Showing papers on "Latent heat published in 1989"

Estimation of regional surface resistance to evapotranspiration from NDVI and thermal-IR AVHRR data

Abstract: Infrared surface temperatures from satellite sensors have been used to infer evaporation and soil moisture distribution over large areas. However, surface energy partitioning to latent versus sensible heat changes with surface vegetation cover and water availability. We tested a hypothesis that the relationship between surface temperature and canopy density is sensitive to seasonal changes in canopy resistance of conifer forests. Surface temperature (Ts) and canopy density were computed for a 20 × 25 km forested region in Montana, from the NOAA/AVHRR for 8 days during the summer of 1985. A forest ecosystem model, FOREST-BGC, simulated canopy resistance (Rc) for the same period. For all eight days. surface temperatures had high association with canopy density, measured as Normalized Difference Vegetation Index (NDVI) (R2 = 0.73 − 0.91), implying that latent heat exchange is the major cause of spatial variations in surface radiant temperatures. The slope of Ts and NDVI, σ, was sensitive to changes ...

Effects of implementing the simple biosphere model in a general circulation model

Abstract: The Simple Biosphere Model (SiB) of Sellers et al., was designed to simulate the interactions between the earth's land surface and the atmosphere by treating the vegetation explicitly and realistically, thereby incorporating the biophysical controls on the exchanges of radiation, momentum, sensible and latent heat between the two systems. This paper describes the steps taken to implement SiB in a modified version of the National Meteorological Center's global spectral general circulation model (GCM) and explores the impact of the implementation on the simulated land surface fluxes and near-surface meteorological conditions. The coupled model (SiB-GCM) was used to produce summer and winter simulations. The same GCM was used with a conventional hydrological model (Ctl-GCM) to produce comparable 'control' summer and winter simulations for comparison. It was found that SiB-GCM produced a more realistic partitioning of energy at the land surface than Ctl-GCM. Generally, SiB-GCM, produced more sensible heat flux and less latent heat flux over vegetated land than did Ctl-GCM and this resulted in a much deeper daytime planetary boundary layer and reduced precipitation rates over the continents in SiB-GCM. In the summer simulation, the 200 mb jet stream was slightly weakened in the SiB-GCM relative to the Ctl-GCM results and analyses made from observations.

Climatic Equilibrium of the Atmospheric Convective Boundary Layer over a Tropical Ocean

Abstract: A radiative-convective boundary layer model was developed by coupling a thermodynamic model of a partially mixed convective boundary layer (CBL) with a radiation model, and energy balance constraints were used to study coupled boundary layer (CBL) equilibrium over three timescales (about 1 day, about 10 days, and more than 100 days). It is shown that the variation in cloud top decreases with greater coupling to the atmosphere and the ocean. The slope of the latent heat flux with increasing SST decreases with more tropospheric coupling, and reverses sign with a coupled ocean.

Modelling liquid-solid phase changes with melt convection

Abstract: SUMMARY Methods are described for modelling of phase change processes using the finite element method to simulate freezing and melting including convection in the melt. Evaluation of several enthalpy/specific heat methods and time marching schemes is also included. Suppression of velocities in the solid region is described, and example problems are given. Comparison is made to simulations performed by other researchers using finite difference methods. Substantially different results were found for one of these problems, and this result is shown to be caused by numerical problems in the earlier work. strong effect on the resulting microstructure. A number of researchers have shown reorientation of columnar grains,' alteration of the size and location of equiaxed zones' and macro~egregation,~. all due to melt convection. Mathematical models have been used in attempts to better understand the processes and thus control them. Although the most convenient mathematical models would use analytical solutions to the coupled heat and momentum transport equations, very few such solutions exist for these problems, and none would extend to the realistic problems where complicated geometries and temperature dependent material properties are included. For this reason, nearly all of the efforts in this area have been numerical. There are different types of numerical methods which are appropriate to phase change problems, depending on the kind of material involved. In pure materials, eutectics or congruent melting phases, the liquid-solid interface is sharp and corresponds to an isotherm. For these kinds of problems it may be appropriate to have part of the mesh coincide with the solidification front at all times, and distort the mesh in both phases as the boundary moves. A number of these front- tracking methods have been de~eloped,~, but none exists for three-dimensional problems. For alloys which freeze over a range of temperatures, front-tracking methods are no longer applicable. Instead, what is normally done is to specify the evolution of latent heat over a freezing range as part of the material properties. The phase boundaries are then recovered from the solution as the isotherms corresponding to the beginning and end of the transformation. The two

Physical modeling of the composting ecosystem.

Abstract: A composting physical model with an experimental chamber with a working volume of 14 × 103 cm3 (0.5 ft3) was designed to avoid exaggerated conductive heat loss resulting from, relative to field-scale piles, a disproportionately large outer surface-area-to-volume ratio. In the physical model, conductive flux (rate of heat flow through chamber surfaces) was made constant and slight through a combination of insulation and temperature control of the surrounding air. This control was based on the instantaneous conductive flux, as calculated from temperature differentials via a conductive heat flow model. An experiment was performed over a 10-day period in which control of the composting process was based on ventilative heat removal in reference to a microbially favorable temperature ceiling (temperature feedback). By using the conduction control system (surrounding air temperature controlled), 2.4% of the total heat evolved from the chamber was through conduction, whereas the remainder was through the ventilative mechanisms of the latent heat of vaporization and the sensible temperature increase of air. By comparison, with insulation alone (the conduction control system was not used) conduction accounted for 33.5% of the total heat evolved. This difference in conduction resulted in substantial behavioral differences with respect to the temperature of the composting matrix and the amount of water removed. By emphasizing the slight conduction system (2.4% of total heat flow) as being a better representative of field conditions, a comparison was made between composting system behavior in the laboratory physical model and field-scale piles described in earlier reports. Numerous behavioral patterns were qualitatively similar in the laboratory and field (e.g., temperature gradient, O2 content, and water removal). It was concluded that field-scale composting system behavior can be simulated reasonably faithfully in the physical model.

A numerical investigation of sea surface temperature variability in the Arabian Sea

Abstract: A numerical model is developed to study the thermodynamics of the Arabian Sea. The model consists of a surface mixed layer of thickness hm and temperature Tm, embedded in a dynamic layer of thickness h≥hm. Entrainment and detrainment in the mixed layer are determined by wind stirring and cooling at the oceanic surface, as in the Kraus and Turner (1967) model. The dynamic layer is a 1½-layer model which allows entrainment due to shear instability at the base of the layer, similar to the Pollard et al. (1973) model. Monthly climatological data, along with the model sea surface temperature (SST), are used to determine the wind stress and heat fluxes forcing the model. The model is very successful in simulating the observed SST patterns, generally differing by no more than 0.5°C. During the Southwest Monsoon (June-September), Tm decreases markedly near Somalia and the Arabian peninsula owing to the entrainment of cool subsurface water at the coast and its subsequent advection offshore; farther offshore in the central Arabian Sea it decreases owing to increased evaporative cooling. During the Northeast Monsoon (December-March), the decrease in Tm is caused in part by reduced solar radiation and by increased evaporative cooling, with additional cooling by entrainment in the northern Arabian Sea. An interesting observed feature is that there is a net annual surface heat flux into the Arabian Sea. In the western Arabian Sea this flux is a direct result of coastal upwelling during the Southwest Monsoon, the cold water reducing the latent heat flux out of the ocean. In the central and eastern Arabian Sea it is caused by the southward advection of this upwelled water toward the equator. The annual heat and mass budgets are closed by equatorial currents: a westward undercurrent is the source of cool subsurface water that is entrained in the Arabian Sea, and a warm eastward surface current removes the excess heat and entrained water from the upper layer.

Two-Wavelength Method of Measuring Path-Averaged Turbulent Surface Heat Fluxes

Abstract: Because few geophysical surfaces are horizontally homogeneous, point measurements of the turbulent surface fluxes can be unrepresentative. Path-averaging techniques are therefore desirable. This paper presents a method that yields path-averaged measurements of the sensible and latent heat fluxes with a potential accuracy as good as that for eddy-correlation measurements. The method relies on electro-optical measurements of the refractive index structure parameter Cn2 at two wavelengths: one in the visible-to-mid-infrared region, where Cn2 depends largely on turbulent temperature fluctuations, and a second in the near-millimeter-to-radio region, where Cn2 depends more strongly on humidity fluctuations. A sensitivity analysis, the cornerstone of the study, provides quantitative guidelines for selecting wavelength pairs to use for the measurements. The sensitivity analysis also shows that the method is not uniformly accurate for all meteorological conditions; for limited ranges of the Bowen ratio, t...

Surface Energy and Radiation Balance Systems: General Description and Improvements

Abstract: Surface evaluation of sensible and latent heat flux densities and the components of the radiation balance were desired for various vegetative surfaces during the ASCOT84 experiment to compare with modeled results and to relate these values to drainage winds. Five battery operated data systems equipped with sensors to determine the above values were operated for 105 station days during the ASCOT84 experiment. The Bowen ratio energy balance technique was used to partition the available energy into the sensible and latent heat flux densities. A description of the sensors and battery operated equipment used to collect and process the data is presented. In addition, improvements and modifications made since the 1984 experiments are given. Details of calculations of soil heat flow at the surface and an alternate method to calculate sensible and latent heat flux densities are provided.

Turbulent exchange above a pine forest i. fluxes and gradients

Abstract: Measurements of gradients of wind, temperature and humidity and of the corresponding turbulent fluxes have been carried out over a sparse pine forest at Jadra»s in Sweden. In order to ascertain that correct gradient estimates were obtained, two independent measuring systems were employed: one system with sensors at 10 fixed levels on a 51 m tower and another with reversing sensors for temperature and humidity, covering the height interval 23 to 32 m. Turbulent fluxes were measured at three levels simultaneously. Data from three field campaigns: in June 1985, June 1987 and September 1987 have been analyzed. The momentum flux is found on the average to be virtually constant from tree top level, at 20 to 50 m. The average fluxes of sensible and latent heat are not so well behaved. The ratio of the non-dimensional gradients of wind and temperature to their corresponding values under ‘ideal conditions’ (low vegetation) are both found to be small immediately above the canopy (about 0.3 for temperature and 0.4 for wind). With increasing height, the ratios increase, but the values vary substantially with wind direction. The ratios are not found to vary systematically with stability (unstable stratification only studied). The ratio of the non-dimensional humidity gradient to the corresponding non-dimensional potential temperature gradient (equivalent to k h /k w ) is found to be unity for (z − d)/L v less than about −0.1 and about 1.4 for near neutral stratification, but the scatter of the data is very large.

Uncertainties in estimates of surface heat fluxes derived from marine reports over the tropical and subtropical oceans

Abstract: Estimates are made of the uncertainties in calculations of the heat fluxes at the surface of the tropical and subtropical oceans based upon the bulk formulae and archived marine weather reports. Major contributions are identified not only in the basic observations of such variables as temperature and wind but also in uncertainties in parameters in the bulk formulae themselves. All identified factors are defined as either random or systematic. The potential effects of archiving and sampling errors are also explored. The total uncertainties for individual observations of the net solar and infrared irradiances and the latent and sensible heat fluxes are about 80, 10, 83 and 12 W m -2 , respectively. Because uncertainties associated with random errors decrease when many observations are averaged, the uncertainties in the fluxes decrease substantially when fifty or more observations are averaged together. However, since all of the surface fluxes have some systematic uncertainties associated with them, sizeable uncertainties remain, especially in the latent heat flux, even if an unlimited number of observations is available for calculating the means. Representative maps of uncertainties in 20-year monthly means of the component fluxes over the tropical Pacific show large uncertainties in the equatorial and southeastern oceans. Elsewhere, the net solar and infrared irradiance and sensible heat flux have uncertainties of 10 W m -2 or less. Unfortunately, the uncertainties in the latent heat flux exceed 30 W m -2 everywhere, because of the large systematic component. Total uncertainties in the net heating of the ocean surface are relatively large over the entire tropical Pacific with the smallest relative values in the eastern tropical region. DOI: 10.1111/j.1600-0870.1989.tb00388.x

Fine Adjustment of Large Scale Air-Sea Energy Flux Parameterizations by Direct Estimates of Ocean Heat Transport

Abstract: An inverse technique is used to adjust uncertain coefficients and parameters in the bulk formulae of climatological air-sea energy fluxes in order to obtain an agreement of indirect estimates of meridional heat transport with direct estimates in the North Atlantic Ocean. Three oceanographic estimates of ocean heat transport at the equator, at 25°N, and 32°N are compatible with meteorological evidence provided that the uncertainties of both direct and indirect estimates are taken into account. The transport coefficient CE for estimation of the latent heat flux is the major contributor to the overall uncertainty in estimates of ocean heat transport. The constraint of 1 PW northward transport across 25°N leads to a set of parameterizations for which the parameter adjustments are only less than half as large as the estimated uncertainties. Based on this set of constrained parameterizations monthly climatological fields of the individual fluxes in the North Atlantic Ocean are computed which are consis...

Response of the Hadley circulation to convective forcing in the ITCZ

Abstract: Through the use of a zonal balance model we investigate the response of the mean meridional circulation to a specified diabatic forcing for both resting and nonresting zonal flows. The use of a potential latitude coordinate and transformed meridional circulation components results in a simplified meridional circulation equation in which the variable coefficients are the normalized potential vorticity and inertial stability. Solutions of this equation illustrate how latent heat release away from the equator forces a winter hemisphere Hadley cell that is more intense than the summer hemisphere cell. This asymmetric response is due primarily to the anisotropy associated with the spatial variation of the inertial stability field. Despite the sensitivity of the meridional circulation to the location and breadth of the forcing, the low latitude thermodynamic response is for the most part insensitive as long as the total latent heat release remains the same. Numerical solutions of the zonal balance mode...

Wintertime air‐sea interaction processes across the Gulf Stream

Abstract: Aircraft, buoy and satellite measurements have been used to study the wintertime air-sea interaction processes across the Gulf Stream during January 25–30, 1986. The turbulent flux regime in the marine atmospheric boundary layer exhibited considerable spatial and temporal variability during this 6-day period, which was related to both the evolution of the synoptic scale atmospheric conditions and the sea surface temperature (SST) field. During the pre-storm conditions prior to January 25, the spatial structure of the SST field played an important role in generating a shallow atmospheric frontal zone along the Gulf Stream front by causing differential heating of the marine atmospheric boundary layer over the stream versus over the cooler shelf waters. As this front moved shoreward on January 25, the warm, moist, maritime air flowing northwestward behind the front induced moderate ocean-to-atmosphere heat fluxes (∼300 W m−2 total heat flux measured over the core of the Gulf Stream). The subsequent outbreak of eastward flowing cold, dry, continental air over the ocean on January 27 and 28 generated high total heat fluxes (∼1060 W m−2 over the core of the Stream), as did a second, somewhat weaker outbreak which followed on January 30 (∼680 W2 over the core of the Stream). During each of these outbreaks, with air flowing from land out over the continental shelf, Gulf Stream and Sargasso Sea waters, the SST field again affected the spatial structure of the flux fields. The near-surface fluxes of both sensible and latent heat were found to be relatively low over the cool continental shelf waters, while higher fluxes were seen over the Gulf Stream and Sargasso Sea. Similar spatial structure was seen in the near-surface momentum flux values, but relative changes were typically smaller from one location to another on a particular day. The most noticeable responses of the Gulf Stream to these surface fluxes were the deepening of its mixed layer and a loss of upper layer heat; however, no direct current observations were made in the stream, so velocity changes may not be assessed. An average mixed layer deepening of about 35 m was observed in the stream, and the upper layer heat loss was estimated to be 3.2×1013 J m−1 alongstream, an amount sufficient to decrease the average mixed layer temperature by 0.62°C. No path changes in the stream could be attributed to the atmospheric forcing of this period, since there was a large offshore movement of the stream in the region of the Charleston bump at this time due to other processes. Any path changes that may have been associated with the atmospheric forcing would have been masked by that offshore movement.

Deep Valley Radiation and Surface Energy Budget Microclimates. Part II: Energy Budget

Abstract: Surface energy budget measurements were made concurrently at five sites located on the valley floor, sidewalls and ridgetop of Colorado's 650-m deep Brush Creek Valley (39°32′N, 108°24′W) on the nearly clear day of 25 September 1984 using the Bowen ratio energy budget technique. Daily average surface heat flux values for a natural sagebrush ecosystem on the floor of the semiarid valley included an input of 109 W m−2 net all-wave radiation and 15 W m−2 ground heat flux, and a loss of 48 W m−2 latent heat flux and 76 W m−2 sensible heat flux. Significant differences in instantaneous, daily, and daytime fluxes occurred from site to site as a function of slope aspect and inclination angles and surface properties, including vegetation cover and soil moisture. Strong contrasts in instantaneous latent and sensible heat fluxes occurred between the opposing northeast-and southwest-facing sidewalls of the valley as solar insolation varied through the course of the day and as shadows propagated across the v...

Annual heat balance and equilibrium temperature of Lake Aegeri, Switzerland

Abstract: The mean heat budget of Lake Aegeri, Switzerland, is 950 MJ·m−2, comparable to that of neighbouring lakes. The annual variation in the net heat flux can be adequately described using a six-term heat balance equation based on 12 years of monthly mean meteorological and surface temperature data. Although the magnitude of the net heat flux is dominated by the radiative terms of the equation, the one-month backward shift of the net flux and total heat content extrema from the solstices and equinoxes respectively is due to the phase shift of the non-radiative with respect to the radiative terms. A linear approximation was used to express the net heat flux in terms of a heat exchange coefficient and an equilibrium temperature. The former varies from 17 to 28 W·m−2·K−1 in the course of a year; fluctuations in the latter are found to depend mainly on fluctuations in cloud cover and relative humidity, whilst the effect of fluctuations in air temperature and wind speed is slight.

Modes of operation of thermo-mechanically coupled ice sheets

Abstract: A dimensionless model of thermo-mechanically coupled ice sheets is used to analyse the operation of the system. Three thermal processes are identified: (i) dissipation, having a maximum time-scale of thousands of years; (ii) advection, having a time-scale of tens of thousands of years; and (iii) conduction, having a time-scale of 100000 years. Kinematical processes occur on two time-scales: (i) a marginal advective time-scale of thousands of years; and (ii) a diffusive time-scale of tens of thousands of years dominant in the divide area. The coupling with the temperature field in the bed produces fluctuations to the depth of a few kilometres, which means that horizontal conduction in the bed can be ignored except perhaps in the marginal area. The thermal inertia of the bed could produce significant fluctuations in the geothermal heat gradient. The operation of the thermo-mechanically coupled system is explored with a time-dependent thermo-mechanically coupled numerical algorithm. Dependence of the basal friction on temperature is introduced heuristically, and an enthalpy method is used to represent the effect of latent heat. The marginal area is shown to be dissipation-driven, and always reaches melting point. The divide area can show two modes of behaviour: a warm-based mode where the ice sheet is thin, and a cold-based mode where the ice sheet is thick. Which mode operates depends upon the applied temperature field and the amount of heat conducted from the bed. Calculations where sliding is limited were not found to be possible owing to problems with the reduced model which resulted in a violation of the approximation conditions at the margin. Cases which did work required a substantial sliding component; as a result, a significant coupling between geometry and temperature can only be demonstrated when sliding is made temperature-dependent.

Phase Change Heat Transfer During Melting and Resolidification of Melt Around Cylindrical Heat Source(s)/Sink(s)

Abstract: Melting and resolidification of a phase change material around two cylindrical heat exchangers spaced vertically have been investigated experimentally Experiments have been performed to examine the effects of the cylinder surface temperatures on heat transfer during the melting and freezing cycle The processes have been clarified on the basis of observations of timewise variations in the solid/liquid interface and of temperature distribution measurements in the phase change material The results show that the solid/liquid interface contour during the melting and resolidification of liquid from the upper cylinder is greatly affected by the surface temperature of the lower cylinder The results show that multiple liquid regions may develop in the phase change material around the embedded heat sources/sinks, and the temperature swings and melting and freezing periods needed to be selected properly to effectively utilize the phase change material in a latent heat energy storage unit

Phase changes following the initiation of a hot turbulent flow over a cold solid surface

Abstract: We analyse the melting and/or freezing that can occur when a very large layer of hot fluid begins to flow turbulently over a cold solid retaining boundary. This is a form of Stefan problem and the response is determined by the balance between the turbulent heat flux from the fluid, H, and the (initially infinite) conductive flux into the solid. We show that solidification of the flow at the boundary must always occur initially, unless the freezing temperature of the fluid, Tf, is less than the initially uniform temperature, T0, of the semi-infinite solid. We determine the evolution of the solidified region and show that with time it will be totally remelted. Melting and ablation of the solid retaining boundary will then generally follow, unless its melting temperature exceeds that of the turbulent flow. The maximum thickness of the solidified crust is shown to scale with k2(Tf − T0)2/ρkHL and its evolution takes place on a timescale of k2(Tf − T0)2/kH2, where k is the thermal conductivity, k the thermal diffusivity, ρ the density and L the latent heat, with all these material properties assumed to be equal for fluid and solid.

Air conditioning apparatus having variable sensible heat ratio

Abstract: An air conditioning system with a variable sensible heat ratio The system includes a servomechanism that monitors the sensible and latent heat in the air being conditioned and adjusts the operation of the system accordingly A microprocessor calculates the respective rates of change in sensible and latent heat and adjusts the operation of the system so that the desired amount of sensible and latent heat is removed at the same time, thereby conserving energy The system includes a variable speed supply air fan and a plurality of subcooling coils Under a first set of conditions, the fan is slowed down and the subcooling of the refrigerant fluid is increased Under a second set of conditions, the fan is sped up and the subcooling is decreased

A coupled ocean-atmosphere climate model: temperature versus salinity effects on the thermohaline circulation

Abstract: A simple nonlinear three-box ocean model of the North Atlantic Ocean including the rudiments of eddy mixing, vertical stratification and thermohaline circulation is first presented. It is subject to uniform latitudinal differential heating, q, and net evaporation me, and includes a linear equation of state. Two quite different limiting steady-state solutions exist. The first has a warm saline surface water and a cold, low-salinity deep ocean; deep water is primarily formed in higher latitudes by the prevalence of differential heating. A second limiting solution consists of a warm saline deep ocean underlying a cool, low-salinity surface ocean; deep water is formed primarily in lower latitudes as a consequence of large differential evaporation. A coupled ocean-atmosphere model, in which the oceanic surface heat fluxes are determined internally but with differential evaporation at the ocean surface me remaining an external parameter, is next presented. The atmosphere component is a simple energy balance model that emphasizes the vertical fluxes of radiative, sensible and latent heat fluxes but does not include temperature-albedo feedback. Model response depends on the external parameters me and μ, controlling the magnitude of the thermohaline-driven circulation, and on the magnitudes of the eddy mixing coefficients and the solar constant. For small me, a steady-state solution corresponding to a cold fresh deep ocean is found, qualitatively similar to the modern ocean. For large me, a steady-state solution with a warm saline deep ocean occurs; this solution resembles conceptual models that have been proposed for the warm saline Cretaceous ocean. There exists an intermediate region of values of me for which the solutions are more complex. On the lower end of this region, both the cold fresh deep-ocean and warm saline deep-ocean circulations coexist as stable equilibria. On the upper end, the cold-deep ocean becomes unstable, manifesting oscillations with growing amplitude, and ultimately reaches the warm saline deep-ocean solution. In the neighborhood of a ‘cusp’ on the μ, me plane, that is, for relatively small μ, more complex behaviour occurs, which has not yet been fully analyzed. The model response in the region of complexity is not sensitive to changes in the solar constant but is sensitive to the eddy mixing coefficients.

Water and surface energy balance model with a multilayer canopy representation for remote sensing purposes

Abstract: A surface energy balance model with a multilayer canopy representation has been developed to simulate the vertical temperature distribution of the foliage elements and the soil underneath. This model allows one to simulate the radiative temperature of the complex vegetation-covered surface as a function of the angle of observation. The model was implemented for a two-layer canopy and has been tested by comparing simulated radiative surface temperatures (observed under a look angle of 45°), latent heat, sensible heat, momentum, and ground heat fluxes, and soil temperatures at different depths, with observed data, gathered in a maize field. The fluxes above the canopy were measured by eddy correlation methods. This paper describes the model structure and simulation results as compared with the field measurements. Except for the ground heat fluxes, all the simulated and measured parameters match reasonably well. Further, the model was used to study the sensitivity of the radiative temperature of the complex surface to variations in the roughness length z0, the leaf area index LAI, and the drag coefficient Cd. The radiative surface temperature turned out to be very insensitive to variations in Cd and LAI, and it was found that resulting variations in the radiative surface temperature fall well within the detection error of the remotely sensed surface temperature.

A Comparison of Sensible and Latent Heat Flux Calculations Using the Bowen Ratio and Aerodynamic Methods

Abstract: An analysis technique is outlined that calculates the sensible and latent heat fluxes by the Bowen ratio and aerodynamic methods, using profile measurements at any number of heights. Field measurements at two sites near Churchill, Manitoba, comprising over 4000 hours of data from June through September, are used to assess the relative accuracy of the two methods. If hourly data are eliminated when the Bowen ratio method gives the wrong sign for the fluxes, or when the Bowen ratio is close to −1, the two methods agree very well. The results also indicate that the aerodynamic method can provide acceptable results with only a single measurement of wind speed and a good estimate of the surface roughness length. The relative error associated with the use of only a single anemometer is small for unstable conditions, and only becomes significant under very stable conditions when the fluxes themselves are small. The overall comparison of the two methods yields a mean bias error of less than 10 W m−2, and...

Heater for a stirling engine

Abstract: A heater for use with a Stirling engine and a method for heating a working fluid for a Stirling engine is disclosed. The heater has a burner, heater tubes disposed in the burner, a space formed around the heater tubes which is filled with heat-storing material, and a high-temperature heat source. The heat-storing material is sealed by a seal member. Heat produced by the high-temperature heat source is supplied to the heater tubes via the heat-storing material; hence the heat-storing material acts as a secondary heat source. Heat is stored in the heat-storing material in the form of sensible heat or latent heat, or a chemical reaction is employed.

The Use of Mean Atmospheric Parameters in the Calculation of Modeled Mean Surface Heat Fluxes over the World's Oceans

Abstract: There are a number of atlases that display the distribution of ocean-atmosphere sensible and latent heat fluxes over various regions. Many are based on the “classical” method, in which time mean quantities are used in the bulk aerodynamic formulas, rather than the more accurate “sampling” method, which computes the mean of the instantaneous fluxes. Much of the justification for the use of this approximation comes from some studies conducted in the North Pacific and Atlantic oceans. How valid is it when applied globally? In this study we use large datasets, generated by January and July simulations of a general circulation model of the atmosphere, to examine comprehensively the differences between the two methods. We find that the ocean zonal averages of the two fluxes differ by less than 10 W m−2 at most latitudes in both months. However, at high southern latitudes in winter the sensible heat fluxes north of the Antarctic ice pack are up to 17 W m−2 (25%) greater when calculated with the sampling...