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Kaicun Wang - One of the best experts on this subject based on the ideXlab platform.
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Measurement Biases Explain Discrepancies between the Observed and Simulated Decadal Variability of Surface Incident Solar Radiation
Scientific Reports, 2014Co-Authors: Kaicun WangAbstract:Observations have reported a widespread dimming of surface Incident Solar Radiation (Rs) from the 1950s to the 1980s and a brightening afterwards. However, none of the state-of-the-art earth system models, including those from the Coupled Model Intercomparison Project phase 5 (CMIP5), could successfully reproduce the dimming/brightening rates over China. We find that the decadal variability of observed Rs may have important errors due to instrument sensitivity drifting and instrument replacement. While sunshine duration (SunDu), which is a robust measurement related to Rs, is nearly free from these problems. We estimate Rs from SunDu with a method calibrated by the observed Rs at each station. SunDu-derived Rs declined over China by −2.8 (with a 95% confidence interval of −1.9 to −3.7) W m−2 per decade from 1960 to 1989, while the observed Rs declined by −8.5 (with a 95% confidence interval of −7.3 to −9.8) W m−2 per decade. The former trend was duplicated by some high-quality CMIP5 models, but none reproduced the latter trend.
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urban impacts on mean and trend of surface Incident Solar Radiation
Geophysical Research Letters, 2014Co-Authors: Kaicun Wang, Xiaoyan Wang, Martin WildAbstract:Abstract Anthropogenic aerosols over urban areas may have important effects on surface Incident Solar Radiation ( R s ). Studies have claimed that R s decreased significantly more in urban areas than in rural areas from 1964 to 1989. However, these estimates have substantial biases because they ignored the spatial inhomogeneity of R s measurements. To address this issue, we selected urban-rural station pairs collocated within 2°2° and found 105 such pairs based on the Global Energy Balance Archive (GEBA). On average, the impact of urban aerosols on mean and trend of R s is 0.2(0.7, median)11.2 W m -2 and 0.1(-0.7, median)6.6 W m -2 per decade from 1961 to 1990, respectively. Hence the averaged urban impacts on the mean and trend of R s averaged over Europe, China and Japan from 1961 to 1990 are small although they may be significant at specific sites. Key Points: (1) Urbanization has small impacts on mean and trend of surface Solar Radiation (2) Our estimates are based on urban-rural station pairs (3) Previous estimates include substantial spatial biases
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critical assessment of surface Incident Solar Radiation observations collected by surfrad uscrn and ameriflux networks from 1995 to 2011
Journal of Geophysical Research, 2012Co-Authors: Kaicun Wang, John A Augustine, Robert E DickinsonAbstract:[1] Surface Incident Solar Radiation (Rs) drives weather and climate changes. Observations of Rs have been widely used as reference data to evaluate climate model simulations and satellite retrievals. However, few have studied uncertainties of Rs observations, especially long term. This paper compares Rs from 1995 to 2011 at collocated sites collected by the Surface Radiation Budget Network (SURFRAD), the U.S. Climate Reference Network (USCRN) and the AmeriFlux network. SURFRAD stations have measured separately the diffuse and direct components of Rs as well as Rs by a pyranometer, while Rs was measured by a pyranometer or a net radiometer at the USCRN and AmeriFlux sites. Rs can be calculated by summing the diffuse and direction Radiation measurements. Rs measured by the summation technique was compared those measured by a pyranometer or a net radiometer at collocated sites. Agreement among these four independent Rs measurements is good with correlation coefficients higher than 0.98 and an average error (one standard deviation) of about 4% at both hourly and monthly time scales. Rs has a large spatial variability at the hourly time scale, even exceeding 100 W m−2 in ∼6 km. This spatial variability is substantially reduced at the monthly time scale. The two independent measurement systems at the SURFRAD sites agree rather well in annual variability of Rs with an average relative standard deviation error of 34%. The errors are 71% and 85% for the USCRN and AmeriFlux sites. Evidently, caution should be taken when using the Rs data collected at the USCRN and AmeriFlux sites to study annual variability of Rs.
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atmospheric impacts on climatic variability of surface Incident Solar Radiation
Atmospheric Chemistry and Physics, 2012Co-Authors: Kaicun Wang, Martin Wild, Robert E Dickinson, Shunlin LiangAbstract:Abstract. The Earth's climate is driven by surface Incident Solar Radiation (Rs). Direct measurements have shown that Rs has undergone significant decadal variations. However, a large fraction of the global land surface is not covered by these observations. Satellite-derived Rs has a good global coverage but is of low accuracy in its depiction of decadal variability. This paper shows that daily to decadal variations of Rs, from both aerosols and cloud properties, can be accurately estimated using globally available measurements of Sunshine Duration (SunDu). In particular, SunDu shows that since the late 1980's Rs has brightened over Europe due to decreases in aerosols but dimmed over China due to their increases. We found that variation of cloud cover determines Rs at a monthly scale but that aerosols determine the variability of Rs at a decadal time scale, in particular, over Europe and China. Because of its global availability and long-term history, SunDu can provide an accurate and continuous proxy record of Rs, filling in values for the blank areas that are not covered by direct measurements. Compared to its direct measurement, Rs from SunDu appears to be less sensitive to instrument replacement and calibration, and shows that the widely reported sharp increase in Rs during the early 1990s in China was a result of instrument replacement. By merging direct measurements collected by Global Energy Budget Archive with those derived from SunDu, we obtained a good coverage of Rs over the Northern Hemisphere. From this data, the average increase of Rs from 1982 to 2008 is estimated to be 0.87 W m−2 per decade.
Duncan Mitchell - One of the best experts on this subject based on the ideXlab platform.
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orientation to Solar Radiation in black wildebeest connochaetes gnou
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2005Co-Authors: Graeme Moss, Shane K Maloney, Duncan MitchellAbstract:We recorded the body axis orientation of free-living black wildebeest relative to Incident Solar Radiation and wind. Observations were made on three consecutive days, on six occasions over the course of 1 year, in a treeless, predominantly cloudless habitat. Frequency of orientation parallel to Incident Solar Radiation increased, and perpendicular to Incident Solar Radiation decreased, as ambient dry-bulb temperature or Solar Radiation intensity increased, or wind speed decreased. We believe these changes were mediated via their effect on skin temperature. Parallel orientation behavior was more prominent when the wildebeest were standing without feeding than it was when they were feeding. We calculate that a black wildebeest adopting parallel orientation throughout the diurnal period would absorb 30% less radiant heat than the same animal adopting perpendicular orientation. Parallel orientation was reduced at times when water was freely available, possibly reflecting a shift from behavioral to autonomic thermoregulatory mechanisms. The use of orientation behavior by black wildebeest is well developed and forms part of the suite of adaptations that help them to maintain heat balance while living in a shadeless, often hot, environment.
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orientation to Solar Radiation in black wildebeest connochaetes gnou a neuroethology sensory neural and behavioral physiology
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2005Co-Authors: Shane K Maloney, Graeme Moss, Duncan MitchellAbstract:We recorded the body axis orientation of free-living black wildebeest relative to Incident Solar Radiation and wind. Observations were made on three consecutive days, on six occasions over the course of 1 year, in a treeless, predominantly cloudless habitat. Frequency of orientation parallel to Incident Solar Radiation increased, and perpendicular to Incident Solar Radiation decreased, as ambient dry-bulb temperature or Solar Radiation intensity increased, or wind speed decreased. We believe these changes were mediated via their effect on skin temperature. Parallel orientation behavior was more prominent when the wildebeest were standing without feeding than it was when they were feeding. We calculate that a black wildebeest adopting parallel orientation throughout the diurnal period would absorb 30% less radiant heat than the same animal adopting perpendicular orientation. Parallel orientation was reduced at times when water was freely available, possibly reflecting a shift from behavioral to autonomic thermoregulatory mechanisms. The use of orientation behavior by black wildebeest is well developed and forms part of the suite of adaptations that help them to maintain heat balance while living in a shadeless, often hot, environment.
Shane K Maloney - One of the best experts on this subject based on the ideXlab platform.
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The fur of mammals in exposed environments; do crypsis and thermal needs necessarily conflict? The polar bear and marsupial koala compared
Journal of Comparative Physiology B, 2014Co-Authors: Terence J. Dawson, Koa N. Webster, Shane K MaloneyAbstract:The furs of mammals have varied and complex functions. Other than for thermoregulation, fur is involved in physical protection, sensory input, waterproofing and colouration, the latter being important for crypsis or camouflage. Some of these diverse functions potentially conflict. We have investigated how variation in cryptic colouration and thermal features may interact in the coats of mammals and influence potential heat inflows from Solar Radiation, much of which is outside the visible spectral range. The coats of the polar bear ( Ursus maritimus ) and the marsupial koala ( Phascolarctus cinereus ) have insulative similarities but, while they feature cryptic colouration, they are of contrasting colour, i.e. whitish and dark grey. The reflectance of Solar Radiation by coats was measured across the full Solar spectrum using a spectroradiometer. The modulation of Incident Solar Radiation and resultant heat flows in these coats were determined at a range of wind speeds by mounting them on a heat flux transducer/temperature-controlled plate apparatus in a wind tunnel. A lamp with a spectral distribution of Radiation similar to the Solar spectrum was used as a proxy for the sun. Crypsis by colour matching was apparent within the visible spectrum for the two species, U. maritimus being matched against snow and P. cinereus against Eucalyptus forest foliage. While reflectances across the full Solar spectrum differed markedly, that of U. maritimus being 66 % as opposed to 10 % for P. cinereus , the heat influxes from Solar Radiation reaching the skin were similar. For both coats at low wind speed (1 m s^−1), 19 % of Incident Solar Radiation impacted as heat at the skin surface; at higher wind speed (10 m s^−1) this decreased to approximately 10 %. Ursus maritimus and P. cinereus have high and comparable levels of fur insulation and although the patterns of reflectance and depths of penetrance of Solar Radiation differ for the coats, the considerable insulation limited the radiant heat reaching the skin. These data suggest that generally, if mammal coats have high insulation then heat flow from Solar Radiation into an animal is much restricted and the impact of coat colour is negligible. However, comparisons with published data from other species suggest that as fur insulation decreases, colour increasingly influences the heat inflow associated with Solar Radiation.
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orientation to Solar Radiation in black wildebeest connochaetes gnou
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2005Co-Authors: Graeme Moss, Shane K Maloney, Duncan MitchellAbstract:We recorded the body axis orientation of free-living black wildebeest relative to Incident Solar Radiation and wind. Observations were made on three consecutive days, on six occasions over the course of 1 year, in a treeless, predominantly cloudless habitat. Frequency of orientation parallel to Incident Solar Radiation increased, and perpendicular to Incident Solar Radiation decreased, as ambient dry-bulb temperature or Solar Radiation intensity increased, or wind speed decreased. We believe these changes were mediated via their effect on skin temperature. Parallel orientation behavior was more prominent when the wildebeest were standing without feeding than it was when they were feeding. We calculate that a black wildebeest adopting parallel orientation throughout the diurnal period would absorb 30% less radiant heat than the same animal adopting perpendicular orientation. Parallel orientation was reduced at times when water was freely available, possibly reflecting a shift from behavioral to autonomic thermoregulatory mechanisms. The use of orientation behavior by black wildebeest is well developed and forms part of the suite of adaptations that help them to maintain heat balance while living in a shadeless, often hot, environment.
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orientation to Solar Radiation in black wildebeest connochaetes gnou a neuroethology sensory neural and behavioral physiology
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2005Co-Authors: Shane K Maloney, Graeme Moss, Duncan MitchellAbstract:We recorded the body axis orientation of free-living black wildebeest relative to Incident Solar Radiation and wind. Observations were made on three consecutive days, on six occasions over the course of 1 year, in a treeless, predominantly cloudless habitat. Frequency of orientation parallel to Incident Solar Radiation increased, and perpendicular to Incident Solar Radiation decreased, as ambient dry-bulb temperature or Solar Radiation intensity increased, or wind speed decreased. We believe these changes were mediated via their effect on skin temperature. Parallel orientation behavior was more prominent when the wildebeest were standing without feeding than it was when they were feeding. We calculate that a black wildebeest adopting parallel orientation throughout the diurnal period would absorb 30% less radiant heat than the same animal adopting perpendicular orientation. Parallel orientation was reduced at times when water was freely available, possibly reflecting a shift from behavioral to autonomic thermoregulatory mechanisms. The use of orientation behavior by black wildebeest is well developed and forms part of the suite of adaptations that help them to maintain heat balance while living in a shadeless, often hot, environment.
Dorin Stanciu - One of the best experts on this subject based on the ideXlab platform.
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optimum tilt angle for flat plate collectors all over the world a declination dependence formula and comparisons of three Solar Radiation models
Energy Conversion and Management, 2014Co-Authors: Camelia Stanciu, Dorin StanciuAbstract:Abstract The paper presents a theoretical study on the optimum tilt angle for flat plate collectors at different geographical locations and different time moments over a year. The Solar Radiation density is estimated based on three analysis models, namely Hottel and Woertz model (the simplest), Isotropic diffuse model (Liu & Jordan model) and HDKR model (Hay–Davis–Klucker–Reindl), passing from the simplest to the most complex one. Further, the absorbed Solar Radiation density is computed and the optimum tilt angle is found for different geographical locations (covering the Globe latitudes). The optimum value for the tilt angle is researched for maximum Incident Solar Radiation and also for maximum absorbed one. The results indicate that the same angle is obtained when looking for maximum Incident and for maximum absorbed Solar Radiation. When comparing the three above mentioned models, different tilt angles are supplied by applying the Hottel and Woertz model and respectively the others two (both of them providing the same angle). Although, the predicted absorbed Solar Radiation is the same in the summertime for all three models, and probably overestimated by the last model in the springtime. The obtained results give an overview over the whole year operation at different geographical latitudes. When using the Hottel & Woertz model for estimating the Incident Solar Radiation, the optimum tilt angle for a flat plate collector should be computed as simplest as β opt = φ − δ function on the latitude and declination. If a fixed value is easier to be used over a specific operation period, an optimum value is provided by this research. The novelty consists in finding this global optimum instead of “local” ones for which monthly adjustment is required. The results are compared to the approximation given in the technical literature according to which the optimum tilt angle should be local latitude plus or minus (for winter or summer seasons, respectively) 10° or 15° (with small variations as it is further presented).
Aldo Steinfeld - One of the best experts on this subject based on the ideXlab platform.
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three dimensional optical and thermal numerical model of Solar tubular receivers in parabolic trough concentrators
Journal of Solar Energy Engineering-transactions of The Asme, 2012Co-Authors: Men Wirz, Matthew Roesle, Aldo SteinfeldAbstract:Monte Carlo ray tracing, coupled to a finite volume solver, is used to model 3D heat transfer in a parabolic trough Solar concentrator system. The nonuniform distribution of the Incident Solar Radiation, the radiative exchange between the various receiver surfaces, and the heat gain/loss around the receiver's circumference and along the system's axis are determined for spectral radiative properties of the receiver and concentrator surfaces. The computed heat losses and thermal efficiencies agree well with experimental data. Besides the beneficial information on peak temperatures and heat flux, the 3D model is able to predict glass temperatures more accurately than previous gray models and temperature correlations. [DOI: 10.1115/1.4007494]
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three dimensional optical and thermal numerical model of Solar tubular receivers in parabolic trough concentrators
International Conference on Fuel Cell Science Engineering and Technology FUELCELL Collocated with ASME International Conference on Energy Sustainabili, 2012Co-Authors: Men Wirz, Matthew Roesle, Aldo SteinfeldAbstract:Monte Carlo ray tracing, coupled to a finite volume solver, is used to model 3D heat transfer in a parabolic trough Solar concentrator system. The non-uniform distribution of the Incident Solar Radiation, the radiative exchange between the various receiver surfaces, and the heat gain/loss around the receiver’s circumference and along the system’s axis are determined for spectral radiative properties of the receiver and concentrator surfaces. The computed heat losses and thermal efficiencies agree well with experimental data. Besides the beneficial information on peak temperatures and heat flux, the 3D model also has a potential to predict glass temperatures more accurately than previous gray models and temperature correlations.Copyright © 2012 by ASME
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Analysis of Conduction Heat Loss From a Parabolic Trough Solar Receiver with Active Vacuum by Direct Simulation Monte Carlo
Numerical Heat Transfer Part A: Applications, 2012Co-Authors: Matthew Roesle, Philipp Good, Volkan Coskun, Aldo SteinfeldAbstract:Results are reported of a numerical analysis of conduction heat loss from a parabolic trough Solar receiver with controlled pressure within the annular gap between the tubular absorber and the glass vacuum jacket. A direct simulation Monte Carlo (DSMC)model of rarefied gas within the annular gap is coupled to Radiation heat transfer for directional- and spectral-dependent concentrated Incident Solar Radiation. This modeling approach is valid for high Knudsen numbers, and consistently predicts slightly higher heat loss than a continuum model using slip boundary conditions in the range of pressures of interest around 1 Pa. 3-D simulations of axial flow through the annular gap predict higher gas conductance by the DSMC method than by slip flow models, with values converging as pressure increases.
