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1.
Latent and sensible heat flux predictions from a uniform pine forest using surface renewal and flux variance methods 总被引：1，自引：0，他引：1
Gabriel Katul Cheng-I Hsieh Ram Oren David Ellsworth Nathan Phillips 《Boundary-Layer Meteorology》1996,80(3):249-282
A surface renewal model that links organized eddy motion to the latent and sensible heat fluxes is tested with eddy correlation measurements carried out in a 13m tall uniform Loblolly pine plantation in Duke Forest, Durham, North Carolina. The surface renewal model is based on the occurance of ramp-like patterns in the scalar concentration measurements. To extract such ramp-like patterns from Eulerian scalar concentration measurements, a newly proposed time-frequency filtering scheme is developed and tested. The time-domain filtering is carried out using compactly-supported orthonormal wavelets in conjunction with the Universal Wavelet Thresholding approach of Donoho and Johnstone, while the frequency filtering is carried out by a band-pass sine filter centered around the ramp-occurrence frequency as proposed by other studies. The method was separately tested for heat and water vapour with good agreement between eddy correlation flux measurements and model predictions. The usefulness of the flux-variance method to predict sensible and latent heat fluxes is also considered. Our measurements suggest that the simple flux-variance method reproduces the measured heat and momentum fluxes despite the fact that the variances were measured within the roughness sublayer and not in the surface layer. Central to the predictions of water vapour fluxes using the flux-variance approach is the similarity between heat and water vapour transport by the turbulent air flow. This assumption is also investigated for this uniform forest terrain. 相似文献
2.
W. M. L. Meijninger A. E. Green O. K. Hartogensis W. Kohsiek J. C. B. Hoedjes R. M. Zuurbier H. A. R. De Bruin 《Boundary-Layer Meteorology》2002,105(1):63-83
A large aperture scintillometer (LAS) andradio wave scintillometer (RWS)were installed over a heterogeneous areato test the applicability of the scintillation method.The heterogeneity in the area, whichconsisted of many plots, was mainly caused bydifferences in thermal properties ofthe crops; the variations in theaerodynamic roughness lengthwere small. The water vapour fluxesderived from the combined LAS-RWSsystem, also known as the two-wavelengthmethod, agreed fairly well with the aggregatedwater vapour fluxes derived from in-situeddy covariance measurements. The water vapourfluxes derived from a stand-alone LASare also presented. It was found that a single LASand an estimate of the area averagedavailable energy (using a simple parameterisationscheme) can provide also reasonablearea-averaged water vapour fluxes. 相似文献
3.
Mean Profiles of Moisture Fluxes in Snow-Filled Boundary Layers 总被引：1，自引：0，他引：1
Profiles of moisture fluxes have been examined for convective boundary layers containing clouds and snow, using data derived from aircraft measurements taken on four dates during the 1983/1984 University of Chicago lake-effect snow project. Flux profiles were derived from vertical stacks of aircraft cross-wind flight legs taken at various heights over Lake Michigan near the downwind shore. It was found that, if ice processes are taken into account, profiles of potential temperature and water content were very similar to those presented in past studies of convective boundary layers strongly heated from below. Profiles of total water content and equivalent potential temperature adjusted for ice were nearly invariant with height, except very near the top of the boundary layer, suggesting that internal boundary-layer mixing processes were rapid relative to the rates at which heat and vapour were transported into the boundary layer through entrainment and surface fluxes. Ice was found to play a significant, measurable role in boundary-layer moisture fluxes. It was estimated that 40 to 57% of the upward vapour flux was returned to the surface in the form of snow, converting about 45 to 64% of the surface latent heat flux into sensible heat in the snow-producing process. Assuming advective fluxes are relatively small (thought to be appropriate after the first few tens of km over the lake as suggested by past studies), the boundary layer was found to warm at a rate faster than could be explained by surface heat fluxes and latent heat releases alone, the remainder of the heating presumably coming from radiational processes and entrainment. Discussions of moisture phase change processes throughout the boundary layer and estimates of errors of these flux measurements are presented. 相似文献
4.
Xia Zhang 《Asia-Pacific Journal of Atmospheric Sciences》2012,48(1):97-105
A soil-atmosphere-transfer model (SATM) was evaluated using observational data from the Tongyu Cropland Station and Audubon Research Ranch in semiarid areas, where the land cover was nearly bare soil during the simulation period. Simulations by the SATM at both sites were conducted using the new and original surface thermal roughness length parameterization schemes, respectively. Comparisons of simulations and observations have demonstrated that using the new surface thermal roughness length scheme in this model made sound improvements in the simulation of soil surface temperatures, sensible heat fluxes and net radiation fluxes in the daytime at both sites, compared to the original scheme, because the new scheme produced a larger aerodynamic resistance for turbulent heat transfer in the daytime. With respect to latent heat fluxes, the improvement was not as obvious as that attained for soil surface temperature since the soil water content in the surface layer in a semiarid area is a more important factor than surface soil temperature in controlling evaporation rate. Accordingly, it can be concluded that the new surface thermal roughness length parameterization scheme could improve the ability of the SATM to simulate bare soil surface energy budget with latent heat flux component being innegligible in semiarid areas. 相似文献
5.
The heat exchange between ocean and atmosphere over cold water is studied by calculating all terms in the energy balance twice each day for the year 1971 for the Sable Island region. The atmospheric long‐wave radiation is relatively constant because of frequent overcast and low clouds. The surface long‐wave balance is markedly negative in winter but slightly positive for a short time in summer, due to strong advection of warm moist air over the cold water. In winter, the turbulent fluxes are directed upwards and are strong, the upward fluxes beginning after the middle of August and lasting until mid‐March. The maximum daily values of latent heat flux are 400 to 500 ly day?1 (194 to 242 W m?2), about a third or a quarter of the magnitude over the warmer Gulf Stream water. The summer fluxes are fairly constant and directed downward. The water of the Labrador Current in the Sable Island region warms substantially from March to September and conversely cools intensely in the period November‐January. A comparison of the energy exchange for a current and for water without motion shows that the surface temperatures would be similar in summer, and the temperature drop would be about equal until November. From that time on, the surface temperature would level off for a water body with no current, but in actual conditions the surface temperature continues to drop to a late winter minimum of about 1°C. Atmospheric advection of latent heat was calculated by assuming that the daily precipitation was always caused first by condensation of all locally evaporated water with any remainder being supplied by water‐vapour advection. The main cause for atmospheric heating in the Sable Island area was found to be condensation of imported water vapour. The region is, in summer, a marked sink for atmospheric heat and water content. For water it remains a sink even in winter. For sensible heat it becomes a source from November to March. The warming of the atmosphere is caused by release of latent heat of advected water vapour in the period February‐August. During the months September‐January the heat sources are both water‐vapour advection and surface turbulent terms. 相似文献
6.
Monin–Obukhov similarity functions for the structure parameters of temperature and humidity are needed to derive surface heat and water vapour fluxes from scintillometer measurements and it is often assumed that the two functions are identical in the atmospheric surface layer. Nevertheless, this assumption has not yet been verified experimentally. This study investigates the dissimilarity between the turbulent transport of sensible heat and water vapour, with a specific focus on the difference between the Monin–Obukhov similarity functions for the structure parameters. Using two datasets collected over homogeneous surfaces where the surface sources of sensible heat and water vapour are well correlated, we observe that under stable and very unstable conditions, the two functions are similar. This similarity however breaks down under weakly unstable conditions; in that regime, the absolute values of the correlations between temperature and humidity are also observed to be low, most likely due to large-scale eddies that transport unsteadiness, advection or entrainment effects from the outer layer. We analyze and demonstrate how this reduction in the correlation leads to dissimilarity between the turbulent transport of these two scalars and the corresponding Monin–Obukhov similarity functions for their structure parameters. A model to derive sensible and latent heat fluxes from structure parameters without measuring the friction velocity is tested and found to work very well under moderately to strongly unstable conditions (−z/L > 0.5). Finally, we discuss the modelling of the cross-structure parameter over wet surfaces, which is crucial for correcting water vapour effects on optical scintillometer measurements and also for obtaining surface sensible and latent heat fluxes from the two-wavelength scintillometry. 相似文献
7.
Abstract A physically‐based numerical model was developed to estimate the temporal course of the surface energy flux densities and the soil temperatures in dry and wet bare soils. Aerodynamic heat, vapour and momentum transfer theory was used to calculate the sensible and latent heat flux densities at the surface under diabatic and adiabatic conditions. A finite‐difference solution of the differential equation describing one‐dimensional heat transfer was used to calculate the surface soil heat flux density and soil profile temperatures. The surface temperature was determined iteratively by the simultaneous solution of equations describing radiative, heat and momentum transfer at the surface. The model was tested with measurements from energy balance studies conducted on a dry, sandy soil and a wet, silt loam soil, and was found to predict accurately the surface energy fluxes and soil temperatures over three‐day periods under conditions of potential and negligible evaporation. The sensitivity of the model to uncertainties in the aerodynamic roughness lengths for momentum (z0) and heat (zT) is reported. Values for z0 and Z0/ZT of 0.5 mm and 3.0, respectively, resulted in the best agreement between modelled and measured values of the fluxes and temperatures for both soils. 相似文献
8.
Dissimilarity of Scalar Transport in the Convective Boundary Layer in Inhomogeneous Landscapes 总被引：1，自引：1，他引：0
A land-surface model (LSM) is coupled with a large-eddy simulation (LES) model to investigate the vegetation-atmosphere exchange
of heat, water vapour, and carbon dioxide (CO2) in heterogeneous landscapes. The dissimilarity of scalar transport in the lower convective boundary layer is quantified
in several ways: eddy diffusivity, spatial structure of the scalar fields, and spatial and temporal variations in the surface
fluxes of these scalars. The results show that eddy diffusivities differ among the three scalars, by up to 10–12%, in the
surface layer; the difference is partly attributed to the influence of top-down diffusion. The turbulence-organized structures
of CO2 bear more resemblance to those of water vapour than those of the potential temperature. The surface fluxes when coupled with
the flow aloft show large spatial variations even with perfectly homogeneous surface conditions and constant solar radiation
forcing across the horizontal simulation domain. In general, the surface sensible heat flux shows the greatest spatial and
temporal variations, and the CO2 flux the least. Furthermore, our results show that the one-dimensional land-surface model scheme underestimates the surface
heat flux by 3–8% and overestimates the water vapour and CO2 fluxes by 2–8% and 1–9%, respectively, as compared to the flux simulated with the coupled LES-LSM. 相似文献
9.
10.
Regional turbulent statistics over contrasting natural surfaces 总被引：1，自引：0，他引：1
T. J. Lyons Li Fuqin J. M. Hacker Wan-Li Cheng Huang Xinmei 《Meteorology and Atmospheric Physics》2001,78(3-4):183-194
Summary
Regional turbulent fluxes of momentum, sensible and latent heat collected over both agricultural and native vegetation in
the south west of Australia are presented. Analysis of the energy spectrum illustrates that the most energetic eddies are
between scales of 20 metres to 5 kilometres and highlights the spatial distance required to obtain representative regional
fluxes. For the sensible heat flux, this distance is a function of measurement height whereas the latent flux is also influenced
by surface variability. Statistics of these fluxes highlight that for the unstable surface layer, despite marked differences
in the underlying vegetation and the corresponding sources of heat and moisture, heat is transported more efficiently than
water vapour from the ground surface.
Received October 9, 2000/Revised April 23, 2001 相似文献
11.
为了研究大气环流模式次网格中尺度通量的参数化问题，本文发展了一个Pielke中尺度边界层与陆面过程的耦合模式，陆面过程模式中包括一个简单植被水热传输模式及一个裸土沙漠模式。利用这一耦合模式，对黑河试验区中沙漠和绿洲这种典型的非均匀下垫面进行了模拟，20多个数值试验的模拟结果表明:（1）中尺度通量在特定的情况下具有和湍流通量相当的重要性，因此，大尺度模式中对中尺度通量的参数化是十分必要的。（2）对于中尺度通量的发展存在一个明显的最优尺度和最优块数，即当绿洲尺度为60 km，3块时，中尺度通量最大。而且当块数增加到一定数目时，可以忽略非均匀效应。（3）背景风速的增大可以使中尺度通量减小；粗糙度的试验说明非均匀块之间的热力差异的减小可使中尺度通量非线性地减小。 相似文献
12.
A. R. G. Lang K. G. McNaughton Chen Fazu E. F. Bradley E. Ohtaki 《Boundary-Layer Meteorology》1983,25(1):89-102
Terms in the heat and vapour flux equations, appropriate to the atmospheric surface layer with horizontal heterogeneity in one direction, have been evaluated empirically. The experimental site was a flooded rice field, which was bounded to windward by a semi-arid region. Local conditions over the rice were always stable, but the vertical fluxes of heat and water vapour were large. All terms in the flux equations were either measured directly, or, if sufficiently small, estimated, except the term containing fluctuating pressure, which was obtained by difference. The relative magnitudes of the major terms (production and pressure covariance) were similar to those reported previously for horizontally homogeneous flow with similar stabilities. Current parameterizations of the pressure covariance terms sometimes gave values which differed by factors of five or ten from the experimental results, and the interrelationships depended upon the stability. 相似文献
13.
A novel approach for upscaling land-surface parameters based on inverse stochastic surface-vegetation-atmosphere transfer
(SVAT) modelling is presented. It allows estimation of effective parameters that yield scale invariant outputs e.g. for sensible
and latent heat fluxes and evaporative fraction. The general methodology is used to estimate effective parameters for the
Oregon State University Land-Surface Model, including surface albedo, surface emissivity, roughness length, minimum stomatal
resistance, leaf area index, vapour pressure deficit factor, solar insolation factor and the Clapp–Hornberger soil parameter.
Upscaling laws were developed that map the mean and standard deviation of the distributed land-surface parameters at the subgrid
scale to their corresponding effective parameter at the grid scale. Both linear and bi-parabolic upscaling laws were obtained
for the roughness length. The bi-parabolic upscaling law fitted best for the remaining land-surface parameters, except surface
albedo and emissivity, which were best fitted with linear upscaling laws. 相似文献
14.
Helmut Kraus 《Boundary-Layer Meteorology》1993,66(3):219-235
The Prandtl-layer concept, assuming constant turbulent fluxes in the lowest meters or decameters of the atmosphere under horizontal homogeneous and steady-state conditions, is widely used; and it is also one of the fundamentals of Monin-Obukhov similarity theory. Thus, surface-layer condensation processes-essentially formation of shallow fog layers-implying convergence and divergence of turbulent fluxes of water vapour, liquid water content and sensible heat, cannot be treated within this concept. This paper tries to overcome this restriction by a modified Monin-Obukhov theory, which deals with constant fluxes of total water content and moist static energy (instead of water vapour and sensible heat). It shows that surface-layer fog situations (under steady-state and horizontally homogeneous conditions and neglecting radiational effects) can be treated by this modified theory, which yields turbulent vertical fluxes of sensible heat, water vapour and liquid water content and their divergences.The paper also derives a simple formula for the divergence of the turbulent flux of water vapour (E/z) under saturation conditions, which elucidates convergence ofE very close to the ground and divergence ofE higher up independent of whether the stratification is stable or unstable, i.e., whether there is fog over cold or warm ground. Model computations with the modified Monin-Obukhov theory are in full accordance with this formula. Thus a steam-fog case can be given as a demonstration of vertical profiles of turbulent fluxes of sensible heat, water vapour and liquid water content and their divergences. 相似文献
15.
16.
Summary Profile measurements of wind and temperature have been performed at the Agricultural University of Norway on a routine basis since 1997. 10-min. averages are stored in a database together with other relevant meteorological parameters. The database can be used to determine the seasonal variation of surface aerodynamic roughness, showing the growth of grass between cutting during the growing season, the effect of snowfall and the melting of snow etc. However, careful screening of the data must be conducted before reliable estimates can be made. The main objective of this study is to establish simple practical rules for filtering out unreliable datasets for the evaluation of the surface roughness parameter z0, and to present its annual variation. The resulting values for the summer period agree well with values found in the literature for homogenous grass covered surfaces. In the transition periods during autumn and spring, and during wintertime in mild weather conditions, the surface is generally non-homogenous with a mixture of snow patches, ponds of melting water and shrubs of withered grass. The results show that the mechanical interaction between a non-homogeneous land surface and the boundary layer flow can be described by one roughness parameter, with a numeric value somewhere in between the ideal values for the different surface characteristics. Another use of the database is to investigate drainage flow and the relationship between drainage flow, prevailing wind direction and the mean vertical velocity of the air. Most micrometeorological studies of the fluxes of heat and water vapour in the surface layer, assume the mean vertical velocity to be zero, focusing on eddy fluxes and thereby excluding any transport in the mean flow. In certain situations, this may lead to serious errors. This work shows that convergence of horizontal flow leads to an upward movement of air, which is enhanced if the prevailing direction of the wind opposes the outflow of the cold drainage winds from the area. 相似文献
17.
C. R. Lloyd R. J. Harding T. Friborg M. Aurela 《Theoretical and Applied Climatology》2001,70(1-4):19-33
Summary Measurements of the surface fluxes of heat and water vapour were taken at four sites across the European Arctic as part of
the EU funded LAPP project. The sites cover a range of latitudinal, altitudinal and climatic conditions. The most northerly
site is near Ny-?lesund, Svalbard, a polar semi-desert with continuous permafrost. A second permafrost site is a fen area
in the Zackenberg valley, East Greenland. Finally two sites in northern Finland, Skalluvaara and Kaamanen are on the southern
boundary of the region affected by permafrost. At all sites measurements were made of the turbulent fluxes of heat and water
vapour using eddy correlation equipment for at least one active season.
The net radiation totals for July and August are similar at all sites. At the sites with permafrost a substantial proportion
(over 20%) of the net radiation goes into soil heat flux, to thaw the soil moisture in the top metre. Of the remaining energy
just over half is used for evaporation. At the Finnish sites the vegetation is largely deciduous and this is seen in the record
with higher evaporative ratios in July and August, after the vegetation becomes green. The Finnish sites tend to have higher
surface resistance to evaporation; however, the evaporative demand is greater leading to slightly higher evaporation rates.
The two Finnish sites have a similar seasonal pattern determined by the water table and seasonality of the vegetation. The
two northern sites show a pattern that is determined primarily by the variation of water table only. It is concluded that
the water balance through the active season is influenced primarily by the history of snow cover. The seasonality of the vegetation,
the permafrost and the depth of water table are also important influences.
Received November 1, 1999 Revised April 17, 2000 相似文献
18.
Some evaluations of drag and bulk transfer coefficients over water bodies of different sizes 总被引：1，自引：0，他引：1
B. B. Hicks 《Boundary-Layer Meteorology》1972,3(2):201-213
Three recent experiments allow evaluation of the bulk transfer coefficients for momentum, water vapour and sensible heat over water bodies of different sizes. As part of a study of evaporation rates from a swamp, measurements of latent and sensible heat fluxes were made over Lake Wyangan in southern N.S.W., Australia. This lake is of several kilometers diameter. In a later experiment, Reynolds stress and sensible heat transfer were measured from a natural-gas platform standing in Bass Strait, south of mainland Australia. The most recent experiment involved the direct measurement of each of these turbulent fluxes from a fixed tower erected in Lake Michigan, U.S.A.Perhaps the most important of the results is the finding that drag coefficients measured over Bass Strait are not significantly different from those over Lake Michigan, despite the obvious differences in depth, fetch, and hence surface wave structure. At both locations, drag coefficients are found to increase slightly with increasing wind speed, while at low wind speeds they are not significantly different from those corresponding to aerodynamic smoothness.Near-neutral bulk transfer coefficients for sensible heat and for water vapour are found to be similar. An average value of about 1.4 × 10–3 is obtained.It is emphasized that stability effects should be considered in any discussion of drag coefficients or bulk transfer coefficients. Large errors can result if near-neutrality is incorrectly assumed. 相似文献
19.
We assessed in absolute and relative terms how solar radiation and water vapour pressure deficit control the latent heat flux density in a Scots pine (Pinus sylvestris L.) forest growing under boreal conditions. The absolute and relative total control can be expressed as sums of the physical and biological forms of control. Physical control is based on the direct effects of solar radiation and water vapour pressure deficit on latent heat flux density, and biological control on the effects of solar radiation and water vapour pressure deficit on latent heat flux density through surface resistance. Measurements based on the eddy covariance method were used in the assessment, which defined the scale adopted in the study. Relative physical control over latent heat flux density was mainly exercised by water vapour pressure deficit, and the role of solar radiation was only marginal. The relative biological control exercised by solar radiation over latent heat flux density was higher in the morning and afternoon, unlike the control exercised by water vapour pressure deficit, which was strongest around noon. The values for the relative total control exercised by solar radiation over latent heat flux density were in general higher than those for relative total control exercised by water vapour pressure deficit. This is inconsistent with expectations based on Omega theory, where a decoupling coefficient () indicates the relative control exercised by surface resistance over latent heat flux density. Solar radiation and water vapour pressure deficit do not necessarily act in opposite directions in the absolute or relative total control that they maintain over latent heat flux density. 相似文献
20.
P. P. Harris C. Huntingford J. H. C. Gash M. G. Hodnett P. M. Cox Y. Malhi A. C. Araújo 《Theoretical and Applied Climatology》2004,78(1-3):27-45
Summary A land-surface model (MOSES) was tested against observed fluxes of heat, water vapour and carbon dioxide for two primary forest sites near Manaus, Brazil. Flux data from one site (called C14) were used to calibrate the model, and data from the other site (called K34) were used to validate the calibrated model. Long-term fluxes of water vapour at C14 and K34 simulated by the uncalibrated model were good, whereas modelled net ecosystem exchange (NEE) was poor. The uncalibrated model persistently underpredicted canopy conductance (g
c
) from mid-morning to mid-afternoon due to saturation of the response to solar radiation at low light levels. This in turn caused a poor simulation of the diurnal cycles of water vapour and carbon fluxes. Calibration of the stomatal conductance/photosynthesis sub-model of MOSES improved the simulated diurnal cycle of g
c
and increased the diurnal maximum NEE, but at the expense of degrading long-term water vapour fluxes. Seasonality in observed canopy conductance due to soil moisture change was not captured by the model. Introducing realistic depth-dependent soil parameters decreased the amount of moisture available for transpiration at each depth and led to the model experiencing soil moisture limitation on canopy conductance during the dry season. However, this limitation had only a limited effect on the seasonality in modelled NEE. 相似文献