Radiative Gain Research Articles

Optical absorption and emission spectral studies of phthalocyanine molecules in DMF

Optical absorption and emission spectral studies of various phthalocyanine ( Pc ) molecules in dimethyl formamide (DMF) solvent are reported in this paper. Measurements have been done for free base, Eu , Fe , Mn , Sm , Cu , Zn , Nd and La Pc - s . The principal optical transitions viz B and Q are identified and some of the important spectral parameters such as molar extinction coefficient (ε), absorption cross section (σa), dipole strength (q) and oscillator strength (f) are evaluated for the prominent Q-band. The measured radiative parameters viz emission cross section (σe), fluorescence bandwidth (Δλ) and optical gain (G) show wide variation among different systems. The results obtained are compared with other solid matrices such as glass and polymer.

Optical studies of phthalocyanine molecules in PVA film

Optical absorption and emission spectral studies of various phthalocyanine (Pc) molecules in PVA matrix have been reported for the first time. The recorded spectra are analyzed to get the important spectral parameters, such as optical absorption cross-section ( σ a), emission cross-section ( σ e), oscillator strength ( f), fluorescence bandwidth (Δ λ), emission wavelength ( λ), radiative decay time ( τ) and optical gain ( G). Analysis shows that the emission cross-section and optical gain are maximum in the NdHPc 2-doped PVA matrix. However, a comparison of the calculated emission parameters with that of borate glass matrix show that they are many times smaller in the present matrix.

The effect of wind, radiation and body orientation on the thermal environment of Greater Snow goose goslings

1. Using four heated taxidermic mounts of Greater Snow goose goslings of different ages (3–30 d), we found that exposure to wind (up to 5 m/s) or artificial radiation (up to 500 W/m 2) could change the standard operative temperature of gosling mounts by up to −20 or +18°C, respectively. 2. These values could vary by as much as 9°C due to the interaction between wind and radiation, or to changes in body orientation with respect to both these variables. In the presence of wind, radiative heat gain was reduced, and the interaction was generally more important when wind was perpendicular to the incoming radiation. 3. Predictive equations based on these results can be used to estimate the standard operative temperature of goslings in the field and their ability to modify their thermal environment by changing orientation with respect to wind and sun.

Formation and spreading of Arabian Sea high‐salinity water mass

The formation and seasonal spreading of the Arabian Sea High‐Salinity Water (ASHSW) mass were studied based on the monthly mean climatology of temperature and salinity in the Arabian Sea, north of the equator and west of 80°E, on a 2° × 2° grid. The ASHSW forms in the northern Arabian Sea during winter and spreads southward along a 24 sigma‐t surface against the prevailing weak zonal currents. The eastern extent of the core is limited by the strong northward coastal current flowing along the west coast of India. During the southwest monsoon the northern part of the core shoals under the influence of the Findlater Jet, while the southern part deepens. Throughout the year the southward extent of the ASHSW is inhibited by the equatorial currents. The atmospheric forcing that leads to the formation of ASHSW was delineated using the monthly mean climatology of heat and freshwater fluxes. Monsoon winds dominate all the flux fields during summer (June‐September), while latent heat release during the relative calm of the winter (November‐February) monsoon, driven by cool, dry continental air from the north, results in an increased density of the surface layer. Thus excess evaporation over precipitation and turbulent heat loss exceeding the radiative heat gain cool the surface waters of the northern Arabian Sea during winter and drive convective formation of ASHSW.

Transient responses of the CSIRO climate model to two different rates of CO 2 increase

The responses of the CSIRO coupled atmosphere-ocean-sea ice model to two greenhouse gas induced warming scenarios are described and compared to a control run with the current CO2 level. In one scenario, denoted IS92a, the atmospheric CO2 increases such that it reaches doubling after 128 years. In the other, the CO2 increases at 1% per year compounding (doubling after 70 y). As the CO2 increases in both scenarios, the top-of-atmosphere outgoing longwave radiation increases giving enhanced cooling of the coupled system, while the outgoing short wave radiation decreases contributing to a warming of the system. The latter overcompensates the former leading to a global mean net radiative heat gain. The distribution of this heat gain produces the well-known interhemispheric asymmetry in warming, despite a decrease in the sea ice around Antarctica in this model. It is found that the volume mean temperature response over the southern ocean is greater than that over the northern hemispheric oceans, and a maximum warming takes place at the subsurface rather at the surface of the ocean in the southern mid-to-high latitude region. The enhanced high-latitude freshening associated with the strengthened hydrological cycle significantly affects the latitudinal distribution of warming and other responses. It enhances the warming immediately equatorward of the deep water formation regions while produces a reduced warming, even a cooling, in these regions. In both runs, there is a decrease in the large-scale oceanic currents which have a significant thermohaline-driven component. The reduction in these currents reduces the poleward transport of salt out of the tropical and subtropical regions of these oceans. This and the enhanced evaporation contribute to considerable increases in surface salinity in the tropical and subtropical regions. In IS92a, the warming rate before doubling is smaller than that in 1% scenario, but the cumulative effects of the two experiments at the time of doubling are similar. Nevertheless, significant contrasts exist. For example, at the time of doubling in IS92a, the warming of the upper ocean is greater because a more developed temperature-albedo feedback occurs. In addition, a longer time is allowed for heat anomalies to spread downward, and so the effective heat penetration depth is greater than that in the 1% scenario. Thus the oceanic response is influenced by the CO2 increase scenario used.

Seasonal adjustment of solar heat gain independent of coat coloration in a desert mammal.

Despite the apparent importance of solar radiation as a source of heat for free-living animals, there exists no substantial body of empirical data describing physiological responses to solar radiation under the range of convective conditions likely to occur in nature. We therefore quantified effects of simulated solar radiation and wind on metabolic heat production in the rock squirrel, Spermophilus variegatus. This diurnal mammal inhabits the Sonoran Desert and seasonally replaces its pelage in a fashion in which it retains constant external appearance but incorporates optical and structural changes that are thought to significantly alter heat-transfer properties of the coat. At a given wind speed, the presence of 950 W m-2 of simulated solar radiation reduces metabolic heat production by 15% (at a wind speed of 4 m s-1) to 37% (at a wind speed of 0.25 m s-1). Independent of effects of irradiance, metabolic heat production significantly increases with wind speed such that as wind speed is increased from 0.25 m s-1 to 4.0 m s-1, metabolic heat production is elevated by 66% (sunlight absent) or 88% (sunlight present). Previous analyses demonstrated that when exposed to identical radiative and convective environments rock squirrels with summer pelages accrue solar heat loads 33%-71% lower than those experienced by animals with winter coats. This reduction of solar heat gain during the extremely hot Sonoran Desert summer apparently constitutes a previously unappreciated mode of thermal adaptation by seasonal adjustment of radiative heat gain without changes in the animal's appearance.

Measurements of diurnal heat exchange on the Quelccaya Ice Cap, Peruvian Andes

Measurements of the surface heat budget were conducted on an ice cap in the Andes of Southern Peru at 5645 m during an expedition in July 1977. Because of the high surface albedo, net software radiative gain is nearly offset by the longwave loss in the average over the diurnal cycle. The diurnal temperature wave has at the surface an amplitude of about 5°C, and by 50 cm depth this is nearly dampened out. During the day, the shortwave radiative gain is in part used to balance the longwave loss, some heat is stored in the top snow layer and lost by sensible heat transfer to the overlying atmosphere, and the greater part fuels the sublimation. At night, the longwave radiative loss is not completely compensated by heat depletion and downward directed sensible heat transfer. This deficit is made up by the downward transfer of latent heat, resulting in heat release at the surface and deposition. Regarding the mass balance, the nighttime deposition approximately cancels the daytime sublimation. At lower elevations of the ice cap, albedo is much less, allowing larger absorption of solar radiation. As a consequence, more energy is available for ablation. Melting occurs during the day, so that re-freezing and concurrent latent heat release can help to compensate the longwave radiative loss at night.

Sensitivity of an atmospheric general circulation model to the parameterization of leads in sea ice

Open-water leads in sea ice dominate the exchange of heat between the ocean and atmosphere in ice-covered regions, and so must be included in climate models. A parameterization of leads used in one such model is compared to observations and the results of a detailed Arctic sea-ice model. Such comparisons, however, are hampered by the errors in observed lead fraction, but the parameterization appears to compare better in winter than in summer. Simulations with an atmospheric general circulation model (AGCM), using prescribed sea-surface temperatures and ice extent, are used to illustrate the effect of parameterized lead fraction on atmospheric climate, and so provide some insight into the importance of improved lead-fraction parameterizations and observations. The effect of leads in the AGCM is largest in Northern Hemisphere winter, with zonal mean surface-air temperatures over ice increasing by up to 5 K when lead fraction is increased from 1% to near 5%. The effect of leads on sensible heat loss in winter is more important than the effect on radiative heat gain in summer. No significant effect on sea-level pressure, and hence on atmospheric circulation, is found, however. Indirect effects, due to feedbacks between the atmosphere and ice thickness and extent, were not included in these simulations, but could amplify the response.

Sensitivity of an atmospheric general circulation model to the parameterization of leads in sea ice

Open-water leads in sea ice dominate the exchange of heat between the ocean and atmosphere in ice-covered regions, and so must be included in climate models. A parameterization of leads used in one such model is compared to observations and the results of a detailed Arctic sea-ice model. Such comparisons, however, are hampered by the errors in observed lead fraction, but the parameterization appears to compare better in winter than in summer. Simulations with an atmospheric general circulation model (AGCM), using prescribed sea-surface temperatures and ice extent, are used to illustrate the effect of parameterized lead fraction on atmospheric climate, and so provide some insight into the importance of improved lead-fraction parameterizations and observations. The effect of leads in the AGCM is largest in Northern Hemisphere winter, with zonal mean surface-air temperatures over ice increasing by up to 5 K when lead fraction is increased from 1% to near 5%. The effect of leads on sensible heat loss in winter is more important than the effect on radiative heat gain in summer. No significant effect on sea-level pressure, and hence on atmospheric circulation, is found, however. Indirect effects, due to feedbacks between the atmosphere and ice thickness and extent, were not included in these simulations, but could amplify the response.

High zenithal directivity from a dipole antenna on a photonic crystal

A strip dipole on a (111)-oriented face centered cubic photonic crystal is found to have a copolarized directivity and radiative gain of 9.1 and 7.2±1.4, respectively, along the zenith and at a frequency in the first stop band of 18.0 GHz. Under the same conditions, the maximum copolarized directivity and radiative gain were 10.0 and 8.1±1.6, respectively, in the H-plane 5° down from the zenith. The zenithal results correspond to a 5.5-times greater radiation intensity than displayed by the same dipole in free space. From power balance measurements, only 10% of this enhancement is attributed to superior power transfer between the generator and antenna. The remainder is associated with constructive interference between the primary antenna radiation and radiation reflected from the crystal.

Field Quantization and Radiative Processes in Dispersive Dielectric Media

The electromagnetic field in a dispersive dielectric medium is quantized in a straightforward manner based on the classical expression for the field energy away from absorption resonances. Results for spontaneous and stimulated radiative rates, and absorption and gain coefficients, are obtained and compared with other expressions in the literature. Local field corrections, when they exist, are included. A level shift for an atom in a host dielectric medium is obtained and interpreted as the van der Waals interaction between that atom and its neighbours in the host medium.

Effects of Solar Radiation and Wind Speed on Metabolic Heat Production by Two Mammals With Contrasting Coat Colours

We report the first empirical data describing the interactive effects of simultaneous changes in irradiance and convection on energy expenditure by live mammals. Whole-animal rates of solar heat gain and convective heat loss were measured for representatives of two ground squirrel species, Spermophilus lateralis and Spermophilus saturatus, that contrast in coloration. Radiative heat gain was quantified as the decrease in metabolic heat production caused by the animal's exposure to simulated solar radiation. Changes in convective heat loss were quantified as the variation in metabolic heat production caused by changes in wind speed. For both species, exposure to 780 W m-2 of simulated solar radiation significantly reduced metabolic heat production at all wind speeds measured. Reductions were greatest at lower wind speeds, reaching 42% in S. lateralis and 29% in S. saturatus. Solar heat gain, expressed per unit body surface area, did not differ significantly between the two species. This heat gain equalled 14-21% of the radiant energy intercepted by S. lateralis and 18-22% of that intercepted by S. saturatus. Body resistance, an index of animal insulation, declined by only 10% in S. saturatus and 13% in S. lateralis as wind speed increased from 0.5 to 4.0 ms-1. These data demonstrate that solar heat gain can be essentially constant, despite marked differences in animal coloration, and that variable exposure to wind and sunlight can have important consequences for both thermoregulatory stress experienced by animals and their patterns of energy allocation.

Parameterization study of the overall thermal-transfer value equation for buildings

Modern buildings in Hong Kong are characterized by high window-to-wall ratios. This leads to large energy consumption due to the solar radiative heat gain. The problem is now of great concern to the industry not just because of the energy usage, but also due to the environmental problem that arises from overusage of energy. The government is considering implementing some regulations for controlling the cooling load in centrally air-conditioned buildings. The concept of overall thermal-transfer value (OTTV) is proposed to be used as a guideline for designing the building envelopes. However, those equations for calculating the OTTV recommended by the draft design guide are rather unclear. Many parameters that influence the OTTV equation have not been studied thoroughly yet. This paper aims at carrying out a parameterization study on the OTTV equation. The window-to-wall ratio, shading coefficient, wall absorptance and wall heat capacity are found to be important parameters. Modification of the equivalent temperature that appears in the OTTV equation is recommended. Finally, the effect of overhang on the solar load value is also investigated.

Observations on the Effect of a Partial Solar Eclipse on Calling in Some Desert Cicadas (Homoptera: Cicadidae)

While collecting cicadas in Arizona during the summer of 1991, a partial solar eclipse in our study area allowed us to observe its effects on the calling activity of cicadas. Maximal obstruction during the July 11 eclipse, occurred across Mexico and the southwestern United States and reached about 70% in our area north of Tucson at approximately 11:41 AM MST. The eclipse coincided with a period of high-level activity in the cicadas. We were able to view the eclipse and note the amount of coverage by using a solar filter throughout the 3 h period. Although it has been reported that some cicada species exhibit endothermy (Sanborn et al. 1989, Sanborn 1990), most cicadas are apparently ectothermic (Heath 1967, Heath & Wilkin 1970, Heath et al. 1972, Heath 1972, Hastings 1989, Hastings & Toolson 1991, Sanborn et al. in press), using radiant energy to elevate body temperature to a range necessary for activity. Body temperature in these ectothermic species is then regulated through behavioral and/or physiological mechanisms (Heath 1967, Heath & Wilkin 1970, Heath et al. 1972, Heath 1972, Hastings 1989, Hastings & Toolson 1991, Sanborn et al. in press). On the day of the eclipse, Diceroprocta semicincta (Davis) and Cacama valvata (Uhler) began calling in Tucson before 8:00 AM and were calling normally as the eclipse began, at 10:15 AM. Soon after the coverage of the sun had reached approximately 50%, the cicadas ceased calling. The interruption in calling continued for about 40 min during the eclipse; about 20 min on each side of the maximal eclipse. The effect of the eclipse on radiant solar energy levels in the field was easily noticed. Standing in the sun during the eclipse was comfortable. Before and after the eclipse standing in the sun was uncomfortable due to the intense solar radiation characteristic of the desert. Additionally, the need for sunglasses during the eclipse was reduced due to the lower intensity of the sun. Ambient temperature fell about 1?C during the eclipse, but this by itself should not be sufficient to inhibit calling in D. semicincta and Okanagodes gracilis Davis, the two species most active where we were collecting. Two typical Sonoran Desert cicadas Diceroprocta apache (Davis) and 0. gracilis began calling when ambient temperatures reach about 25?C (Heath & Wilkin 1970) and 34?C (Sanborn et al. in press) respectively, when there is access to solar radiation. Ambient temperature during the peak of the eclipse was about 34?C. The decrease in radiative heat gain during the eclipse appears to be responsible for the inhibition of calling in the cicadas. Without the normal degree of radiant energy present in their environment, the cicadas may not have been able to maintain the elevated body temperature that is necessary for activity.

Thermal constraints on use of cover types and activity time of elk

Use of cover types and activity patterns of radio-collared elk ( Cervus elaphus roosevelti) inhabiting the Mount St. Helens blast zone in the State of Washington, U.S.A., were studied under different climatic conditions. Elk use of forest cover during the midday period was not greater ( P < 0.12) on clear days than on cloudy days. Estimates of the heat load of a foraging elk indicated that normal body temperatures could be maintained in the seral plant communities of the blast zone despite high radiative heat gain. An increase in wind speeds in mid to late afternoon suggested an increase in convective heat loss. Additionally, elk became inactive and selected bedding sites with little vegetation. Elk compensated for the decrease in diurnal activity time by increasing nocturnal feeding. Abundant, high quality forage in the Mount St. Helens blast zone most likely facilitated these responses to heat stress.

The thermal behavior of a concrete ‘finned’ wall in a hot-arid zone

The thermal behavior of an exposed concrete slab with a grid of truncated pyramids on its outer surface was found to differ considerably from that of a similar slab with a smooth outer surface, under hot-arid conditions. When the slab was placed vertically facing south (simulating a south-facing wall), the three-dimensional geometry of its exterior reduced radiative heat gain. Placed horizontally, radiative heat gain increased. Painting the slabs white reduced the relative contribution of radiative heat gain, while the increased surface are resulted in the creation of a thick ‘boundary’ layer that affected the thermal behavior of the slab under certain conditions.

Convergence of Solar Heat Gain in Two Squirrel Species with Contrasting Coat Colors

Two otherwise similar species of golden-mantled ground squirrels differ in coloration; the dorsal fur of Spermophilus lateralis exhibits a reflectivity to solar radiation 58% greater than does that of S. saturatus. Despite this substantial difference in coloration, however, solar heat loads transferred to the skin are indistinguishable. This convergence of radiative heat gain results primarily from differences in the structure, optics, and thickness of fur beneath the superficial layer that produces the animal's external appearance. The results of this research support the view that coat properties modifying solar heat gain independent of surface coloration may represent an important mechanism for adjustment of heat balance in nature.

Behavioral Responses of the Robber Fly Stenopogon inquinatus (Diptera: Asilidae) to Variation in the Thermal Environment

Stenopogon inquinatus Loew forages across a wide range of diurnal temperatures. Changes in perch height and body posture allowed the flies to maximize air temperatures experienced when environmental temperatures were low and to encounter a relatively narrow range of air temperatures in the middle of the day. In addition, early in the day they basked by orienting their longitudinal and dorsoventral body axes perpendicular to the sun. Their behavior varied with environmental temperatures in ways that indicate that perching flies thermoregulate by influencing radiative heat gain and the air temperatures and wind speeds that they experience.

The significance of fur structure for solar heat gain in the rock squirrel, Spermophilus variegatus.

The coats of birds and mammals typically vary through their depth in structure, insulation and optical qualities. Physical models predict that such variation can substantially affect the solar heat load acquired by an animal. This study quantifies the consequences of complex coat structure for solar heat gain in the rock squirrel (Spermophilus variegatus (Erxleben, 1777)), a species normally exposed to intense solar radiation. This species' pelage consists of two well-defined layers: a dense inner coat of fine, dark hairs, and a sparse outer coat of coarse, light hairs. The optics, structure and thermal insulation of the inner and outer coats are quantified and used to predict rates of radiative heat gain using a physical model. The radiative heat load measured at the skin compares well with model predictions. The validated model is then used to explore the consequences for solar heat gain of varying the relative proportions of the inner and outer coat layers. Results demonstrate that the ratio of inner to outer coat depths occurring in rock squirrels is very near that theoretically predicted to minimize solar heat gain. This indicates that optimization of fur structure may represent an effective means of adjusting solar heat gain independent of coat insulation and surface coloration.

Radiative Energy Budget Estimates for the 1979 Southwest Summer Monsoon

Obsemations of temperature moisture, cloud amount, cloud height and soil-derived aerosols are incorporated into radiative transfer models to yield estimates of the tropospheric and surface radiative energy budgets for the summer Monsoon of 1979. Results are presented for six phases of the monsoon for the region 30°S to 40°N latitude and 30°E to 100°E longitude. The derived radiative fields are significantly different from climatological estimates. The evolution of the radiative energy budgets are discussed in relation to monsoon activity. Total tropospheric convergence (TTC) for the January and February phases exhibits a minimum cooling over the southern Indian Ocean and a maximum tropospheric radiative energy loss over the Arabian Sea and Bay of Bengal. The early May, pre-onset, onset and post-onset periods exhibit cellular patterns in TTC, with maximum cooling over the cloud-free oceanic regions, and minimum cooling associated with continental regions and areas with large amounts of cloud. This cellular structure is still evident when TTC is averaged over 10° regions. Large seasonal variations in TTC are observed over the deserts, due to the presence of dust in the summer. Regions with large seasonal variations in cloud cover (e.g., the Arabian Sea) also display large variations in TTC. Regionally averaged radiative heating profiles also change significantly with period. These variations result primarily from changes in the cloud distribution associated with the evolution of the monsoon. The net surface radiative flux varies markedly from period to period, and within the same period. As expected, all six periods have a maximum surface radiative energy gain for the cloud-free oceanic regions, while cloudy and continental regions tend to have relative minimae. Large spatial and temporal variations exist in the net surface flux.