Active infrared imaging is one of the promising remote and whole field characterisation techniques for non-destructive testing and evaluation of various solids irrespective of their electrical and ...magnetic prosperities. This technique relies on a mapping of thermal response for a predefined incident heat flux over the test object to detect the presence of surface and subsurface anomalies. Due to its fast, non-contact, safe and quantitative testing capabilities, infrared thermography has gained significant importance in the testing of fibre reinforced polymers. This Letter highlights testing and evaluation of glass fibre-reinforced polymer (GFRP) specimen for detection of subsurface hidden defects using pulse compression favourable thermal wave imaging techniques (for an imposed digitised chirp as well as a 7-bit Barker coded modulated heat fluxes over the test specimen). Further depth scanning capabilities of the proposed schemes have been compared using a time-domain pulse compression based approach. Proposed analytical, as well as simulation studies, have been validated with the experimental results on GFRP material having flat bottom holes as defects.
In this study, land surface temperature (LST) and leaf area index (LAI) observations are merged with a coupled two‐source surface energy budget–vegetation dynamic model (TSEB–VDM) via a variational ...data assimilation (VDA) system to predict turbulent heat fluxes and gross primary productivity (GPP). The TSEB and VDM are coupled by relating photosynthesis in the VDM to transpiration in the TSEB equation. Unknown parameters of the VDA approach are the neutral bulk heat transfer coefficient (CHN), evaporative fractions for soil and canopy (EFS and EFC), and specific leaf area (cg). The VDA approach is evaluated at six AmeriFlux sites with distinct vegetative and climatic characteristics. The modeled sensible (H) and latent (LE) heat fluxes, and GPP agree well with the corresponding eddy covariance measurements in different environmental conditions. The six‐site average root mean square error (RMSE) of estimated daily H, LE, and GPP is 42.2 W m−2, 51.5 W m−2, and 1.8 gC m−2 d−1, respectively. The outcomes show that the developed VDA approach is able to exploit the implicit information in the sequences of LST and LAI measurements to estimate H, LE, and GPP. Our findings also indicate that the estimates of the H and LE are more sensitive to uncertainties in LST measurements, while the GPP retrievals are more affected by uncertainties in the LAI observations.
Key Points
Land surface temperature (LST) and leaf area index (LAI) measurements are merged with a coupled two‐source surface energy budget‐vegetation dynamic model within a variational data assimilation system to estimate sensible (H) and latent (LE) heat fluxes as well as gross primary productivity (GPP)
H, LE, and GPP estimates agree well with the corresponding eddy covariance measurements in different environmental conditions
H and LE estimates are more sensitive to uncertainties in LST measurements, while GPP retrievals are affected by errors in LAI observations
•The ITER-grade tungsten limiters tested in the T-10 tokamak.•Strong destruction of the limiters under the combination of the high heat and particle fluxes observed.•Intensive cracking of the ...tungsten tiles observed at the heat loads from 1 MW/m2 up to 30 MW/m2.•In the areas of highest heat loads, tungsten plates were melted and close to full destruction.•The nonambipolar flow due to the arcs and sparks can explain the observed overheating and melting of the tungsten surface.
The tungsten limiters were tested in the T-10 tokamak during the 2015–2017 experimental campaign. The limiters were made from the ITER-grade WMP “POLEMA” tungsten. Inspection of the tungsten limiters after experimental campaign has revealed their strong destruction due to the combination of the high heat and particle fluxes from the edge plasma toward the limiters surface. The influence of the edge tokamak plasma on tungsten limiters leads to significant cracking of the tungsten. Heat load up to 2 MW m−2 leads to micro-cracks at the grain boundaries. Heat loads exceeding 5 MW m−2 lead to macro-cracks formation. In the areas of highest heat loads, tungsten plates are melted and close to full destruction. In these zones, intensive sparking and arcing were observed. Arc craters have been scattered across the surface, and along the cracks. It is supposed that the nonambipolar flow due to the arcs and sparks can explain the observed overheating and melting of the tungsten surface. Disruptions and runaway electrons beams have driven extreme heat loads of more than 1 GW/m2 causing strong melting of the tungsten on the outer board of the ring limiter.
Recent simulations suggest that submesoscale motions with scales smaller than 30 km and frequencies greater than 1 day−1 drive upward vertical heat transport. These simulations have prompted us to ...revisit the mechanisms that explain high‐frequency (HF) vertical heat fluxes (VHFs) within the surface mixed layer (ML). Here, an idealized numerical simulation of a re‐entrant channel flow with an unbalanced submesoscale thermal front is used to analyze the impact of surface cooling on HF VHFs. Two types of simulations are analyzed: forced and unforced. The VHFs cospectrum analysis shows that surface diurnal cooling increases VHFs, reaching frequencies larger than 1 day−1. However, the fastest‐growing length scale of ML instabilities limits the extension of positive VHFs toward fine scales. Symmetric and gravitational instabilities are the main conduits producing ageostrophic HF and small‐scale structures, which in turn enhance upward VHFs across the diurnal frequency. A comparison between forced‐idealized simulations with the K‐profile parameterization scheme and a realistic regional simulation in the frequency‐wavenumber space, reveals that the two simulation types reproduce similar VHFs near the diurnal frequency. However, the realistic simulation displays higher VHFs than the forced‐idealized simulation. This study emphasizes that surface diurnal cooling significantly impacts HF VHFs. However, this impact is not sufficient to reach the HF VHFs estimated in realistic submesoscale‐permitting and tidal‐resolving simulations.
Plain Language Summary
Recent research has highlighted the importance of balanced motions in the ocean with horizontal dimensions less than 30 km, as these motions play a crucial role in carrying heat upward with frequencies greater than 1 day−1 in the surface mixed layer (ML). These motions are influenced by atmospheric forcing, which impacts the heat flux. This study investigates how high‐frequency vertical heat fluxes (VHFs) respond to atmospheric cooling by using numerical simulations to generate structures with horizontal dimensions less than 30 km in two scenarios: one with active surface cooling and one without. The simulations reveal that surface diurnal cooling amplifies VHFs with frequencies higher than 1 day−1. This amplification occurs through the enhancement of the generation of structures driven by convective motions in the ML. Through comparison with a realistic numerical simulation that generates horizontal motions less than 30 km and tidal motions, the study finds that diurnal cooling partially explains the vertical fluxes with frequencies greater than 1 day−1 estimated in the realistic simulations. This research sheds light on the complex mechanisms involved in vertical heat transport in the ocean and highlights the roles of balanced motions with horizontal dimensions of less than 30 km and atmospheric forcing.
Key Points
Surface diurnal cooling amplifies vertical heat fluxes with frequencies higher than 1 day−1
Such amplification occurs through ageostrophic motions driven by symmetric and gravitational instabilities
Diurnal cooling partially explains the high‐frequency vertical fluxes estimated in submesoscale‐permitting and tide‐resolving simulations
•Ion-acoustic, firehose and mirror instabilities considered behind shocks in collisionless plasma.•Parallel shock waves can excite instabilities in a stable anisotropic plasma.•Plots are given for ...critical values of the plasma anisotropy and plasma beta.
Firehose, mirror and ion-acoustic instabilities behind MHD shock waves are discussed for collisionless anisotropic plasma with heat fluxes. For the parallel shock wave it has been demonstrated that initially stable plasma can be destabilized by the shock which leads to turbulence generation in the downstream flow. Upstream parameter domains are determined where such destabilization occurs.
Innovative methods to combat internal loading issues in eutrophic lakes are urgently needed to speed recovery and restore systems within legislative deadlines. In stratifying lakes, internal ...phosphorus loading is particularly problematic during the summer stratified period when anoxia persists in the hypolimnion, promoting phosphorus release from the sediment. A novel method to inhibit stratification by reducing residence times is proposed as a way of controlling the length of the hypolimnetic anoxic period, thus reducing the loading of nutrients from the sediments into the water column. However, residence time effects on stratification length in natural lakes are not well understood. We used a systematic modelling approach to investigate the viability of changes to annual water residence time in affecting lake stratification and thermal dynamics in Elterwater, a small stratifying eutrophic lake in the northwest of England. We found that reducing annual water residence times shortened and weakened summer stratification. Based on finer-scale dynamics of lake heat fluxes and water column stability we propose seasonal or sub-seasonal management of water residence time is needed for the method to be most effective at reducing stratification as a means of controlling internal nutrient loading.
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•Reducing water residence times (WRTs) shortened and weakened summer stratification.•Stratification length may be effectively controlled by fine-scale WRT management.•Lake modelling can establish WRT change impacts pre-intervention.•Advective heat flux changes should be compared to annual surface heat flux dynamics.
ABSTRACT
The observed surface energy balance fluxes are essential to improve model forecasting ability but such data are scarce for subtropical cities and urban areas with tall buildings. One year of ...eddy covariance flux data for an area within Shanghai with a wide range of building heights (8–150 m, mean by direction) are analysed by wind direction. Consideration is given to how to distinguish between local‐ and micro‐scale fluxes. At the local‐scale, median daily peaks of sensible heat flux occur in the early afternoon (winter: 87 W m−2, spring: 205 W m−2, summer: 292 W m−2, autumn: 135 W m−2). The latent heat flux is small in winter (median daily maxima 21 W m−2) and slightly larger in spring, summer and autumn (49, 65, 49 W m−2, respectively). The monthly mean daytime Bowen ratio under all‐sky conditions ranges from 2 to 4.7. At this site, with predominately impervious surface (85% buildings/pavement, 14% vegetation), the enhancement of evaporation following rainfall usually lasts for about 12 h. Consistently larger Bowen ratios at the micro‐scale than the local‐scale are attributed to roughness effects and the impact of extensive areas of dry walls. The daily median CO2 flux is dominated by traffic emissions, with two peaks associated with morning and evening rush hours. The data provide insights into urban surface controls on momentum, energy and carbon dynamics, with implications for urban planning strategies in the context of rapid global urbanization and climate change.
Using bulk formulas, two-year platform (fastened to the seabed) hourly observations from 2016 to 2017 in the East China Sea (121.6° E, 32.4° N) are used to investigate the role of the tide-induced ...surface elevation in changing the fixed observational height and modifying the momentum and air-sea turbulent heat fluxes. The semidiurnal tide-dominated elevation anomalies ranging from −3.6 to 3.9 m change the fixed platform observational height. This change causes hourly differences in the wind stress and latent and sensible heat fluxes between estimates with and without considering surface elevation, with values ranging from −1.5 × 10−3 Nm−2, −10.2 Wm−2, and −3.6 Wm−2 to 2.2 × 10−3 Nm−2, 8.4 Wm−2, and 4.6 Wm−2, respectively. More significant differences occur during spring tides. The differences show weak dependence on the temperature, indicating weak seasonal variations. The mean (maximum) difference percentage relative to the mean magnitude is approximately 3.5% (7%), 1.5% (3%), and 1.5% (3%) for the wind stress and latent and sensible heat fluxes, respectively. The boundary layer stability (BLS) can convert from near-neutral conditions to stable and unstable states in response to tide-induced changes in the observational height, with a probability of occurrence of 2%. Wind anomalies play dominant roles in determining the hourly anomalies of the latent heat flux, regardless of the state of the BLS. Extreme cases, including the cold air outbreak in 2016, tropical cyclones Meranti in 2016, and Ampil in 2018, are also examined. This study will facilitate future observation-reanalysis comparisons in the studied coastal region where ocean–atmosphere-land interactive processes are significant.
Quantifying and predicting the drawdown of dissolved oxygen (DO) in lakes is important to ensuring healthy ecosystems and safe water sources. The characterization of DO depletion using available ...definitions and models requires extensive monitoring to obtain reliable results. These approaches have been mostly developed for seasonally stratified monomictic and dimictic lakes, limiting their applicability for polymictic systems which stratify and mix repeatedly. We compared the predicted duration of hypoxic events in the three basins of a large eutrophic polymictic lake (Clear Lake, CA, USA) by using three different one‐dimensional (1‐D) analytical approaches; two being original and requiring minimal input variables. Data on meteorology, lake temperature, and DO were all measured at multiple locations for one year and used to develop a novel method, named the Birge‐Winkler method. The daily net surface heat fluxes provided an energy term from which estimates of the onset and length of hypoxic periods could be made with minimal calibration. We used the Lake Number method to evaluate the level of accuracy of the Birge‐Winkler method. Finally, we estimated DO values next to the sediments using a Buoyancy Frequency method. Our results from the two original methods provided simple and effective tools for early warning of onset and duration of hypoxia, with a maximum of ±3–5 days uncertainty in the predictions. These indices can become powerful decision support tools for addressing aquatic ecological challenges triggered by hypoxia, including fish kills, internal nutrient loading, heavy metals release, and harmful algal blooms.
Key Points
We present a new one‐dimensional method to estimate onset and duration of hypoxic events in eutrophic polymictic lakes
The model only requires basic meteorological variables, lake surface temperatures, and dissolved oxygen at the lake bottom for calibration
The method can be a cost‐effective decision‐making tool for management actions affecting ecosystem health and water quality
Abstract Sea spray, originating from wave breaking under high wind conditions, can significantly affect turbulent heat fluxes at the air–sea interface. Even though polar lows (PLs) can become extreme ...weather features with gale‐force wind, the impact of sea spray on their development has rarely been investigated and is not considered in operational forecast models. In this study, the impact of sea spray on the development of two PLs over the Barents Sea is studied based on sensitivity experiments with an atmosphere–wave coupled model, where the spray‐mediated heat fluxes are parameterized. The results show that the impact of sea‐spray‐mediated heat fluxes on PL development is sensitive to the surface wind speed. In the case of the stronger PL, the higher surface wind speed results in significantly higher spray‐mediated heat fluxes. Consequently, these spray‐mediated heat fluxes intensify the convection and diabatic heating of the PL, resulting in its intensification. In comparison, the case with a weaker PL experiences less sea spray production and lower spray‐mediated heat fluxes due to its weaker surface wind speeds. Overall, we find that spray‐mediated sensible heat fluxes play an important role in the development of PLs, while the latent heat fluxes induced by sea spray have a relatively minor impact.
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