Beniamino Gioli

Bridging the gap between atmospheric concentrations and local ecosystem measurements.

This paper demonstrates that atmospheric inversions of CO2 are a reliable tool for estimating regional fluxes. We compare results of an inversion over 18 days and a 300 × 300 km2 domain in southwest France against independent measurements of fluxes from aircraft and towers. The inversion used concentration measurements from 2 towers while the independent data included 27 aircraft transects and 5 flux towers. The inversion reduces the mismatch between prior and independent fluxes, improving both spatial and temporal structures. The present mesoscale atmospheric inversion improves by 30% the CO2 fluxes over distances of few hundreds of km around the atmospheric measurement locations

Intercomparison of UAV, aircraft and satellite remote sensing platforms for precision viticulture

Precision Viticulture is experiencing substantial growth thanks to the availability of improved and cost-effective instruments and methodologies for data acquisition and analysis, such as Unmanned Aerial Vehicles (UAV), that demonstrated to compete with traditional acquisition platforms, such as satellite and aircraft, due to low operational costs, high operational flexibility and high spatial resolution of imagery. In order to optimize the use of these technologies for precision viticulture, their technical, scientific and economic performances need to be assessed. The aim of this work is to compare NDVI surveys performed with UAV, aircraft and satellite, to assess the capability of each platform to represent the intra-vineyard vegetation spatial variability. NDVI images of two Italian vineyards were acquired simultaneously from different multi-spectral sensors onboard the three platforms, and a spatial statistical framework was used to assess their degree of similarity. Moreover, the pros and cons of each technique were also assessed performing a cost analysis as a function of the scale of application. Results indicate that the different platforms provide comparable results in vineyards characterized by coarse vegetation gradients and large vegetation clusters. On the contrary, in more heterogeneous vineyards, low-resolution images fail in representing part of the intra-vineyard variability. The cost analysis showed that the adoption of UAV platform is advantageous for small areas and that a break-even point exists above five hectares; above such threshold, airborne and then satellite have lower imagery cost.

Cold season emissions dominate the Arctic tundra methane budget

Significance Arctic ecosystems are major global sources of methane. We report that emissions during the cold season (September to May) contribute ≥50% of annual sources of methane from Alaskan tundra, based on fluxes obtained from eddy covariance sites and from regional fluxes calculated from aircraft data. The largest emissions were observed at the driest site (<5% inundation). Emissions of methane in the cold season are linked to the extended “zero curtain” period, where soil temperatures are poised near 0 °C, indicating that total emissions are very sensitive to soil climate and related factors, such as snow depth. The dominance of late season emissions, sensitivity to soil conditions, and importance of dry tundra are not currently simulated in most global climate models. Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the “zero curtain” period, when subsurface soil temperatures are poised near 0 °C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH4 y−1, ∼25% of global emissions from extratropical wetlands, or ∼6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.

Entrainment process of carbon dioxide in the atmospheric boundary layer

Received 2 March 2004; revised 7 June 2004; accepted 23 June 2004; published 23 September 2004. [1] Aircraft and surface measurements of turbulent thermodynamic variables and carbon dioxide (CO2) were taken above a grassland in a convective atmospheric boundary layer. The observations were analyzed to assess the importance of the entrainment process for the distribution and evolution of carbon dioxide in the boundary layer. From the observations we were able to estimate the vertical profiles of the fluxes, the correlation coefficients, and the skewness of the virtual potential temperature, the specific humidity, and the carbon dioxide. These profiles indicate that important entrainment events occurred during the observed period. The data were also used to estimate the budgets for heat, moisture, and carbon dioxide. By studying this observational data we find that the entrainment of air parcels containing lower concentrations of water vapor and carbon dioxide significantly dries and dilutes the concentration of these two constituents in the boundary layer. This process is particularly important in the morning hours which are characterized by a rapidly growing boundary layer. The observations show that the CO2 concentration in the boundary layer is reduced much more effectively by the ventilation with entrained air than by CO2 uptake by the vegetation. We quantify this effect by calculating the ratio of the entrainment flux of CO2 to the surface flux of CO2(bc = � (wc)e/(wc)o). A value of bc equal to 2.9 is estimated at around 1300 UTC from the vertical profile of the carbon dioxide flux. We corroborate this observational evidence by reproducing the observed situation using a mixed layer model. The mixed layer model also yields the variation in time of bc. During the morning the ventilation process is more important than the CO2 uptake by the vegetation (bc > 1), whereas in the afternoon the assimilation by grass at the surface becomes the dominant process (bc < 1). This research points out the relevance of the entrainment process on the budget of carbon dioxide in the lower troposphere and the relevance of boundary layer dynamics in controlling the diurnal variation of carbon dioxide. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0368 Atmospheric Composition and Structure: Troposphere— constituent transport and chemistry; KEYWORDS: entrainment carbon dioxide, mixed layer model Citation: de Arellano, J. V.-G., B. Gioli, F. Miglietta, H. J. J. Jonker, H. K. Baltink, R. W. A. Hutjes, and A. A. M. Holtslag (2004), Entrainment process of carbon dioxide in the atmospheric boundary layer, J. Geophys. Res., 109, D18110,

The CarboEurope Regional Experiment Strategy

Quantification of sources and sinks of carbon at global and regional scales requires not only a good description of the land sources and sinks of carbon, but also of the synoptic and mesoscale meteorology. An experiment was performed in Les Landes, southwest France, during May?June 2005, to determine the variability in concentration gradients and fluxes of CO2. The CarboEurope Regional Experiment Strategy (CERES; see also http://carboregional.mediasfrance.org/index) aimed to produce aggregated estimates of the carbon balance of a region that can be meaningfully compared to those obtained from the smallest downscaled information of atmospheric measurements and continental-scale inversions. We deployed several aircraft to concentration sample the CO2 and fluxes over the whole area, while fixed stations observed the fluxes and concentrations at high accuracy. Several (mesoscale) meteorological modeling tools were used to plan the experiment and flight patterns. Results show that at regional scale the relation between profiles and fluxes is not obvious, and is strongly influenced by airmass history and mesoscale flow patterns. In particular, we show from an analysis of data for a single day that taking either the concentration at several locations as representative of local fluxes or taking the flux measurements at those sites as representative of larger regions would lead to incorrect conclusions about the distribution of sources and sinks of carbon. Joint consideration of the synoptic and regional flow, fluxes, and land surface is required for a correct interpretation. This calls for an experimental and modeling strategy that takes into account the large spatial gradients in concentrations and the variability in sources and sinks that arise from different land use types. We briefly describe how such an analysis can be performed and evaluate the usefulness of the data for planning of future networks or longer campaigns with reduced experimental efforts.

Carbon Dioxide Emissions of the City Center of Firenze, Italy: Measurement, Evaluation, and Source Partitioning

Abstract An eddy covariance station was installed in the city center of Firenze, Italy, to measure carbon fluxes at half-hourly intervals over a mostly homogeneous urban area. Carbon dioxide (CO2) emission observations made over an initial period of 3.5 months were compared with indirect estimates of CO2 emissions based on inventory data sources of vehicle circulation and natural gas consumption for domestic heating and cooking. Such a comparison provided proper evaluation of the measurements. Using seasonal dynamics of observed fluxes, the overall CO2 source of the city center was partitioned into its major components (i.e., road traffic and domestic heating). Results were directly compared with CO2 source estimates based on inventory sources.

Annual patterns and budget of CO2 flux in an Arctic tussock tundra ecosystem

The functioning of Arctic ecosystems is not only critically affected by climate change, but it also has the potential for major positive feedback on climate. There is, however, relatively little information on the role, patterns, and vulnerabilities of CO2 fluxes during the nonsummer seasons in Arctic ecosystems. Presented here is a year-round study of CO2 fluxes in an Alaskan Arctic tussock tundra ecosystem, and key environmental controls on these fluxes. Important controls on fluxes vary by season. This paper also presents a new empirical quantification of seasons in the Arctic based on net radiation. The fluxes were computed using standard FluxNet methodology and corrected using standard Webb-Pearman-Leuning density terms adjusted for influences of open-path instrument surface heating. The results showed that the nonsummer season comprises a significant source of carbon to the atmosphere. The summer period was a net sink of 24.3 g C m−2, while the nonsummer seasons released 37.9 g C m−2. This release is 1.6 times the summer uptake, resulting in a net annual source of +13.6 g C m−2 to the atmosphere. These findings support early observations of a change in this particular region of the Arctic from a long-term annual sink of CO2 to an annual source from the terrestrial ecosystem and soils to the atmosphere. The results presented here demonstrate that nearly continuous observations may be required in order to accurately calculate the annual net ecosystem CO2 exchange of Arctic ecosystems and to build predictive understanding that can be used to estimate, with confidence, Arctic fluxes under future conditions.

Mesoscale circulations over complex terrain in the Valencia coastal region, Spain – Part 1: Simulation of diurnal circulation regimes

We collected ground-based and aircraft vertical profile measurements of meteorological parameters during a 2-week intensive campaign over the Valencia basin, in order to understand how mesoscale circulations develop over complex terrain and affect the atmospheric transport of tracers. A high-resolution version of the RAMS model was run to simulate the campaign and characterize the diurnal patterns of the flow regime: night-time katabatic drainage, morning sea-breeze development and its subsequent coupling with mountain up-slopes, and evening flow-veering under larger-scale interactions. An application of this mesoscale model to the transport of CO 2 is given in a companion paper. A careful evaluation of the model performances against diverse meteorological observations is carried out. Despite the complexity of the processes interacting with each other, and the uncertainties on modeled soil moisture boundary conditions and turbulence parameterizations, we show that it is possible to simulate faithfully the contrasted flow regimes during the course of one day, especially the inland progression and organization of the sea breeze. This gives confidence with respect to future applicability of mesoscale models to establish a reliable link between surface sources of tracers and their atmospheric concentration signals over complex terrain.

FLEX — Fluorescence Explorer: A Remote Sensing Approach to Quantify Spatio-Temporal Variations of Photosynthetic Efficiency from Space

Photosynthetic efficiency is greatly affected by internal and external factors and until now no remote sensing approach is available to globally quantify photosynthetic efficiency from air- or space-borne platforms. Quantification of sun-induced steady State fluorescence that can be detected in the atmospheric absorption bands is currently the most promising approach towards a global monitoring platform. This approach was recently highlighted due to the selection of the FLEX proposal as one of the future candidate missions for an ‘Earth Explorer’. Currently several modeling, laboratory and field studies are undertaken to (i) better understand the technical feasibility to monitor the comparably weak fluorescence signals from space; (ii) to proof the correlation of steady State fluorescence with photosynthetic carbon uptake; and (iii) to test the approach for a better modeling of regional carbon fluxes. This paper gives an overview over the status of this ESA project that may be the first and most ambitious remote sensing approach ever undertaken to globally map photosynthesis.

N2O fluxes of a bio‐energy poplar plantation during a two years rotation period

Nitrous oxide emissions are of critical importance for the assumed climate neutrality of bio‐energy. In this study we report on the N2O fluxes from a bio‐energy poplar plantation measured with eddy covariance for 2 years, after conversion of agricultural fields to few months after harvesting of the plantation. A pulse peak of N2O was detected after the land use change and in the wake of the first heavy rainfall. The N2O‐N emission during just a single week was 2.7 kg N2O‐N ha−1 which represented approximately 42% of the total N2O‐N emitted during the 2 years of measurements. After this peak emission, N2O fluxes were constantly rather low, not increasing after rainfall events any longer. Lowest emissions (and even N2O sink) occurred mostly during the end of the second growing season with maximum canopy development, and water table deeper than 80 cm. Gross primary production (GPP) explained 68% of the monthly averaged variability in N2O emission from August to December 2011. Probably N uptake by vegetation during the peak of the second growing season limited N2O emission, which in fact increased again after the plantation was coppiced. For the majority of the measuring period, N2O fluxes did not present a well‐defined diurnal pattern, with the exception of two periods: (1) from 19–22 August 2010 and (2) from September–November 2011. In both cases wind speed played a major role in controlling the diurnal pattern in these fluxes (explaining up to 80% of the diurnal variability in N2O fluxes on 19–22 August 2010), whereas at the end of the second growing season (September–November 2011), GPP explained 73% of the diurnal pattern in N2O fluxes.