Showing papers on "Latent heat published in 2002"
Oak Ridge National Laboratory1, University of California, Berkeley2, Institut national de la recherche agronomique3, University of Amsterdam4, Carnegie Institution for Science5, Swedish University of Agricultural Sciences6, University of Göttingen7, Oregon State University8, University of Edinburgh9, University of Colorado Boulder10, San Diego State University11, University of Nebraska–Lincoln12
TL;DR: A comprehensive evaluation of energy balance closure is performed across 22 sites and 50 site-years in FLUXNET, a network of eddy covariance sites measuring long-term carbon and energy fluxes in contrasting ecosystems and climates as mentioned in this paper.
2,052 citations
TL;DR: In this paper, the global scale wave model (GSWM) is used to investigate mesospheric and lower thermospheric migrating and non-migrating diurnal tidal components that propagate upward from the troposphere, where they are excited by latent heat release associated with deep tropical convection.
Abstract: [1] The global-scale wave model (GSWM) is used to investigate mesospheric and lower thermospheric migrating and nonmigrating diurnal tidal components that propagate upward from the troposphere, where they are excited by latent heat release associated with deep tropical convection. Our diurnal tidal forcing parameterization is derived from a 7-year database of global cloud imagery. The GSWM migrating response is sufficiently large to modulate the dominant radiatively excited migrating diurnal tide in the middle and upper atmosphere during every month of the year. Five additional nonmigrating diurnal components, the eastward propagating zonal wave numbers 2 and 3, the westward propagating zonal wave number 2, and the standing oscillations, also introduce significant longitudinal variability of the diurnal tide in these regions. The comparative importance of the nonmigrating components evolves from month to month and varies with tidal field. Our GSWM investigation suggests that other dynamical models must account for the tropospheric latent heat source in order to make realistic predictions of the diurnal tide in the middle and upper atmosphere.
789 citations
TL;DR: In this paper, a new statistical model is used to estimate fresh snow density as a function of the measured atmospheric conditions and a statistical model for the snow albedo, which is necessary to determine the absorbed radiation.
492 citations
TL;DR: In this paper, a linked set of simple equations specifically designed to calculate heat fluxes for the urban environment is presented, which has similarities to the hybrid plume dispersion model (HPDM) scheme.
Abstract: A linked set of simple equations specifically designed to calculate heat fluxes for the urban environment is presented. This local-scale urban meteorological parameterization scheme (LUMPS), which has similarities to the hybrid plume dispersion model (HPDM) scheme, requires only standard meteorological observations and basic knowledge of surface cover. LUMPS is driven by net all-wave radiation. Heat storage by the urban fabric is parameterized from net all-wave radiation and surface cover information using the objective hysteresis model (OHM). The turbulent sensible and latent heat fluxes are calculated using the available energy and are partitioned using the approach of de Bruin and Holtslag, and Holtslag and van Ulden. A new scheme to define the Holtslag and van Ulden α and β parameters for urban environments is presented; α is empirically related to the plan fraction of the surface that is vegetated or irrigated, and a new urban value of β captures the observed delay in reversal of the sign of...
384 citations
TL;DR: In this paper, the effects of large-scale human modification of land cover on regional and global climate were investigated using a general circulation model coupled with a biophysically-based land surface model.
Abstract: This study investigates the effects of large-scale human modification of land cover on regional and global climate. A general circulation model (Colorado State University GCM) coupled to a biophysically-based land surface model (SiB2) was used to run two 15-yr climate simulations. The control run used current vegetation distribution as observed by satellite for the year 1987 to derive the vegetation's physiological and morphological properties. The twin simulation used a realistic approximation of vegetation type distribution that would exist in the absence of human disturbance.In temperate latitudes, where anthropogenic modification of the landscape has converted large areas of forest and grassland to cropland, conversion cools canopy temperatures up to 0.7 ° C in summer and 1.1 ° C in winter. This cooling results from both (1) morphological changes in vegetation which increase albedo and (2) physiological changes in vegetation which increase latent heat flux of crops compared with undisturbed vegetation during the growing season. In the tropics and subtropics, conversion warms canopy temperature by about 0.8 ° C year round. The warming results from a combination of morphological changes in vegetation offset by physiological changes that reduce latent heat flux of existing compared with undisturbed vegetation. If water efficient, tropical C4 grasses replace C3 vegetation, latent heat flux is further reduced.The overall effect of land cover conversion is cooling in temperate latitudes and warming in the tropics. Because the effects are opposite in sign in tropics and middle latitudes, they cancel each other when averaged globally. Over land, the surface temperature increased by 0.2 C in winter and remained essentially unchanged in summer. The effects on land surface hydrology were also small when averaged globally. The results suggest that the effects of land use change of the observed magnitude do not have a strong impact on the globally averaged climate but their signature at regional scales is significant and vary according to the type of land cover conversion.
341 citations
TL;DR: In this paper, the energy and water budgets of a tropical rain forest near Manaus, Brazil, in central Amazonia, collected between September 1995 and August 1996, were measured using a three-dimensional eddy covariance system mounted above the forest canopy.
Abstract: [1] This paper presents measurements of the energy and water budgets of a tropical rain forest near Manaus, Brazil, in central Amazonia, collected between September 1995 and August 1996. Fluxes of sensible and latent heat were measured using a three-dimensional eddy covariance system mounted above the forest canopy. Using a new approach to analysis of eddy covariance data, we found that the measured fluxes increased significantly when turbulent transport on timescales of 1 to 4 hours was taken into account. With this new analysis, the measured turbulent fluxes almost balanced the incoming net radiation, giving increased confidence in the accuracy of the measured fluxes. Of the 5.56 GJ m−2 yr−1 of solar radiation supplied over the year, 11% were reflected, 15% were lost as net thermal emission, 27% were transported through sensible heat convection, 46% used in evapotranspiration, and 0.5% were used in net carbon fixation. Total annual evapotranspiration was calculated to be 1123 mm, accounting for 54% of total precipitation. Seasonality was an important influence: limited water availability during the dry season caused evapotranspiration to reduce by 50%. Total canopy conductance was linearly correlated to soil moisture content, with typical midday values ranging between 0.8 mol m−2 s−1 in the wet season and 0.3 mol m−2 s−1 in the dry season. Such seasonal behavior is likely to be prevalent in most tropical forest regions, and correct description of dry-season evapotranspiration will require accurate modeling of plant and soil hydraulic properties and knowledge of root distributions.
326 citations
TL;DR: In this paper, the eddy covariance technique was used to measure evapotranspiration and sensible heat flux continuously for 2.5 years (three growing seasons) in a northern grassland near Lethbridge, Alta., Canada.
303 citations
TL;DR: In this article, a time series of meteorological surface layer observational data taken on board the R/V Knorr was compared with model analysis data from the European Centre for Medium-Range Weather Forecasting (ECMWF) and the National Centers for Environmental Prediction (NCEP).
Abstract: Comparisons are made between a time series of meteorological surface layer observational data taken on board the R/V Knorr, and model analysis data from the European Centre for Medium-Range Weather Forecasting (ECMWF) and the National Centers for Environmental Prediction (NCEP). The observational data were gathered during a winter cruise of the R/V Knorr, from 6 February to 13 March 1997, as part of the Labrador Sea Deep Convection Experiment. The surface layer observations generally compare well with both model representations of the wintertime atmosphere. The biases that exist are mainly related to discrepancies in the sea surface temperature or the relative humidity of the analyses.
The surface layer observations are used to generate bulk estimates of the surface momentum flux, and the surface sensible and latent heat fluxes. These are then compared with the model-generated turbulent surface fluxes. The ECMWF surface sensible and latent heat flux time series compare reasonably well, with overestimates of only 13% and 10%, respectively. In contrast, the NCEP model overestimates the bulk fluxes by 51% and 27%, respectively. The differences between the bulk estimates and those of the two models are due to different surface heat flux algorithms. It is shown that the roughness length formula used in the NCEP reanalysis project is inappropriate for moderate to high wind speeds. Its failings are acute for situations of large air–sea temperature difference and high wind speed, that is, for areas of high sensible heat fluxes such as the Labrador Sea, the Norwegian Sea, the Gulf Stream, and the Kuroshio. The new operational NCEP bulk algorithm is found to be more appropriate for such areas.
It is concluded that surface turbulent flux fields from the ECMWF are within the bounds of observational uncertainty and therefore suitable for driving ocean models. This is in contrast to the surface flux fields from the NCEP reanalysis project, where the application of a more suitable algorithm to the model surface-layer meteorological data is recommended
213 citations
Journal Article•
TL;DR: A regional coupled ocean-atmosphere-ice general circulation model for northern Europe is introduced for climate study purposes as discussed by the authors, which is validated in a 5-year hindcast experiment with a focus on surface quantities and atmosphere-ocean heat fluxes.
Abstract: A regional coupled ocean-atmosphere-ice general circulation model for northern Europe is introduced for climate study purposes. The Baltic Sea is interactively coupled. The coupled model is validated in a 5-year hind-cast experiment with a focus on surface quantities and atmosphere-ocean heat fluxes. The coupled sea surface temperature matches observations well. The system is free of drift, does not need flux corrections and is suitable for multi-year climate runs. With flux forcing from the atmospheric model the regional ocean model gives sea surface temperatures statistically equivalent to the uncoupled ocean model forced by observations. Other oceanic surface quantities do not reach this quality in combination with the current atmosphere model. A strong dependence of sea ice extent on details of the atmospheric radiation scheme is found. Our standard scheme leads to an overestimation of ice, most likely due to a negative bias of long-wave radiation. There is indication that a latent heat flux bias in fall contributes to the ice problem. Other atmosphere-ocean heat fluxes are generally realistic in the long term mean.
204 citations
TL;DR: In this paper, the authors constructed ocean surface data sets using mainly satellite data and called them Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO) The data sets include shortwave radiation, long wave radiation, latent heat flux, sensible heat flux and momentum flux etc.
Abstract: We have constructed ocean surface data sets using mainly satellite data and called them Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO) The data sets include shortwave radiation, longwave radiation, latent heat flux, sensible heat flux, and momentum flux etc This article introduces J-OFURO and compares it with other global flux data sets such as European Centre for Medium Range Weather Forecasting (ECMWF) and National Center for Environmental Prediction (NCEP) reanalysis data and da Silva et al (1994) The usual ECMWF data are used for comparison of zonal wind The comparison is carried out for a meridional profile along the dateline for January and July 1993 Although the overall spatial variation is common for all the products, there is a large difference between them in places J-OFURO shortwave radiation in July shows larger meridional contrast than other data sets On the other hand, J-OFURO underestimates longwave radiation flux at low- and mid-latitudes in the Southern Hemisphere J-OFURO latent heat flux in January overestimates at 10°N–20°N and underestimates at 25°N–40°N Finally, J-OFURO shows a larger oceanic net heat loss at 10°N–20°N and a smaller loss north of 20°N in January The data of da Silva et al in July show small net heat loss around 20°S and large gain around 20°N, while the NCEP reanalysis (NRA) data show the opposite The da Silva et al zonal wind speed overestimates at low-latitudes in January, while ECMWF wind data seem to underestimate the easterlies
176 citations
TL;DR: In this article, the reversible Mg 2 FeH 6 and the mixed Mg2 FeH6 and MgH 2 hydride systems were investigated on a micro- or nanoscale level.
TL;DR: In this paper, the authors measured the energy budget of a subalpine coniferous forest over two complete annual cycles and found that the energy balance was slightly better in the winter as opposed to summer, since numerous periods of high turbulence occur in winter.
TL;DR: In this article, a simple model for the size dependence of latent heat, free of any adjustable parameter, has been extended to the case when the size of the particles decreases to several nanometers.
TL;DR: In this article, the inner-core budgets of potential temperature, moisture, and equivalent potential temperature (e) were examined using a high-resolution (Δx = 6 km), non-hydrostatic, fully explicit simulation of Hurricane Andrew (1992) during its mature or intensifying stage.
Abstract: Although considerable progress has been made in understanding the development of hurricanes, our knowledge of their three-dimensional structures of latent heat release and inner-core thermodynamics remains limited. In this study, the inner-core budgets of potential temperature (θ), moisture (q), and equivalent potential temperature (θe) are examined using a high-resolution (Δx = 6 km), nonhydrostatic, fully explicit simulation of Hurricane Andrew (1992) during its mature or intensifying stage. It is found that the heat energy is dominated by latent heat release in the eyewall, sublimative–evaporative cooling near the eye–eyewall interface, and the upward surface fluxes of sensible and latent heat from the underlying warm ocean. The latent heating (θ) rates in the eyewall range from less than 10°C h–1 to greater than 100°C h–1, depending upon whether latent heat is released in radial inflow or outflow regions. The latent heating rates decrease inward in the inflow regions and become negative near ...
TL;DR: In this article, the eutectic composition ratio of the lauric acid and stearic acid binary system was determined experimentally in a vertical two concentric pipe-energy storage system.
TL;DR: In this article, the entropy budget of the water substance provided an alternative method of determining the irreversible entropy production due to phase changes and diffusion of water vapor, and it was also shown that diffusion can be interpreted as the irreversible counterpart to the continuous dehumidification resulting from condensation and precipitation.
Abstract: In moist convection, atmospheric motions transport water vapor from the earth’s surface to the regions where condensation occurs. This transport is associated with three other aspects of convection: the latent heat transport, the expansion work performed by water vapor, and the irreversible entropy production due to diffusion of water vapor and phase changes. An analysis of the thermodynamic transformations of atmospheric water yields what is referred to as the entropy budget of the water substance, providing a quantitative relationship between these three aspects of moist convection. The water vapor transport can be viewed as an imperfect heat engine that produces less mechanical work than the corresponding Carnot cycle because of diffusion of water vapor and irreversible phase changes. The entropy budget of the water substance provides an alternative method of determining the irreversible entropy production due to phase changes and diffusion of water vapor. This method has the advantage that it does not require explicit knowledge of the relative humidity or of the molecular flux of water vapor for the estimation of the entropy production. Scaling arguments show that the expansion work of water vapor accounts for a small fraction of the work that would be produced in the absence of irreversible moist processes. It is also shown that diffusion of water vapor and irreversible phase changes can be interpreted as the irreversible counterpart to the continuous dehumidification resulting from condensation and precipitation. This leads to a description of moist convection where it acts more as an atmospheric dehumidifier than as a heat engine.
TL;DR: In this paper, the authors investigated the role of oceanic dynamics and surface heat fluxes in the initiation and development of the Indian Ocean dipole by analyzing results from an oceanic general circulation model.
Abstract: [1] The relative role of oceanic dynamics and surface heat fluxes in the initiation and development of the Indian Ocean dipole was investigated by analyzing results from an oceanic general circulation model. The model was forced by observed surface wind stress and heat flux fields for 1958–1997. The results show that it was capable of reproducing observed dipole events over the tropical Indian Ocean. The diagnosis of the mixed-layer heat budget indicates that the SST anomaly (SSTA) in the east pole is primarily induced by anomalous surface latent heat flux and vertical temperature advection, whereas in the west pole it is mainly caused by meridional and vertical temperature advection anomalies. In both regions shortwave radiation anomalies tend to damp the SSTA. The ocean Rossby waves are essential in linking the anomalous wind and SST off Sumatra and subsurface temperature variations in southwest Indian Ocean.
TL;DR: In this paper, the authors present an efficient algorithm for solving nonlinear heat problems involving phase change. But the authors do not consider the nonlinearity of the phase change problem in this paper.
TL;DR: Schmidt and Haberland as discussed by the authors studied the solid to liquid transition of clusters, mainly from an experimental point of view, and showed that the melting temperatures are about 30% less than the bulk value and fluctuate strongly, one additional atom can change it by ±10 K.
TL;DR: In this paper, a model of a moist equatorial atmosphere is presented in which the precipitation rate is assumed to depend on just the vertically averaged saturation deficit and the convective available potential energy.
Abstract: A minimal model of a moist equatorial atmosphere is presented in which the precipitation rate is assumed to depend on just the vertically averaged saturation deficit and the convective available potential energy. When wind-induced surface heat exchange (WISHE) and cloud–radiation interactions are turned off, there are no growing modes. Gravity waves with wavenumbers smaller than a certain limit respond to a reduced static stability due to latent heat release, and therefore propagate more slowly than dry modes, while those with larger wavenumbers respond to the normal dry static stability. In addition, there exists a stationary mode that decays slowly with time. For realistic parameter values, the effect of reduced static stability on gravity waves is limited to wavelengths greater than the circumference of the earth. WISHE and cloud–radiation interactions both destabilize the stationary mode, but not the gravity waves.
TL;DR: In this paper, the surface energy budget of coastal polynyas in the southern Weddell Sea has been evaluated for the period 1992-1998 using a combination of satellite observations, meteorological data, and simple physical models.
Abstract: [1] The surface energy budget of coastal polynyas in the southern Weddell Sea has been evaluated for the period 1992–1998 using a combination of satellite observations, meteorological data, and simple physical models. The study focuses on polynyas that habitually form off the Ronne Ice Shelf. The coastal polynya areal data are derived from an advanced multichannel polynya detection algorithm applied to passive microwave brightness temperatures. The surface sensible and latent heat fluxes are calculated via a fetch-dependent model of the convective-thermal internal boundary layer. The radiative fluxes are calculated using well-established empirical formulae and an innovative cloud model. Standard meteorological variables that are required for the flux calculations are taken from automatic weather stations and from the National Centers for Environmental Production/National Center for Atmospheric Research reanalyses. The 7 year surface energy budget shows an overall oceanic warming due to the presence of coastal polynyas. For most of the period the summertime oceanic warming, due to the absorption of shortwave radiation, is approximately in balance with the wintertime oceanic cooling. However, the anomalously large summertime polynya of 1997–1998 allowed a large oceanic warming of the region. Wintertime freezing seasons are characterized by episodes of high heat fluxes interspersed with more quiescent periods and controlled by coastal polynya dynamics. The high heat fluxes are primarily due to the sensible heat flux component, with smaller complementary latent and radiative flux components. The average freezing season area-integrated energy exchange is 3.48 × 1019 J, with contributions of 63, 22, and 15% from the sensible, latent, and radiative components, respectively. The average melting season area-integrated energy exchange is −5.31 × 1019 J, almost entirely due to the radiative component. There is considerable interannual variability in the surface energy budget. The standard deviation of the energy exchange during the freezing (melting) season is 28% (95%) of the mean. During the freezing season, positive surface heat fluxes are equated with ice production rates. The average annual coastal polynya ice production is 1.11 × 1011 m3 (or 24 m per unit area), with a range from 0.71 × 1011 (in 1994) to 1.55 × 1011 m3 (in 1995). This can be compared to the estimated total ice production for the entire Weddell Sea: on average the coastal polynya ice production makes up 6.08% of the total, with a range from 3.65 (in 1994) to 9.11% (in 1995).
TL;DR: In this article, the authors investigated the effect of microporous coating on the nucleate pool boiling and found that the coating significantly increased the critical heat flux for a plain surface due to decreased latent heat transfer and increased hydrodynamic stability from increased vapor incrtia.
Abstract: The present study is an experimental investigation of the nucleate pool boiling heat transfer enhancement mechanism of microporous surfaces immersed in saturated FC-72. Measurements of bubble size, frequency, and vapor flow rate from a plain and microporous coated 390 μm diameter platinum wire using the consecutive-photo method were taken to determine the effects of the coating on the convective and latent heat transfer mechanisms. Results of the study showed that the microporous coating augments nucleate boiling performance through increased latent heat transfer in the low heat flux region and through increased convection heat transfer in the high heat flux region. The critical heat flux for the microporous coated surface is significantly enhanced over the plain surface due to decreased latent heat transfer (decreased vapor generation rate) and/or increased hydrodynamic stability from increased vapor incrtia; both of which are a direct result of increased nucleation site density.
TL;DR: In this paper, the surface heat budget over the Weddell Sea ice cover in 1996 was studied on the basis of data from Argos buoys equipped with meteorological sensors.
Abstract: [1] The surface heat budget over the Weddell Sea ice cover in 1996 was studied on the basis of data from Argos buoys equipped with meteorological sensors. In addition, a thermodynamic sea ice model, satellite-based data on the sea ice concentration, sonar results on ice thickness distribution, and output from large-scale meteorological models were all utilized. Applying the buoy data, the sensible heat flux over sea ice was calculated by Monin-Obukhov theory using the gradient method, and the latent heat flux was obtained by the bulk method. A second estimate for the surface fluxes was obtained from the thermodynamic sea ice model, which was forced by the buoy observations. The results showed a reasonable agreement. The dominating component in the heat budget over ice was the net longwave radiation, which had a mean annual cooling effect of −28 W m−2. This was balanced by the net shortwave radiation (annual mean 13 W m−2), the sensible (13 W m−2) and latent (−3 W m−2) heat fluxes, and the conductive heat flux through the ice (5 W m−2). The regional surface fluxes over the fractured ice cover were estimated using the buoy data and Special Sensor Microwave Imager (SSMI)-derived ice concentrations. In winter the regional surface sensible heat flux was sensitive to the ice concentration and thickness distribution. The estimate for the area-averaged formation rate of new ice in leads in winter varies from 0.05 to 0.21 m per month depending on the SSMI processing algorithm applied. Countergradient fluxes occurred 8–10% of the time. The buoy observations were compared with the operational analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the reanalyses of the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR). The 2 m air temperature and surface temperature were 3.5° and 4.4°C too high, respectively, in the ECMWF and 3.2° and 3.0°C too low in the NCEP/NCAR fields, but the models reproduced the synoptic-scale temperature variations well. The errors seem to be related to the cloud cover and the surface boundary conditions. Neither of the models recognizes leads in the ice pack, and the ice and snow thicknesses are often far from reality. The distribution of the cloud cover in the both models differed a lot from observations.
TL;DR: In this article, a two-dimensional coupled heat and mass transfer model is presented to simulate the heat transfer in a desiccant wheel, which takes into account the resistance in the solid in both the axial and the thickness directions.
TL;DR: In this article, the authors compared the global scale wave model (GSWM) and the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) for the observed diurnal wave signatures.
Abstract: [1] Temperature measurements from the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment taken during the U.S. Space Shuttle mission STS-66 in November 1994 provide a variety of zonally symmetric and asymmetric tidal signatures in the altitude range from 40–90 km. The most prominent zonally asymmetric tidal pattern is identified to be the westward propagating nonmigrating diurnal tide of zonal wavenumber 2 (s = −2). This mode has an amplitude of approximately half the amplitude of the migrating (s = −1) component of the diurnal tide. The observational findings are compared to model results from the Global Scale Wave Model (GSWM) and from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM). GSWM and TIME-GCM account for different tidal sources and therefore allow an analysis of the tidal forcing responsible for the observed signatures. The GSWM tidal forcing in the model version used is based upon latent heat release associated with tropical deep convection while nonmigrating tides in the TIME-GCM are predominantly forced by nonlinear interactions between the migrating diurnal tide and stationary planetary waves. It is shown that the latter mechanism forces a large part of the s = −2 mode while the stationary, zonally uniform (s = 0) diurnal nonmigrating tide is mainly driven by latent heat release. This result suggests that dynamical models for the mesosphere/lower thermosphere (MLT) region need to account for the tropospheric latent heat source and stationary planetary wave activity in order to predict realistic longitudinal diurnal tidal variability.
TL;DR: In this article, the vertical fluxes of mass, momentum, and energy were derived from point measurements in a horizontally homogeneous atmosphere, and a formula for the mean vertical velocity was found that is accurate to the ideal gas approximation.
Abstract: In a horizontally homogeneous atmosphere, the calculation of thevertical fluxes of mass, momentum, and heat from point measurementsare to lowest order calculated as the standard eddy covariance.Additional terms primarily related to the mean vertical velocity areadded to improve the accuracy of the calculation. A review ofprevious work is undertaken. The fluxes are reformulated beginningwith the equations of conservation of mass, momentum, and energy. Aformula for the mean vertical velocity is found that is accurate tothe ideal gas approximation. Relations are developed between fluxesat different heights. In addition to the relations for fluxes ofmass, sensible heat, and latent heat, the fluxes of momentum andturbulent kinetic energy are also considered.
TL;DR: In this article, the authors presented data of nine Automatic Weather Stations (AWS) which are located in Dronning Maud Land (DML), East Antarctica, since the austral summer of 1997.
Abstract: [1] We present data of nine Automatic Weather Stations (AWS), which are located in Dronning Maud Land (DML), East Antarctica, since the austral summer of 1997. Potential temperature and wind speed are maximum at the sites with the steepest surface slope, i.e., at the edge of the Antarctic plateau. Specific humidity and accumulation decrease with elevation and distance from the coast. The annual average energy gain at the surface from the downward sensible heat flux varies between ∼3 W m−2 and ∼25 W m−2, with the highest values at the sites with the largest surface inclination and wind speeds. The net radiative flux is negative and largely balances this sensible heat flux and ranges from ∼−2 W m−2 to ∼−28 W m−2; maximum values can be linked to maxima in surface slope and wind speed, and suggest a strong connection between the heat budget and the katabatic flow in DML. The average latent heat flux is generally small and negative (∼−1 W m−2) indicating a slight net mass loss through sublimation.
TL;DR: In this paper, the authors used the Gutman-Ignatov (G-I) and the Carlson-Ripley (C-R) schemes to compute the vegetation fraction.
Abstract: [1] Oklahoma Atmospheric Surface-Layer Instrumentation System (OASIS) measurements of net radiation (Rn), latent heat flux (LH), sensible heat flux (SH), and ground heat flux (GH) were used to validate the NOAH-Oregon State University Land Surface Model (NOAH-OSU LSM). A 1-year study period was used. Rn, LH, SH and GH data from seven sites were screened based on an energy balance closure criterion (daily/hourly sum of the flux components within the range of −10 to +10 W m−2). The vegetation fraction used in the model was computed using both the Gutman-Ignatov (G-I) and the Carlson-Ripley (C-R) schemes. The simulated net radiation and ground heat fluxes seem less sensitive to the choice of schemes for computing green vegetation fraction, while latent and sensible heat flux show more sensitivity particularly for soil dry-down period. Therefore, the G-I approach was used for the validation study, as it is widely used and linear in its form. The daily aggregated model outputs showed that the predicted Rn had a positive bias of 0.8 MJ m−2 d−1 and an RMSE of 1.6 MJ m−2 d−1 when averaged over all seven sites. The seven-site average bias in LH was about 0.9 MJ m−2 d−1 with an RMSE of 2.5 MJ m−2 d−1. The bias in SH and GH was low and positive with an RMSE of about 2.2 MJ m−2 d−1 in SH estimation. The hourly average output showed similar results, with the exception that GH had a negative bias. The overall performance of the NOAH-OSU LSM was good for a diverse set of Oklahoma conditions.
TL;DR: In this article, the authors investigated the evolution of a severe storm and flood event that occurred over the southern coastal regions of South Africa on 14-15 December 1998 using NCEP reanalyses, Meteosat, and Tropical Rainfall Measuring Mission (TRMM) satellite data and local station and radiosonde observations.
Abstract: Ocean‐atmosphere interaction above warm western boundary currents such as the Gulf Stream, the Kuroshio Current, and the Agulhas Current often leads to very high evaporation rates. In the case of the Agulhas Current, which flows just off the southeast coast of Africa, such high latent heat fluxes may lead to increased low-level advection of moisture onshore and local intensification of storm systems. Observational evidence for the significant latent heat fluxes in the Agulhas Current area was obtained during the Agulhas Current Air Sea Exchange Experiment, which showed that about 5 times as much water vapor is transferred to the atmosphere above the 80‐100-km-wide core of the current than from the neighboring waters. Using NCEP reanalyses, Meteosat, and Tropical Rainfall Measuring Mission (TRMM) satellite data and local station and radiosonde observations, this study investigates the evolution of a severe storm and flood event that occurred over the southern coastal regions of South Africa on 14‐15 December 1998. Heavy rainfall occurred in two widely separated locations, and tornadoes were reported. Moisture flux transects through the storm region and backward trajectories of air parcels suggest that low-level onshore flow of moisture from the Agulhas Current region played a significant role in the storm evolution. However, because the NCEP data on which these moisture fluxes are based are known to significantly underestimate the surface latent heat flux when compared with ship observations, it is suggested that the actual contribution of the Agulhas Current moisture source to the storm may have been even greater than is documented in this paper.
TL;DR: Energy and latent heat fluxes were measured over ombrotrophic bogs in European Russia (Fyodorovskoye) and in central Siberia (Zotino) using the eddy covariance technique, as part of the EuroSiberian Carbonflux Project as mentioned in this paper.
Abstract: Energy and latent heat fluxes λ E were measured over ombrotrophic bogs in European Russia (Fyodorovskoye) and in central Siberia (Zotino) using the eddy covariance technique, as part of the EuroSiberian Carbonflux Project. The study covered most of the snowfree periods in 1998, 1999 and 2000; in addition some data were also collected under snow in early spring and late autumn 1999 and 2000. The snowfree period in Europian Russia exceeds the snowfree period in central Siberia by nearly 10 weeks. Marked seasonal and interannual differences in temperatures and precipitation, and hence energy partitioning, were observed at both sites. At both bogs latent heat fluxes (λ E ) exceeded sensible heat fluxes ( H ) during most of the snowfree period: maximum λ E were between 10 and 12 MJ m −2 d −1 while maximum H were between 3 and 5 MJ m −2 d −1 . There was a tendency towards higher Bowen ratios at Fyodorovskoye. Net radiation was the most influential variable that regulated daily evaporation rates, with no obvious effects due to surface dryness during years with exceptionally dry summers. Total snowfree evaporation at Fyodorovskoye (320 mm) exceeded totals at Zotino (280 mm) by 15%. At the former site, evaporation was equal to or less than precipitation, contrasting the Zotino observations, where summer evaporation was distinctly higher than precipitation. During the entire observation period evaporation rates were less than 50% of their potential rate. These data suggest a strong ‘mulching’ effect of a rapidly drying peat surface on total evaporation, despite the substantial area of free water surfaces during parts of the year. This effect of surface dryness was also observed as close atmospheric coupling. DOI: 10.1034/j.1600-0889.2002.01354.x