Emission Of Longwave Radiation Research Articles

A TEST OF THE RADIATIVE ENERGY BALANCE OF THE SHAW MODEL FOR SNOWCOVER

Snow and ice present interesting challenges to hydrologists. Simulating the radiative balance over snow, which is an important part of surface–atmosphere interactions, is particularly challenging because of the decay in albedo over time and the difficulty in estimating surface temperature and incoming long-wave radiation fluxes. Few models are available that include a comprehensive energy and water balance for cold season conditions. The simultaneous heat and water model (SHAW) is a detailed, physical process model of a vertical, one-dimensional canopy–snow–residue–soil system which integrates the detailed physics of heat and water transfer through a plant canopy, snow, residue and soil into one simultaneous solution. Detailed provisions for metamorphosis of the snowpack are included. The SHAW model was applied to data for one winter/spring season (November to May) on a ploughed field in Minnesota without prior calibration to test the performance of the radiation components. Maximum snow depth during this period was 30 cm. For the nearly 100 days of snowcover, the model accounted for 69% of the variation in net solar radiation, 66% of the variation in incoming long-wave radiation, 87% of the variation in emitted long-wave radiation, 26% of the variation in net long-wave radiation and 55% of the variation in net radiation balance. Mean absolute error in simulated values ranged from 10 W m−2 for emitted long-wave radiation to 27 W m−2 for the entire net radiation balance. Mean bias error ranged from 8 W m−2 for emitted long-wave radiation to −16 W m−2 for the entire net radiation balance. When the entire 170 days of simulation, which included periods without snowcover, were included in the analysis, the variation in observed values increased greatly. As a result, the variation in observed values accounted for by the model increased to 97, 71, 93, 56 and 94%, respectively, while the mean absolute and mean bias errors in simulated values remained nearly the same. Model modifications and parameter adjustments necessary to improve winter-time simulation were investigated. Simulation results suggest that the SHAW model may be a useful tool in simulating the interactive influences of radiative transfer at the surface–atmosphere interface.

The Sensitivity of Surface Energy Balance to Convective Parameterization in a General Circulation Model

This study investigates the interaction between convection and the surface energy fluxes, and its sensitivity to convective parameterization schemes using a general circulation model. Two simulations of the global circulation averaged annually from 1 June 1985 to 31 May 1986 are performed, with particular emphasis on the tropical Pacific. In the control simulation, a convective scheme that parameterizes convection based on low-level moisture convergence is used. A second experiment employs a parameterization scheme that uses the time rate of change of convective available potential energy (CAPE) to determine convection. When the low-level moisture convergence is used as the closure for convective parameterization, convection and low-level convergence occur near the landmass of Southeast Asia. The large-scale circulation is such that a fairly strong surface wind that provides moisture to fuel convection is located in the western tropical Pacific warm pool regions, giving rise to relatively high latent heat flux there. When the time rate of change of CAPE is used to close convective parameterization, convection and its associated low-level large-scale convergence and weak surface, wind speed occur in the warm pool region, resulting in low latent heat flux there. Response of surface solar radiative flux to convection is found to be the largest in the surface energy budget. Convection affects surface radiation through the generation of clouds. In the experiment, more clouds are produced over the tropical oceans, leading to less solar radiation received on the surface. More clouds in the experiment also load to less net emission of longwave radiation from the ocean surface due to the cloud green-house effect albeit the magnitude is much smaller than that for solar radiation. The large changes in surface latent heat and solar radiative fluxes from the control run to the experiment suggest that the surface energy balance in the atmospheric general circulation model is highly sensitive to convective parameterization.

The Surface Energy Balance of Antarctic Snow and Blue Ice

Abstract Little is known about the surface energy balance of Antartic blue-ice areas although there have been some studies of the surface energy balance of snow surfaces. Therefore, a detailed meteorological experiment was carded out in the vicinity of a blue-ice area in the Heimefrontfjella, Dronning Maud Land, Antarctica, during the austral summer of 1992/93. Since not all the surface fluxes could be measured directly, the use of a model was necessary. The main purpose of the model is to calculate the surface and subsurface temperatures from which the emitted longwave radiation and the turbulent fluxes can be calculated. The surface energy balance was evaluated at four locations: one on blue ice, and three on snow. Differences are due mainly to the fact that ice has a lower albedo (0.56) than snow (0.80). To compensate for the larger solar absorption of ice, upward fluxes of longwave radiation and turbulent fluxes are larger over ice. Moreover, the energy flux into the ice is larger than into snow due t...

Towards accurate estimate of the entropy production due to radiative processes: Results with a gray atmosphere mode

Recently, there have been attempts at computing the various terms in the steady entropy balance of the climate system. Differing numbers have been published. The global atmospheric entropy production rate by absorption and emission of long-wave radiation is one contribution among many others. This paper is mainly devoted to the calculation of just that contribution for the simple model of a gray atmosphere. The inescapable conclusion is that it is substantial, out-weighing, with the unlikely exception of phase changes, all other contributions not explicitly considered here. The results are compared with those in accounts of a similar nature.

Radiation Balance of a Soil‐Straw Surface Modified by Straw Color

AbstractStraw color may alter the net radiative flux at the soil‐straw surface and, consequently, the availability of energy for soil, biological, and atmospheric processes. This study ascertained the radiation balance of a soil‐straw surface as modified by the color of the straw on the surface. Barley (Hordeum vulgare L.) stubble and loose straw on 36‐m2 plots near Fairbanks, AK, was painted black, white, or remained unpainted (natural) in a randomized block experimental design. Reflected global radiation was measured in the spring of 1988–1990 and net radiation was monitored in the spring of 1990. Midday reflected global radiation and soil‐straw surface temperatures were measured on clear days in 1989. The albedo of the black straw treatment was 0.05, of the natural straw treatment was 0.2, and of the white straw treatment was 0.3. The black straw treatment resulted in higher midday surface temperatures and consequently higher emission of longwave radiation compared with other straw color treatments. A soilstraw‐atmosphere system model provided good estimates of the measured net radiative flux in 1990 (R2 = 0.91). The model predicted that a soil‐black straw surface would absorb 10% more radiation than a soil‐natural straw surface and 15% more radiation than a soil‐white straw surface averaged over the three years. The results suggest that straw color management can be an option for altering the surface radiation balance in regions with extreme climates.

The Modulation of the Low-Latitude Radiation Budget by Cloud and Surface Forcing on Interannual Time Scales

Regionally confined interannual perturbations in the tropical radiation budget associated with east-west circulations are examined along with the forcing mechanisms of these perturbations in relation to surface and cloudiness variability. A zonal harmonic analysis of emitted longwave radiation emphasizes that these variations are largely controlled at the planetary wave scale. The overall effect leads to an approximately 50 deg/yr propagation phase speed that is considerably slower than the oceanic Kelvin wave capable of driving east-west longwave (LW) anomalies through SST feedback. Examination of the time-dependent radiative energetics over the tropics reveals that the aforementioned anomaly LW propagation is mainly due to cloud forcing associated with east-west circulation changes. Diabatic heating associated with coupled ocean-atmosphere feedback appears to be larger responsible for the LW anomaly propagation.

Development of models for thermal infrared radiation above and within plant canopies

Any significant angular dependance of the emitted longwave radiation could result in errors in remotely-estimated energy budgets or evapotranspiration. In this paper thermal infrared radiation models are reviewed in reference to anisotropic emissions from the plant canopy. The biometeorological aspects of linking longwave models with plant canopy energy budgets and micrometeorology are discussed and a new model is described. Time variation of thermal infrared emission measurements is found to sometimes be interpreted as anisotropy. Recently relatively sophisticated biometeorological and radiative models have been coupled, but future developments are still needed.

Entropy budget of the atmosphere

The balance equations for the entropy in the atmosphere are presented and discussed. Using observed energy fluxes and atmospheric temperatures, we present estimates of the various terms in the global mean entropy budget. The largest boundary fluxes of entropy are associated with the emission of longwave radiation. The fluxes of entropy associated with turbulent and molecular diffusion are found to be much smaller. On the planetary scale the mean outgoing flux of entropy at the top of the atmosphere is found to be about 22 times larger than the mean incoming flux of entropy through solar radiation. The rates of entropy production and destruction by the various irreversible processes that occur in the atmosphere are also computed. The entropy production terms involved in the release of latent heat and the absorption of solar radiation are, by far, the largest sources of entropy for the atmosphere, whereas the production of entropy associated with the absorption of longwave radiation is an order of magnitude smaller. The destruction is mainly accomplished through cooling by outgoing longwave radiation. The contributions of the sensible heat fluxes and friction are relatively small. Regional contributions to the total entropy generation in the atmosphere are studied by considering an equatorial region bounded by two latitudinal walls at 15°N and 15°S and a polar region poleward of 70°N. The rates of entropy generation by the various diabatic processes are highest in the equatorial region; part of the generated entropy is exported to higher latitudes.

Microclimate and actual evapotranspiration in a humid coastal-plain environment

Continuous hourly measurements of twelve meteorologic variables recorded during 1983 and 1984 were used to examine the microclimate and actual evapotranspiration at a low-level radioactive-waste burial site near Barnwell, South Carolina. The study area is in the Atlantic Coastal Plain of southwestern South Carolina. Monthly, daily, and hourly trends in net radiation, incoming and reflected short-wave radiation, incoming and emitted long-wave radiation, soil-heat flux, dry- and wet-bulb temperatures, soil temperatures, wind direction and speed, and precipitation were used to characterize the microclimate. Average daily air temperatures ranged from −9 to 32° Celsius during the period of study. Net radiation varied from about −27 to 251 watts m −2 and was dominated by incoming short-wave radiation throughout the year. The peak net radiation during a summer day generally occurred 2–3h before the peak vapor pressure deficit. In the winter, these peaks occurred at about the same time of day. Monthly precipitation varied from 15 to 241 mm. The Bowen ratio method was used to estimate hourly evapotranspiration, which was summed to also give daily and monthly evapotranspiration. Actual evapotranspiration varied from 0.0 to 0.7 mm h −1, 0.8−5 mm d −1, and 20–140 mm month −1 during 1983 and 1984. The maximum rate of evapotranspiration generally occurred at the same time of day as maximum net radiation, suggesting net radiation was the main driving force for evapotranspiration. Precipitation exceeded evapotranspiration during 14 months of the 2yr study period. Late fall, winter, and early spring contained the majority of these months. The maximum excess precipitation was 115 mm in February 1983.

Regional-Scale Diurnal Variations of Outgoing Infrared Radiation Observed by METEOSAT

Abstract For any given area, diurnal variation of the emitted longwave radiation reveals the response of the surface and atmosphere to the astronomical diurnal forcing. However, the diurnal rhythm can be masked locally by changes in cloud cover linked to passage of weather systems. To eliminate this weather “noise” we construct histograms of the pixel radiance counts from the METEOSAT IR window channel, for regions of dimensions 250 to 1000 km, and we study their evolution with time. We find that considerable information on the diurnal variation, both of surface temperature and of cloud cover at all levels, can be obtained from short sequences (3 days) of hourly METEOSAT data. In West Africa, diurnal variation of clear-sky emergent radiances, corresponding to amplitudes of 30–50 K in surface skin temperature, is found not only in the Saharan desert regions but also during the dry season in the Sahel–Sudan–Guinea zone. In the August wet season, in this last area, the amplitude is lower, while diurnally var...

A Comparison Between Satellite-Defined and Parameterized Land-Water Differences in Emitted Longwave Radiation

An analysis is performed to qualitatively compare the seasonal variation in emitted longwave radiation over land and over water areas as determined from 12 months of Nimbus 6 satellite data with that defined from parameterizations of this radiation budget component. These variations are noted when land and water surface areas are mapped to corresponding areas at the 'top' of the atmosphere. Variations of a surface-temperature-dependent parameterization of emitted longwave radiation originally suggested by Budyko (1969) are considered. The longwave radiation parameterizations indicate small differences between land and water profiles of emitted longwave radiation at the top of an atmospheric column in low latitudes in comparison to large differences in this feature shown to exist in the satellite data. The small differences are noted in linear parameterizations of emitted flux when zonally-averaged satellite data are used to define equation coefficients.

The First 18 Months of Planetary Radiation Budget Measurements from the Nimbus 6 ERB Experiment

The Nimbus 6 satellite Earth Radiation Budget (ERB) experiment has continuously monitored the solar radiation input and the reflected shortwave and emitted longwave radiation exitance from the earth-atmosphere system since July 1975. In this paper, the planetary radiation budget parameters observed during the first eighteen months in orbit (July 1975–December 1976) are presented. The results show that the annual mean planetary albedo and longwave radiation flux are 31% and 234 W m−2> (radiative equilibrium temperature of 254 K), respectively. The earth atmosphere system is observed to be in complete radiation balance over a one-year period to within the experimental error of observation. There is an annual cycle of the mean monthly planetary net radiation which is due predominantly to the annual cycle of incoming solar radiation caused by the time variation of earth-sun distance and the sun's declination. Monthly variations in outgoing longwave radiation due to variation in global cloudiness and snow and ice cover are generally compensated by the simultaneous variations in the planetary albedo so that there is generally little monthly variability of the total radiation to space compared to that of the net radiation.

Energy exchange over young sea ice in the central Arctic

A simple model of heat transport through young sea ice is combined with climatological data on air temperatures and incoming radiation in the central Arctic to predict how each component of the surface heat balance is affected by changes in ice thickness. Results indicate that during the cold months the net heat input to the atmosphere from ice in the 0‐ to 0.4‐m range is between 1 and 2 orders of magnitude larger than that from perennial ice. Once the ice exceeds a meter in thickness, there is little change in any of the heat fluxes as the ice thickens. Although both the amount of absorbed shortwave radiation and the emitted longwave radiation depend on ice thickness, it is the turbulent fluxes which undergo the largest changes. The rate of heat exchange over thin ice is shown to be extremely sensitive to snow depth and assumed boundary layer temperatures. It is concluded that with the present ice thickness distribution in the central Arctic, total heat input to the atmospheric boundary layer from regions of young ice is equal to or greater than that from regions of open water or thick ice.

Large-scale precipitation estimates using satellite data; Application to the Indian Monsoon

Thirty months of continuous low resolution statellite measurements of albedo and emitted longwave radiation are used to study precipitation associated with the Indian Monsoon. Combined with rainfall data for the Indian subcontinent, the satellite data are employed to develop a precipitation intensity index. It is postulated that such an index must first adequately depict the extreme monsoon rainfall regime before it can be applied to the study of rainfall over other regions, especially those devoid of conventional precipitation measurements.

The Radiation Balance of the Planet Earth from Radiation Measurements of the Satellite Nimbus II

The net flux of radiation at the top of the atmosphere and associated quantities (albedo and outgoing longwave radiation) were computed for five successive semimonthly periods from measurements of the radiance of emitted longwave radiation and reflected solar radiation obtained over the entire globe from the satellite Nimbus II during the period 16 May–28 July 1966. The anisotropy of the reflection characteristics of the earth-atmosphere system was considered for the first time with gross empirical models derived from airplane and balloon observations. The global planetary albedo was found to be between 29 and 31%, while the mean planetary temperature ranged between 254 and 255K. Both results deviate from the corresponding values of earlier investigations in such a way as to suggest that in those investigations the cloudiness or its effect on radiative tranfer, especially in the tropics and subtropics, was overestimated. The global averages of the radiation balance indicate a slight deficit of about 0.005 cal cm−2 min−1, when computed with a value of the solar constant of 2.00 cal cm−2 min−1. Seasonal trends and day-to-day variations of the earth's radiation field are also discussed.

GENERATION OF AVAILABLE POTENTIAL ENERGY IN HURRICANE HILDA (1964)

The energetics of hurricane Hilda (1964) are studied through the theory of available potential energy applied to a limited fixed region surrounding the storm. The generation of available potential energy is shown to be closely dependent on differential heating within the baroclinic structure of the hurricane, occurring primarily in the middle and upper troposphere of the core of the storm. The diabatic heating components (condensation, emission of long wave radiation, direct absorption of solar radiation, and sensible heating) are modeled and the contribution to the total generation from each component computed. The results from the latent heating model based on Kuo's work portray the dependence of the deep cumulus convection on the sea surface temperature. The best estimate of the total generation of available potential energy within the hurricane scale is 10.3 × 1012 watts, of which 77 percent is generated by latent heating, 17 percent by infrared cooling, and 6 percent by direct solar absorption. The total generation compares favorably with estimates of kinetic energy production in mature hurricanes. Energy considerations in the steady state condition of the hurricane system are discussed within the framework of the available potential energy theory.

An investigation on packed-bed collectors

This work is aimed at investigating the performance characteristics of packed-bed solar collectors in order to improve solar-energy collection with considerable reduction in cost. Solid and hollow spheres, metallic screens, and other irregular shapes are used as absorbing materials. Water is in direct contact with the absorbing materials, thus effecting heat-transfer by convection and radiation rather than by conduction. The materials absorb the transmitted solar radiation and emit long-wave radiation. Water, being a strong absorber of long-wave radiation especially in the the infra-red region of the solar spectrum, absorbs directly from the solar radiation and intercepts the emitted long-wave radiation from the collector materials. The result is a slightly higher water exit temperature than the bed temperature. The average collector efficiency is about 80 percent for most of the materials tested and the variation remains within ± 10 percent. Over-all efficiency ranging from 20 to 60 percent is obtained and this compares favorably with the performance of most ordinary flat-plate collectors, although temperatures obtained are not as high.