Showing papers on "Latent heat published in 1995"
TL;DR: In this paper, a two-layer model of turbulent exchange that includes the view geometry associated with directional radiometric surface temperature is developed and evaluated by comparison of model predictions with field measurements.
1,448 citations
TL;DR: The naphthalene sublimation method can be used to study mass and heat transfer with confidence for a variety of applications, but with certain restrictions as discussed by the authors, such as high-velocity flows.
386 citations
01 Jan 1995
TL;DR: In this paper, a Surface Energy Balance Algorithm for Land (SEBAL) has been developed in a way that the need for collateral measurements is partly eliminated, a very accurate surface temperature map is no longer required (although it should be as good as possible) and a land use classification to relate surface temperature to evaporation is not needed.
Abstract: The growing concern about environment has increased the number of land surface processes studies. Computer simulation models of land surface processes have been developed for a range of scales and with different levels of physical complexity. Because the interactions between soil, vegetation and atmosphere vary both spatially and temporally, regional evaporation in heterogeneous natural landscapes is difficult to predict by means of computer simulation models. Remote sensing measurements of land surface radiative properties offer however a means to indirectly measure land surface state conditions at a range of scales. A straightforward estimation of evaporation from radiative properties of the land surface is hampered by the fact that only a very few parameters of the classical flux-profile relationships can be estimated directly from remote sensing measurements. Moreover, the accuracy of surface temperature measurements necessary to solve flux-profile relationships is still poor. Inclusion of ground measurements is a possible solution, but the absence of such data on large scales and for heterogeneous land surfaces where these parameters are not measured, forms an immediate obstacle for the implementation of remote sensing algorithms. A Surface Energy Balance Algorithm for Land (SEBAL) has been developed in a way that the need for collateral measurements is partly eliminated, a very accurate surface temperature map is no longer required (although it should be as good as possible) and a land use classification to relate surface temperature to evaporation is not needed. Each pixel is characterized by a surface hemisherical reflectance, surface temperature and a vegetation index. The methodology composes of multiple flux-profile relationships for small sub-areas. Although the concept has a physical basis, the parameters are estimated by empirical relationships, for instance a relationship between near-surface vertical air temperature difference and surface temperature forms an essential component in the estimation of the sensible heat flux density. The absolute surface energy balance terms are estimated on an instantaneous time basis. Temporal integration of instantaneous surface flux densities is feasible using the evaporative fraction (latent heat flux density/net available energy): The evaporative fraction remains fairly constant during daytime hours for both homogeneous and heterogeneous areas. A physical explanation for this is given. A bulk surface resistance of a heterogeneous landscape has been related analytically to canopy and bare soil evaporation resistances. Measurements in central Spain have shown that the evaporative fraction and bulk surface resistance are suitable indicators to describe areal patterns of near-surface soil water content. Although the bulk surface resistance has a distinct diurnal variation, it is much less affected by changes in net available energy and therefore preferred to describe the energy partitioning for longer time series (weeks, months). SEBAL has been validated with data available from regional evaporation projects in Egypt and Spain. The error of high resolution evaporative fraction estimations decreases from 20% to 10% at a scale of 1 km to 5 km respectively, The error of low resolution evaporative fraction images at a scale of 100 km is approximately 1 to 5 %. Hence, the error averages out if a larger set of pixels is considered. It is concluded that the uncertainty of evaporation in regional water balances and model studies can be substantially reduced by estimating evaporation with remote sensing measurements using the proposed SEBAL technique.
369 citations
TL;DR: In this paper, the development of a simple coupled surface and PBL model, which is planned for incorporation into the Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM4/5), is described.
Abstract: Although the development of soil, vegetation, and atmosphere interaction models has been driven primarily by the need for accurate simulations of long-term energy and moisture budgets in global climate models, the importance of these processes at smaller scales for short-term numerical weather prediction and air quality studies is becoming more appreciated. Planetary boundary layer (PBL) development is highly dependent on the partitioning of the available net radiation into sensible and latent heat fluxes. Therefore, adequate treatmentof surface properties such as soil moisture and vegetation characteristics is essential for accurate simulation of PBL development, convective and low-level cloud processes, and the temperature and humidity of boundary layer air. In this paper, the development ofa simple coupled surface and PBL model, which is planned for incorporation into the Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM4/5), is described. The soil-vege...
290 citations
TL;DR: In this paper, the authors proposed a model driven by meteorological forcing at a reference level (incoming solar and long-wave radiation, air temperature, humidity and wind speed, and rainfall), which can be divided into four main compartments in the soil, coupled heat and mass transfer equations, including liquid and vapour phase transfer, are solved In the atmosphere, stability is taken into account in the calculation of the aerodynamic resistances At the soil-plant-atmosphere interface, one vegetation layer is considered, with two energy budgets: one for the bare soil fraction
222 citations
TL;DR: In this article, the relationship between sea surface temperature (SST) and latent heat flux from the ocean is investigated, and it is found that at low SST the latent heat heat flux increases with SST; at high SST it decreases with increasing SST, which cannot be explained by thermodynamic considerations alone.
Abstract: Moored buoy data from the equatorial Pacific are analyzed to investigate the relationship between sea surface temperature (SST) and latent heat flux from the ocean. It is found that at low SST the latent heat flux increases with SST; at high SST the latent heat flux decreases with increasing SST, a relationship that cannot be explained by thermodynamic considerations alone. Analysis of the wind speeds and humidity differences between the surface air and the saturation humidity at the sea surface temperature indicates that while at low SST the humidity difference primarily determines the latent heat flux, and at high SST a sharp decrease in wind speed is mostly responsible for the low latent heat flux. A mechanism that leads to low latent heat flux at high SST is suggested; it involves the interaction between convection and the large-scale circulation. The longitudinal distribution of SST, wind speed, humidity difference, and latent heat flux is found to be similar to that in previous studies. In ...
174 citations
TL;DR: In this article, five methods are described for extracting information about the surface energy budget from a combination of satellite thermal observations and various amounts of ancillary data and the importance of distinguishing between aerodynamic and radiative temperatures is discussed and definitions for each are proposed.
168 citations
TL;DR: In this article, a simple model of the lowest layer of the atmosphere is developed for coupling to ocean models used to simulate sea surface temperature (SST), which is designed to avoid the need to specify observed atmospheric data (other than surface winds), or the SST, in the surface flux calculations of ocean models and to allow a realistic representation of the feedbacks between SST and the fluxes.
Abstract: A simple model of the lowest layer of the atmosphere is developed for coupling to ocean models used to simulate sea surface temperature (SST). The model calculates the turbulent fluxes of sensible and latent heat in terms of variables that an ocean model either calculates (SST) or is forced by (winds). It is designed to avoid the need to specify observed atmospheric data (other than surface winds), or the SST, in the surface flux calculations of ocean models and, hence, to allow a realistic representation of the feedbacks between SST and the fluxes. The modeled layer is considered to be either a dry convective layer or the subcloud layer that underlies marine clouds. The turbulent fluxes are determined through a balance of horizontal advection and diffusion, the surface flux and the flux at the mixed layer top, and, for temperature, radiative cooling. Reasonable simulations of the global distribution of latent and sensible heat flux are obtained. This includes the large fluxes that occur east of ...
157 citations
TL;DR: In this article, the Monin and Obukhov (1954) variance similarity functions were compared with direct measurements for momentum and heat but not for water vapor, and it was demonstrated that the non-uniformity in water vapor sources reduced the surface flux when compared to an equivalent uniform terrain subjected to identical shear stress, sensible heat flux, and atmospheric water vapor variance.
Abstract: Eddy-correlation measurements above an uneven-aged forest, a uniform-irrigated bare soil field, and within a grass-covered forest clearing were used to investigate the usefulness of the fluxvariance method above uniform and non-uniform terrain. For this purpose, the Monin and Obukhov (1954) variance similarity functions were compared with direct measurements. Such comparisons were in close agreement for momentum and heat but not for water vapor. Deviations between measured and predicted similarity functions for water vapor were attributed to three factors: 1) the active role of temperature in surface-layer turbulence, 2) dissimilarity between sources and sinks of heat and water vapor at the ground surface, and 3) the non-uniformity in water vapor sources and sinks. It was demonstrated that the latter non-uniformity contributed to horizontal gradients that do not scale with the vertical flux. These three factors resulted in a turbulence regime that appeared more efficient in transporting heat than water vapor for the dynamic convective sublayer but not for the dynamic sublayer. The agreement between eddy-correlation measured and flux-variance predicted sensible heat flux was better than that for latent heat flux at all three sites. The flux-variance method systematically overestimated the latent heat flux when compared to eddy-correlation measurements. It was demonstrated that the non-uniformity in water vapor sources reduced the surface flux when compared to an “equivalent” uniform terrain subjected to identical shear stress, sensible heat flux, and atmospheric water vapor variance. Finally, the correlation between the temperature and water vapor fluctuations was related to the relative efficiency of surface-layer turbulence in removing heat and water vapor. These relations were used to assess critical assumptions in the derivation of the flux-variance formulation.
155 citations
TL;DR: In this paper, the authors describe a general framework for the correct interpretation of field measurements of soil heat flux, which can be used to determine accurately soil surface heat flux from measurements of heat flux at some depth below the surface.
127 citations
TL;DR: In this article, a new model for the upper North Atlantic Ocean is presented and used to hindcast the SST from 1950 to 1988, which consists of a matrix of one-dimensional (independent) columns in which a variable-depth, bulk mixed layer overlies a diffusive convective thermocline.
Abstract: A new model for the upper North Atlantic Ocean is presented and used to hindcast the SST from 1950 to 1988. The model consists of a matrix of one-dimensional (independent) columns in which a variable-depth, bulk mixed layer overlies a diffusive convective thermocline. The climatological annual cycle of heat flux convergence by the oceanic circulation is implicitly included in the formulation of the forcing. The 39-yr control integration of the model includes as surface forcing the shortwave and net longwave radiation from a control integration of the community climate model. Sensible and latent heat fluxes are determined from instantaneous values of surface temperature, humidity, and wind speed from the atmospheric model, and the SST simulated by the ocean model using the bulk formulae. The hindcast is performed by repeating the control integration, adding the observed, monthly mean surface anomalies in surface temperature, humidity, and wind speed for the period 1950–88. Thus, the simulated SST ...
TL;DR: In this article, the mesocyclonic activity in the southwestern Ross Sea is examined, with emphasis on its forcing by katabatic winds, and it is shown that latent heat release due to precipitation formation in the fronts does not significantly affect the deepening of the trough.
Abstract: The mesocyclonic activity in the southwestern Ross Sea is examined, with emphasis on its forcing by katabatic winds. The three-dimensional version of the meso-gamma-scale primitive equation model Modele Atmospherique Regional is used in which a representation of cloud microphysical processes has been introduced. Idealized boundary conditions are prescribed. In particular, the ocean is assumed to be completely ice-free or partially ice-covered. The former case corresponds to a fall situation that coincides with the climatological maximum of estimated precipitation at McMurdo Station on Ross Island. Due to the propagation of katabatic winds over the ocean, boundary layer fronts form. Clouds are generated in the fronts. A surface pressure trough also forms and extends northeastward from Terra Nova Bay. Mesocyclones are simulated in the trough. When the ocean is ice-free, strong sensible heat fluxes toward the atmosphere amplify the strength of the trough up to typically observed values. Tn this case, snow precipitation is associated with the boundary layer fronts and occurs in particular over McMurdo Sound. It is also found that latent heat release due to precipitation formation in the fronts does not significantly affect the deepening of the trough.
TL;DR: In this article, several integrations were performed using a GCM with idealized geography to improve understanding of the mechanisms responsible for CO2-induced, midcontinental summer dryness obtained by earlier modeling studies.
Abstract: To improve understanding of the mechanisms responsible for CO2-induced, midcontinental summer dryness obtained by earlier modeling studies, several integrations were performed using a GCM with idealized geography. The simulated reduction of soil moisture in middle latitudes begins in late spring and is caused by the excess of evaporation over precipitation. The increase of carbon dioxide and the associated increase of atmospheric water vapor enhances the downward flux of terrestrial radiation at the continental surface at all latitudes. However, due mainly to the CO2-induced change in midtropospheric relative humidity, the increase in the downward flux of terrestrial radiation is larger in the equatorward side of the rain belt, making more energy available there for both sensible and latent heat. Since the saturation vapor pressure at the surface increases nonlinearly with surface temperature, a greater fraction of the additional radiative energy is realized as latent heat flux at the expense of ...
TL;DR: This article used the eddy covariance technique to measure exchanges of water vapor, energy, and CO 2 between California serpentine grassland and the atmosphere, using an inexpensive, one-dimensional sonic anemometer and a closed-path CO 2 analyzer.
Abstract: We used the eddy covariance technique to measure exchanges of water vapor, energy, and CO 2 between California serpentine grassland and the atmosphere. Even though the system was built around an inexpensive, one-dimensional sonic anemometer and a closed-path CO 2 analyzer, energy balance closure was accurate to ± 20% at a net radiation of 500 W/m 2 , and the spectra and cospectra indicated only modest information loss from incompletely resolved high-frequency turbulence. In the early and middle parts of the growing season, net radiation, latent heat, and sensible heat all had similar diurnal dynamics, with latent heat accounting for 60% of the net radiation. Late in the growing season, energy dissipation by latent heat dropped dramatically, even though the vapor pressure gradient remained high. The Ω factor, an index of the role of canopy conductance in regulating transpiration (Jarvis and McNaughton 1986), decreased from 0.8 early in the growing season (indicating predominant control of transpiration by net radiation) to 0.1 late in the growing season (indicating a shift to control of transpiration by canopy conductance and vapor pressure deficit). Canopy conductance was a linear function of the product of net photosynthesis and relative humidity, divided by the CO 2 concentration, as predicted by Ball (1988). The slope of the relationship, however, was greater early in the growing season than at other times. Whole-ecosystem carbon exchange rates were modest, with midday net photosynthesis reaching maximum values of 6-8 μmol.m -2 .s -1 in early April. Diurnal variation in photosynthesis roughly paralleled variation in photosynthetically active photon flux density (PFD), but with the daily maximum increasing with canopy development early in the growing season and decreasing with drought at the end of the growing season. Photosynthesis did not clearly saturate at high levels of PFD. Ecosystem dark respiration increased strongly (Q 10 =4.6) with increasing soil surface temperature. The efficiency with which absorbed radiation was used in ecosystem photosynthesis, integrated over entire days, was 0.0115 ± 0.0015 mol CO 2 /mol PFD (20% of the values measured for healthy, single leaves under low light conditions) until late in the growing season, when the efficiency fell sharply. Using simple assumptions to extrapolate measurements from 11 d to the entire growing season, we estimate ecosystem annual gross primary production to be 11.1 mol CO 2 /m 2 , yielding an annual net primary production of 133 g biomass/m 2 . This is near the center of the range of published values from aboveground harvest studies.
TL;DR: In this paper, a microphysical model was developed to compute the temperature correction from first principles for tropical warm pool conditions, where the difference between rain drop temperature and the wet-bulb temperature has a maximum of only 0.2 K for normal conditions.
Abstract: Precipitation affects the buoyancy of the upper ocean by altering the salinity and temperature distribution. If precipitation exceeds evaporation, salinity decreases and the buoyancy of the upper ocean increases. If the temperature of the rain drops and the sea surface temperature are different, precipitation induces a sensible heat flux into the ocean. Generally, it is assumed that the rain drop temperature is close to the sea level wet-bulb temperature. However, because of the finite thermal relaxation time of large rain drops, the temperature of the rain drops could be colder than the sea-level wet-bulb temperature and the sensible heat flux enhanced. We test this possibility by developing a microphysical model to compute the temperature correction from first principles. For tropical warm pool conditions the temperature correction (i.e., difference between rain drop temperature and the wet-bulb temperature) has a maximum of only 0.2 K for normal conditions. The theoretical calculation thus corroborates the general assumption. The model is used to calculate sensible heat flux contributions with rain rate and surface meteorological data to estimate the rain cooling obtained during the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE). The average heat flux from rainfall over the entire TOGA-COARE period for the rain was approximately 2.5 W m -2. However, during intense rainfall events the rainfall sensible heat flux may be as high as 200 W m -2. During these periods the magnitude of the rainfall sensible heat flux rain cooling matches that of the latent heat flux. Because of the uncertainties in measuring meteorological parameters and because the heat flux calculated from the wet-bulb temperature differed by only about 0.1 W m -2, the wet-bulb temperature is still a reasonable value to use for the temperature of falling rain in sensible heat flux computations.
TL;DR: In this paper, a quasi-steady state analysis of the vertical Bridgman growth of large-diameter, cadmium zinc telluride is conducted using a finite element model which accounts for the details of heat transfer, melt convection, and solid/liquid interface shape.
TL;DR: In this article, the evolution of convective wakes was studied using composite time series calculated from data collected in the western Pacific warm pool during a pilot cruise and intensive observation period (IOP) of the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE).
Abstract: The evolution of convective wakes was studied using composite time series calculated from data collected in the western Pacific warm pool during a pilot cruise and intensive observation period (IOP) of the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE). Hourly averaged observations from 42 convective wakes were used to compute wake-relative composite time series of the bulk meteorological variables, as well as sensible and latent heat fluxes. These analyses show great similarities between the convective wake characteristics of the pilot cruise and the IOP, despite differences in season and location. This result, combined with a strong correlation between individual wakes and the composite time series, demonstrates the representativeness of the composites. TOGA convective wakes were found to cause a significant decrease in air temperature, a significant increase in wind speed, and thus significant increases in sensible and latent heat fluxes, which is ...
TL;DR: A combination of passive microwave measurements from the Special Sensor Microwave/Imager (SSM/I) with infrared imagery from the Advanced Very High Resolution Radiometer (AVHRR) is used to derive flux densities of latent heat and longwave radiation at the sea surface.
TL;DR: In this paper, the average of daily latent heat fluxes over the oceans for February and August 1988 are estimated using a stability-dependent bulk scheme using an EOF (empirical orthogonal function) method.
Abstract: Monthly averages of daily latent heat fluxes over the oceans for February and August 1988 are estimated using a stability-dependent bulk scheme. Daily fluxes are computed from daily SSM/I (Special Sensor Microwave/Imager) wind speeds and EOF-retrieved SSM/I surface humidity, National Meteorological Center sea surface temperatures, and the European Centre for Medium-Range Weather Forecasts analyzed 2-m temperatures. Daily surface specific humidity (Q) is estimated from SSM/I precipitable water of total (W) and a 500-m bottom layer (WB) using an EOF (empirical orthogonal function) method. This method has six W-based categories of EOFs (independent of geographical locations) and is developed using 23 177 FGGE IIb humidity soundings over the global oceans. For 1200 FGGE IIb humidity soundings, the accuracy of EOF-retrieved Q is 0.75 g kg−1 for the case without errors in W and WB, and increases to 1.16 g kg−1 for the case with errors in W and WB. Compared to 342 collocated radiosonde observations, the...
TL;DR: The results indicate that once significant ice forms, the sun is increasingly more effective in reducing the surface freezing rate and in shutting off convective mixing in the ocean under the lead as discussed by the authors.
Abstract: During a 1-month deployment for the Arctic Leads Experiment (LEADEX) in March and April 1992 on the Arctic ice cap roughly 200 km north of Prudhoe Bay, Alaska, surface-based mean meteorological and flux instruments plus a variety of remote sensors were operated at the main base camp. Identical systems were also deployed by helicopter on the upwind and downwind edges of several Arctic leads, two of which we describe in this paper. At the base camp the diurnal amplitude for sensible heat flux was +10 W m -2 about a mean of-3 W m -2, net radiation was +30 W m -2 about a mean of -15 W m '2, and net surface energy flux was +20 W m -2 about a mean of-12 W m -2. The mean latent heat flux was +1 W m -2 with a diurnal variation of about +1.5 W m -2. Mean values for the momentum and sensible heat transfer coefficients were C o = (1.20 + 0.20) x 10 '3 and Cn = (0.75 + 0.25) x 10 -3 at a 10-m reference height with only modest diurnal variations. Two lead deployments were examined. Lead 3 was approximately 1 km across. Only limited meteorological data were obtained for about 6 hours at the end of April 7 and beginning of April 8 when the lead was covered with about 10 cm of ice. Downwind of the lead, the sensible heat flux increased to about 170 W m -2 and the stress doubled, suggesting an ice-covered lead 10-m drag coefficient of 2.2 x 10 -3. More than 36 hours of data were obtained upwind and downwind of lead 4, which varied in width from 80 to 120 m. Doppler minisodars upwind and downwind of the lead indicated a doubling in the depth (5 to 10 m) of the shear-driven turbulent surface layer downwind of the lead and an intensification of intermittent wave interactions exceeding 60 m (sodar range maximum). Three prominent waves with strong downward motion were observed in this period, apparently causing increases in the downwind stress magnitude. Various sources of data were used to compute estimates over a 36-hour period of the net surface heat flux Qg over the lead, the adjacent pack ice, and any open water that might have occurred in the lead. The results indicate that once significant ice forms, the sun is increasingly more effective in reducing the surface freezing rate and in shutting off convective mixing in the ocean under the lead. Over the period of observations the average net surface heat flux was -75 W m -2 over the pack ice, -130 W m -2 over the lead, and -250 W m '2 over the open water.
TL;DR: In this paper, the authors present energy conservation and techno-economic assessment studies of a hybrid solar space-conditioning system consisting of conventional vapour-compression (V-C) and liquid-desiccant cycles.
TL;DR: In this article, a modified version of the simple biosphere model (SiB) was used to investigate the impact of spatial variability in the fields of topography, vegetation cover, and soil moisture on the area-averaged fluxes of sensible and latent heat for an area of 2×15 km (the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) testbed area) located within the FIFE area).
Abstract: A modified version of the simple biosphere model (SiB) of Sellers et al. (1986) was used to investigate the impact of spatial variability in the fields of topography, vegetation cover, and soil moisture on the area-averaged fluxes of sensible and latent heat for an area of 2×15 km (the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) testbed area) located within the FIFE area. This work builds on a previous study of Sellers et al. (1992a) but makes use of a superior data set (FIFE 1989 rather than FIFE 1987) and has a sharper focus on the nonlinear effects of soil wetness on evapotranspiration. The 2×15 km testbed area was divided into 68×501 pixels of 30×30 m spatial resolution, each of which could be assigned topographic, vegetation condition, and soil moisture parameters from satellite and in situ observations gathered in FIFE-89. One or more of these surface fields was area averaged in a series of simulation runs to determine the impact of using large-area means of these initial/boundary conditions on the area-integrated (aggregated) surface fluxes. Prior to these simulations some validation work was done with the model. The results of the study can be summarized as follows: (1) SiB was initialized with satellite and airborne remotely sensed data for vegetation condition and soil wetness, respectively. The surface fluxes calculated by SiB compared well with surface-based and airborne flux observations. (2) Analyses and some of the simulations indicated that the relationships describing the effects of moderate topography on the surface radiation budget are near linear and thus largely scale invariant. The relationships linking the simple ratio (SR) vegetation index, the canopy conductance parameter ∇F, and the canopy transpiration flux are also near linear and similarly scale invariant to first order (see also Sellers et al., 1992a). Because of this it appears that simple area-averaging operations can be applied to these fields with relatively little impact on the calculated surface heat fluxes. (3) The relationships linking surface and root-zone soil wetness to the soil surface and canopy transpiration rates are nonlinear. However, simulation results and observations indicate that soil moisture variability decreases significantly as the study area dries out, which partially cancels out the effects of these nonlinear functions. (4) The near-infrared surface reflectance ρN estimated from atmospherically corrected satellite data may be a better predictor of vegetation condition than a two-band vegetation index, such as the SR, at least for the grasslands represented in the FIFE area. These results support the use of simple averages of topographic and vegetation parameters to calculate surface energy and heat fluxes over a wide range of spatial scales, from a few meters up to many kilometers. Although the relationships between soil moisture and evapotranspiration are nonlinear for intermediate soil wetnesses, the dynamics of soil drying act to progressively reduce soil moisture variability and thus the impacts of these nonlinearities on the area-averaged surface fluxes. These findings indicate that we can use mean values of topography, vegetation condition, and soil moisture to calculate the surface-atmosphere fluxes of energy, heat, and moisture at larger length scales to within an acceptable accuracy for climate-modeling work.
TL;DR: In this paper, the surface energy balance and ablation at an elevation of 100 m asl on the Ecology Glacier, which is an outlet glacier of the main ice cap of King George Island, Antarctica, were evaluated using a model with input from meteorological data.
Abstract: Meteorological measurements performed during the austral summer of 1990–91 are used to evaluate the surface energy balance and ablation at an elevation of 100 m asl on the Ecology Glacier, which is an outlet glacier of the main ice cap of King George Island, Antarctica. Strong, gusty westerly winds prevail, although occasional south-easterly winds from the Weddell Sea reach the island. Generally, the climate can be characterized as relatively warm and humid with mean summer temperatures well above 0°C. As a result, considerable ablation (0.75 m water equivalent per month) takes place in the lower parts of the Ecology Glacier. The surface energy balance and ablation are calculated using a model with input from meteorological data. In spite of the large amount of cloud (0.83), solar radiation provided most of the energy used for melting (70.3 W m−2). The longwave radiation, sensible heat flux and latent heat flux contributed −9.5, 27.4 and 7.4 W m−2 respectively. Calculations show that a temperature rise of 1°C increases the ablation by almost 15%. This indicates that the ice caps and glaciers currently present on the subantarctic islands and the Antarctic Peninsula may be quite sensitive to climate change.
TL;DR: In this paper, the authors investigated the heat and mass transfer characteristics along an inclined heated plate over which the water at room temperature flows downward as a film and found that an increase in inclined angle φ, inlet liquid film thickness δ or free stream velocity ϑ causes reductions in the wall and interfacial temperatures.
TL;DR: In this article, the authors developed a technique for independent measurement of soil heat and water vapor transfer coefficients at the soil surface beneath a plant canopy, where heat and vapor source plates were installed level with the ground soil surface to provide areas of known and controllable temperature and/or vapor pressure.
TL;DR: In this paper, the response of the boundary layer over a site with well-defined extreme differences in sensible and latent heat fluxes over clearly separated areas, each with characteristic length scales of 10 km or more.
Abstract: This paper describes results from a June 1992 field program to study the response of the boundary layer over a site with well-defined extreme differences in sensible and latent heat fluxes over clearly separated areas, each with characteristic length scales of 10 km or more. The experiment region consisted of semiarid grassland steppe and irrigated farmland. Sensible heat flux maxima over the steppe regularly reached values in excess of 300 W m−2 and were typically a factor of 4 or more greater than those over the farmland. Two days were selected for analysis: one with moderate winds of 710 m s−1 and one with lighter winds of 47 m s−1 over the steppe. In both cases the wind directions were nearly perpendicular to the boundary between the steppe and farm. An analysis of potential temperature soundings showed that mixed-layer characteristics over both the farm and the steppe were largely determined by heating over the steppe, with advection from the steppe to the farm playing a significant role. ...
TL;DR: In this article, three models of the partitioning of net radiation into latent and sensible heat fluxes over Sahelian savannah are described, each model has a different configuration of stomatal and aerodynamic resistances.
Abstract: Three models of the partitioning of net radiation into latent and sensible heat fluxes over Sahelian savannah are described. Each model has a different configuration of stomatal and aerodynamic resistances. Their performance was assessed by comparison against field measurements of latent heat flux over savannah vegetation consisting of bushes interspersed with a herbaceous understorey. The modelled results indicate that in dry conditions, a Penman-Monteith based single source model performs adequately when predicting the latent heat flux. However, the models with two sources demonstrate that the bushes and herbs have very different responses to local climate. In all the models, evaporation is highly sensitive to stomatal resistance, suggesting that a better understanding of stomatal response would improve the accuracy of the models.
TL;DR: In this article, various theories required to calculate grid-averaged fluxes are discussed, and a two-dimensional mesoscale boundary layer model has been applied to simulate the flow and heat exchange processes inside a single grid element of a hypothetical atmospheric general circulation model.
Abstract: The parameterization of heat and momentum fluxes over a heterogeneous surface consisting of sea ice and large areas of open ocean (polynyas) has been studied. Various theories required to calculate grid-averaged fluxes are discussed, and a two-dimensional mesoscale boundary layer model has been applied to simulate the flow and heat exchange processes inside a single grid element of a hypothetical atmospheric general circulation model. The theories are compared with model results. Considering the surface fluxes of sensible and latent heat, a mosaic method, based on the use of estimates for local surface temperature, air temperature, specific humidity, and wind speed over the ice-covered and ice-free parts of the grid square, performed well in the comparison. Parameterizing the net longwave radiation, an estimate for the subgrid distribution of cloudiness was useful. Parameterization of surface momentum flux seemed to be most reasonable on the basis of the surface pressure field and a geostrophic drag coefficient depending on the air-surface temperature difference.
TL;DR: In this paper, a four-variable land-atmosphere model is developed to investigate the coupled exchanges of water and energy between the land surface and atmosphere and the role of these exchanges in the statistical behavior of continental climates.
Abstract: A four-variable land-atmosphere model is developed to investigate the coupled exchanges of water and energy between the land surface and atmosphere and the role of these exchanges in the statistical behavior of continental climates. The land-atmosphere system is substantially simplified and formulated as a set of ordinary differential equations that, with the addition of random noise, are suitable for analysis in the form of the multivariate Ito equation. The model treats the soil layer and the near-surface atmosphere as reservoirs with storage capacities for heat and water. The transfers between these reservoirs are regulated by four states: soil saturation, soil temperature, air specific humidity, and air potential temperature. The atmospheric reservoir is treated as a turbulently mixed boundary layer of fixed depth. Heat and moisture advection, precipitation, and layer-top air entrainment are parameterized. The system is forced externally by solar radiation and the lateral advection of air and water mass. The remaining energy and water mass exchanges are expressed in terms of the state variables. The model development and equilibrium solutions are presented. Although comparisons between observed data and steady state model results re inexact, the model appears to do a reasonable job of partitioning net radiation into sensible and latent heat flux in appropriate proportions for bare-soil midlatitude summer conditions. Subsequent work will introduce randomness into the forcing terms to investigate the effect of water-energy coupling and land-atmosphere interaction on variability and persistence in the climatic system.
TL;DR: In this article, the authors examined the relationship between surface heat flux and the time rate of change of sea surface temperature (SST tendency) using the singular value decomposition (SVD) analysis.
Abstract: Large scale relationships between surface heat flux (defined as the sum of sensible and latent heat fluxes at sea surface) and the atmospheric circulation in the Northern Hemisphere during the northern winter have been examined, using the singular value decomposition (SVD) analysis. The dominant heat flux anomaly pattern in the North Pacific has large amplitude in the western and the central part of the subtropical gyre, and the one in the North Atlantic exhibits a north-south seesaw in the western Atlantic. These patterns are closely related to the dominant atmospheric circulation anomaly patterns known as the teleconnection patterns, i.e., the dominant surface heat flux pattern in the North Pacific is related to the Pacific/North American (PNA) teleconnection pattern and the one in the North Atlantic is tied to the Western Atlantic (WA) pattern (Wallace and Gutzler, 1981). Variations with a time scale of a few years are dominant in time coefficients of the leading SVD modes for both oceans. Decadal scale or trend-like variation is also seen in those for the North Pacific but is not apparent for the North Atlantic. We also investigated the relation between the surface heat flux and the time rate of change of sea surface temperature (SST tendency). Local correlation coefficients between them are generally high but not close to unity. This suggests that the SST tendency is determined not only by the surface heat flux but also by other processes such as horizontal temperature advection and vertical mixing in the upper ocean. The spatial patterns of the first SVD mode for the surface heat flux and the SST tendency in each ocean are quite similar. They also resemble the heat flux patterns of the first SVD mode paired with atmospheric variables such as 500 hPa height in each ocean. This indicates that the dominant pattern of the SST tendency in each ocean is organized by the dominant large scale atmospheric circulation pattern such as the PNA teleconnection pattern.