites to globe: synthesis and evaluation of the FLUXCOM approach
2020
FLUXNET comprises globally distributed eddy-covariance-based estimates of carbon fluxes between the biosphere and the atmosphere. Since eddy covariance flux towers have a relatively small footprint and are distributed unevenly across the world, upscaling the observations is necessary to obtain global-scale estimates of biosphere–atmosphere exchange. Based on cross-consistency checks with atmospheric inversions, sun-induced fluorescence (SIF) and dynamic global vegetation models (DGVMs), here we provide a systematic assessment of the latest upscaling efforts for gross primary production (GPP) and net ecosystem exchange (NEE) of the FLUXCOM initiative, where different machine learning methods…
Improved meteorology and surface fluxes in mesoscale modelling using adjusted initial vertical soil moisture profiles
2018
The Regional Atmospheric Modeling System (RAMS) is being used for different and diverse purposes, ranging from atmospheric and dispersion of pollutants forecasting to agricultural meteorology and ecological modelling as well as for hydrological purposes, among others. The current paper presents a comprehensive assessment of the RAMS forecasts, comparing the results not only with observed standard surface meteorological variables, measured at FLUXNET stations and other portable and permanent weather stations located over the region of study, but also with non-standard observed variables, such as the surface energy fluxes, with the aim of evaluating the surface energy budget and its relation …