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1
Gao, Wen, Xiaoning Yang, Jing Wang, Yanqiang Bi, Boying Lin, Yonghong Shang e Xinguang Cui. "Mass Transfer Theory Based Analysis of Influencing Factors on Component Gradient of Near-surface Atmosphere on Venus". Astrophysical Journal 954, n. 1 (22 agosto 2023): 50. http://dx.doi.org/10.3847/1538-4357/ace622.
Testo completoAbstract (sommario):
Abstract The atmosphere of Venus differs completely from that of Earth despite the planets’ similarity in size and mass. At Venus's surface, the atmosphere is hot and dense, with a temperature of approximately 735 K and a pressure of approximately 92 bar. The temperature profile from the Soviet VeGa-2 probe shows high instability of the near-ground potential temperature, which, according to relevant research, can be explained by the vertical gradient of N2 mole fraction. Based on the Maxwell–Stefan mass transfer theory, we propose a theoretical model of binary gas component for a quantitative discussion of influencing factors for the N2 vertical concentration gradient, which consist of temperature, gravity, specific heat ratio, mass relative factor, thermal diffusion factor, and CO2 flux. Our model shows that the 0%–3.5% N2 concentration gradient cannot be generated without CO2 flux in the near-ground atmosphere of Venus. And the result with CO2 source indicates that the 0.000001%–3.5% N2 concentration gradient at 0–7 km atmosphere can be generated by the 2.7 × 10−6 mol m−2 s−6 CO2 flux on Venusian surface, which is in agreement of gradient reckoned by VeGa-2's data. This magnitude of CO2 flux is close to the one produced by volcanic eruptions on Earth, indicating possible existence of volcanic activities on the surface of Venus. This work has provided the community a new vision to understand the influencing factors of Venusian atmospheres composition distribution.
2
Witkowski, Andrzej, Mirosław Majkut e Sebastian Rulik. "Analysis of pipeline transportation systems for carbon dioxide sequestration". Archives of Thermodynamics 35, n. 1 (1 marzo 2014): 117–40. http://dx.doi.org/10.2478/aoter-2014-0008.
Testo completoAbstract (sommario):
Abstract A commercially available ASPEN PLUS simulation using a pipe model was employed to determine the maximum safe pipeline distances to subsequent booster stations as a function of carbon dioxide (CO2) inlet pressure, ambient temperature and ground level heat flux parameters under three conditions: isothermal, adiabatic and with account of heat transfer. In the paper, the CO2 working area was assumed to be either in the liquid or in the supercritical state and results for these two states were compared. The following power station data were used: a 900 MW pulverized coal-fired power plant with 90% of CO2 recovered (156.43 kg/s) and the monothanolamine absorption method for separating CO2 from flue gases. The results show that a subcooled liquid transport maximizes energy efficiency and minimizes the cost of CO2 transport over long distances under isothermal, adiabatic and heat transfer conditions. After CO2 is compressed and boosted to above 9 MPa, its temperature is usually higher than ambient temperature. The thermal insulation layer slows down the CO2 temperature decrease process, increasing the pressure drop in the pipeline. Therefore in Poland, considering the atmospheric conditions, the thermal insulation layer should not be laid on the external surface of the pipeline.
3
Witkowski, Andrzej, Andrzej Rusin, Mirosław Majkut e Katarzyna Stolecka. "The Analysis of Pipeline Transportation Process for CO2 Captured From Reference Coal-Fired 900 MW Power Plant to Sequestration Region". Chemical and Process Engineering 35, n. 4 (1 dicembre 2014): 497–514. http://dx.doi.org/10.2478/cpe-2014-0037.
Testo completoAbstract (sommario):
Abstract Three commercially available intercooled compression strategies for compressing CO2 were studied. All of the compression concepts required a final delivery pressure of 153 bar at the inlet to the pipeline. Then, simulations were used to determine the maximum safe pipeline distance to subsequent booster stations as a function of inlet pressure, environmental temperature, thickness of the thermal insulation and ground level heat flux conditions. The results show that subcooled liquid transport increases energy efficiency and minimises the cost of CO2 transport over long distances under heat transfer conditions. The study also found that the thermal insulation layer should not be laid on the external surface of the pipe in atmospheric conditions in Poland. The most important problems from the environmental protection point of view are rigorous and robust hazard identification which indirectly affects CO2 transportation. This paper analyses ways of reducing transport risk by means of safety valves.
4
Demezhko, Dmitry Yu, Anastasia A. Gornostaeva, Georgy V. Tarkhanov e Oleg A. Esipko. "30,000 Years of Ground Surface Temperature and Heat Flux Changes in Karelia Reconstructed from Borehole Temperature Data". Bulletin of Geography. Physical Geography Series 6, n. 1 (1 dicembre 2013): 7–25. http://dx.doi.org/10.2478/bgeo-2013-0001.
Testo completoAbstract (sommario):
Abstract Analyses of temperature-depth profiles logged in deep boreholes (> 1 km) permit the reconstruction of ground surface temperature (GST) and surface heat flux (SHF) histories in the period of global climate change at the border of the Pleistocene and the Holocene. We reconstructed past GST and SHF histories using data obtained from the 3.5-km-deep Onega borehole (Karelia, north-west Russia). The resulting reconstructions include information on the basal thermal regime of the Scandinavian Ice Sheet, which covered the region in the Last Glacial Maximum (LGM). The surface temperature history reveals a high amplitude of Pleistocene/ Holocene warming equal to 18-20 K. The heat flux changes precede the surface temperature changes and are close to the variations of insolation at a latitude of 60°N. A comparison of the reconstructed GST and SHF histories with the records of carbon dioxide contents in Antarctic ice cores shows that CO2 changes are much closer to temperature changes than they are to heat flux changes.
5
Cawse-Nicholson, Kerry, Joshua B. Fisher, Caroline A. Famiglietti, Amy Braverman, Florian M. Schwandner, Jennifer L. Lewicki, Philip A. Townsend et al. "Ecosystem responses to elevated CO<sub>2</sub> using airborne remote sensing at Mammoth Mountain, California". Biogeosciences 15, n. 24 (14 dicembre 2018): 7403–18. http://dx.doi.org/10.5194/bg-15-7403-2018.
Testo completoAbstract (sommario):
Abstract. We present an exploratory study examining the use of airborne remote-sensing observations to detect ecological responses to elevated CO2 emissions from active volcanic systems. To evaluate these ecosystem responses, existing spectroscopic, thermal, and lidar data acquired over forest ecosystems on Mammoth Mountain volcano, California, were exploited, along with in situ measurements of persistent volcanic soil CO2 fluxes. The elevated CO2 response was used to statistically model ecosystem structure, composition, and function, evaluated via data products including biomass, plant foliar traits and vegetation indices, and evapotranspiration (ET). Using regression ensemble models, we found that soil CO2 flux was a significant predictor for ecological variables, including canopy greenness (normalized vegetation difference index, NDVI), canopy nitrogen, ET, and biomass. With increasing CO2, we found a decrease in ET and an increase in canopy nitrogen, both consistent with theory, suggesting more water- and nutrient-use-efficient canopies. However, we also observed a decrease in NDVI with increasing CO2 (a mean NDVI of 0.27 at 200 g m−2 d−1 CO2 reduced to a mean NDVI of 0.10 at 800 g m−2 d−1 CO2). This is inconsistent with theory though consistent with increased efficiency of fewer leaves. We found a decrease in above-ground biomass with increasing CO2, also inconsistent with theory, but we did also find a decrease in biomass variance, pointing to a long-term homogenization of structure with elevated CO2. Additionally, the relationships between ecological variables changed with elevated CO2, suggesting a shift in coupling/decoupling among ecosystem structure, composition, and function synergies. For example, ET and biomass were significantly correlated for areas without elevated CO2 flux but decoupled with elevated CO2 flux. This study demonstrates that (a) volcanic systems show great potential as a means to study the properties of ecosystems and their responses to elevated CO2 emissions and (b) these ecosystem responses are measurable using a suite of airborne remotely sensed data.
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Cusano, Paola, Teresa Caputo, Enza De Lauro, Mariarosaria Falanga, Simona Petrosino, Fabio Sansivero e Giuseppe Vilardo. "Tracking the Endogenous Dynamics of the Solfatara Volcano (Campi Flegrei, Italy) through the Analysis of Ground Thermal Image Temperatures". Atmosphere 12, n. 8 (22 luglio 2021): 940. http://dx.doi.org/10.3390/atmos12080940.
Testo completoAbstract (sommario):
In the last decades, thermal infrared ground-based cameras have become effective tools to detect significant spatio-temporal anomalies in the hydrothermal/volcanic environment, possibly linked to impending eruptions. In this paper, we analyzed the temperature time-series recorded by the ground-based Thermal Infrared Radiometer permanent network of INGV-OV, installed inside the Solfatara-Pisciarelli area, the most active fluid emission zones of the Campi Flegrei caldera (Italy). We investigated the temperatures’ behavior in the interval 25 June 2016–29 May 2020, with the aim of tracking possible endogenous hydrothermal/volcanic sources. We performed the Independent Component Analysis, the time evolution estimation of the spectral power, the cross-correlation and the Changing Points’ detection. We compared the obtained patterns with the behavior of atmospheric temperature and pressure, of the time-series recorded by the thermal camera of Mt. Vesuvius, of the local seismicity moment rate and of the CO2 emission flux. We found an overall influence of exogenous, large scale atmospheric effect, which dominated in 2016–2017. Starting from 2018, a clear endogenous forcing overcame the atmospheric factor, and dominated strongly soil temperature variations until the end of the observations. This paper highlights the importance of monitoring and investigating the soil temperature in volcanic environments, as well as the atmospheric parameters.
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Inguaggiato, Salvatore, Fabio Vita, Iole Serena Diliberto, Agnes Mazot, Lorenzo Calderone, Andrea Mastrolia e Marco Corrao. "The Extensive Parameters as a Tool to Monitoring the Volcanic Activity: The Case Study of Vulcano Island (Italy)". Remote Sensing 14, n. 5 (5 marzo 2022): 1283. http://dx.doi.org/10.3390/rs14051283.
Testo completoAbstract (sommario):
On Vulcano Island (Italy), many geochemical crises have occurred during the last 130 years of solfataric activity. The main crises occurred in 1978–1980, 1988–1991, 1996, 2004–2007, 2009–2010 and the ongoing 2021 anomalous degassing activity. These crises have been characterized by early signals of resuming degassing activity, measurable by the increase of volatiles and energy output emitted from the summit areas of the active cone, and particularly by increases of gas/water ratios in the fumarolic area at the summit. In any case, a direct rather than linear correspondence has been observed among the observed increase in the fluid output, seismic release and ground deformation, and is still a subject of study. We present here the results obtained by the long-term monitoring (over 13 years of observations) of three extensive parameters: the SO2 flux monitored in the volcanic plume, the soil CO2 flux and the local heat flux, monitored in the mild thermal anomaly located to the east of the high-temperature fumarole. The time variations of these parameters showed cyclicity in the volcanic degassing and a general increase in the trend in the last period. In particular, we focused on the changes in the mass and energy output registered in the period of June–December 2021, to offer in near-real-time the first evaluation of the level and duration of the actual exhalative crisis affecting Vulcano Island. In this last event, a clear change in degassing style was recorded for the volatiles emitted by the magma. For example, the flux of diffused CO2 from the soils reached the maximum never-before-recorded value of 34,000 g m−2 d−1 and the flux of SO2 of the plume emitted by the fumarolic field on the summit crater area reached values higher than 200 t d−1. The interpretation of the behavior of this volcanic system, resulting from the detailed analyses of these continuous monitoring data, will complete the framework of observations and help in defining and possibly forecasting the next evolution of the actual exhaling crisis.
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Setina, Janina. "Preparation of Synthetic Cordierite by Solide-State-Reaction with Addition of Dolomite". Advances in Science and Technology 45 (ottobre 2006): 77–82. http://dx.doi.org/10.4028/www.scientific.net/ast.45.77.
Testo completoAbstract (sommario):
Cordierite was obtained from the mixture of aluminum hydroxide, sand, different magnesium compounds by a solid-state reaction method. The effect of dolomite doping on phase-transformation kinetics and microstructure has been investigated during thermal treatment by keeping a stoichiometric cordierite compound. Adding of dolomite has been used as a flux for preparation of a cordierite precursor by a coprecipitation process. Subsequently, DTA and XRD analyses were conducted to identify the phases formed in the sintered products. Morphological changes of the ground mixtures and sintered product were observed using SEM. The crystallization process of metastable quartz like μ-cordierite can be obtained at 1250…13000C. In this range of temperature form other compounds, such as spinel, quartz. Increase of sintering temperature and prolonged holding times promote the formation of only one phase – indialite or α-cordierite, the hexagonal form of cordierite. Experimental observation shows two steps in the solid-state reaction. First step – formation of volatiles compounds and pores, second – formation and growing of crystalline phases. Evolution of CO, CO2 and H2O that occurred during the thermal treatment of compositions is very important fact in the nucleation process. The intensity of crystallization depends on the gas volume and amount of pore in the sample. The experiments indicated that the intrinsic concentration of volatiles like CO, CO2, H2O influence the appearance of the cordierite phase. SEM photographs sowed that crystallization of cordierite start on the surface of pore. Growth of α-cordierite inside of pores is considerably affected by the time of thermal treatment and amount of adding of dolomite. A remarkable change in peak intensity of XRD patterns of the compositions was observed. Up to 20 wt. % addition of dolomite to the precursor allowed the fabrication of synthetic cordierite at lower temperature.
9
Guo, Liang, Tiecheng Qiu, Qian Zhang, Zhanping Guo e Ming Shan. "Influences of temperature on the property of ITO/Teflon/Ag in atomic oxygen environment". Journal of Physics: Conference Series 2720, n. 1 (1 marzo 2024): 012016. http://dx.doi.org/10.1088/1742-6596/2720/1/012016.
Testo completoAbstract (sommario):
Abstract This paper uses ground simulation equipment for an atomic oxygen environment to conduct experimental research on ITO/Teflon/Ag, which is used in spacecraft using an atomic oxygen environment. The atomic oxygen integrated flux selected in the study is 9.1× 1019 atoms/cm2, with a vacuum degree of 10-2 Pa, and sample temperatures of 20°C, 70°C, and 120°C, respectively, were selected to investigate the possible impact of sample temperature on atomic oxygen environment simulation experiments. After the test, a high-precision microelectronic balance was used to test the mass loss of the sample and calculate the reaction rate of the material. The thermal emissivity and solar absorption ratio of the sample were tested using TEMP 2000A and LPSR 300, respectively. Through experiments and analysis, it was found that as the sample temperature increased, the ITO/Teflon/Ag reaction rate with atomic oxygen gradually increased but remained at 10-25. Atomic oxygen and temperature have a significant impact on the thermal physical properties of the material.
10
Wang, Sheng, Monica Garcia, Andreas Ibrom e Peter Bauer-Gottwein. "Temporal interpolation of land surface fluxes derived from remote sensing – results with an unmanned aerial system". Hydrology and Earth System Sciences 24, n. 7 (22 luglio 2020): 3643–61. http://dx.doi.org/10.5194/hess-24-3643-2020.
Testo completoAbstract (sommario):
Abstract. Remote sensing imagery can provide snapshots of rapidly changing land surface variables, e.g. evapotranspiration (ET), land surface temperature (Ts), net radiation (Rn), soil moisture (θ), and gross primary productivity (GPP), for the time of sensor overpass. However, discontinuous data acquisitions limit the applicability of remote sensing for water resources and ecosystem management. Methods to interpolate between remote sensing snapshot data and to upscale them from an instantaneous to a daily timescale are needed. We developed a dynamic soil–vegetation–atmosphere transfer model to interpolate land surface state variables that change rapidly between remote sensing observations. The “Soil–Vegetation, Energy, water, and CO2 traNsfer” (SVEN) model, which combines the snapshot version of the remote sensing Priestley–Taylor Jet Propulsion Laboratory ET model and light use efficiency GPP models, now incorporates a dynamic component for the ground heat flux based on the “force-restore” method and a water balance “bucket” model to estimate θ and canopy wetness at a half-hourly time step. A case study was conducted to demonstrate the method using optical and thermal data from an unmanned aerial system at a willow plantation flux site (Risoe, Denmark). Based on model parameter calibration with the snapshots of land surface variables at the time of flight, SVEN interpolated UAS-based snapshots to continuous records of Ts, Rn, θ, ET, and GPP for the 2016 growing season with forcing from continuous climatic data and the normalized difference vegetation index (NDVI). Validation with eddy covariance and other in situ observations indicates that SVEN can estimate daily land surface fluxes between remote sensing acquisitions with normalized root mean square deviations of the simulated daily Ts, Rn, θ, LE, and GPP of 11.77 %, 6.65 %, 19.53 %, 14.77 %, and 12.97 % respectively. In this deciduous tree plantation, this study demonstrates that temporally sparse optical and thermal remote sensing observations can be used to calibrate soil and vegetation parameters of a simple land surface modelling scheme to estimate “low-persistence” or rapidly changing land surface variables with the use of few forcing variables. This approach can also be applied with remotely-sensed data from other platforms to fill temporal gaps, e.g. cloud-induced data gaps in satellite observations.
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Rascher, U., G. Agati, L. Alonso, G. Cecchi, S. Champagne, R. Colombo, A. Damm et al. "CEFLES2: the remote sensing component to quantify photosynthetic efficiency from the leaf to the region by measuring sun-induced fluorescence in the oxygen absorption bands". Biogeosciences Discussions 6, n. 1 (24 febbraio 2009): 2217–66. http://dx.doi.org/10.5194/bgd-6-2217-2009.
Testo completoAbstract (sommario):
Abstract. The CEFLES2 campaign during the Carbo Europe Regional Experiment Strategy was designed to provide simultaneous airborne measurements of solar induced fluorescence and CO2 fluxes. It was combined with extensive ground-based quantification of leaf- and canopy-level processes in support of ESA's Candidate Earth Explorer Mission of the "Fluorescence Explorer" (FLEX). The aim of this campaign was to test if fluorescence signal detected from an airborne platform can be used to improve estimates of plant mediated exchange on the mesoscale. Canopy fluorescence was quantified from four airborne platforms using a combination of novel sensors: (i) the prototype airborne sensor AirFLEX quantified fluorescence in the oxygen A and B bands, (ii) a hyperspectral spectrometer (ASD) measured reflectance along transects during 12 day courses, (iii) spatially high resolution georeferenced hyperspectral data cubes containing the whole optical spectrum and the thermal region were gathered with an AHS sensor, and (iv) the first employment of the high performance imaging spectrometer HYPER delivered spatially explicit and multi-temporal transects across the whole region. During three measurement periods in April, June and September 2007 structural, functional and radiometric characteristics of more than 20 different vegetation types in the Les Landes region, Southwest France, were extensively characterized on the ground. The campaign concept focussed especially on quantifying plant mediated exchange processes (photosynthetic electron transport, CO2 uptake, evapotranspiration) and fluorescence emission. The comparison between passive sun-induced fluorescence and active laser-induced fluorescence was performed on a corn canopy in the daily cycle and under desiccation stress. Both techniques show good agreement in detecting stress induced fluorescence change at the 760 nm band. On the large scale, airborne and ground-level measurements of fluorescence were compared on several vegetation types supporting the scaling of this novel remote sensing signal. The multi-scale design of the four airborne radiometric measurements along with extensive ground activities fosters a nested approach to quantify photosynthetic efficiency and gross primary productivity (GPP) from passive fluorescence.
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Rascher, U., G. Agati, L. Alonso, G. Cecchi, S. Champagne, R. Colombo, A. Damm et al. "CEFLES2: the remote sensing component to quantify photosynthetic efficiency from the leaf to the region by measuring sun-induced fluorescence in the oxygen absorption bands". Biogeosciences 6, n. 7 (17 luglio 2009): 1181–98. http://dx.doi.org/10.5194/bg-6-1181-2009.
Testo completoAbstract (sommario):
Abstract. The CEFLES2 campaign during the Carbo Europe Regional Experiment Strategy was designed to provide simultaneous airborne measurements of solar induced fluorescence and CO2 fluxes. It was combined with extensive ground-based quantification of leaf- and canopy-level processes in support of ESA's Candidate Earth Explorer Mission of the "Fluorescence Explorer" (FLEX). The aim of this campaign was to test if fluorescence signal detected from an airborne platform can be used to improve estimates of plant mediated exchange on the mesoscale. Canopy fluorescence was quantified from four airborne platforms using a combination of novel sensors: (i) the prototype airborne sensor AirFLEX quantified fluorescence in the oxygen A and B bands, (ii) a hyperspectral spectrometer (ASD) measured reflectance along transects during 12 day courses, (iii) spatially high resolution georeferenced hyperspectral data cubes containing the whole optical spectrum and the thermal region were gathered with an AHS sensor, and (iv) the first employment of the high performance imaging spectrometer HYPER delivered spatially explicit and multi-temporal transects across the whole region. During three measurement periods in April, June and September 2007 structural, functional and radiometric characteristics of more than 20 different vegetation types in the Les Landes region, Southwest France, were extensively characterized on the ground. The campaign concept focussed especially on quantifying plant mediated exchange processes (photosynthetic electron transport, CO2 uptake, evapotranspiration) and fluorescence emission. The comparison between passive sun-induced fluorescence and active laser-induced fluorescence was performed on a corn canopy in the daily cycle and under desiccation stress. Both techniques show good agreement in detecting stress induced fluorescence change at the 760 nm band. On the large scale, airborne and ground-level measurements of fluorescence were compared on several vegetation types supporting the scaling of this novel remote sensing signal. The multi-scale design of the four airborne radiometric measurements along with extensive ground activities fosters a nested approach to quantify photosynthetic efficiency and gross primary productivity (GPP) from passive fluorescence.
13
Sirotyuk, V. V. "Heat treatment of ground surface using an electric arc plasma generator". Construction and Geotechnics 14, n. 4 (15 dicembre 2023): 46–61. http://dx.doi.org/10.15593/2224-9826/2023.4.04.
Testo completoAbstract (sommario):
The article presents a generalization of the results of experimental and theoretical studies on the intensive thermal effect on the surface of foundations from cohesive soils (as opposed to deep heat treatment) using an electric arc generator of low-temperature plasma (plasmatron). A plasmatron with massive consumable electrodes made of borosilicated graphite and a wide "blurred" plasma torch was used for heat treatment. Physical and mathematical modeling of the thermal effect on the surface of clay soil by a moving high-temperature source has been performed. For the first time, a special installation was manufactured and experimental studies were carried out on the heat treatment of ground surfaces on the site with an electric arc plasma torch. It is established that the effective heat flux density reaches 2.5-.3.5 kW/cm2. The main part of the thermal energy for the used plasmatron enters the material due to radiant heat transfer. An analytical mathematical model of the temperature field of a three-dimensional semi-bounded body in the technological process under consideration is given by an essentially nonlinear boundary value problem for a nonlinear heat equation with nonlinear boundary conditions of the second kind. When solving thermophysical problems, the ground semi-bounded space was considered as a quasi-homogeneous medium having a constant initial temperature and initial thermophysical parameters that change in the process of temperature increase. The effective values of the thermophysical characteristics were determined on the basis of experimental data. Calculations and experiments have shown that the temperature boundary leading to significant changes in the structural properties of soils drops to a depth of 4-6 cm from the surface, despite the boiling of the ground melt with a temperature of 2500 ...2800 K on the ground surface. Therefore, a new technological principle of heat treatment is proposed, which consists in building up the ground melt in layers of 4-5 cm up from the initial surface. The impossibility of obtaining a positive effect even with the use of a powerful high-temperature source of exposure in the case of traditional surface heat treatment technology has been confirmed. The new plasma technology of surface heat treatment of ground surfaces to the stage of silicate melt allows to obtain a common layer of the required thickness. At the same time, the efficiency of surface heat treatment is significantly increased. The new technology of layer-by-layer surface deposition reduces cracking in the layer when the melt cools, but does not eliminate this negative process.
14
Houweling, S., F. M. Breon, I. Aben, C. Rödenbeck, M. Gloor, M. Heimann e P. Ciais. "Inverse modeling of CO<sub>2</sub> sources and sinks using satellite data: a synthetic inter-comparison of measurement techniques and their performance as a function of space and time". Atmospheric Chemistry and Physics 4, n. 2 (25 marzo 2004): 523–38. http://dx.doi.org/10.5194/acp-4-523-2004.
Testo completoAbstract (sommario):
Abstract. Currently two polar orbiting satellite instruments measure CO2 concentrations in the Earth's atmosphere, while other missions are planned for the coming years. In the future such instruments might become powerful tools for monitoring changes in the atmospheric CO2 abundance and to improve our quantitative understanding of the leading processes controlling this. At the moment, however, we are still in an exploratory phase where first experiences are collected and promising new space-based measurement concepts are investigated. This study assesses the potential of some of these concepts to improve CO2 source and sink estimates obtained from inverse modelling. For this purpose the performance of existing and planned satellite instruments is quantified by synthetic simulations of their ability to reduce the uncertainty of the current source and sink estimates in comparison with the existing ground-based network of sampling sites. Our high resolution inversion of sources and sinks (at 8°x10°) allows us to investigate the variation of instrument performance in space and time and at various temporal and spatial scales. The results of our synthetic tests clearly indicate that the satellite performance increases with increasing sensitivity of the instrument to CO2 near the Earth's surface, favoring the near infra-red technique. Thermal infrared instruments, on the contrary, reach a better global coverage, because the performance in the near infrared is reduced over the oceans owing to a low surface albedo. Near infra-red sounders can compensate for this by measuring in sun-glint, which will allow accurate measurements over the oceans, at the cost, however, of a lower measurement density. Overall, the sun-glint pointing near infrared instrument is the most promising concept of those tested. We show that the ability of satellite instruments to resolve fluxes at smaller temporal and spatial scales is also related to surface sensitivity. All the satellite instruments performed relatively well over the continents resulting mainly from the larger prior flux uncertainties over land than over the oceans. In addition, the surface networks are rather sparse over land increasing the additional benefit of satellite measurements there. Globally, challenging satellite instrument precisions are needed to compete with the current surface network (about 1ppm for weekly and 8°x10° averaged SCIAMACHY columns). Regionally, however, these requirements relax considerably, increasing to 5ppm for SCIAMACHY over tropical continents. This points not only to an interesting research area using SCIAMACHY data, but also to the fact that satellite requirements should not be quantified by only a single number. The applicability of our synthetic results to real satellite instruments is limited by rather crude representations of instrument and data retrieval related uncertainties. This should receive high priority in future work.
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Houweling, S., F. M. Breon, I. Aben, C. Rödenbeck, M. Gloor, M. Heimann e P. Ciais. "Inverse modeling of CO<sub>2</sub> sources and sinks using satellite data: A synthetic inter-comparison of measurement techniques and their performance as a function of space and time". Atmospheric Chemistry and Physics Discussions 3, n. 5 (20 ottobre 2003): 5237–74. http://dx.doi.org/10.5194/acpd-3-5237-2003.
Testo completoAbstract (sommario):
Abstract. Currently two polar orbiting satellite instruments measure CO2 concentrations in the Earth's atmosphere, while other missions are planned for the coming years. In the future such instruments might become powerful tools for monitoring changes in the atmospheric CO2 abundance and to improve our quantitative understanding of the leading processes controlling this. At the moment, however, we are still in an exploratory phase where first experiences are collected and promising new space-based measurement concepts are investigated. This study assesses the potential of some of these concepts to improve CO2 source and sink estimates obtained from inverse modelling. For this purpose the performance of existing and planned satellite instruments is quantified by synthetic simulations of their ability to reduce the uncertainty of the current source and sink estimates in comparison with the existing ground-based network of sampling sites. Our high resolution inversion of sources and sinks (at 8º x 10º allows us to investigate the variation of instrument performance in space and time and at various temporal and spatial scales. The results of our synthetic tests clearly indicate that the satellite performance increases with increasing sensitivity of the instrument to CO2 near the Earth's surface, favoring the near infra-red technique. Thermal infrared instruments, on the contrary, reach a better global coverage, because the performance in the near infrared is reduced over the oceans owing to a low surface albedo. Near infra-red sounders can compensate for this by measuring in sun-glint, which will allow accurate measurements over the oceans, at the cost, however, of a lower measurement density. Overall, the sun-glint pointing near infrared instrument is the most promising concept of those tested. We show that the ability of satellite instruments to resolve fluxes at smaller temporal and spatial scales is also related to surface sensitivity. All the satellite instruments performed relatively well over the continents resulting mainly from the larger prior flux uncertainties over land than over the oceans. In addition, the surface networks are rather sparse over land increasing the additional benefit of satellite measurements there. Globally, rather challenging satellite instrument precisions are needed to compete with the surface network (about 1 ppmv for weekly and 8° × 10° averaged SCIAMACHY columns). Regionally, however, these requirements relax considerably, increasing to 5 ppmv for SCIAMACHY over tropical continents. This points not only to an interesting research area using SCIAMACHY data, but also to the fact that satellite requirements should not be quantified by only a single number. The applicability of our synthetic results to real satellite instruments is limited by rather crude representations of instrument and data retrieval related uncertainties. This should receive high priority in future work.
16
Delfini, Andrea, Roberto Pastore, Marta Albano, Fabio Santoni, Fabrizio Piergentili e Mario Marchetti. "Synergistic Effects of Atomic Oxygen and UV Radiation on Carbon/Carbon Plates at Different Attitude Positions". Applied Sciences 14, n. 13 (4 luglio 2024): 5850. http://dx.doi.org/10.3390/app14135850.
Testo completoAbstract (sommario):
Atomic oxygen (AtOx) is a major component of the space environment between 200 and 800 km (LEO—low Earth orbit region) and is the principal source of erosion for exposed aerospace structures. The damage to surface materials is proportional to the AtOx fluence, which depends on altitude, exposure time, orbital inclination, and solar activity, and it is caused by the formation of volatile oxides which do not adhere to the surface; furthermore, the mass loss may also be worsened by UV radiation, which increases the chemical degradation of the exposed material. Carbon/carbon (C/C) is an advanced ceramic composite that is frequently found as a base component of thermal protection systems (TPS), rocket nozzles, or other spacecraft subsystems. In this work, a simulation of the AtOx/UV synergistic effects on C/C plates exposed at different attitude positions were carried out by experimental tests performed at the Aerospace Systems Laboratory (LSA—Sapienza University of Rome) by means of an Atomic Oxygen OS-Prey RF plasma source, which also included a high-power UV-ray generator. The present experimental plan was built on the activity developed during recent years at LSA concerning the study of C/C materials for protecting aerospace structures from thermal shock in re-entry missions. The tests were conceived by considering a fixed time of exposure with a base fluence of 7.6 × 1019 n.s./cm2, as evaluated from the erosion of the reference samples exposed to AtOx flux at a normal incidence; the simulation of the different attitude positions was then analyzed, also considering the simultaneous effect of UV radiation. The results of the aging ground test suggest the following: (i) C/C oxidation in LEO must be taken into full consideration in the TPS design with reference to protective coating solutions, (ii) the LEO environment simulation is closely related to AtOx/UV combined irradiation, as well as to the spacecraft’s in-orbit attitude.
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Deyneko, Nataly, Mikhailo Divizinyuk, Оlexandr Levterov, Volodymyr Mirnenko e Olga Shevchenko. "New approaches to the implementation of information and technical methods for the prevention of emergencies as a result of fire in conditions of damage to the power supply of emergency response systems". Legal, regulatory and metrological support of information security system in Ukraine, n. 2(38) (21 luglio 2021): 103–10. http://dx.doi.org/10.20535/2074-9481.2(38).2019.235226.
Testo completoAbstract (sommario):
The paper proposes the development of new approaches to the creation of emergency response systems using non-traditional power supplies in the event of damage to traditional power supply systems.The main idea of the work is the formation of integrated approaches to alternative methods based on the phenomenon of acoustic emission (AE) using an unconventional power source based on film solar cells on flexible substrates. The creation of photoconverters based on thin films from a variety of materials and compounds is a promising direction in the development of solar energy. Unfortunately, the efficiency of these photoconverters is not yet high enough, but the cost of equipment for their creation, and hence the cost of instrument structures, is already quite acceptable.The investigated solar cells were obtained by the method of thermal vacuum evaporation using a UVN67 vacuum unit with modified internal equipment.After manufacturing, solar cells (SCs) were investigated under standard laboratory conditions adopted for the study of solar cells for ground-based use, i.e. in the AM 1.5 mode with a luminous flux power of 100 mW / cm2 and a temperature of 25 ° C. To study degradation processes in such solar cells after measuring the initial parameters The solar cells were placed in a sealed plastic box and kept for 4 years at a temperature of 15-25 ° СChecking the elements demonstrate high degradation resistance, which provides general requirements for the material and the conditions for its creation promising for use as unconventional sources of power supply for emergency response systems and ensuring the use of information and technical methods for preventing emergency situations as a result of fire in conditions of damage to the power supply of emergency response systems.
18
SINGH, A. K. "An estimate of ground heat flux for a seasonal snow cover". MAUSAM 50, n. 2 (17 dicembre 2021): 153–58. http://dx.doi.org/10.54302/mausam.v50i2.1840.
Testo completoAbstract (sommario):
An estimation of ground heat flux for two locations has been done using temperature gradient method. Effective media approach has been adopted for predicting the effective thermal conductivity of ground. For comparison, in situ measurement of effective thermal conductivity of ground has also been done by thermal probe method. The measured values of thermal conductivity are in agreement with the calculated values. The estimated values of ground heat flux have been used to evaluate the melt rate at ground-snow interface.
19
Panov, Alexey, Anatoly Prokushkin, Mikhail Korets, Ilya Putilin, Galina Zrazhevskaya, Roman Kolosov e Mikhail Bondar. "Variation in Soil CO2 Fluxes across Land Cover Mosaic in Typical Tundra of the Taimyr Peninsula, Siberia". Atmosphere 15, n. 6 (9 giugno 2024): 698. http://dx.doi.org/10.3390/atmos15060698.
Testo completoAbstract (sommario):
Increased warming in the Arctic is of great concern. This is particularly due to permafrost degradation, which is expected to accelerate microbial breakdown of soil organic carbon, with its further release into the atmosphere as carbon dioxide (CO2). The fine-scale variability of CO2 fluxes across highly mosaic Arctic tundra landscapes can provide us with insights into the diverse responses of individual plant communities to environmental change. In the paper, we contribute to filling existing gaps by investigating the variability of CO2 flux rates within different landscape units for dominant vegetation communities and plant species across typical tundra of the southern part of the Taimyr Peninsula, Siberia. In general, the variability of soil CO2 flux illustrates a four-fold increase from non-vascular vegetation, mainly lichens and mosses (1.05 ± 0.36 µmol m−2 s−1), towards vascular plants (3.59 ± 0.51 µmol m−2 s−1). Barren ground (“frost boils”) shows the lowest value of 0.79 ± 0.21 µmol m−2 s−1, while considering the Arctic “browning” phenomenon, a further substantial increase of CO2 flux can be expected with shrub expansion. Given the high correlation with top soil temperature, well-drained and relatively dry habitats such as barren ground and non-vascular vegetation are expected to be the most sensitive to the observed and projected temperature growth in the Arctic. For mixed vegetation and vascular species that favor wetter conditions, soil moisture appears to play a greater role. Based on the modeled seasonal pattern of soil CO2 flux and precipitation records, and applying the rainfall simulations in situ we outlined the role of precipitation across enhanced CO2 emissions (i.e., the “Birch” effect). We found that a pulse-like growth of soil CO2 fluxes, observed within the first few minutes after rainfall on vegetated plots, reaches 0.99 ± 0.48 µmol m−2 s−1 per each 1 mm of precipitation, while barren ground shows 55–70% inhibition of CO2 emission during the first several hours. An average additive effect of precipitation on soil CO2 flux may achieve 7–12% over the entire growing season, while the projected increased precipitation regime in the Arctic may strengthen the total CO2 release from the soil surface to the atmosphere during the growing season.
20
Lv, Peng Peng, Feng Wang, Yu Hai Guo e Hong Yan Tang. "CO2 Desorption by Hydrophilic PTFE Hollow Fiber Membranes via a Membrane Flash Process". Key Engineering Materials 671 (novembre 2015): 293–99. http://dx.doi.org/10.4028/www.scientific.net/kem.671.293.
Testo completoAbstract (sommario):
In this study, hydrophilic PTFE hollow fiber membranes were prepared and applied for CO2 desorption via a membrane flash process, which is a new CO2 desorption process by utilizing waste thermal energy. The methyldiethanolamine was selected as the absorbent. Effects of the flashing temperature, flashing pressure, rich solution flow rate and MDEA concentration on CO2 release ratio and CO2 desorption flux were deeply investigated. The results show that flashing temperature is positive to the CO2 release ratio and CO2 desorption flux. However, the flashing pressure, rich solution flow rate and MDEA concentration are negative to the CO2 release ratio and CO2 desorption flux.
21
Bennett, William B., Jingfeng Wang e Rafael L. Bras. "Estimation of Global Ground Heat Flux". Journal of Hydrometeorology 9, n. 4 (1 agosto 2008): 744–59. http://dx.doi.org/10.1175/2008jhm940.1.
Testo completoAbstract (sommario):
Abstract This study investigates the use of a previously published algorithm for estimating ground heat flux (GHF) at the global scale. The method is based on an analytical solution of the diffusion equation for heat transfer in a soil layer and has been shown to be effective at the point scale. The algorithm has several advantageous properties: 1) it only needs a single-level input of surface (skin) temperature, 2) the time-mean GHF can be derived directly from time-mean skin temperature, 3) it has reduced sensitivity to the variability in soil thermal properties and moisture, 4) it does not requires snow depth, and 5) it is computationally effective. A global map of the necessary thermal inertia parameter is derived using reanalysis data as a function of soil type. These parameter estimates are comparable to values obtained from in situ observations. The new global GHF estimates are generally consistent with the reanalysis GHF output simulated using two-layer soil hydrology models. The authors argue that the new algorithm is more robust and trustworthy in regions where they differ. The proposed algorithm offers potential benefits for direct assimilation of observations of surface temperature as well as GHF into the reanalysis models at various time scales.
22
Runkov, R. A., e D. V. Ilyasov. "SPATIAL VARIABILITY OF METHANE EMISSIONS FROM SOILS OF WET FORESTS: A BRIEF REVIEW". Environmental Dynamics and Global Climate Change 14, n. 3 (18 gennaio 2024): 167–80. http://dx.doi.org/10.18822/edgcc375293.
Testo completoAbstract (sommario):
Methane is one of the most important greenhouse gases that cause climate change [Karol and Kiselev, 2003]. An increase in the atmospheric concentration of methane contributes to an increase in the temperature on the Earth, because this gas absorbs outgoing thermal radiation from the Earth's surface [Berdin, 2004]. Methane has a much shorter atmospheric lifetime than carbon dioxide (CO2), but CH4 absorbs certain wavelengths of energy more efficiently than СО2. The global warming potential of CH4 is 28 times greater than that of CO2 over a 100-year period [IPCC, 2013]. Its contribution to the formation of the greenhouse effect is 30% of the value assumed for carbon dioxide (Bazhin, 2006). Methane is removed from the atmosphere by photochemical oxidation in the troposphere and, to a lesser extent, by microbial oxidation in soils (Kirschke et al., 2013).
Methane sources can be both natural and anthropogenic. The latter includes, firstly, industrial processes:
fuel use [Omara et al., 2018; Johnson et al., 2023] (if the fuel is not completely burned, then methane gas is emitted into the air, besides it can also be released during the extraction and transportation of natural gas [Hawken et al., 2017]);
food production (eg CH4 can be generated from the fermentation of food residues that were not used in the production process [Stephan et al., 2006]);
as a result of microbial activity during the processing of waste in landfills and compost heaps (for example, in the process of biological waste treatment, methane can be produced in large quantities if the process is not properly controlled [Singh et al., 2017]).
Secondly, two types of agricultural production are anthropogenic sources:
rice cultivation [Seiler et al., 1984; Dannenberg and Conrad, 1999; Wang et al. 1997; Wang et al., 1999];
cattle breeding [Gerber et al., 2013; Johnson et al., 2023; Ellis et al., 2007].
CH4 is formed as a result of the biological decomposition of organic matter in the absence of oxygen [Dlugokencky and Houweling, 2003]. The most significant natural sources of methane are wetlands. Besides, methane can be emitted from aquatic ecosystems such as lakes and rivers. The decomposition of organic wastes in the soil, such as plant residues and animal manure, is also a natural source of methane (Smith et al., 2014) if this decomposition occurs under anaerobic conditions.
Of great interest is the study of wet forests [Glukhova et al., 2021], since their contribution to methane emission can be quite significant. It is generally recognized that forests are CH4 sinks [Lemer and Roger, 2001; Megonigal and Guenther, 2008; Smith et al., 2000]. Nevertheless, very high CH4 fluxes were detected during spot measurements in some wet forests [Lohila et al., 2016; Tathy et al., 1992], that were comparable to the fluxes observed in wetlands [Harriss et al., 1982; Sabrekov et al., 2011; Glagolev et al., 2012; Davydov et al., 2021] (Fig. 1). However, single measurements of fluxes at individual spatial sites are clearly not enough to assess the role of wet forests in the overall methane balance. This role can be assessed only by knowing the dynamics of emission in time and its distribution in space.
A comprehensive study of the variability of methane emission (from soils in general) began at the end of the 20th century in countries with significant areas of waterlogged soils: Brazil, Canada, the USA, and Russia [Bartlett et al., 1988; Moore et al., 1990; Disse, 1993; Glagolev et al., 1999]. At present, the emission spatial variability is studied in almost all regions of the world, including Finland, Mexico, and China [Zhang et al., 2020; Gonzalez-Valencia et al., 2021; Que et al., 2023]. However, there is very little data on the spatial variability of methane emissions in wet forests. Therefore, it is evident that current research should be focused on assessing the spatial variability of emissions in different types of wet forests.
Emission of methane in wet forests. The main works devoted to measurements of the specific flux of methane in wet forests are summarized in Table 1. 1-3. It can be seen from the tables (and Fig. 2) that there is no clear relationship between the specific flux and the geographic location of the wet forest: in the “north” (in the boreal zone - about 57-67oN), values of ~4÷9 mg∙h-1∙m-2 can be measured [Lohila et al., 2016; Mochenov et al., 2018], that are similar to those typical for the tropics (~3÷8 mg∙h-1∙m-2 [Devol et al., 1990; Tathy et al., 1992]). On the contrary, in the south, values 1 or even 0.1 mg∙h-1∙m-2 can be measured that are more typical for northern territories.
There is no doubt, everything is determined by environmental factors. The results of [Ulah and Moor, 2011] show that changes in soil temperature and moisture can have a significant impact on CH4 fluxes from forest soils. This often leads to so-called "hotspots" such as peak emissions from poorly drained soils when the pore space is filled with water and to a lower CO2:CH4 emission ratio. However, these factors are likely to be unequal.
In fact, the flow rate is determined rather by the degree of anaerobiosis, depending on the conditions of humidity, than the temperature (the formation of CH4 should be very active at both 40o and 20°C assuming that temperatures around 20°C are quite common for the summer period in the boreal zone). It is certain, under the same humidity conditions, based on the well-known van't Hoff low, one can expect that the rate of methane production in the tropics at 40°C should be approximately 4-9 times higher than that at 20°C under boreal conditions. Yet, if there is a very deep anaerobiosis in the boreal zone (due to the complete watering of the soil) but wet soil in the tropics, then the above mentioned ratio can be reversed.
The extremely strong dependence of methane production on the degree of anaerobiosis (and, hence, on humidity conditions) provides a very wide spatial variability of the emission. It can be seen from the data in Table 1 that, for example, in three seasonally flooded forests in Western Siberia, located at a distance of only about 5-10 km from each other, the entire spectrum of possible specific CH4 fluxes was observed at the same time, from absorption at a level of ~0.1 mg h-1 m-2 to a very active emission of ~10 mg h-1 m-2 [Mochenov et al., 2018]. An even more contrasting picture is observed, for example, in the mountain forest in Brazil and in the tropical forest of the Congo: within the same forest, the specific flux varies from 0 to 54 mg∙h-1∙m-2 [Bartlett et al., 1988] and from -0.31 to 150 mg∙h-1∙m-2, respectively (see Table 3). However, it is not always possible to find out the dependence of the flow on certain factors. For example, the measurements reported in Tang et al. [2018] showed that CH4 flux from tropical peat forest was similar to that from other managed and natural wetland ecosystems, including those located in different climate zones. However, meteorological variability in the rainforest does not correlate well with CH4 flux. Such apparent lack of correlation can be explained by the small range of micrometeorological variables in the tropical peat ecosystem.
Ambus and Christensen [1995] studied several ecosystems where temporary waterlogging was possible. They made the following important assumption: the calculation of the total flux for periodically waterlogged ecosystems should be performed taking into account the topography of the landscape. Indeed, a more accurate estimate of methane consumption and emission can be obtained in this way, but the correct estimations of the gas flow by the chamber method requires taking into account the relative water levels during flooding. Knowing the topography and hydrology of each site in the area makes it possible to determine how long and how often this site remains relatively wet or dry [Glagolev et al., 2018].
From the above data, it is clear that there is a need to improve the quantitative assessment of the global methane emission from the soils of wet forests. Despite the establishment of a complex infrastructure for monitoring greenhouse gases on a global scale (eg ICOS, GMB, etc.), ground-based observations in wet forests on various continents are still underrepresented. Therefore, the contribution of forests to the global atmospheric exchange of CH4 remains uncertain.
23
Tang, Chun Li, e Xiao Wei Zhang. "Thermal Behavior of Double Glass Window Filled with Absorbing and Non-Absorbing Gas". Advanced Materials Research 805-806 (settembre 2013): 1603–11. http://dx.doi.org/10.4028/www.scientific.net/amr.805-806.1603.
Testo completoAbstract (sommario):
This paper presents a radiant model based on the radiant resistance analysis theory and the results of numerical simulations of double glass window. The two-dimensional steady state model is formulated based upon the radiation and free convection heat transfer at different external and internal ambient conditions.The properties of glass which change with incident wavelength are also considered. Specifically, air and CO2 are used as the medium in the 8mm and 10mm cavity of the double glass window, respectively. Several parameters, including transmitted solar radiation flux, temperature distribution, surface heat transfer coefficient for free convection and total surface heat flux are calculated. The results show that transmitted solar radiation flux is slightly lower when filled with CO2 in the cavity than with air due to their absorption difference. Also, the temperature of gas closing to internal glass sheet and the total surface heat flux of internal glass sheet are decreased when filled with CO2 than with air, although the surface heat transfer coefficient is slightly higher when it is CO2. .The temperature variation curves show that less heat flows into the room when filled with CO2 than air in double glass window.
24
Ambrožová, Klára, Filip Hrbáček e Kamil Láska. "The Summer Surface Energy Budget of the Ice-Free Area of Northern James Ross Island and Its Impact on the Ground Thermal Regime". Atmosphere 11, n. 8 (18 agosto 2020): 877. http://dx.doi.org/10.3390/atmos11080877.
Testo completoAbstract (sommario):
Despite the key role of the surface energy budget in the global climate system, such investigations are rare in Antarctica. In this study, the surface energy budget measurements from the largest ice-free area on northern James Ross Island, in Antarctica, were obtained. The components of net radiation were measured by a net radiometer, while sensible heat flux was measured by a sonic anemometer and ground heat flux by heat flux plates. The surface energy budget was compared with the rest of the Antarctic Peninsula Region and selected places in the Arctic and the impact of surface energy budget components on the ground thermal regime was examined. Mean net radiation on James Ross Island during January–March 2018 reached 102.5 W m−2. The main surface energy budget component was the latent heat flux, while the sensible heat flux values were only 0.4 W m−2 lower. Mean ground heat flux was only 0.4 Wm-2, however, it was negative in 47% of January–March 2018, while it was positive in the rest of the time. The ground thermal regime was affected by surface energy budget components to a depth of 50 cm. The strongest relationship was found between ground heat flux and ground surface temperature. Further analysis confirmed that active layer refroze after a sequence of three days with negative ground heat flux even in summer months. Daily mean net radiation and ground heat flux were significantly reduced when cloud amount increased, while the influence of snow cover on ground surface temperature was negligible.
25
Iqbal, Mochamad, e Taiki Kubo. "Experimental Preliminary Measurements of CO2 Flux for Exploring Hidden Geothermal Systems". IOP Conference Series: Earth and Environmental Science 1293, n. 1 (1 gennaio 2024): 012003. http://dx.doi.org/10.1088/1755-1315/1293/1/012003.
Testo completoAbstract (sommario):
Abstract Geothermal energy is a promising renewable energy source, and to enhance its use, identifying Hidden Geothermal Systems (HGS) without thermal manifestations on the surface is a challenging subject. Soil CO2 flux monitoring has become an effective method for detecting HGS, different from traditional methods that target thermal indicators. Expensive portable CO2 gas analyzers are commonly used for this purpose, but their high cost prevents wide applications. Thus, this study tries to design and test a cost-effective solution for measuring CO2 flux while keeping high accuracy and reliability of measured data. The method incorporates a self-made accumulation chamber connected to a relatively inexpensive CO2 portable meter, the GasLab Pro Carbon Dioxide Sampling Data Logger CM-1000. The device uses non-dispersive infrared (NDIR) to detect CO2 and is equipped with a data logger for continuous monitoring. The CO2 flux measurement is performed using the accumulation chamber method. The reliability of this tool for detecting CO2 flux is evaluated, and the experimental results are verified by comparing them with an intelligent gas flow meter, the Shimadzu Intelligent Flow Meter DFM-1000. The tool is tested in various conditions, with CO2 flux values ranging from 3.30 to 1013.02 g m-2 day-1, proving capable of measuring CO2 flux up to 1000 g m-2 day-1. Field tests were conducted at 60 sites to evaluate the tool’s performance. The results suggest that the lower measurement limit of the tool is approximately 0.1 g m-2 day-1. Overall, the cost-effective solution holds promise as a reliable tool for investigating HGS, with potential applications in other environments with similar or higher CO2 flux rates. In addition, conducting further comparison studies with a common sophisticated automatic flux tool such as LI-COR 850 can help improve the accuracy and reliability of the tool.
26
Striegl, Robert G., e Kimberly P. Wickland. "Soil respiration and photosynthetic uptake of carbon dioxide by ground-cover plants in four ages of jack pine forest". Canadian Journal of Forest Research 31, n. 9 (1 settembre 2001): 1540–50. http://dx.doi.org/10.1139/x01-092.
Testo completoAbstract (sommario):
Soil carbon dioxide (CO2) emission (soil respiration), net CO2 exchange after photosynthetic uptake by ground-cover plants, and soil CO2 concentration versus depth below land surface were measured at four ages of jack pine (Pinus banksiana Lamb.) forest in central Saskatchewan. Soil respiration was smallest at a clear-cut site, largest in an 8-year-old stand, and decreased with stand age in 20-year-old and mature (6075 years old) stands during May September 1994 (12.1, 34.6, 31.5, and 24.9 mol C·m2, respectively). Simulations of soil respiration at each stand based on continuously recorded soil temperature were within one standard deviation of measured flux for 48 of 52 measurement periods, but were 10%30% less than linear interpolations of measured flux for the season. This was probably due to decreased soil respiration at night modeled by the temperature-flux relationships, but not documented by daytime chamber measurements. CO2 uptake by ground-cover plants ranged from 0 at the clear-cut site to 29, 25, and 9% of total growing season soil respiration at the 8-year, 20-year, and mature stands. CO2 concentrations were as great as 7150 ppmv in the upper 1 m of unsaturated zone and were proportional to measured soil respiration.
27
Rezapour, N., M. Fattahi e A. A. Bidokhti. "Possible soil thermal response to seismic activities in Alborz region (Iran)". Natural Hazards and Earth System Sciences 10, n. 3 (15 marzo 2010): 459–64. http://dx.doi.org/10.5194/nhess-10-459-2010.
Testo completoAbstract (sommario):
Abstract. In this investigation, relations between the ground's thermal properties and 70 earthquakes with a magnitude >4 Richter in the Alborz region during a period of 12 years (1992 to 2004) were studied. Typical changes of ground temperature, 0.4 °C; thermal diffusivity, 0.028 m2 s−1×10−6 and ground heat flux take place a few hours prior to the earthquakes. The values of thermal diffusivity depend on the ground moisture content, which may change during seismic activities. The analysis of ground heat flux from the epicentre and it's surrounding regions show some anomalous behavior before the earthquakes but with different signs in the areas close to the sea and far away from the sea. The changes of the ground's thermal properties prior to the earthquakes in the Alborz region are attributed to the increase in seismic activities in the epicentre and it's surrounding regions. The anomalous behavior in the ground thermal properties shows great potential in providing early warning of imminent earthquake.
28
Leski, Krystian, Przemysław Luty, Monika Gwadera e Barbara Larwa. "Numerical Analysis of Minimum Ground Temperature for Heat Extraction in Horizontal Ground Heat Exchangers". Energies 14, n. 17 (2 settembre 2021): 5487. http://dx.doi.org/10.3390/en14175487.
Testo completoAbstract (sommario):
In this work, numerical simulation calculations were performed to investigate the minimum ground temperature that occurs when extracting thermal energy in a horizontal ground heat exchanger system in the Central European climate. The influence of ground thermal conductivity, heat flux extracted from the ground, periodic interruptions in the operation of the heat exchanger, periodic supply of heat energy to the ground, relative humidity of the ambient air, evaporation rate coefficient, and convective heat transfer coefficient on the ground minimum temperature were investigated. Based on the simulation, it was found that the high value of ground thermal conductivity favorably affects the operation of the installation with a ground heat exchanger. Both the reduction of the maximum heat flux taken from the ground, as well as periodic interruptions in the operation of the exchanger effectively protects the ground against excessive cooling. Further, it was found that heat supply to the ground in summer only slightly raises its minimum temperature, as well as the decrease of the relative humidity of the ambient air and evaporation rate coefficient. The change of the convective heat transfer coefficient has no significant impact on the minimum annual ground temperature.
29
Woo, Ming-ko, e Zhaojun Xia. "Effects of Hydrology on the Thermal Conditions of the Active Layer". Hydrology Research 27, n. 1-2 (1 febbraio 1996): 129–42. http://dx.doi.org/10.2166/nh.1996.0024.
Testo completoAbstract (sommario):
Ground thawing and soil warming are governed by ground heat flux, soil thermal properties and the ice content of the soil, all of which are directly or indirectly influenced by the soil moisture status. Ground temperature and moisture were measured at two Arctic sites: a wetland site of frequent saturation and an adjacent pebbly loam site which was much drier. Both thermal conductivity and heat capacity were strongly affected by the ice and water contents. At both sites, about half of the ground heat flux was consumed by latent heat for ground thawing and a large fraction of heat was also conducted from the seasonally thawed zone into the permafrost, leaving only a small amount of heat to warm the active layer. The wetland soil had a shallower maximum depth of thaw than the drier site and this was due to the large ice content in its active layer. Our results demonstrate the ground thaw response to the thermal properties of the soil and its ice content, both of which are influenced by the hydrological conditions of the active layer.
30
Lubenow, Brady L., Jerry P. Fairley, Cary R. Lindsey e Peter B. Larson. "Influences on shallow ground temperatures in high flux thermal systems". Journal of Volcanology and Geothermal Research 323 (settembre 2016): 53–61. http://dx.doi.org/10.1016/j.jvolgeores.2016.04.039.
Testo completo
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van Asperen, H., T. Warneke, S. Sabbatini, G. Nicolini, D. Papale e J. Notholt. "The role of photo- and thermal degradation for CO<sub>2</sub> and CO fluxes in an arid ecosystem". Biogeosciences Discussions 12, n. 3 (4 febbraio 2015): 2429–57. http://dx.doi.org/10.5194/bgd-12-2429-2015.
Testo completoAbstract (sommario):
Abstract. Recent studies have suggested the potential importance of abiotic degradation in arid ecosystems. In this study, the role of photo- and thermal degradation in ecosystem CO2 and CO exchange is assessed. A field experiment was performed in Italy using a FTIR-spectrometer coupled to a flux gradient system and to flux chambers. In a laboratory experiment, field samples were exposed to different temperatures and radiation intensities. No photodegradation-induced CO2 and CO fluxes were found in the field and in the laboratory study. In the laboratory, thermal degradation fluxes for CO2 and CO have been observed. In the field, CO uptake and emission have been observed and are proposed to be a result of biological uptake and abiotic thermal degradation-production. We suggest that previous studies, studying direct photodegradation, have overestimated the role of photodegradation and observed fluxes might be due to thermal degradation, which is an indirect effect of radiation. The potential importance of abiotic decompostion in the form of thermal degradation, especially for arid regions, should be considered in future studies.
32
Barbour, Margaret M., Lucas A. Cernusak, David Whitehead, Kevin L. Griffin, Matthew H. Turnbull, David T. Tissue e Graham D. Farquhar. "Nocturnal stomatal conductance and implications for modelling δ18O of leaf-respired CO2 in temperate tree species". Functional Plant Biology 32, n. 12 (2005): 1107. http://dx.doi.org/10.1071/fp05118.
Testo completoAbstract (sommario):
Variation in the oxygen isotope composition of within-canopy CO2 has potential to allow partitioning of the ecosystem respiratory flux into above- and below-ground components. Recent theoretical work has highlighted the sensitivity of the oxygen isotope composition of leaf-respired CO2 (δRl) to nocturnal stomatal conductance. When the one-way flux model was tested on Ricinus communis L. large enrichments in δRl were observed. However, most species for which the isotope flux partitioning technique has been or would be applied (i.e. temperate tree species) are much more conservative users of water than R. communis. So, high stomatal conductance and very high enrichment of δRl observed may not be typical for temperate tree species. Using existing gas-exchange measurements on six temperate tree species, we demonstrate significant water loss through stomata for all species (i.e. statistically significantly greater than cuticular loss alone) at some time for some leaves during the night. δRl values predicted by the one-way flux model revealed that δRl might be very much more enriched than when the net flux alone is considered, particularly close to sunrise and sunset. Incorporation of the one-way flux model into ecosystem respiration partitioning studies will affect model outputs and interpretation of variation in the oxygen isotope composition of atmospheric CO2.
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Queißer, Manuel, Domenico Granieri, Mike Burton, Fabio Arzilli, Rosario Avino e Antonio Carandente. "Increasing CO<sub>2</sub> flux at Pisciarelli, Campi Flegrei, Italy". Solid Earth 8, n. 5 (29 settembre 2017): 1017–24. http://dx.doi.org/10.5194/se-8-1017-2017.
Testo completoAbstract (sommario):
Abstract. The Campi Flegrei caldera is located in the metropolitan area of Naples (Italy) and has been undergoing different stages of unrest since 1950, evidenced by episodes of significant ground uplift followed by minor subsidence, increasing and fluctuating emission strengths of water vapor and CO2 from fumaroles, and periodic seismic crises. We deployed a scanning laser remote-sensing spectrometer (LARSS) that measured path-integrated CO2 concentrations in the Pisciarelli area in May 2017. The resulting mean CO2 flux is 578 ± 246 t d−1. Our data suggest a significant increase in CO2 flux at this site since 2015. Together with recent geophysical observations, this suggests a greater contribution of the magmatic source to the degassing and/or an increase in permeability at shallow levels. Thanks to the integrated path soundings, LARSS may help to give representative measurements from large regions containing different CO2 sources, including fumaroles, low-temperature vents, and degassing soils, helping to constrain the contribution of deep gases and their migration mechanisms towards the surface.
34
Keppel-Aleks, G., P. O. Wennberg, R. A. Washenfelder, D. Wunch, T. Schneider, G. C. Toon, R. J. Andres et al. "The imprint of surface fluxes and transport on variations in total column carbon dioxide". Biogeosciences Discussions 8, n. 4 (27 luglio 2011): 7475–524. http://dx.doi.org/10.5194/bgd-8-7475-2011.
Testo completoAbstract (sommario):
Abstract. New observations of the vertically integrated CO2 mixing ratio, ⟨CO2⟩, from ground-based remote sensing show that variations in ⟨CO2⟩ are primarily determined by large-scale flux patterns. They therefore provide fundamentally different information than observations made within the boundary layer, which reflect the combined influence of large scale and local fluxes. Observations of both ⟨CO2⟩ and CO2 concentrations in the free troposphere show that large-scale spatial gradients induce synoptic-scale temporal variations in ⟨CO2⟩ in the Northern Hemisphere midlatitudes through horizontal advection. Rather than obscure the signature of surface fluxes on atmospheric CO2, these synoptic-scale variations provide useful information that can be used to reveal the meridional flux distribution. We estimate the meridional gradient in ⟨CO2⟩ from covariations in ⟨CO2⟩ and potential temperature, θ, a dynamical tracer, on synoptic timescales to evaluate surface flux estimates commonly used in carbon cycle models. We find that Carnegie Ames Stanford Approach (CASA) biospheric fluxes underestimate both the ⟨CO2⟩ seasonal cycle amplitude throughout the Northern Hemisphere midlatitudes as well as the meridional gradient during the growing season. Simulations using CASA net ecosystem exchange (NEE) with increased and phase-shifted boreal fluxes better reflect the observations. Our simulations suggest that boreal growing season NEE (between 45–65° N) is underestimated by ~40 % in CASA. We describe the implications for this large seasonal exchange on inference of the net Northern Hemisphere terrestrial carbon sink.
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Keppel-Aleks, G., P. O. Wennberg, R. A. Washenfelder, D. Wunch, T. Schneider, G. C. Toon, R. J. Andres et al. "The imprint of surface fluxes and transport on variations in total column carbon dioxide". Biogeosciences 9, n. 3 (1 marzo 2012): 875–91. http://dx.doi.org/10.5194/bg-9-875-2012.
Testo completoAbstract (sommario):
Abstract. New observations of the vertically integrated CO2 mixing ratio, ⟨CO2⟩, from ground-based remote sensing show that variations in CO2⟩ are primarily determined by large-scale flux patterns. They therefore provide fundamentally different information than observations made within the boundary layer, which reflect the combined influence of large-scale and local fluxes. Observations of both ⟨CO2⟩ and CO2 concentrations in the free troposphere show that large-scale spatial gradients induce synoptic-scale temporal variations in ⟨CO2⟩ in the Northern Hemisphere midlatitudes through horizontal advection. Rather than obscure the signature of surface fluxes on atmospheric CO2, these synoptic-scale variations provide useful information that can be used to reveal the meridional flux distribution. We estimate the meridional gradient in ⟨CO2⟩ from covariations in ⟨CO2⟩ and potential temperature, θ, a dynamical tracer, on synoptic timescales to evaluate surface flux estimates commonly used in carbon cycle models. We find that simulations using Carnegie Ames Stanford Approach (CASA) biospheric fluxes underestimate both the ⟨CO2⟩ seasonal cycle amplitude throughout the Northern Hemisphere midlatitudes and the meridional gradient during the growing season. Simulations using CASA net ecosystem exchange (NEE) with increased and phase-shifted boreal fluxes better fit the observations. Our simulations suggest that climatological mean CASA fluxes underestimate boreal growing season NEE (between 45–65° N) by ~40%. We describe the implications for this large seasonal exchange on inference of the net Northern Hemisphere terrestrial carbon sink.
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Viru, Birgit, Gert Veber, Jaak Jaagus, Ain Kull, Martin Maddison, Mart Muhel, Mikk Espenberg, Alar Teemusk e Ülo Mander. "Wintertime Greenhouse Gas Fluxes in Hemiboreal Drained Peatlands". Atmosphere 11, n. 7 (10 luglio 2020): 731. http://dx.doi.org/10.3390/atmos11070731.
Testo completoAbstract (sommario):
The aim of this study is to estimate wintertime emissions of greenhouse gases CO2, N2O and CH4 in two abandoned peat extraction areas (APEA), Ess-soo and Laiuse, and in two Oxalis site-type drained peatland forests (DPF) on nitrogen-rich sapric histosol, a Norway spruce and a Downy birch forest, located in eastern Estonia. According to the long-term study using a closed chamber method, the APEAs emitted less CO2 and N2O, and more CH4 than the DPFs. Across the study sites, CO2 flux correlated positively with soil, ground and air temperatures. Continuous snow depth > 5 cm did not influence CO2, but at no snow or a thin snow layer the fluxes varied on a large scale (from −1.1 to 106 mg C m−2 h−1). In all sites, the highest N2O fluxes were observed at a water table depth of −30 to −40 cm. CH4 was consumed in the DPFs and was always emitted from the APEAs, whereas the highest flux appeared at a water table >20 cm above the surface. Considering the global warming potential (GWP) of the greenhouse gas emissions from the DPFs in the wintertime, the flux of N2O was the main component of warming, showing 3–6 times higher radiative forcing values than that of CO2 flux, while the role of CH4 was unimportant. In the APEAs, CO2 and CH4 made up almost equal parts, whereas the impact of N2O on GWP was minor.
37
Liu, E. J., A. Aiuppa, A. Alan, S. Arellano, M. Bitetto, N. Bobrowski, S. Carn et al. "Aerial strategies advance volcanic gas measurements at inaccessible, strongly degassing volcanoes". Science Advances 6, n. 44 (ottobre 2020): eabb9103. http://dx.doi.org/10.1126/sciadv.abb9103.
Testo completoAbstract (sommario):
Volcanic emissions are a critical pathway in Earth’s carbon cycle. Here, we show that aerial measurements of volcanic gases using unoccupied aerial systems (UAS) transform our ability to measure and monitor plumes remotely and to constrain global volatile fluxes from volcanoes. Combining multi-scale measurements from ground-based remote sensing, long-range aerial sampling, and satellites, we present comprehensive gas fluxes—3760 ± [600, 310] tons day−1 CO2 and 5150 ± [730, 340] tons day−1 SO2—for a strong yet previously uncharacterized volcanic emitter: Manam, Papua New Guinea. The CO2/ST ratio of 1.07 ± 0.06 suggests a modest slab sediment contribution to the sub-arc mantle. We find that aerial strategies reduce uncertainties associated with ground-based remote sensing of SO2 flux and enable near–real-time measurements of plume chemistry and carbon isotope composition. Our data emphasize the need to account for time averaging of temporal variability in volcanic gas emissions in global flux estimates.
38
van Asperen, H., T. Warneke, S. Sabbatini, G. Nicolini, D. Papale e J. Notholt. "The role of photo- and thermal degradation for CO<sub>2</sub> and CO fluxes in an arid ecosystem". Biogeosciences 12, n. 13 (14 luglio 2015): 4161–74. http://dx.doi.org/10.5194/bg-12-4161-2015.
Testo completoAbstract (sommario):
Abstract. Recent studies have suggested the potential importance of abiotic degradation in arid ecosystems. In this study, the role of photo- and thermal degradation in ecosystem CO2 and CO exchange is assessed. A field experiment was performed in Italy using an FTIR-spectrometer (Fourier Transform Infrared) coupled to a flux gradient system and to flux chambers. In a laboratory experiment, field samples were exposed to different temperatures and radiation intensities. No photodegradation-induced CO2 and CO fluxes of in literature suggested magnitudes were found in the field nor in the laboratory study. In the laboratory, we measured CO2 and CO fluxes that were derived from thermal degradation. In the field experiment, CO uptake and emission have been measured and are proposed to be a result of biological uptake and abiotic thermal degradation-production. We suggest that previous studies, addressing direct photodegradation, have overestimated the role of photodegradation and observed fluxes might be due to thermal degradation, which is an indirect effect of radiation. The potential importance of abiotic decomposition in the form of thermal degradation, especially for arid regions, should be considered in future studies.
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Lohila, A., K. Minkkinen, M. Aurela, J. P. Tuovinen, T. Penttilä e T. Laurila. "Greenhouse gas flux measurements in a forestry-drained peatland indicate a large carbon sink". Biogeosciences Discussions 8, n. 3 (21 giugno 2011): 5787–825. http://dx.doi.org/10.5194/bgd-8-5787-2011.
Testo completoAbstract (sommario):
Abstract. Drainage for forestry purposes changes the conditions in the peat and leads to increased growth of shrubs and trees. Concurrently, the production and uptake of the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are likely to change: due to the accelerated decomposition of oxic peat, drained peatlands are generally considered to loose peat carbon (C). We measured CO2 exchange with the eddy covariance (EC) method above a drained nutrient-poor peatland forest in Southern Finland for 16 months in 2004–2005. The site, classified as a dwarf-shrub pine bog, had been ditched about 35 years earlier. CH4 and N2O fluxes were measured at 2–5 week intervals with the chamber technique. Drainage had resulted in a relatively little change in the water table level, being on average 40 cm below the ground in 2005. The annual net ecosystem exchange was −870 g CO2 m−2 yr−1 in the calendar year 2005, varying from −810 to −900 g CO2 m−2 yr−1 during the 16 month period under investigation. The site was a small sink of CH4 (−0.12 g CH4 m−2 yr−1) and a small source of N2O (0.10 g N2O m−2 yr−1). Photosynthesis was detected throughout the year when the air temperature exceeded −3 °C. As the annual accumulation of C in the above and below ground tree biomass (550 g CO2 m−2) was significantly less than the net exchange of CO2, about 300 g CO2 m−2 yr−1 (~80 g C m−2) was likely to have accumulated as organic matter into the peat soil. This is a higher average accumulation rate than previously reported for natural northern peatlands, and the first time C accumulation has been shown, by EC measurements, to occur in a drained peatland. Our results suggest that forestry-drainage may significantly increase the CO2 uptake rate of nutrient-poor peatland ecosystems.
40
Lüers, J., S. Westermann, K. Piel e J. Boike. "Annual CO<sub>2</sub> budget and seasonal CO<sub>2</sub> exchange signals at a High Arctic permafrost site on Spitsbergen, Svalbard archipelago". Biogeosciences Discussions 11, n. 1 (23 gennaio 2014): 1535–59. http://dx.doi.org/10.5194/bgd-11-1535-2014.
Testo completoAbstract (sommario):
Abstract. The annual variability of CO2 exchange in most ecosystems is primarily driven by the activities of plants and soil microorganisms. However, little is known about the carbon balance and its controlling factors outside the growing season in arctic regions dominated by soil freeze/thaw-processes, long-lasting snow cover, and several months of darkness. This study presents a complete annual cycle of the CO2 net ecosystem exchange (NEE) dynamics for a High Arctic tundra area on the west coast of Svalbard based on eddy-covariance flux measurements. The annual cumulative CO2 budget is close to zero grams carbon per square meter per year, but shows a very strong seasonal variability. Four major CO2 exchange seasons have been identified. (1) During summer (ground snow-free), the CO2 exchange occurs mainly as a result of biological activity, with a predominance of strong CO2 assimilation by the ecosystem. (2) The autumn (ground snow-free or partly snow-covered) is dominated by CO2 respiration as a result of biological activity. (3) In winter and spring (ground snow-covered), low but persistent CO2 release occur, overlain by considerable CO2 exchange events in both directions associated with changes of air masses and air and atmospheric CO2 pressure. (4) The snow melt season (pattern of snow-free and snow-covered areas), where both, meteorological and biological forcing, resulting in a visible carbon uptake by the high arctic ecosystem. Data related to this article are archived under: http://doi.pangaea.de/10.1594/PANGAEA.809507.
41
PESHIN, SUNILKUMAR, DK CHAKRABORTY e SIDDHARTH SINGH. "kya jalavaayu parivartan saur badalaav se prabhaavit hota hai?" MAUSAM 65, n. 4 (28 dicembre 2021): 585–90. http://dx.doi.org/10.54302/mausam.v65i4.1300.
Testo completoAbstract (sommario):
At present, climate change is a matter of great concern to mankind. This change, which is due to the manmade activities, is changing global temperature and the concentration of CO2 and O3 in the atmosphere. But there are some changes in the sun also. Solar changes could be assessed by solar flux at 10.7cm wavelength. Climate change could be assessed by long time temperature records. In this study we have examined whether solar change has any effect on climate change? We have analyzed two sets of data, 10.7cm solar flux (TSI) and global temperature record, along with total ozone, UV-B flux at ground and satellite data of total solar irradiance. Global temperature anomaly curve (GTAC) shows a slow increase of temperature up to about 1975 and a rapid rise after this year. Solar flux at 10.7cm wavelength shows a decreasing trend up to about 1970 and an increasing trend after this year. It also has 11 year cycle. GTAC, total ozone, UV-flux at ground and TSI also show 11 year cycle and some trend, but none of them matches the long-term trend found in solar flux at 10.7cm wavelength.
42
Marotta, Enrica, Rosario Peluso, Rosario Avino, Pasquale Belviso, Stefano Caliro, Antonio Carandente, Giovanni Chiodini, Giovanni Macedonio, Gala Avvisati e Barbara Marfè. "Thermal Energy Release Measurement with Thermal Camera: The Case of La Solfatara Volcano (Italy)". Remote Sensing 11, n. 2 (17 gennaio 2019): 167. http://dx.doi.org/10.3390/rs11020167.
Testo completoAbstract (sommario):
Quiescent volcanoes dissipate a large part of their thermal energy through hot soils and ground degassing mainly in restricted areas called Diffuse Degassing Structures. La Solfatara crater represents the main spot of thermal release for the Campi Flegrei volcano (Italy) despite its reduced dimensions with regards to the whole caldera. The purpose of this study was to develop a method to measure thermal energy release extrapolating it from the ground surface temperature. We used imaging from thermal cameras at short distances (1 m) to obtain a mapping of areas with thermal anomalies and a measure of their temperatures. We built a conceptual model of the energy release from the ground to atmosphere, which well fits the experimental data taken in the La Solfatara crater. Using our model and data, we could estimate the average heat flux in a portion of the crater as q a v g = 220 ± 40 W / m 2 , compatible with other measurements in literature.
43
Lüers, J., S. Westermann, K. Piel e J. Boike. "Annual CO<sub>2</sub> budget and seasonal CO<sub>2</sub> exchange signals at a high Arctic permafrost site on Spitsbergen, Svalbard archipelago". Biogeosciences 11, n. 22 (24 novembre 2014): 6307–22. http://dx.doi.org/10.5194/bg-11-6307-2014.
Testo completoAbstract (sommario):
Abstract. The annual variability of CO2 exchange in most ecosystems is primarily driven by the activities of plants and soil microorganisms. However, little is known about the carbon balance and its controlling factors outside the growing season in Arctic regions dominated by soil freeze/thaw processes, long-lasting snow cover, and several months of darkness. This study presents a complete annual cycle of the CO2 net ecosystem exchange (NEE) dynamics for a high Arctic tundra area at the west coast of Svalbard based on eddy covariance flux measurements. The annual cumulative CO2 budget is close to 0 g C m−2 yr−1, but displays a strong seasonal variability. Four major CO2 exchange seasons have been identified. (1) During summer (snow-free ground), the CO2 exchange occurs mainly as a result of biological activity, with a dominance of strong CO2 assimilation by the ecosystem. (2) The autumn (snow-free ground or partly snow-covered) is dominated by CO2 respiration as a result of biological activity. (3) In winter and spring (snow-covered ground), low but persistent CO2 release occurs, overlayed by considerable CO2 exchange events in both directions associated with high wind speed and changes of air masses and atmospheric air pressure. (4) The snow melt season (pattern of snow-free and snow-covered areas) is associated with both meteorological and biological forcing, resulting in a carbon uptake by the high Arctic ecosystem. Data related to this article are archived at http://doi.pangaea.de/10.1594/PANGAEA.809507.
44
Hermans, Renée, Rebecca McKenzie, Roxane Andersen, Yit Arn Teh, Neil Cowie e Jens-Arne Subke. "Net soil carbon balance in afforested peatlands and separating autotrophic and heterotrophic soil CO<sub>2</sub> effluxes". Biogeosciences 19, n. 2 (19 gennaio 2022): 313–27. http://dx.doi.org/10.5194/bg-19-313-2022.
Testo completoAbstract (sommario):
Abstract. Peatlands are a significant global carbon (C) store, which can be compromised by drainage and afforestation. Quantifying the rate of C loss from peat soils under forestry is challenging, as soil CO2 efflux includes both CO2 produced from heterotrophic peat decomposition and CO2 produced by tree roots and associated fungal networks (autotrophic respiration). We experimentally terminated autotrophic below-ground respiration in replicated forest plots by cutting through all living tree roots (trenching) and measured soil surface CO2 flux, litter input, litter decay rate, and soil temperature and moisture over 2 years. Decomposition of cut roots was measured and CO2 fluxes were corrected for this, which resulted in a large change in the fraction heterotrophic : autotrophic flux, suggesting that even 2 years after trenching decaying root biomass makes significant contributions to the CO2 flux. Annual peat decomposition (heterotrophic CO2 flux) was 115 ± 16 g C m−2 yr−1, representing ca. 40 % of total soil respiration. Decomposition of needle litter is accelerated in the presence of an active rhizosphere, indicating a priming effect by labile C inputs from roots. This suggests that our estimates of peat mineralization in our trenched plots are conservative and underestimate overall rates of peat C loss. Considering also input of litter from trees, our results indicate that the soils in these 30-year-old drained and afforested peatlands are a net sink for C, since substantially more C enters the soil organic matter than is decomposed heterotrophically. This study does not account for fluvial C fluxes, which represent a small flux compared to the CO2 soil efflux; further, root litter and exudate deposition could be a significant C source that is only partially sampled by our approach, adding to these plantations being a potential carbon sink. However, the C balance for these soils should be taken over the lifespan of the trees, in order to determine if the soils under these drained and afforested peatlands are a sustained sink of C or become a net source over longer periods of forestry.
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Pauwels, Valentijn R. N., e Edoardo Daly. "Advantages of analytically computing the ground heat flux in land surface models". Hydrology and Earth System Sciences 20, n. 11 (24 novembre 2016): 4689–706. http://dx.doi.org/10.5194/hess-20-4689-2016.
Testo completoAbstract (sommario):
Abstract. It is generally accepted that the ground heat flux accounts for a significant fraction of the surface energy balance. In land surface models, the ground heat flux is typically estimated through a numerical solution of the heat conduction equation. Recent research has shown that this approach introduces errors in the estimation of the energy balance. In this paper, we calibrate a land surface model using a numerical solution of the heat conduction equation with four different vertical spatial resolutions. It is found that the thermal conductivity is the most sensitive parameter to the spatial resolution. More importantly, the thermal conductivity values are directly related to the spatial resolution, thus rendering any physical interpretation of this value irrelevant. The numerical solution is then replaced by an analytical solution. The results of the numerical and analytical solutions are identical when fine spatial and temporal resolutions are used. However, when using resolutions that are typical of land surface models, significant differences are found. When using the analytical solution, the ground heat flux is directly calculated without calculating the soil temperature profile. The calculation of the temperature at each node in the soil profile is thus no longer required, unless the model contains parameters that depend on the soil temperature, which in this study is not the case. The calibration is repeated, and thermal conductivity values independent of the vertical spatial resolution are obtained. The main conclusion of this study is that care must be taken when interpreting land surface model results that have been obtained using numerical ground heat flux estimates. The use of exact analytical solutions, when available, is recommended.
46
Aalto, T., J. Hatakka, U. Karstens, M. Aurela, T. Thum e A. Lohila. "Modeling atmospheric CO<sub>2</sub> concentration profiles and fluxes above sloping terrain at a boreal site". Atmospheric Chemistry and Physics Discussions 5, n. 5 (14 ottobre 2005): 10019–53. http://dx.doi.org/10.5194/acpd-5-10019-2005.
Testo completoAbstract (sommario):
Abstract. CO2 fluxes and concentrations were simulated in the planetary boundary layer above subarctic hilly terrain using a three dimensional model. The model solves the transport equations in the local scale and includes a vegetation sub-model. A WMO/GAW background concentration measurement site and an ecosystem flux measurement site are located inside the modeled region at a hilltop and above a mixed boreal forest, respectively. According to model results, the concentration measurement at the hill site was representative for continental background. However, this was not the case for the whole model domain. Concentration at few meters above active vegetation represented mainly local variation. Local variation became inseparable from the regional signal at about 60–100 m above ground. Flow over hills changed profiles of environmental variables and height of inversion layer, however CO2 profiles were more affected by upwind land use than topography. The hill site was above boundary layer during night and inside boundary layer during daytime. The CO2 input from model lateral boundaries dominated in both cases. Daily variation in the CO2 assimilation rate was clearly seen in the CO2 profiles. Concentration difference between the hill site and the forest site was about 5 ppm during afternoon according to both model and measurements. The average modeled flux to the whole model region was about 40% of measured and modeled local flux at the forest site.
47
Aalto, T., J. Hatakka, U. Karstens, M. Aurela, T. Thum e A. Lohila. "Modeling atmospheric CO<sub>2</sub> concentration profiles and fluxes above sloping terrain at a boreal site". Atmospheric Chemistry and Physics 6, n. 2 (3 febbraio 2006): 303–14. http://dx.doi.org/10.5194/acp-6-303-2006.
Testo completoAbstract (sommario):
Abstract. CO2 fluxes and concentrations were simulated in the planetary boundary layer above subarctic hilly terrain using a three dimensional model. The model solves the transport equations in the local scale and includes a vegetation sub-model. A WMO/GAW background concentration measurement site and an ecosystem flux measurement site are located inside the modeled region at a hilltop and above a mixed boreal forest, respectively. According to model results, the concentration measurement at the hill site was representative for continental background. However, this was not the case for the whole model domain. Concentration at few meters above active vegetation represented mainly local variation. Local variation became inseparable from the regional signal at about 60-100 m above ground. Flow over hills changed profiles of environmental variables and height of inversion layer, however CO2 profiles were more affected by upwind land use than topography. The hill site was above boundary layer during night and inside boundary layer during daytime. The CO2 input from model lateral boundaries dominated in both cases. Daily variation in the CO2 assimilation rate was clearly seen in the CO2 profiles. Concentration difference between the hill site and the forest site was about 5ppm during afternoon according to both model and measurements. The average modeled flux to the whole model region was about 40% of measured and modeled local flux at the forest site.
48
Korkiakoski, Mika, Juha-Pekka Tuovinen, Timo Penttilä, Sakari Sarkkola, Paavo Ojanen, Kari Minkkinen, Juuso Rainne, Tuomas Laurila e Annalea Lohila. "Greenhouse gas and energy fluxes in a boreal peatland forest after clear-cutting". Biogeosciences 16, n. 19 (30 settembre 2019): 3703–23. http://dx.doi.org/10.5194/bg-16-3703-2019.
Testo completoAbstract (sommario):
Abstract. The most common forest management method in Fennoscandia is rotation forestry, including clear-cutting and forest regeneration. In clear-cutting, stem wood is removed and the logging residues are either removed or left on site. Clear-cutting changes the microclimate and vegetation structure at the site, both of which affect the site's carbon balance. Peat soils with poor aeration and high carbon densities are especially prone to such changes, and significant changes in greenhouse gas exchange can be expected. We measured carbon dioxide (CO2) and energy fluxes with the eddy covariance method for 2 years (April 2016–March 2018) after clear-cutting a drained peatland forest. We observed a significant rise (23 cm) in the water table level and a large CO2 source (first year: 3086±148 g CO2 m−2 yr−1; second year: 2072±124 g CO2 m−2 yr−1). These large CO2 emissions resulted from the very low gross primary production (GPP) following the removal of photosynthesizing trees and the decline of ground vegetation, unable to compensate for the decomposition of logging residues and peat. During the second summer (June–August) after the clear-cutting, GPP had already increased by 96 % and total ecosystem respiration decreased by 14 % from the previous summer. The mean daytime ratio of sensible to latent heat flux decreased after harvesting from 2.6 in May 2016 to 1.0 in August 2016, and in 2017 it varied mostly within 0.6–1.0. In April–September, the mean daytime sensible heat flux was 33 % lower and latent heat flux 40 % higher in 2017, probably due to the recovery of ground vegetation that increased evapotranspiration and albedo of the site. In addition to CO2 and energy fluxes, we measured methane (CH4) and nitrous oxide (N2O) fluxes with manual chambers. After the clear-cutting, the site turned from a small CH4 sink into a small source and from N2O neutral to a significant N2O source. Compared to the large CO2 emissions, the 100-year global warming potential (GWP100) of the CH4 emissions was negligible. Also, the GWP100 due to increased N2O emissions was less than 10 % of that of the CO2 emission change.
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Eugster, W., K. Zeyer, M. Zeeman, P. Michna, A. Zingg, N. Buchmann e L. Emmenegger. "Nitrous oxide net exchange in a beech dominated mixed forest in Switzerland measured with a quantum cascade laser spectrometer". Biogeosciences Discussions 4, n. 2 (12 aprile 2007): 1167–200. http://dx.doi.org/10.5194/bgd-4-1167-2007.
Testo completoAbstract (sommario):
Abstract. Nitrous oxide fluxes were measured at the Lägeren CarboEurope IP flux site over the multi-species mixed forest dominated by European beech and Norway spruce. Measurements were carried out during a four-week period in October–November 2005 during leaf senescence. Fluxes were measured with a standard ultrasonic anemometer in combination with a quantum cascade laser absorption spectrometer that measured N2O, CO2, and H2O mixing ratios simultaneously at 5 Hz time resolution. To distinguish insignificant fluxes from significant ones it is proposed to use a new approach based on the significance of the correlation coefficient between vertical wind speed and mixing ratio fluctuations. This procedure eliminated roughly 56% of our half-hourly fluxes. Based on the remaining, quality checked N2O fluxes we quantified the mean efflux at 0.8 ± 0.4 μmol m−2 h−1 (mean ± standard error). Most of the contribution to the N2O flux occurred during a 6.5-h period starting 4.5 h before each precipitation event. No relation with precipitation amount could be found. Visibility data representing fog density and duration at the site indicate that wetting of the canopy may have as strong an effect on N2O effluxes as does below-ground microbial activity. It is speculated that above-ground N2O production from the senescing leaves at high moisture (fog, drizzle, onset of precipitation event) may be responsible for part of the measured flux. In comparison with the annual CO2 budget of –342 g C m−2 yr−1 it is estimated that concurrent N2O fluxes offset at least 5% of the greenhouse forcing reduction via net CO2 uptake.
50
Sur, Chanyang, Do-Hyuk Kang, Kyoung Jae Lim, Jae E. Yang, Yongchul Shin e Younghun Jung. "Soil Moisture–Vegetation–Carbon Flux Relationship under Agricultural Drought Condition using Optical Multispectral Sensor". Remote Sensing 12, n. 9 (25 aprile 2020): 1359. http://dx.doi.org/10.3390/rs12091359.
Testo completoAbstract (sommario):
Agricultural drought is triggered by a depletion of moisture content in the soil, which hinders photosynthesis and thus increases carbon dioxide (CO2) concentrations in the atmosphere. The aim of this study is to analyze the relationship between soil moisture (SM) and vegetation activity toward quantifying CO2 concentration in the atmosphere. To this end, the MODerate resolution imaging spectroradiometer (MODIS), an optical multispectral sensor, was used to evaluate two regions in South Korea for validation. Vegetation activity was analyzed through MOD13A1 vegetation indices products, and MODIS gross primary productivity (GPP) product was used to calculate the CO2 flux based on its relationship with respiration. In the case of SM, it was calculated through the method of applying apparent thermal inertia (ATI) in combination with land surface temperature and albedo. To validate the SM and CO2 flux, flux tower data was used which are the observed measurement values for the extreme drought period of 2014 and 2015 in South Korea. These two variables were analyzed for temporal variation on flux tower data as daily time scale, and the relationship with vegetation index (VI) was synthesized and analyzed on a monthly scale. The highest correlation between SM and VI (correlation coefficient (r) = 0.82) was observed at a time lag of one month, and that between VI and CO2 (r = 0.81) at half month. This regional study suggests a potential capability of MODIS-based SM, VI, and CO2 flux, which can be applied to an assessment of the global view of the agricultural drought by using available satellite remote sensing products.