Estimating Heat Storage Research Articles

Heat strain differences walking in hot-dry and warm-wet environments of equivalent wet bulb globe temperature

ABSTRACT Wet bulb globe temperature (WBGT) is a commonly used measure to predict heat strain in workers. Different combinations of environmental conditions can create equivalent WBGT, yet it remains unknown whether biophysical, physiological, and perceptual responses vary when working in different but equivalent hot conditions. The purpose of the study was to compare body heat storage and physiological and perceptual strain during walking in hot-dry and warm-wet conditions of the same WBGT. Twelve subjects (age: 22 ± 2 y) walked for 90 min at 60% maximum heart rate in a 27.8°C WBGT environment of hot-dry (HD: 40°C, 19% relative humidity) or warm-wet (WW: 30°C, 77% relative humidity) conditions. Partitional calorimetry was used to estimate heat storage. Core temperature at 90 min (HD: 38.5 ± 0.5°C; WW: 38.4 ± 0.3°C, p = 0.244) and cumulative heat storage (HD: 115 ± 531 Kj; WW: 333 ± 269 Kj, p = 0.242) were not different. At 90 min, heart rate was not different (HD: 160 ± 19 bpm; WW: 154 ± 15 bpm, p = 0.149) but skin temperature (HD: 36.6 ± 0.9°C; WW: 34.7 ± 0.6°C, p < 0.001), thirst (HD: 6.8 a.u.; WW: 5.3 a.u. p = 0.043), and sweat rate (HD: 15.1 ± 4.4 g·min−1; WW: 10.0 ± 4.1 g·min−1, p < 0.001) were greater in HD compared to WW. Hot environments of equivalent 27.8°C WBGT created equivalent core temperature despite differences in physiological strain during exercise, including earlier onset of cardiovascular strain, greater sweat rate, and higher skin temperature compared to a WW environment. ClinicalTrials.gov ID NCT04624919.

Estimating heat storage in urban areas using multispectral satellite data and machine learning

A satellite-derived hysteresis model is presented for estimate heat storage in urban areas. Storage heat flux, one of the dominant terms in the urban surface energy budget (USEB), is largely unknown despite its critical relationship to various urban environmental processes. This study introduces a novel technique for quantifying heat storage by relating multispectral satellite radiances and geophysical properties to ground-truth residual heat storage computed with flux instruments. Gradient-boosted regression trees serve as the method of maximizing the relationship between satellite data and flux measurements. Several flux networks are used to train and validate the model over varying land cover types, which strengthens the robustness of the model. The model performs well under variable weather conditions such as cloudy rainy days. In comparison with other studies, the RMSE and MAE values were found to be lower than some ground-to-ground studies, and is one of few satellite-derived methods that computes direct comparison over a range of different land cover types.

Urban energy exchanges monitoring from space

One important challenge facing the urbanization and global environmental change community is to understand the relation between urban form, energy use and carbon emissions. Missing from the current literature are scientific assessments that evaluate the impacts of different urban spatial units on energy fluxes; yet, this type of analysis is needed by urban planners, who recognize that local scale zoning affects energy consumption and local climate. Satellite-based estimation of urban energy fluxes at neighbourhood scale is still a challenge. Here we show the potential of the current satellite missions to retrieve urban energy budget fluxes, supported by meteorological observations and evaluated by direct flux measurements. We found an agreement within 5% between satellite and in-situ derived net all-wave radiation; and identified that wall facet fraction and urban materials type are the most important parameters for estimating heat storage of the urban canopy. The satellite approaches were found to underestimate measured turbulent heat fluxes, with sensible heat flux being most sensitive to surface temperature variation (−64.1, +69.3 W m−2 for ±2 K perturbation). They also underestimate anthropogenic heat fluxes. However, reasonable spatial patterns are obtained for the latter allowing hot-spots to be identified, therefore supporting both urban planning and urban climate modelling.

A long-term study of soil heat flux under a forest canopy

International programmes such as EUROFLUX focus on the analysis of long-term fluxes and energy budgets in the biosphere. Reliable estimates of hourly energy budgets require an accurate estimation of soil heat flux, that is often non-negligible even in a forest, and can be predominant during the night. Over long periods of time such as one to several months, its contribution can also be significant. The present work has been carried out to get good estimates of the soil heat flux in a maritime pine stand in the southwest of France, one of the 15 EUROFLUX sites. Using a whole year’s worth of data, soil heat flux was estimated by a two-step version of the null-alignment method using soil temperature, water content and bulk density measurements between the soil surface and a depth of 1 m. A data subset was firstly used to estimate and model the soil thermal conductivity at various depths. The full data set was then used with the modelled conductivity to estimate heat storage between the surface and a reference depth, and calculate the heat flux at the soil surface. Throughout the investigated year and at a 30 min time scale, the soil heat flux represents 5–10% of the incident net radiation, i.e. 30–50% of the net radiation over the understorey. Cumulative values from September 1997 to March 1998 reach a maximum of −70 MJ m −2, which represents nearly 50% of the cumulative values of transmitted net radiation (140 MJ m −2) over the same period. These estimates of soil heat flux allowed the energy budgets of the whole stand and the understorey to be closed, and showed that the storage terms are significant not only at a 30 min time scale but also at longer time scales (a few weeks). An attempt was finally made to model soil heat flux from meteorological data, which has rarely been done for a forest soil and over a long-term data set. In most of the existing models, soil heat flux is taken as a fraction of net radiation or sensible heat flux. Here, the litter acts as a mulch at the soil surface so that the only significant terms of the energy balance at this level are soil heat flux, transmitted net radiation and turbulent sensible heat flux. Soil heat flux is shown to be a linear combination of (1) net radiation above the understorey with a clear dependence of the coefficient on the soil cover fraction, and (2) the difference between the air and litter temperatures, with little influence of soil water content or wind speed on the coefficient.

Importance of salinity measurements in the heat storage estimation from TOPEX/POSEIDON

Sea surface height anomalies from satellite altimeter data are used to estimate heat storage. Since variability in sea surface height is mostly due to expansion and contraction of the water column it can be correlated with variations in the heat and salt content. Therefore, estimation of heat storage from altimeter data, when compared to in situ estimates, requires corrections for the haline effect. Three sites with a nearly continuous time series of temperature and salinity profiles simultaneous with TOPEX/POSEIDON data are studied: HOT, CalCOFI and Hydrostation “S”. Haline corrections based on in situ and climatological salinity measurements are contrasted. For the studied regions, the haline corrections based on climatology provide equivalent or worse results than not applying a correction at all. The use of in situ salinity estimates decreased the differences between the heat storage estimates (up to 17 × 107 J m−2) and significantly improved their correlation (up to 0.18).

Heat Storage in the Eastern Mediterranean

Results of the monthly climatological fields of heat storage for the Eastern Mediterranean are presented. The zonal annual trend of monthly mean storage in the Levantine, Aegean, and Ionian seas are shown as well as the horizontal distribution of the amplitude of the annual signal. These distributions are presented for the upper 100- and 300-m layers to describe the global geographic characteristics of the annual cycle of heat storage for the Mediterranean Sea east of 20°E. The data used to estimate heat storage are the 0.5-degree objectively analyzed fields, which are based on about 1300 hydrographic stations retrieved from the NODC, Washington, D.C., data file as of 1985. For both of the layers considered, the minimum heat storage is observed in March, whereas the maximum occurs in August for the upper 0–100-m layer and in September for the 0-300-m layer. The heat storage is generally higher, and the duration of heat storage is longer in the Levantine Basin. The geographical distribution of the amplitude of the annual signal is in good agreement with some general circulation schemes of the area under study.

Comparison of two methods for estimating the evaporation of a Pinus pinaster (Ait.) stand: sap flow and energy balance with sensible heat flux measurements by an eddy covariance method

A method combining sensible heat flux measurement based on temperature and vertical wind speed fluctuations, and energy balance, was used to estimate evaporation above the canopy and the understorey of a Pinus pinaster (Ait.) stand in Les Landes forest. The problems of the horizontal homogeneity of net radiation and sensible heat flux under the canopy, and of estimating heat storage, are reviewed. The differences between above- and below-canopy evaporation are compared with sap flow on five experimental days. Except for one overcast day with little tree transpiration, the method fits sap flow within ± 15%.

Rate of Change of Heat Storage of the World Ocean

Abstract Results or a Fourier analysis of climatological fields of the monthly rate of change of heat storage for the world ocean are presented. The amplitude and Phase of the first harmonic are shown, as well as the percent variance of the annual cycle accounted for by this harmonic. These distributions are presented to describe the global geographical characteristics of the annual cycle of the rate of change of heat storage of the world ocean integrated through a depth of 275 m. We have used the results of our Fourier analysis at each gridpoint to synthesize monthly mean estimates of the rate of change of heat storage based on the annual mean and first two harmonies of the annual cycle. We have zonally averaged these time-smoothed monthly estimates over the world ocean and individual ocean basins and present time-latitude plots of these zonal averages. The climatological monthly temperature fields used to estimate heat storage are one-degree objectively analyzed fields which are based on the approximate...

Estimating heat storage in Amazonian tropical forest

A method is described whereby changes in biomass heat storage can be estimated from measurements of biomass temperature and information on biomass distribution. The method takes into account the non-uniform changes in biomass temperature and indicates the appropriate locations for its measurement. Results of applying the method to a 35 m high tropical rain forest show that hourly changes in total heat storage can account for up to ± 80 W m −2 of the surface energy budget, with approximately equal contributions from changes in canopy air temperature, humidity and biomass heat storage components. Daily values are frequently about 5% and occasionally in excess of 10% of net radiation. Simplified expressions for estimating heat storage of Amazon forest using climatological data are proposed.