Energy Flux Measurements Research Articles

Measurements of methane emissions from a beef cattle feedlot using the eddy covariance technique

The eddy covariance (EC) technique has been extensively used in several sites around the world to measure energy fluxes and CO2 exchange at the ecosystem scale. Recent advances in optical sensors have allowed the use of the EC approach to measure other trace gases (e.g. CH4, NH3 and N2O), which has expanded the use of eddy covariance for other applications, including measuring gas emissions from livestock production systems. The main objectives of this study were to assess the performance of a closed-path EC system for measuring CH4, CO2, and H2O fluxes in a beef cattle feedlot and to investigate the spatial variability of eddy covariance fluxes measured above the surface of a feedlot using an analytical flux footprint analysis. A closed-path EC system was used to measure CH4, CO2, and H2O fluxes. To evaluate the performance of this closed-path system, an open-path EC system was also deployed on the flux tower to measure CO2 and H2O exchange. The performance assessment of the closed-path EC system showed that this system was suitable for EC measurements. The frequency attenuations, observed for the closed-path system CO2 and CH4 cospectra in this study, are in agreement with results from previous instrument comparison studies. For the water vapor closed-path cospectra, larger attenuations were likely caused by water vapor molecule interaction with the sampling tube walls. Values of R2 for the relationship between H2O and CO2 fluxes, measured by open-path and closed-path systems, were 0.94–0.98, respectively. The closed-path EC system overestimated the CO2 by approximately 5% and underestimated the latent heat fluxes by about 10% when compared with the open-path system measurements. Measured CH4 and CO2 fluxes during the study period from the feedlot averaged 2.63μmolm−2s−1 and 103.8μmolm−2s−1, respectively. Flux values were quite variable during the field experiment and the footprint analysis was useful to interpret flux temporal and spatial variation. This study shows indication that consideration of atmospheric stability condition, wind direction and animal movement are important to improve estimates of CH4 emissions per pen surface or per head of cattle.

Surface water and heat exchange comparison between alpine meadow and bare land in a permafrost region of the Tibetan Plateau

Patch degradation of the alpine meadow on the Tibetan Plateau (TP) induced by climate warming and anthropogenic activities affects the pattern of coupled water and heat cycling between the land surface and the atmosphere, which could positively feedback to the regional and global climate warming. However, previous research has mostly focused on the homogeneous underlying surface rather than heterogeneous underlying surface. Thus, this study aims at forming a better understanding of the difference in water and heat exchange over heterogeneous underlying surface in the permafrost region of the TP hinterland. We based our analysis on two years of weather and energy flux measurements that were collected over two contrasting landscapes under the same climate conditions: a natural alpine meadow (AM) and severely degraded alpine meadow, termed bare land (BL). The major surface characteristics affecting the difference between AM and BL energy budgets are also presented and analyzed (such as land surface albedo and temperature, shallow soil temperature and moisture, soil stratification, and phenology). The results show that the thawing of a shallow active soil layer induced a rapid increase in soil moisture, triggering the dramatic change in main energy partitioning from sensible heat flux (H) to latent heat flux (LE) in both AM and BL sites. Surface albedo decreased but surface cooling increased with the reduction in the vegetation coverage, and temperature gradient between surface and 10cm depth increased with the erosion of root turf that is capable of thermal insulation and high water retention, together could alter the surface energy budget. The annual surface heat source or available energy (Rn−G) in AM was approximately equal to that in BL. However, more available energy was consumed by H to warm the low atmosphere in BL as evidenced by the Bowen ratio increasing from 0.49 to 0.84 in summer and from 2.96 to 5.64 over a whole year. The results of this research suggest that the soil moisture, canopy, and root turf were the major factors affecting the energy partitioning in the hinterland of the TP. The decrease in vegetation coverage results in increases of H and heating of the lower atmosphere. Therefore, this could lead to a potential positive feedback to regional climate warming. In addition, given the background of TP warming, Kobresia turf can effectively prevent permafrost degradation due to its thermal insulation characteristics.

Energy partitioning and its controls over a heterogeneous semi‐arid shrubland ecosystem in the Lake Naivasha Basin, Kenya

AbstractThis paper reports on the energy balance and partitioning analysed from 3‐year micrometeorological flux measurements of energy and water fluxes over a heterogeneous semi‐arid shrubland ecosystem in Lake Naivasha basin. The measurements enabled the characterization of the seasonal and interannual variability of the energy and water fluxes of the ecosystem covering two wet years (2012 and 2013) and one drought year (2014). On an annual scale, more than 60% of net radiation (Rn) was partitioned as latent (LE) and sensible (H) energy flux, with the latter being the larger consumer of Rn (~34%) and dominant for most months. The transition from H to LE dominance occurred from early noon to late afternoon in the wettest months of April and May. The residual energy balance closure term (C) accounted for between 25 and 40% of the Rn with the imbalance tending to be highest during periods of high insolation. Annual evapotranspiration was estimated at 873 mm, 632 mm and 537 mm for year 2012, 2013 and 2014 respectively. This accounted for at least 80% of the annual precipitation received for the respective years. Surface conductance (gs) scaled significantly with leaf expansion and Priestley–Taylor α coefficient, but was limited during periods of drought because of inadequate soil moisture suggesting that, change in LE was paralleled by changes in green leaf area index. Low values of decoupling coefficient (Ω) during these periods indicated that evapotranspiration was strongly controlled by gs and vapour pressure deficit (VPD). However, under non‐limiting moisture conditions evapotranspiration was decoupled from the atmosphere. This suggested that during the dry seasons and periods of prolonged drought, a lack of moisture in combination with high VPD leads to significant decreases in stomatal conductance that eventually limits partitioning of available energy into LE in the semi‐arid ecosystem part of the Lake Naivasha basin. However, during wet season these factors are non‐limiting and radiation is the dominant control of energy partitioning into LE in the ecosystem. The coupling and decoupling pattern provide insights towards formulating models that quantify evapotranspiration for ecosystems that experience seasonal shifts in controlling factors. Copyright © 2016 John Wiley & Sons, Ltd.

Estimation of wet canopy bulk stomatal resistance from energy flux measurements during sprinkler irrigation

Bulk stomatal resistance, also known as surface resistance, is typically assumed to be zero during rainfall or other circumstances when a foliage canopy is wet, such as during sprinkler irrigation. However, some recent studies have suggested that resistance does not necessarily fall completely to zero. Although the assumption of zero bulk stomatal resistance for a wet canopy condition may be reasonable, estimation of actual evaporation as well as bulk stomatal resistance during wet conditions via the Penman-Montieth (P-M) equation is still problematic due to the difficulties in measuring the various energy fluxes in the energy balance. It has recently been demonstrated that eddy covariance (ECV) can be used to estimate the actual evapotranspiration during both irrigation and non-irrigation periods. It has also been shown that advection is important in sprinkler irrigation. . In Tthis paper it is demonstrateddemonstrates how the same technique can also provide an estimate of the bulk stomatal resistance for a wet crop canopy. It is shown that when all significant energy terms (including advected energy) are taken into account, the bulk stomatal resistance was effectively zero, in contrast to dry canopy values for the same crop of order 30 s m–1, both determined under midday, open sky conditions. The study also shows that ignoring advected energy can lead to an overestimation of bulk stomatal resistance and underestimation of ET when the canopy is wet.

Calibration of a distributed hydrology and land surface model using energy flux measurements

In this study we develop and test a calibration approach on a spatially distributed groundwater–surface water catchment model (MIKE SHE) coupled to a land surface model component with particular focus on the water and energy fluxes. The model is calibrated against time series of eddy flux measurements from three sites of different land surface type (agriculture, forest and meadow) and river discharge data from the 2500km2 Skjern River catchment in Denmark. The approach includes initial calibrations of three one-dimensional models representing the three land surface types using the flux measurements for calibration. This step provides initial values for the subsequent modelling and calibration at catchment scale. To test the validity of the approach, two additional catchment scale distributed simulations were performed with no calibration and only calibration of the one-dimensional models, respectively. In addition, a subsequent validation period was simulated. A mean energy closure imbalance of 20% was seen for the three sites. For the distributed simulations, the energy imbalance was accounted for by two energy balance closure hypotheses ascribing the error to either energy fluxes or net radiation. In general, the distributed calibration approach improved model results substantially compared to using default values (no calibration) or calibration of the one-dimensional models only. For the distributed model simulations, the assumption regarding the energy balance closure had a substantial impact on the parameter sensitivities and on the simulated discharge and energy balance. During calibration, the simulation with corrected energy fluxes showed better performance on discharge than the simulation with corrected net radiation whereas the reverse was true for the validation period. Regarding energy fluxes, the simulation with corrected net radiation was superior in both the calibration and validation period.

On the Impact of Electron Temperature in Magnetron Sputtering Benchmarked with Energy Flux Measurements

AbstractIn this work we have investigated the effect of increasing the electron energy as a way to increase the ionization probability of the sputtered metal (Ti) by measuring the impact of three different process gases (Ne, Ar, and Kr). Using a combined Langmuir and calorimetric probe we were able to compare the electron density ne, the electron temperature Te, the total energy influx, as well as the different energy flux contributions from charge carriers, neutrals and surface processes for various discharge conditions. The results show that the electron temperature can be increased by up to a factor of 3 by using Ne instead of Ar (or Kr). Furthermore, it was also found that by using Ne the mean free path for electron impact ionization was decreased by at least 50 %, and for higher pressures even more. In addition, we show that the contributions from sputtered neutrals and film formation represent a large fraction of the total energy influx, whereas the energy flux from ions is very low due to low ne in this type of discharge. However, by investigating changes in the electron energy flux, it was possible to study the effects of using Ne. These results may provide a way to tune the degree of ionization in sputtering processes. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Application of Remote Sensing for Quantifying and Mapping Surface Energy Fluxes in South Central Nebraska: Analyses with Respect to Field Measurements

Large-scale quantification of crop evapotranspiration (ET c ) from various vegetation surfaces can aid in planning, managing, and allocating water resources. Field measurement of surface energy fluxes, including ET c , remains (and should remain) a crucial process for calibration and validation of satellite/remote sensing-based methods, which can provide important supporting information for water balance assessments and for analyzing the spatial distribution of energy fluxes on large scales. The Surface Energy Balance System (SEBS) was evaluated in estimating surface energy fluxes in south central Nebraska using Landsat imagery and meteorological data. SEBS-estimated surface energy fluxes were compared to Bowen Ratio Energy Balance System (BREBS) flux data measured over tall (maize) and short (winter wheat and rainfed grass) vegetation surfaces at Nebraska Water and Energy Flux Measurement, Modeling, and Research Network (NEBFLUX) tower sites. A total of 54 cloud-free Landsat 5 Thematic Mapper and Landsat 7 Enhanced Thematic Mapper Plus images that were available for both path 29 row 31 and path 29 row 32 were analyzed for the spatial distribution of ET c over the study area. On an all-vegetation-average basis (pooled data from all surfaces), the correlation between estimated and measured surface energy balance components had R 2 values of 0.88, 0.90, 0.63, and 0.32 for ET c , net radiation (R n ), sensible heat flux (H), and soil heat flux (G), respectively. SEBS overestimated R n considerably by 46 W m -2 , and estimates for G were also poor. Results were somewhat improved when comparisons were made on an individual vegetation surface basis. In addition to detailed analyses of ET c and other surface energy fluxes of irrigated maize, winter wheat, and rainfed grassland, the spatial distributions of ET c for ten other surfaces (rainfed maize, sorghum, soybean, winter wheat, alfalfa, open water, developed/open space, deciduous forest, grassland/pasture, and woody wetlands) were mapped and evaluated. Substantial variability in ET c was observed over the study area, which was mainly due to the diverse cropping systems and management practices across the area. The SEBS performance was poor and unsatisfactory during days with precipitation events. Additional research is needed to investigate the performance of SEBS for various vegetation surfaces and to develop algorithms to improve the performance of the model to estimate surface energy fluxes for different periods of the growing season and during days with precipitation events.

X-ray Luminescence Efficiency of GAGG:Ce Single Crystal Scintillators for use in Tomographic Medical Imaging Systems

The purpose of the present study was to evaluate different scintillator crystal samples, with a cross section of 3×3mm2 and various thicknesses ranging from 4mm up to 20mm, of the new mixed Gd3Al2Ga3O12:Ce (GAGG:Ce) scintillator material under X-ray irradiation, for potential applications in Tomographic Medical Imaging systems. Evaluation was performed by determining the X-ray luminescence efficiency (XLE) (emitted light energy flux over incident X-ray energy flux) in energies employed in general X-ray imaging. For the luminescence efficiency measurements, the scintillator samples were exposed to X-rays using a BMI General Medical Merate tube, with rotating Tungsten anode and inherent filtration equivalent to 2 mm Al. X-ray tube voltages between 50 to 130 kV were selected. An additional 20 mm filtration was introduced to the beam to simulate beam quality alternation equivalent to a human body. The emitted light energy flux measurements were performed using an experimental set up comprising a light integration sphere coupled to an EMI 9798B photomultiplier tube which was connected to a Cary 401 vibrating reed electrometer. The GAGG:Ce sample with dimensions 3×3×10 mm3 exhibited higher XLE values, in the whole X- ray energy range examined. XLE value equal to 0.013 was recorded for this crystal at 130 kVp - a setting frequently used in Computed Tomography applications.

A comparison of optical and microwave scintillometers with eddy covariance derived surface heat fluxes

Accurate measurements of energy fluxes between land and atmosphere are important for understanding and modeling climatic patterns. Several methods are available to measure heat fluxes, and scintillometers are becoming increasingly popular because of their ability to measure sensible (H) and latent (LvE) heat fluxes over large spatial scales. The main motivation of this study was to test the use of different methods and technologies to derive surface heat fluxes.Measurements of H and LvE were carried out with an eddy covariance (EC) system, two different makes of optical large aperture scintillometers (LAS) and two microwave scintillometers (MWS) with different frequencies at a pasture site in a semi-arid environment of New South Wales, Australia. We used the EC measurements as a benchmark. Fluxes derived from the EC system and LAS systems agreed (R2>0.94), whereas the MWS systems measured lower H (bias ∼60Wm−2) and larger LvE (bias ∼65Wm−2) than EC. When the scintillometers were compared against each other, the two LASs showed good agreement of H (R2=0.98), while MWS with different frequencies and polarizations led to different results. Combination of LAS and MWS measurements (i.e., two wavelength method) resulted in performance that fell in between those estimated using either LAS or MWS alone when compared with the EC system. The cause for discrepancies between surface heat fluxes derived from the EC system and those from the MWS systems and the two-wavelength method are possibly related to inaccurate assignment of the structure parameter of temperature and humidity. Additionally, measurements from MWSs can be associated with two values of the Bowen ratio, thereby leading to uncertainties in the estimation of the fluxes. While only one solution has been considered in this study, when LvE was approximately less than 200Wm−2, the alternate solution may be more accurate. Therefore, for measurements of surface heat fluxes in a semi-arid or dry environment, the optical scintillometer is recommended, whereas further work will be required to improve the estimation of surface heat fluxes from microwave systems.

Superradiance on the Reissner–Nordstrøm metric

In this article, we study the superradiance of charged scalar fields on the sub-extremal Reissner–Nordstrøm metric, a mechanism by which such fields can extract energy from a static spherically symmetric charged black hole. A geometrical way of measuring the amount of energy extracted is proposed. Then we investigate the question numerically. The toy model and the numerical methods used in our simulations are presented and the problem of long time measurement of the outgoing energy flux is discussed. We provide a numerical example of a field exhibiting a behaviour analogous to the Penrose process: an incoming wave packet which splits, as it approaches the black hole, into an incoming part with negative energy and an outgoing part with more energy than the initial incoming one. We also show another type of superradiant solution for which the energy extraction is more important. Hyperradiant behaviour is not observed, which is an indication that the Reissner–Nordstrøm metric is linearly stable in the sub-extremal case.

Evaluation of statistical gap fillings for continuous energy flux (evapotranspiration) measurements for two different land cover types

Over the past few decades, energy and water fluxes have been directly measured by a global flux network, which was established by regional and continental network sites based on an eddy covariance (EC) method. Although, the EC method possesses many advantages, its typical data coverage could not exceed 65 % due to various environmental factors including micrometeorological conditions and systematic malfunctions. In this study, four different methodologies were used to fill the gap in latent heat flux (LE) data. These methods were Food and Agriculture Organization Penman–Monteith (FAO_PM) equation, mean diurnal variation (MDV), Kalman filter, and dynamic linear regression (DLR). We used these methods to evaluate two flux towers at different land cover types located at Seolmacheon (SMC) and Cheongmicheon (CMC) in Korea. The LE estimated by four different approaches was a fairly close match to the observed LE, with the root mean square error ranging from 4.81 to 61.88 W m−2 at SMC and from 0.89 to 60.27 W m−2 at CMC. At both sites, the LE estimated by DLR showed the best result with the value of the coefficient of correlation (R), equal to 0.99. Cost-effectiveness analysis for evaluating four different gap-filling methods also confirmed that DLR showed the best cost effectiveness ratio (C/R). The Kalman filter showed the second highest C/R rank except in the winter season at SMC followed by MDV and FAO_PM. Energy closures with estimated LE led to further improved compare to the energy closure of the observed LE. The results showed that the estimated LE at CMC was a better fit with the observed LE than the estimated LE at SMC due to the more complicated topography and land cover at the SMC site. This caused more complex interactions between the surface and the atmosphere. The estimated LE with all approaches used in this study showed improvement in energy closure at both sites. The results of this study suggest that each method can be used as a gap-filling model for LE. However, it is important to consider the strengths and weaknesses of each method, the purpose of research, characteristics of the study site, study period and data availability.

Accounting for vegetation height and wind direction to correct eddy covariance measurements of energy fluxes over hilly crop fields

AbstractAs agricultural hilly watersheds are widespread throughout the world, there is a strong need for reliable estimates of land surface fluxes, especially evapotranspiration, over crop fields on hilly slopes. In order to obtain reliable estimates from eddy covariance (EC) measurements in such conditions, the current study aimed at proposing adequate planar fit tilt corrections that account for the combined effects of topography, wind direction, and vegetation height on airflow inclinations. EC measurements were collected within an agricultural hilly watershed in northeastern Tunisia, throughout the growth cycles of cereals, legumes, and pasture. The wind had two dominant directions that induced upslope and downslope winds. For upslope winds, the airflows were parallel to the slopes and slightly came closer to the horizontal plane when vegetation grew. For downslope winds, over fields located in the lee of the rim top, the airflows were almost horizontal over bare soil and came closer to the topographical slope when vegetation grew. We therefore adjusted the planar fit tilt correction on EC measurements according to vegetation height and by discriminating between upslope and downslope winds. This adjusted tilt correction improved the energy balance closure in most cases, and the obtained energy balance closures were similar to that reported in the literature for flat conditions. We conclude that EC data collected within crop fields on hilly slopes can be used for monitoring land surface fluxes, provided planar fit tilt corrections are applied in an appropriate manner.

A Comparison between Simulated and Observed Surface Energy Balance at the Svalbard Archipelago

AbstractThe surface energy balance at the Svalbard Archipelago has been simulated at high resolution with the Weather Research and Forecasting Model and compared with measurements of the individual energy fluxes from a tundra site near Ny-Ålesund (located north of Norway), as well as other near-surface measurements across the region. For surface air temperature, a good agreement between model and observations was found at all locations. High correlations were also found for daily averaged surface energy fluxes within the different seasons at the main site. The four radiation components showed correlations above 0.5 in all seasons (mostly above 0.9), whereas correlations between 0.3 and 0.8 were found for the sensible and latent heat fluxes. Underestimation of cloud cover and cloud optical thickness led to seasonal biases in incoming shortwave and longwave radiation of up to 30%. During summer, this was mainly a result of distinct days on which the model erroneously simulated cloud-free conditions, whereas the incoming radiation biases appeared to be more related to underestimation of cloud optical thickness during winter. The model overestimated both sensible and latent heat fluxes in most seasons. The model also initially overestimated the average Bowen ratio during summer by a factor of 6, but this bias was greatly reduced with two physically based model modifications that are related to frozen-ground hydrology. The seasonally averaged ground/snow heat flux was mostly in agreement with observations but showed too little short-time variability in the presence of thick snow. Overall, the model reproduced average temperatures well but overestimated diurnal cycles and showed considerable biases in the individual energy fluxes on seasonal and shorter time scales.

Quantifying the heat flux regulation of metropolitan land use/land cover components by coupling remote sensing modeling with in situ measurement

AbstractQuantifying the effects of urban land use/land cover with regard to surface radiation and heat flux regulation is important to ecological planning and heat stress mitigation. To retrieve the spatial pattern of heat fluxes in the Beijing metropolitan area, China, a remote sensing‐based energy balance model was calibrated with synchronously measured energy fluxes including net radiation, latent heat flux (LE), and sensible heat flux (H). Our model calibration approach avoided the uncertainties due to subjective judgments in previous empirical parameterization methods. The land surface temperature (LST), H, and Bowen ratio (β) of Beijing were found to increase along the outskirt‐suburban‐urban gradient, with strong spatial variation. LST and H were negatively correlated with vegetation fraction cover (VFC). For example, the modern high‐rise residential areas with relatively higher VFC had lower H and β than the traditional low‐rise residential areas. Our findings that indicate thermal dissipation through vegetation transpiration might play an important role in urban heat regulation. Notably, the thermal dissipating strength of vegetation (calculated as LE/VFC) declined exponentially with increased VFC. For the purpose of heat stress regulation, we recommend upgrading the traditional low‐rise residential areas to modern high‐rise residential areas and focusing urban greenery projects in areas whose VFC < 0.1, where the heat regulating service by urban vegetation could be twice as effective as in other places.

Assessing predictive ability of three auroral precipitation models using DMSP energy flux

AbstractOur study statistically compares the total energy flux outputs of Newell et al.'s () oval variation, assessment, tracking, intensity, and online nowcasting (OVATION) Prime model, Hardy et al.'s () Kp‐based model, and a coupled Space Weather Modeling Framework ring current model to energy flux data obtained from 2198 Defense Meteorological Satellite Program (DMSP) satellite passes in the Northern Hemisphere. Our DMSP data set includes 28 days grouped into continuous 3 and 4 day periods between 2000 and 2008 and encompasses magnetic local times (MLTs) between 04:00 and 21:00. We obtain the most equatorward magnetic latitude coordinate, where a DMSP satellite energy flux measurement exceeds 0.4 erg/cm2/s, and use this point as a proxy for the equatorward boundary of the auroral oval in a particular MLT sector. We then calculate a prediction efficiency (PE) score by comparing the DMSP boundary coordinates to each model, using the same energy flux threshold to obtain a model's boundary location. We find that the PE for the OVATION Prime model is 0.55, and the PE for the Hardy Kp model is 0.51. When we accomplish the same analysis using a higher energy flux threshold equal to 0.6 erg/cm2/s, the OVATION Prime model's PE increases to 0.58, while the Hardy Kp model's score drops to 0.41. Our results indicate that more complex modeling techniques, like those used in OVATION Prime, can more accurately model the auroral oval's equatorward boundary. However, Hardy's discretized Kp model, despite its relative simplicity, is still a competitive and viable modeling option.

Long-term energy flux and radiation balance observations over Lake Ngoring, Tibetan Plateau

It remains unclear what are the characteristics of the surface energy budget and the radiation balance over the lake at high altitudes. Here we report a nearly two-year ice-free time measurement (2011–2012) of energy flux and radiation balance using the eddy covariance method over Lake Ngoring, Tibetan Plateau. A persistent unstable atmospheric boundary layer was maintained over the lake, caused by a higher water surface temperature compared with the overlying atmosphere. As a result, the positive sensible heat (H) and latent heat (LE) fluxes almost lasted throughout the entire observation period. The heat storage period of the lake could last until September, and the strongest heating occurred in October from the lake to the atmosphere. Compared with the subtropical lake, Bowen ratios were larger in Lake Ngoring, caused by a large temperature difference and a small specific humidity difference between the water surface and the overlying air. The patterns of H versus the atmospheric stability differed from those of LE. H was large under unstable stratification conditions and significantly decreased in the nearly neutral and stable atmospheric stratification. By contrast, the large LE concentrated in the weak unstable to the nearly neutral atmospheric stratification, and clearly declined with increased atmospheric instability. Overall, the vertical specific humidity difference contributed more to LE than the wind speed. As regards H, the major contributors varied with the atmospheric stability. The intrusion of dry, cold air with strong wind could result in significant increases in H and LE (approximately 2.0–4.5 times as much as those of normal days); during this period, the stored energy in water dramatically decreased and even could provide 70% of the energy for H and LE.

Measurement of energy flux to a substrate by thermal and Langmuir probes during inductively coupled plasma assisted DC magnetron sputtering

To understand the deposition mechanism during the inductively coupled plasma (ICP) assisted DC magnetron sputter-deposition of transparent conductive Al-doped ZnO (AZO) films, energy flux to a substrate was investigated. The total energy flux to a substrate (Jtotal) was measured by two types of thermal probes: one for the absolute value measurement of Jtotal at a fixed position, and the other for the spatial distribution measurement of Jtotal. The contribution due to charged species (Jch) was evaluated by the Langmuir probe measurements of plasma parameters. As a result, it was found that i) Jtotal was about 3000 W m−2 for the typical deposition condition and this value was about one order of magnitude larger than those of conventional planar magnetron sputtering, and ii) most of Jtotal was contributed by plasma charged species.

Microclimate and mass fluxes of debris-laden ice surfaces in Taylor Valley, Antarctica

AbstractThis study investigates the microclimate and hydrology of debris-laden ice surfaces in the Taylor Valley, Antarctica, in early summer, focusing on the onset of melt. Measurements of energy and mass fluxes were made on an outwash fan and in moraines near the terminus of Taylor Glacier. The surface microclimate was strongly controlled by absorbed solar radiation, with a low albedo of 0.17. Seasonal warming of the substrate led to an abrupt shift in thermal and hydrological patterns as temperatures exceeded freezing point. Within a week the Bowen ratio switched from 2.05 to 0.48 and mass losses to the atmosphere increased four-fold from 0.39 to 1.6 mm d-1. Melt onset also produced complex ground temperature patterns with strong diurnal damping below the freezing front. These patterns were caused by phase changes in the freezing front, coupled with an abundant water supply from local runoff. Of secondary importance to the surface energy balance and mass fluxes was the effect of local winds on boundary layer characteristics. This resulted in larger mass losses during the more turbulent, warmer and drier down-valley flows.

Climatic sensitivity of the CO2 flux in a cutaway boreal peatland cultivated with a perennial bioenergy crop (Phalaris arundinaceae, L.): Beyond diplotelmic modeling

In this study, a process-based model (RCG-C) was developed, parameterized and calibrated for studying the annual and seasonal dynamics of the ecosystem CO2 exchange (NEE) in a cutaway peatland (Linnansuo, eastern Finland) cultivated with a perennial bioenergy crop (Phalaris arundinaceae, L., RCG). Based on a number of prior studies and an environmentally controlled experiment, RCG-C emphasized several key processes beyond the generality of previous diplotelmic models for pristine peatlands. These processes included the effects of management (e.g., drainage, peat extraction, tilling, harvesting and fertilization) on the soil hydrology and the cycling of carbon and nitrogen, the influence of climatic factors on photosynthesis and the phenological cycle and phenological and soil-moisture controls on biomass production and canopy development. The model was validated based on continuous measurements of meteorological parameters, energy and CO2 fluxes (eddy covariance system) performed at the site from 2005 to 2010, including variation associated with both wet and dry years. The results showed that the model captured the seasonal and annual trends of the latent heat flux and NEE during the six-year period. Moreover, the simulated values for the total C sink capacity, accumulation of rhizome biomass and peat formation from RCG obtained during the six-year period also agreed well with the field measurements. Based on the FINADAPT climate scenarios, a sensitivity analysis of the model showed that the potential increases in the atmospheric CO2 concentration (Ca) and air temperature (Ta) could be the main forces driving the changes in NEE. The model simulation suggested that the effects of Ta tend to offset those of Ca and lead to a decrease in the total C sink capacity of the site during the main rotation period (4–15th year of cultivation). This decrease tends to become more intensive toward the end of the 21st century. During the period from 2060 to 2099, the total CO2 sink capacity could decrease by 79% during the main rotation period at the Linnansuo site.

Surface energy flux measurements in a flooded and an aerobic rice field using a single eddy-covariance system

About 90 % of the global rice production takes place in Asia, while European production is quantitatively modest. Italy is the Europe’s leading producer, with over half of total production concentrated in a large, traditional paddy rice area in the north of the country. High irrigation requirement for continuous flooding encourages the adoption of water saving techniques. In 2013, an intense monitoring activity was conducted on two fields characterized by continuous flooding and intermittent irrigation regimes, with the aim of comparing their agronomical and hydrological effects, including their influence on the energy balance. An eddy covariance station was installed on the levee between the two fields, to monitor latent (LE) and sensible (H) heat fluxes as a function of wind direction. Additionally, the fields were instrumented with net radiometers, soil heat flux (G) plates, thermistors, tensiometers, and multilevel moisture probes. Three footprint models were applied to determine position and size of the footprint area at each monitoring time step, providing similar results. Two half-hourly turbulent fluxes datasets were obtained, one for each irrigation regime, each one comprising about 10 % of the daytime time steps over the agricultural season. The reliability of the monitoring performed with a single EC station was confirmed by the energy balance closure (H + LE versus Rn-G), showing an imbalance lower than 10 % for both the regimes. A detailed analysis of the effect of the storage terms on the ground heat flux estimation and a more thorough analysis of the radiation balance for the two plots were also performed.