Changes In Heat Storage Research Articles

Improving the Estimation of Hydraulic and Thermal Properties of Heterogeneous Media via the Addition of Heat Loss

Core Ideas Heat loss is the main reason for water flux underestimation. Two methods were proposed to quantify the heat loss. More accurate hydraulic properties can be estimated with the addition of heat loss. Heat has been widely used to investigate water flow in soils and aquifers during the past few decades. However, heat loss as an important characteristic has not been well considered in laboratory heat‐tracing experiments. To evaluate the impact of heat loss on the estimation of hydraulic and thermal properties, a laboratory experiment was conducted using a sandbox packed with heterogeneous silica sand under steady‐state flow condition. Thermocouple probes were used to simultaneously measure the temperature inside and outside of the silica sand during the experiment. The measured temperature of the sand layer was used to estimate the hydraulic conductivities and longitudinal and transverse thermal dispersivities via curve fitting using HYDRUS software. We found that >50% of the sensible heat was dissipated into the shell of sandbox and the surrounding air rather than being absorbed by the sand. Two methods were then proposed to quantify the heat loss and to improve the accuracy of parameter estimation: (i) a conceptual heat balance method that accounted for the change in heat storage in different parts of the system and (ii) a physical process‐based method that described the thermodynamic processes of heat transfer among different parts of the system. On combining these two methods, the relative error between the estimated and measured water flux significantly decreased from 19% to nearly 2%. The results imply that the heat‐tracing method is capable of obtaining accurate hydraulic and thermal properties in a heterogeneous porous medium with the addition of heat loss.

Diurnal land surface energy balance partitioning estimated from the thermodynamic limit of a cold heat engine

Abstract. Turbulent fluxes strongly shape the conditions at the land surface, yet they are typically formulated in terms of semiempirical parameterizations that make it difficult to derive theoretical estimates of how global change impacts land surface functioning. Here, we describe these turbulent fluxes as the result of a thermodynamic process that generates work to sustain convective motion and thus maintains the turbulent exchange between the land surface and the atmosphere. We first derive a limit from the second law of thermodynamics that is equivalent to the Carnot limit but which explicitly accounts for diurnal heat storage changes in the lower atmosphere. We call this the limit of a “cold” heat engine and use it together with the surface energy balance to infer the maximum power that can be derived from the turbulent fluxes for a given solar radiative forcing. The surface energy balance partitioning estimated from this thermodynamic limit requires no empirical parameters and compares very well with the observed partitioning of absorbed solar radiation into radiative and turbulent heat fluxes across a range of climates, with correlation coefficients r2≥95 % and slopes near 1. These results suggest that turbulent heat fluxes on land operate near their thermodynamic limit on how much convection can be generated from the local radiative forcing. It implies that this type of approach can be used to derive general estimates of global change that are solely based on physical principles.

Air temperature feedback and its contribution to global warming

Air temperature feedback results from the thermal-radiative coupling between the atmosphere and the surface and plays an important role in surface energy balance. This paper reveals the contribution of air temperature feedback to the global warming from 1980 to 2000. The air temperature feedback kernel, evaluated using the ERA-Interim reanalysis data, is used to discuss the physical mechanism for air temperature feedback, the dependency of the strength of air temperature feedback on the climatological spatial distributions of air temperature, water vapor and cloud content, and the contributions of air temperature feedback to rapid global warming. The coupling between temperature feedback and each of the external forcings and individual feedback processes will amplify the anomaly of direct energy flux convergence at the surface induced by the external forcings and individual processes. The air temperature feedback amplifies the initial surface warming due to the increase in CO2 concentration, ice and snow melting, increase in water vapor, and change in ocean heat storage. It also amplifies the surface warming due to the longwave radiaitve forcing associated with the increase in cloud cover, which acts to suppress the cooling of the shortwave effect of cloud forcing. Overall, temperature feedback plays an important role in the global warming from 1980 to 2000, as the net positive contribution to the perturbation of global mean energy flux at the surface from the air temperature feedback is larger than the net negative contribution from external forcing and all non-temperature feedbacks.

Latent thermal energy storage for solar process heat applications at medium-high temperatures – A review

Solar thermal energy has the potential to cover the heat demands of industrial processes. However, there may be a time mismatch between energy supplied by the solar field and the process demand. In this case, a thermal energy storage (TES) allows the use of heat at hours without solar irradiation available. Thermal energy storage for solar hot water or heating systems using low temperatures have been optimized since many decades and are in a mature stage. Developments at high temperatures (above 200 °C) for CSP applications have also been deeply studied. However, until this present paper, limited attention has been paid to TES for solar thermal industrial applications at medium-high temperatures (120–400 °C), where there is a potentially huge demand. When talking about TES several aspects have to be discussed: the heat demand that TES is going to be designed to supply, the material where the energy will be stored and the performance of the TES system which includes not only the material but also tanks, piping and connections.In this review, food, brewery and chemical industries were identified as the industries with higher potential in which TES and solar energy could be integrated. Heat integration methodologies have been reviewed to optimize the use of the solar energy in the industrial processes.Regarding the material, latent heat storage or phase change materials (PCM) were selected for this study because they are a very promising type of storage to be integrated in thermal industrial processes, although the state of the art of latent heat thermal energy storage (LHTES) systems is still far from broad commercialization. Until now, no reviews of latent heat storage for industrial applications at medium-high temperatures (120–400 °C) have been published. Therefore, literature related to PCM and latent heat storage (LHS) systems to be used in industrial thermal processes is here reviewed in order to have a general overview of the available technologies for their integration together with solar thermal energy in industrial processes at both experimental and numerical level. More than 100 potential PCMs for heat storage applications in the range of temperatures 120–400 °C have been found. Inorganic eutectic compositions are the group with more potentially available PCM for these applications, with values of heat of fusion between 74 and 535 kJ/kg.Finally, the works related to the performance of the system from the experimental and modelling point of view were presented. The review of experimental TES systems which include PCM in the studied range of temperatures 120–400 °C showed that most of the experimental set-ups were developed for direct steam generation for CSP applications. Regarding numerical modelling, the type of configuration more simulated is the shell and tube configuration.

Attribution of Local Temperature Response to Deforestation

AbstractLand use and land cover change such as deforestation can directly induce changes in land surface temperature (LST). Using observational data from four paired eddy covariance sites, we attribute changes in LST induced by deforestation to changes in radiation, aerodynamic resistance, the Bowen ratio or surface resistance, and heat storage using two different methods: the intrinsic biophysical mechanism (IBM) method and the two‐resistance mechanism method. The two models are first optimized to reduce the root‐mean‐square error of the simulated daily LST change by using daily‐averaged inputs and a weighted average approach for computing the sensitivities. Both methods indicate that the daytime warming effect of deforestation is mostly induced by changes in aerodynamic resistance as the surface becomes smoother after deforestation, and the nighttime cooling effect of deforestation is controlled by changes in aerodynamic resistance, surface resistance, radiation, and heat storage. Both methods also indicate that changes in atmospheric temperature have a large impact on LST and need to be included in the LST attribution. However, there are significant differences between the two methods. The IBM method tends to overestimate the contribution of aerodynamic resistance due to the assumption that aerodynamic resistance and the Bowen ratio are independent. Additionally, the IBM method underestimates the contributions of radiation and heat storage during the daytime but overestimates them at night. By highlighting the similarity and dissimilarity between the two methods, this study suggests that acceptable agreement between observed and modeled LST change is the prerequisite for attribution but does not guarantee correct attribution.

Do Graduated Compression Garments Enhance Whole‐body Heat Loss During an Extreme Heat Exposure in Older Adults?

Graduated compression garments worn on the lower limbs are commonly used in clinical settings to enhance blood circulation and have been shown to elicit elevations in whole‐body heat loss relative to a control condition (no compression) in young men during post‐exercise recovery in the heat (Am J Physiol 2010;299:R119). To date, it remains unknown whether these garments can enhance heat dissipation in heat vulnerable older adults. Relative to their younger counterparts, older adults demonstrate an impaired ability to increase whole‐body heat loss during an extreme heat exposure. Consequently, these individuals store more heat, leading to potentially dangerous increases in body temperature (Temperature (Austin) 2017;4:79). The use of compression garments may help alleviate the level of thermal strain in these individuals. We therefore sought to determine whether lower limb graduated compression garments would enhance whole‐body heat dissipation and reduce body heat storage relative to a control condition (i.e., no compression) in older adults during passive heat exposure. To evaluate this possibility, we assessed changes in whole‐body heat exchange and heat storage in 6 older (mean ± SD: 69 ± 6 years) adults (4 men, 2 women) during a 2‐hour extreme heat exposure (40°C, ~10 %RH) on two separate occasions (separated by ≥48 h). In both trials, participants sat in a semi‐recumbent position wearing a graduated compression garment (SCD Express Sleeves; Kendall, Mansfield, MA) on each leg containing three bladders that either delivered intermittent graded compression (ankle: 45 mmHg, calf: 40 mmHg, thigh: 30 mmHg; Compression trial) or no compression (Control trial) throughout each exposure. Trials were administered in a balanced order. Wholebody heat loss and metabolic heat production were measured continuously by direct and indirect calorimetry, respectively. Body heat storage was quantified as the temporal summation of heat production and loss. Metabolic heat production (Compression: 98 ± 10 W vs. Control: 94 ± 13 W), evaporative heat loss (135 ± 20 W vs. 134 ± 23 W), dry heat exchange (−48 ± 19 W vs. −52 ± 12 W), and net (total) heat loss (89 ± 14 W vs. 82 ± 14 W), were similar between the Compression and Control trials (all P>0.05). Consequently, cumulative body heat storage did not differ between conditions (Compression: 85 ± 11 kJ; Control: 85 ± 24 kJ, P=0.98). Our preliminary findings suggest that graduated compression garments do not enhance whole‐body heat loss in older adults during exposure to hot ambient conditions.Support or Funding InformationThe Canadian Institutes of Health Research (funds held by Dr. Glen Kenny).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Thermal Regime of A Deep Temperate Lake and Its Response to Climate Change: Lake Kuttara, Japan

A deep temperate lake, Lake Kuttara, Hokkaido, Japan (148 m deep at maximum) was completely ice-covered every winter in the 20th century. However, ice-free conditions of the lake over winter occurred three times in the 21st century, which is probably due to global warming. In order to understand how thermal regime of the lake responds to climate change, a change in lake mean water temperature from the heat storage change was calculated by integrating observed water temperature over water depths and by numerical calculation of heat budget components based on hydrometeorological data. As a result, a temporal variation of lake mean water temperature from the heat budget calculation was very reasonable to that from the observed water temperature (determination coefficient R2 = 0.969). The lowest lake mean temperature for non-freeze was then evaluated at −1.87 °C, referring to the zero level at 6.80 °C. The 1978–2017 data at a meteorological station near Kuttara indicated that there are significant (less than 5% level) long-term trends for air temperature (+0.024 °C/year) and wind speed (−0.010 m/s/year). In order to evaluate the effects of climate change on freeze-up patterns, a sensitivity analysis was carried out for the calculated lake mean water temperature. It is noted that, after two decades, the lake could be ice-free once per every two years.

Does a Prolonged Work Day in the Heat Impair Heat Loss on the Next Day in Young Men?

Heat strain is known to be exacerbated on the second of consecutive work days. We therefore evaluated whether prolonged work in the heat would impair whole-body heat loss capacity on the next day. To evaluate this possibility, we assessed changes in whole-body heat exchange and heat storage in eight young (26 ± 4 yr) men during heat stress tests performed on the same day before (day 1) and on the day after (day 2) a prolonged work simulation. Each heat stress test involved three, 30-min bouts of semirecumbent cycling at fixed rates of metabolic heat production (200 W·m (Ex1), 250 W·m (Ex2), and 300 W·m (Ex3)), each separated by 15-min recovery, under hot, dry conditions (40°C, 20% relative humidity). The work simulation (7.5 h) involved three moderate-intensity intermittent work bouts (2 h), each separated by 30-min rest breaks, under similarly hot, dry conditions (38°C, 34% relative humidity). Total heat loss (evaporative ± dry heat exchange) and metabolic heat production were measured using direct and indirect calorimetry, respectively. Body heat storage was quantified as the temporal summation of heat production and loss. Total heat loss did not differ between days 1 and 2 (P = 0.66) and averaged (mean ± 95% confidence interval) 185 ± 7 W (Ex1), 233 ± 7 W (Ex2), and 261 ± 5 W (Ex3) across test days. Consequently, the change in body heat storage was also similar between days 1 and 2 (P = 0.32), averaging 133 ± 15 kJ (Ex1), 99 ± 16 kJ (Ex2), and 184 ± 15 kJ (Ex3) across test days. When assessed under controlled laboratory conditions in young men, prolonged work in the heat does not seem to impair whole-body heat loss or exacerbate heat storage on the following day.

Heat export from the tropics drives mid to late Holocene palaeoceanographic changes offshore southern Australia

The Leeuwin Current (LC), an eastern boundary current, transports tropical waters from the Indo-Pacific Warm Pool (IPWP) towards southern latitudes and modulates oceanic conditions offshore southern Australia. New, high-resolution planktic foraminifer assemblage data and alkenone-derived sea surface temperatures (SST) provide an in-depth view on LC variability and mechanisms driving the current's properties during the mid to late Holocene (last c. 7.4 ka BP). Our marine reconstructions highlight a longer-term mid to late Holocene reduction of tropical heat export from the IPWP area into the LC. Mid Holocene (c. 7.4 to 3.5 ka BP) occurrence of high SSTs (>19.5 °C), tropical planktic foraminifera and a well-stratified water column document an enhanced heat export from the tropics. From c. 3.5 ka BP onwards, a weaker LC and a notably reduced tropical heat export cause oceanic cooling offshore southern Australia. The observed mid to late Holocene trends likely result from large-scale changes in the IPWP's heat storage linked to the El Niño-Southern Oscillation (ENSO) phenomenon. We propose that a strong and warm LC occurs in response to a La Niña-like state of ENSO during the mid Holocene. The late Holocene LC cooling, however, results from a shift towards an El Niño-like state and a more variable ENSO system that causes cooling of the IPWP. Superimposed on these longer-term trends we find evidence of distinct late Holocene millennial-scale phases of enhanced El Niño/La Niña development, which appear synchronous with northern hemispheric climatic variability. Phases of dominant El Niño-like states occur parallel to North Atlantic cold phases: the ‘2800 years BP cooling event’, the ‘Dark Ages’ and the ‘Little Ice Age’, whereas the ‘Roman Warm Period’ and the ‘Medieval Climate Anomaly’ parallel periods of a predominant La Niña-like state. Our findings provide further evidence of coherent interhemispheric climatic and oceanic conditions during the mid to late Holocene, suggesting ENSO as a potential mediator.

Estimating daily lake evaporation from biweekly energy‐budget data

AbstractEstimates of daily lake evaporation based on energy‐budget data are poor because of large errors associated with quantifying change in lake heat storage over periods of less than about 10 days. Energy‐budget evaporation was determined during approximately biweekly periods at a northern Minnesota, USA, lake for 5 years. Various combinations of shortwave radiation, air temperature, wind speed, lake‐surface temperature, and vapour‐pressure difference were related to energy‐budget evaporation using linear‐regression models in an effort to determine daily evaporation without requiring the heat‐storage term. The model that combined the product of shortwave radiation and air temperature with the product of vapour‐pressure difference and wind speed provided the second best fit based on statistics but provided the best daily data based on comparisons with evaporation determined with the eddy‐covariance method. Best‐model daily values ranged from −0.6 to 7.1 mm/day over a 5‐year period. Daily averages of best‐model evaporation and eddy‐covariance evaporation were nearly identical for all 28 days of comparisons with a standard deviation of the differences between the two methods of 0.68 mm/day. Best‐model daily evaporation also was compared with two other evaporation models, Jensen–Haise and a mass‐transfer model. Best‐model daily values were substantially improved relative to Jensen–Haise and mass‐transfer values when daily values were summed over biweekly energy‐budget periods for comparison with energy‐budget results.

Attribution and mitigation of heat wave-induced urban heat storage change

When the urban heat island (UHI) effect coincides with a heat wave (HW), thermal stress in cities is exacerbated. Understanding the surface energy balance (SEB) responses to HWs is critical for improving predictions of the synergies between UHIs and HWs. This study evaluates observed SEB characteristics in four cities (Beijing, Łódź, London and Swindon), along with their ambient meteorological conditions, for both HW and background summer climate scenarios. Using the Analytical Objective Hysteresis Model (AnOHM), particular emphasis is on the heat storage. The results demonstrate that in London and Swindon the amount of daytime heat storage and its fraction relative to the net all-wave radiation increase under HWs. Results further demonstrate that such increases are strongly tied to lower wind speeds. The effects of different UHI mitigation measures on heat storage are assessed using AnOHM. Results reveal that use of reflective materials and maintaining higher soil moisture availability can offset the adverse effects of increased heat storage.

An explanation for the different climate sensitivities of land and ocean surfaces based on the diurnal cycle

Abstract. Observations and climate model simulations consistently show a higher climate sensitivity of land surfaces compared to ocean surfaces. Here we show that this difference in temperature sensitivity can be explained by the different means by which the diurnal variation in solar radiation is buffered. While ocean surfaces buffer the diurnal variations by heat storage changes below the surface, land surfaces buffer it mostly by heat storage changes above the surface in the lower atmosphere that are reflected in the diurnal growth of a convective boundary layer. Storage changes below the surface allow the ocean surface–atmosphere system to maintain turbulent fluxes over day and night, while the land surface–atmosphere system maintains turbulent fluxes only during the daytime hours, when the surface is heated by absorption of solar radiation. This shorter duration of turbulent fluxes on land results in a greater sensitivity of the land surface–atmosphere system to changes in the greenhouse forcing because nighttime temperatures are shaped by radiative exchange only, which are more sensitive to changes in greenhouse forcing. We use a simple, analytic energy balance model of the surface–atmosphere system in which turbulent fluxes are constrained by the maximum power limit to estimate the effects of these different means to buffer the diurnal cycle on the resulting temperature sensitivities. The model predicts that land surfaces have a 50 % greater climate sensitivity than ocean surfaces, and that the nighttime temperatures on land increase about twice as much as daytime temperatures because of the absence of turbulent fluxes at night. Both predictions compare very well with observations and CMIP5 climate model simulations. Hence, the greater climate sensitivity of land surfaces can be explained by its buffering of diurnal variations in solar radiation in the lower atmosphere.

Evaporation and the subcanopy energy environment in a flooded forest

AbstractThe combination of tree canopy cover and a free water surface makes the subcanopy environment of flooded forested wetlands unlike other aquatic or terrestrial systems. Subcanopy vapour fluxes and energy budgets represent key controls on water level and understorey climate but are not well understood. In a permanently flooded forest in south‐eastern Louisiana, USA, an energy balance approach was used to address (a) whether evaporation from floodwater under a forest canopy is solely energy limited and (b) how energy availability was modulated by radiation and changes in floodwater heat storage. A 5‐month continuous measurement period (June–November) was used to sample across seasonal changes in canopy activity and temperature regimes. Over this period, the subcanopy airspace was humid, maintaining saturation vapour pressure for 28% of the total record. High humidity coupled with the thermal inertia of surface water altered both seasonal and diel energy exchanges, including atypical phenomena such as frequent day‐time vapour pressure gradients towards the water surface. Throughout the study period, nearly all available energy was partitioned to evaporation, with minimal sensible heat exchange. Monthly mean evaporation ranged from 0.7 to 1.7 mm/day, peaking in fall when canopy senescence allowed greater radiation transmission; contemporaneous seasonal temperature shifts and a net release of stored heat from the surface water resulted in energy availability exceeding net radiation by 30% in October and November. Relatively stable energy partitioning matches Priestley–Taylor assumptions for a general model of evaporation in this ecosystem.

Measurement of soil‐surface heat flux with a multi‐needle heat‐pulse probe

SummarySoil‐surface heat flux (G0), an important component of the surface energy balance, is often determined by summing soil heat flux (Gz) at a depth (z) below the surface and the rate of change in soil heat storage (ΔS) in the layer above z. The soil heat flux Gz is commonly measured with passive heat flux plates, but self‐calibrating plates or additional corrections are required to obtain accurate data. In some cases, ΔS is neglected because of the difficulty of monitoring the dynamics of volumetric heat capacity (C), which might lead to erroneous estimates of G0. To overcome these limitations, we introduce the heat‐pulse method for measuring G0 with a multi‐needle heat‐pulse probe (HPP). Soil temperature (T) distribution, thermal conductivity (λ) and C of the 0–52‐mm layer were measured hourly on five consecutive days with an 11‐needle HPP, and Gz at 50‐mm depth (G50) and ΔS of the 0–50‐mm layer (ΔS0–50) were determined by the gradient and calorimetric methods, respectively. Independent measurements of G50 with a self‐calibrating heat flux plate and ΔS0–50 calculated with the de Vries model C were used to evaluate the HPP data. With reliable G50 and ΔS0–50 measurements, the HPP‐based G0 data agreed well with those estimated from the independent method (with a mean absolute difference of 4.5 W m−2). Supporting measurements showed that determining Gz at the 50‐mm depth minimized the likelihood of errors from evaporation below the measurement depth. The multi‐needle HPP provides a reliable way to determine G0 in situ. Additional analysis demonstrated that by reducing the number of needles from 11 to 5, the datalogging requirement was reduced by half and G0 was still determined with acceptable accuracy.HighlightsHeat flux at the soil surface (G0) was monitored by the heat‐pulse technique. A multi‐needle heat‐pulse probe (HPP) was used to measure subsurface soil heat flux (Gz) and heat storage concurrently. Appropriate measurement depths of Gz were determined to minimize the effects of subsurface latent heat sink on G0. A simplified calculation reduced the datalogging requirement of the multi‐needle HPP.

Are Type 2 Diabetes-Related Impairments in Heat Dissipation Heat Load Dependent?

Older adults with type 2 diabetes (T2D) have an attenuated physiological ability to dissipate heat during moderate intensity exercise in the heat. However, it is unclear if T2D-related impairments in heat dissipation only occur above a certain exercise-induced heat load and therefore level of heat stress. PURPOSE: To examine whether T2D-related impairments in whole-body heat loss, as assessed by direct calorimetry, occur above a certain heat load threshold. METHODS: Twelve older (60 ± 7 years) habitually active males with (n=6, hemoglobin A1c: 6.8 ± 0.6 %, duration of diabetes: 9 ± 5 years) and without (n=6) T2D (CON) matched for age, body surface area, and fitness (VO2peak) completed three successive 30-min bouts of semi-recumbent cycling performed at fixed incremental rates of metabolic heat production of 300 (Ex1), 400 (Ex2) and 500 (Ex3) W in the heat (40°C). This was equivalent to 37, 50 and 62% of their pre-determined VO2peak. A 15-min recovery period followed each exercise bout. Whole-body heat loss (evaporative and dry heat exchange) was measured using direct calorimetry. The simultaneous measurement of metabolic heat production via indirect calorimetry was used to calculate the change in body heat storage. RESULTS: Whole-body heat loss was reduced in the T2D group relative to CON at the end of Ex1 (T2D: 235 ± 23 W; CON: 261 ± 34 W, p=0.004), Ex2 (T2D: 294 ± 24 W; CON: 335 ± 44 W, p=0.030), and Ex3 (T2D: 330 ± 59 W; CON: 390 ± 39 W, p=0.02). Given that dry heat gain was similar between groups at the end of all exercise bouts (all p>0.05), differences in whole-body heat loss were only due to differences in evaporative heat loss. The relative difference in the maximal level of whole-body heat loss achieved between groups became greater with increasing exercise-induced heat loads (Differences: Ex1=10.5%, Ex2=14.0% and Ex3=20.5%). As such, the individuals with T2D stored more heat during all exercise bouts (Ex1: 197 ± 39 kJ; Ex2: 236 ± 67 kJ; Ex3; 334 ± 78 kJ, p<0.05) compared to the control group (Ex1: 150 ± 61 kJ; Ex2: 160 ± 74 kJ; Ex3; 248 ± 80 kJ). CONCLUSION: Our preliminary findings show that type 2 diabetes impairs the body’s ability to dissipate heat during exercise in the heat and that these differences are first evident at a moderate heat load of 300 W (equivalent to 37% of VO2peak). Supported by the Canadian Institutes of Health Research

Evaluation of three energy balance-based evaporation models for estimating monthly evaporation for five lakes using derived heat storage changes from a hysteresis model

The heat storage changes (Qt) can be a significant component of the energy balance in lakes, and it is important to account for Qt for reasonable estimation of evaporation at monthly and finer timescales if the energy balance-based evaporation models are used. However, Qt has been often neglected in many studies due to the lack of required water temperature data. A simple hysteresis model (Qt = a*Rn + b + c*dRn/dt) has been demonstrated to reasonably estimate Qt from the readily available net all wave radiation (Rn) and three locally calibrated coefficients (a–c) for lakes and reservoirs. As a follow-up study, we evaluated whether this hysteresis model could enable energy balance-based evaporation models to yield good evaporation estimates. The representative monthly evaporation data were compiled from published literature and used as ground-truth to evaluate three energy balance-based evaporation models for five lakes. The three models in different complexity are De Bruin-Keijman (DK), Penman, and a new model referred to as Duan-Bastiaanssen (DB). All three models require Qt as input. Each model was run in three scenarios differing in the input Qt (S1: measured Qt; S2: modelled Qt from the hysteresis model; S3: neglecting Qt) to evaluate the impact of Qt on the modelled evaporation. Evaluation showed that the modelled Qt agreed well with measured counterparts for all five lakes. It was confirmed that the hysteresis model with locally calibrated coefficients can predict Qt with good accuracy for the same lake. Using modelled Qt as inputs all three evaporation models yielded comparably good monthly evaporation to those using measured Qt as inputs and significantly better than those neglecting Qt for the five lakes. The DK model requiring minimum data generally performed the best, followed by the Penman and DB model. This study demonstrated that once three coefficients are locally calibrated using historical data the simple hysteresis model can offer reasonable Qt to force energy balance-based evaporation models to improve evaporation modelling at monthly timescales for conditions and long-term periods when measured Qt are not available. We call on scientific community to further test and refine the hysteresis model in more lakes in different geographic locations and environments.

Effects of soil heat storage and phase shift correction on energy balance closure of paddy fields

The eddy covariance technique was used to measure the energy fluxes of a paddy field under water-saving irrigation in the South China Plain for the stage of rice growth in 2013. This study analyzed the energy balance components and evaluated the energy balance closure. The study also discussed the response of surface energy balance to the change in soil heat storage between the heat flux plates buried at a specific depth and the surface, and the phase shift correction of energy balance components, by using three different statistical methods, namely ordinary least squares (OLS), energy balance ratio (EBR), and energy balance residual (D). The results showed that the OLS slope increased by an average of 8.8%, and the mean daily EBR increased by 5.0% after considering the change in soil heat storage. The range of half-hourly D over a four-month period decreased from -129 - 260 W m−2 to -102 - 194 W m−2, and the absolute value of D decreased by 9.9% on the average. Considering the phase correction, the increase in OLS regression coefficients with an average of 11.3% and the decrease in half-hourly D, ranging from -61 to 176 W m−2, both indicated that phase shift correction improved the surface energy balance closure at the half-hourly scale, specifically in the period from sunrise to noon, but had no use in the daily scale. Thus, the two correction methods are useful in improving the degree of energy balance closure shown in different temporal scales with proper evaluation index. Moreover, further research should be given with more attention for other correction aspects.

Fatigue associated with prolonged graded running.

Scientific experiments on running mainly consider level running. However, the magnitude and etiology of fatigue depend on the exercise under consideration, particularly the predominant type of contraction, which differs between level, uphill, and downhill running. The purpose of this review is to comprehensively summarize the neurophysiological and biomechanical changes due to fatigue in graded running. When comparing prolonged hilly running (i.e., a combination of uphill and downhill running) to level running, it is found that (1) the general shape of the neuromuscular fatigue-exercise duration curve as well as the etiology of fatigue in knee extensor and plantar flexor muscles are similar and (2) the biomechanical consequences are also relatively comparable, suggesting that duration rather than elevation changes affects neuromuscular function and running patterns. However, 'pure' uphill or downhill running has several fatigue-related intrinsic features compared with the level running. Downhill running induces severe lower limb tissue damage, indirectly evidenced by massive increases in plasma creatine kinase/myoglobin concentration or inflammatory markers. In addition, low-frequency fatigue (i.e., excitation-contraction coupling failure) is systematically observed after downhill running, although it has also been found in high-intensity uphill running for different reasons. Indeed, low-frequency fatigue in downhill running is attributed to mechanical stress at the interface sarcoplasmic reticulum/T-tubule, while the inorganic phosphate accumulation probably plays a central role in intense uphill running. Other fatigue-related specificities of graded running such as strategies to minimize the deleterious effects of downhill running on muscle function, the difference of energy cost versus heat storage or muscle activity changes in downhill, level, and uphill running are also discussed.

Changes in the Seoul Metropolitan Area Urban Heat Environment with Residential Redevelopment

AbstractSince the Industrial Revolution, the geographical extent of cities has increased around the world. In particular, following three decades of rapid regional economic growth, many Asian megacities have emerged and continue to expand, resulting in inevitable short-term urban redevelopment. In this region, the microclimatic impacts of urban redevelopment have not been extensively investigated using long-term in situ observations. In this study, changes in surface sensible heat exchange, heat storage, and anthropogenic heat emissions that are due to urban residential redevelopment were quantified and analyzed on the basis of a 3-yr micrometeorological record from the Seoul, South Korea, metropolitan area. The results show that, following urban redevelopment of compact high-rise residential buildings, 1) the daily minimum air temperature near the ground surface increased by ~0.6 K; 2) the ratio between surface sensible heat and net radiation increased by from ~9% (summer) to 31% (winter), anthropogenic heat emissions increased by from 7.6 (summer) to 23.6 (spring) W m−2, and daily maximum heat storage ranged from 35.1 (spring) to 54.5 (summer) W m−2; and 3) there was a transition of local circulation with changes in the surface properties of heat sources and roughness.

Responses to hyperthermia. Optimizing heat dissipation by convection and evaporation: Neural control of skin blood flow and sweating in humans.

Under normothermic, resting conditions, humans dissipate heat from the body at a rate approximately equal to heat production. Small discrepancies between heat production and heat elimination would, over time, lead to significant changes in heat storage and body temperature. When heat production or environmental temperature is high the challenge of maintaining heat balance is much greater. This matching of heat elimination with heat production is a function of the skin circulation facilitating heat transport to the body surface and sweating, enabling evaporative heat loss. These processes are manifestations of the autonomic control of cutaneous vasomotor and sudomotor functions and form the basis of this review. We focus on these systems in the responses to hyperthermia. In particular, the cutaneous vascular responses to heat stress and the current understanding of the neurovascular mechanisms involved. The available research regarding cutaneous active vasodilation and vasoconstriction is highlighted, with emphasis on active vasodilation as a major responder to heat stress. Involvement of the vasoconstrictor and active vasodilator controls of the skin circulation in the context of heat stress and nonthermoregulatory reflexes (blood pressure, exercise) are also considered. Autonomic involvement in the cutaneous vascular responses to direct heating and cooling of the skin are also discussed. We examine the autonomic control of sweating, including cholinergic and noncholinergic mechanisms, the local control of sweating, thermoregulatory and nonthermoregulatory reflex control and the possible relationship between sudomotor and cutaneous vasodilator function. Finally, we comment on the clinical relevance of these control schemes in conditions of autonomic dysfunction.