Net Radiative Loss Research Articles

Energy balance comparison of sorghum and sunflower

An understanding of the energy exchange processes at the surface of the earth is necessary for studies of global climate change. If the climate becomes drier, as is predicted for northern mid-latitudes, it is important to know how major agricultural crops will play a role in the budget of heat and moisture. Thus, the energy balance components of sorghum [Sorghum bicolor (L.) Moench.] and sunflower (Helianthus annuus L.), two drought-resistant crops grown in the areas where summertime drying is forecasted, were compared. Soil water content and evapotranspiration (ET) rates also were determined. Net radiation was measured with net radiometers. Soil heat flux was analyzed with heat flux plates and thermocouples. The Bowen ratio method was used to determine sensible and latent heat fluxes. Sunflower had a higher evapotranspiration rate and depleted more water from the soil than sorghum. Soil heat flux into the soil during the daytime was greater for sorghum than sunflower, which was probably the result of the more erect leaves of sorghum. Nocturnal net radiation loss from the sorghum crop was greater than that from the sunflower crop, perhaps because more heat was stored in the soil under the sorghum crop. But daytime net radiation values were similar for the two crops. The data indicated that models of climate change must differentiate nighttime net radiation of agricultural crops. Sensible heat flux was not always less (or greater) for sorghum compared to sunflower. Sunflower had greater daytime values for latent heat flux, reflecting its greater depletion of water from the soil. Evapotranspiration rates determined by the energy balance method agreed relatively well with those found by the water balance method. For example, on 8 July (43 days after planting), the ET rates found by the energy-balance and water-balance methods were 4.6 vs. 5.5 mm/day for sunflower, respectively; for sorghum, these values were 4.0 vs. 3.5 mm/day, respectively. If the climate does become drier, the lower soil water use and lower latent heat flux of sorghum compared to sunflower suggest that sorghum will be better adapted to the climate change.

A semi-empirical model of sunspot umbra

Based on data obtained with the Kitt Peak Observatory Solar Tower, we have constructed a semi-empirical model of sunspot umbra. Non-LTE calculation was used. The main features are: (1) The temperature structure of the corona and the transition region is similar to the VAL3C quiet sun model. (2) The chromosphere structure is characterized by a temperature plateau; the temperature in the upper layers ishigher than those of the quiet sun and the penumbra; (3) The minimum temperature is 3130 K, about 300 K less than that of the penumbra model. (4) the temperature structure of the photosphere is similar to those in previous models, while the micro-turbulent velocity is somewhat less. We find there is no radiative balance in the whole atmosphere. The net radiative loss rate has a maximum in the middle chromosphere and it is negative in the temperature minimum region.

The longwave radiative heat transfer of the building envelopes

The longwave radiative heat transfer between outside surface of the building envelopes and the thermal environment, is treated in this paper as interesting from the point of view of the studies of the influence of the atmospheric counterradiation on the heat balance of low-sloped roofs and walls. This influence may be taken into account by means of introducing a correction that would lower outside air temperature values. This paper presents the way of calculating this correction (temperature depression) as well as the factors influencing its values. The paper submits also quantitative analysis of the influence of the longwave atmospheric radiation upon the net radiative heat loss of the low-sloped roofs and walls as a function: the thermal resistance of the building partitions, the emissivity of their outside surfaces, wind speed, the sky, the outdoor and the indoor air temperature values.

Frost risk mapping for landscape planning: A methodology

Minimum air temperatures were measured during three winters with a network of stations in open, undulating terrain. It was observed that the change in minimum air temperature with elevation could be predicted from mean nighttime windspeed, total nighttime net radiation loss and a hill-top reference minimum temperature. It was also found that the deviation of temperatures at individual sites could be predicted from a local terrain parameter which reflects the extent of cold air accumulations. Thus a methodology for frost risk mapping has been developed which is based on regional weather dataand local terrain analysis. This paper describes the model and illustrates the regional weather and terrain effects with three-dimensional block diagrams.

Surface temperature and albedo relationships in Senegal derived from NOAA-7 satellite data

Ground temperature and albedo values were studied in a semiarid, sub-Saharan region of Africa, Senegal, for various days in the period of September 1981 to October 1982. The albedo and ground temperature were found to be positively correlated; i.e., regions of high albedo were regions of high ground temperature, and regions of low albedo were regions of low ground temperature. Highest values of ground temperature and albedo were found in a region characterized by sparse vegetation and in the dry season. Lowest values of ground temperature and albedo were found in regions characterized by dense vegetation and in the wet season. These results suggest that regions of high albedo in the sub-Saharan region of west Africa are regions of high ground temperature. Mechanisms for increasing the ground temperature under high albedo conditions are discussed. The increased ground temperature will increase the long wave radiation emitted to the atmosphere and the sensible heat flux at the surface. Therefore, there can be a net heat gain in the local atmosphere which will result in a general rising motion. These results are in contrast to those proposed by Charney (1975), who suggested that an increased albedo in semidesert regions will cause a net radiation loss, contributing to net cooling, sinking, and drying of the air aloft.

Minimum temperature surveys based on near‐surface air temperature measurements and airborne thermal scanner data

AbstractMinimum air temperature measurements and airborne thermal scanner measurements of apparent surface temperature were obtained in a regional frost risk study in gently undulating grazing country in the Southern Tablelands of New South Wales, Australia.The minimum air temperature data obtained at 7 sites on 100 nights have been used to derive a predictive relationship between temperature lapse rate and night‐time wind speed and net radiation loss. An extended network was used on 30 nights using an additional 24 sites. Excellent agreement was observed between the lapse rates collected from both the 7‐station and 31‐station networks on 24 nights.Maps of minimum air temperature across the region have been obtained for selected individual nights using Laplacian smoothing spline functions based on elevation and map co‐ordinates.Thermal scanner data were obtained with an aircraft on two nights and the paper presents detailed comparisons between apparent surface temperature data and minimum air temperatures obtained from the regional maps.These comparisons have made it possible to successfully distinguish between broad topographic controls and the effect of local surface characteristics, especially in the case of high‐resolution thermal scanner data. Such local controls include the effects of trees, surface water and various man‐made features, as well as very local topographic features such as narrow depressions, which are only noticeable from site surveys and detailed aerial photography. It is concluded that thermal imagery is an important aid in understanding spatial distribution patterns of night‐time air temperatures and hence in regional frost risk assessment.

Two-dimensional analysis of free burning arcs in argon

The authors present a theoretical model of a free burning argon arc. Equations describing the conservation of mass, momentum and energy are solved together with Ohm's law and Maxwell's equation for the magnetic field in a cylindrical coordinate system. The material properties used in these solutions are derived theoretically, using the assumption of local thermodynamic equilibrium (LTE). Calculations are made for an axisymmetric, laminar arc burning between a rod electrode and a plane electrode. Comparisons between predicted and measured temperatures and velocities show good agreement for 100 A, 200 A and 400 A arcs in argon for a pre-specified current density of 108 A m-2 at the rod electrode and a plasma pressure of 1 atm. They describe the consequences of variations in the current density at the rod electrode and in the net radiation losses. They also discuss the importance of energy transfer due to the electron convection current and analyse in detail the various components which contribute to the momentum and energy conservation.

Diurnal course of the temperature in a Lithops sp. (Mesembryanthemaceae Fenzl) and its surrounding soil

Abstract. The embedding of Lithops plants into the soil could be an adaptation to protect the plants from critical low or high temperatures. Thermoelectric measurements on Lithops lesliei N.E. Br and L. turbiniformis (Haw.) N.E. Br. were made to determine whether the temperatures of the plant tissues at various depths differ from those in the soil close to the plant. The environmental conditions of their habitat were simulated in a growth chamber equipped with a cold sky to simulate the net radiation loss during a cool and clear night. The effects of microclimatic conditions resulting in dew or hoar‐frost formation on the plant were investigated, as well as the temperature range where freezing occurs.The results provide no evidence that the embedding of a Lithops plant into the soil yields advantages to the plants in respect of critical low or high temperatures. Plant temperatures are always very close to the soil temperatures at the same depth, but heat fluxes from the bottom or the plant and its surrounding soil to the top of the plant can occur if the plant freezes. No positive effect on the temperature relations could be detected when dew or hoar‐frost is formed on the top of the plant. Lithops is frost hard to at least –3°C.

Temperature, heat, and mixing in Lake Valencia, Venezuela1

Water temperature profiles, weather data, and lake level data spanning a 2‐year period for Lake Valencia, Venezuela (10°N, 67°W), are used in an analysis of thermal regime, mixing, and heat flux. The lake, which has an area of 350 km2 and mean depth of 19 m, is warm monomictic; it becomes isothermal annually near the end of November, at the onset of the dry season. The water column during stratification consists of an upper mixed layer, which averages 13 m but varies greatly in thickness, followed by alternating thick layers of positive and negligible density gradients. The number of layers changes through time. Vertical eddy diffusivities during stratification vary from 0.23 cm2·s−1 at 20 m to 0.09 at 35 m. The mean annual heat budget is 5,308 cal · cm−2. Evaporative heat loss and net radiation flux are the two largest heat budget elements; net back radiation and sensible heat loss are important secondary terms. Seasonality is principally traceable to heat budget terms influenced by minimum air temperature, whereas week‐to‐week variation is influenced by other terms as well. Maximum stability of the water column is about 350 g‐cm · cm−2 with little variation between years. Work of the wind in distributing heat is 2,630 g‐cm·cm−2 for 1977 and 3,156 in 1978. Stability responds in a significant way to weather changes, even during stratification.

Long‐term means and short‐term variability of the surface energy balance components at the South Pole

On the basis of a nearly continuous data set obtained between April 1975 and December 1977, a summary of seasonal means of the directly measured and calculated energy fluxes and examples of the short‐term (daily) variability in these components in response to changing synoptic conditions are presented. The seasonally averaged observations are consistent with those of previous studies, indicating that throughout most of the year a net radiative loss from the surface occurs averaging 12 to 13 W m−2 per year. In summer, the downward flux of heat from the air (Hs) exceeds the net radiation losses by 10–20%, resulting in storage of heat in the deep snowpack. In winter the radiative losses average between 16 and 20 W m−2 with Hs supplying 85–90% of this loss and the remaining 10–15% supplied from deep storage in the snow. On daily time scales, the energy balance components are highly variable, with ranges several times their long‐term means. This variability appears to result from variation in forcing associated with variations in the large scale flow, namely, changing large‐scale pressure gradient, cloudiness, and variations in the mean temperature of the lower atmosphere (i.e., Z ≲ 1 km).

Net radiation in the atmosphere of Venus: Measurements and interpretation

Net flux radiometer measurements in the atmosphere of Venus question the effectiveness of the greenhouse mechanism in maintaining the high surface temperature. To search for possible instrumental explanations, new spare instrument tests were conducted. These tests uncovered an error mechanism that is defined well enough in the upper atmosphere to make approximate corrections for the large transient errors initiated at the time of instrument deployment. No direct evidence for significant errors in the lower atmosphere was found. The observed net radiative energy loss near the surface is found not to violate the assumption of a steady state atmosphere. Comparisons of the corrected flux profiles with radiative transfer calculations support the following conclusions: a new source of infrared opacity in the upper cloud is required, possibly a submicron haze; the infrared opacity of the lower cloud is too small for the cloud particles to be concentrated sulfuric acid; the mean water vapor mixing ratio is of the order of several tenths of a per cent immediately below the clouds and of the order of a few parts per million near the surface; water vapor amounts vary greatly from probe to probe, by nearly two orders of magnitude at some levels; there are thin layers of opacity in the subadiabatic layer between 35 and 48 km; and, finally, the north probe flux profile depression near 60 km may be partly a result of temperature inversions immediately above.

Estimates of Radiative Divergence during Phase III of the GARP Atlantic Tropical Experiment: Part II. Analysis of Phase III Results

Abstract The GATE Phase III radiative divergence profiles generally show less upper tropospheric radiative divergence and more middle level divergence than previous cilimatological estimates suggest. These differences are due primarily to the extensive middle and upper tropospheric cloudiness in the GATE area, the large mean values of total precipitable water vapor (∼5.1 cm), and the inclusion in the present study of the effects of the water vapor pressure broadened continuum. Averages for the 6 h local time periods 0000–0600, 0600–1200, 120–1800 and 1800–2400 show all layers of the GATE Phase III B-scale atmosphere experience a net radiative loss of energy. However, actual radiative heating of some layers is evident near midday. For a convectively suppressed composite case all levels above 700 mb show heating for the 1000–1400 LST period. The total troposphere shows a net radiative gain for the same 6 h interval (0900–1500 LST). For the enhanced convection case absolute warming is generally confined to t...

Stellar model chromospheres. VI - Empirical estimates of the chromospheric radiative losses of late-type stars

A method is developed for estimating the nonradiative heating of stellar chromospheres by measuring the net radiative losses in strong Fraunhofer line cores. This method is applied to observations of the Mg II resonance lines in a sample of 32 stars including the sun. At most a small dependence of chromospheric nonradiative heating on stellar surface gravity is found, which is contrary to the large effect predicted by recent calculations based on acoustic-heating theories.

The evaporation of spherical clouds in a hot gas. II - Effects of radiation

The effects of radiation on the evaporation of spherical clouds in a hot medium are considered. The critical cloud radius at which radiative losses balance conductive heating is determined as a function of the external temperature and density. Smaller clouds evaporate, and larger clouds condense. The conditions under which the surfaces of the clouds may be detected are discussed. Net radiative losses for evaporating clouds are calculated, and an effective cooling function for a cloudy medium is obtained. The results may be applied to clouds in supernova remnants, in the interstellar medium, and in clusters of galaxies.

Spatial Distribution of Soil Heat Flux Under a Sour Cherry Tree

AbstractThis paper presents data on the spatial variability of surface soil heat flux in an orchard (Prunus cerasus L.), evaluates the error involved in estimating the surface soil heat flux, and develops a method by which a spatial average may be taken. Surface soil heat flux was calculated from measurements of the heat flux at the approximately 5‐cm depth and of the heat stored above the heat flux plate. The heat flux plate calibrations were corrected for the thermal conductivity of the soil as measured in situ. Measurements were made at six sites both under an orchard tree and in the open between trees. Results showed that the nighttime flux under the tree was occasionally < 50% of the values measured in the open. In contrast, the daytime spatial and temporal variability was very high and occasionally a small upward flux was recorded under the trees while a near maximum downward flux was being recorded in the open or under the tree a short time earlier or later. A spatial average was calculated by weighting the soil heat flux values by the area of the orchard they represented using an integration procedure. The spatial averages showed that 50–80% of the nighttime net radiation loss from the orchard was derived from the soil.

Dynamics of deserts and drought in the Sahel

It is suggested that the high albedo of a desert contributes to a net radiative heat loss relative to its surroundings and that the resultant horizontal temperature gradients induce a frictionally controlled circulation which imports heat aloft and maintains thermal equilibrium through sinking motion and adiabatic compression. In the subtropics this sinking motion is superimposed on the descending branch of the mean Hadley circulation but is more intense. Thus the desert feeds back upon itself in an important manner. If one takes into account the biosphere, this feedback mechanism could conceivably lead to instabilities or metastabilities in desert border regions. It is argued that a reduction of vegetation, with consequent increase in albedo, in the Sahel region at the southern margin of the Sahara would cause sinking motion, additional drying, and would therefore perpetuate the arid conditions. Numerical integrations with the general circulation model of NASA's Goddard Institute for Space Studies appear to substantiate this hypothesis. Increasing the albedo north of the ITCZ from 14% to 35% had the effect of shifting the ITCZ several degrees of latitude south and decreasing the rainfall in the Sahel about 40% during the rainy season.

Dynamics of deserts and drought in the Sahel

AbstractIt is suggested that the high albedo of a desert contributes to a net radiative heat loss relative to its surroundings and that the resultant horizontal temperature gradients induce a frictionally controlled circulation which imports heat aloft and maintains thermal equilibrium through sinking motion and adiabatic compression. In the subtropics this sinking motion is superimposed on the descending branch of the mean Hadley circulation but is more intense. Thus the desert feeds back upon itself in an important manner.If one takes into account the biosphere, this feedback mechanism could conceivably lead to instabilities or metastabilities in desert border regions. It is argued that a reduction of vegetation, with consequent increase in albedo, in the Sahel region at the southern margin of the Sahara would cause sinking motion, additional drying, and would therefore perpetuate the arid conditions. Numerical integrations with the general circulation model of NASA's Goddard Institute for Space Studies appear to substantiate this hypothesis. Increasing the albedo north of the ITCZ from 14% to 35% had the effect of shifting the ITCZ several degrees of latitude south and decreasing the rainfall in the Sahel about 40% during the rainy season.

Radiative Effects of Cirrus Clouds

The divergence of net radiation in a tropical atmosphere with cirrus clouds has been examined in terms of two bulk radiative properties of the cloud: effective shortwave optical thickness τ* and broad–band infrared emissivity ε&ast. The effective shortwave optical thickness of the cirrus cloud is the primary factor controlling the radiative energy budget at the earth's surface while the cloud's broad–band infrared emissivity is the primary factor influencing the heat budget of the atmosphere. The net radiative energy budget of the tropical atmosphere over an ocean surface in the presence and absence of a cirrus cloud has been examined. The total net radiative energy at the top of the atmosphere is relatively unchanged from the clear sky value by the presence of a cirrus cloud layer while the surface energy budget shows a significant decrease in the shortwave component. The total net radiative energy loss of the atmosphere when a cirrus layer is present is shown to be 22 to 78% of the loss from a cloudless sky. This reduction of divergence when cirrus are present generates in 24 hr an amount of energy which is 32 to 100% of the estimated net latent heat released to the atmosphere by precipitation processes in a cumulonimbus cloud. The divergence of net radiation through three layers encompassing the atmosphere is shown to be linearly dependent on the broad–band infrared emissivity and effective shortwave optical thickness of cirrus clouds.

Alteration of nocturnal radiation balance of “red blush” grapefruit trees by application of aluminum powder suspensions to upper leaves

Theoretical considerations indicate that radiational energy loss and air-leaf temperature depressions may be reduced by lowering canopy emissivity. Aluminum powder suspensions applied to the upper leaves of “Red Blush” grapefruit ( Citrus paradisi Macf.) trees reduced canopy emissivity (4–12%) and increased leaf temperature (0.6-0.9°C). Net radiation loss was reduced up to 9%. When net radiation loss was not reduced, air-leaf temperature depression reductions were greater.

On radiative transfer in gas discharges

Radiative transfer in spectral lines under non-equilibrium conditions in an optically thick plasma is dealt with. A method has been developed to calculate the excited-state density by defining a position-dependent loss function A(r) which describes the net radiative loss, and which is determined by the spectral-line profile and the variation of n2(r) as a function of the coordinates. A(r) is compared with the loss function in certain approximations. As an application a three-level model is solved for a low-pressure Na-Ne discharge.