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1.
A. J. Pitman A. Henderson-Sellers C. E. Desborough Z.-L. Yang F. Abramopoulos A. Boone R. E. Dickinson N. Gedney R. Koster E. Kowalczyk D. Lettenmaier X. Liang J.-F. Mahfouf J. Noilhan J. Polcher W. Qu A. Robock C. Rosenzweig C. A. Schlosser A. B. Shmakin J. Smith M. Suarez D. Verseghy P. Wetzel E. Wood Y. Xue 《Climate Dynamics》1999,15(9):673-684
Using atmospheric forcing data generated from a general circulation climate model, sixteen land surface schemes participating
in the Project for the Intercomparison of Land-surface Parametrization Schemes (PILPS) were run off-line to equilibrium using
forcing data from a GCM representative of a tropical forest and a mid-latitude grassland grid point. The values for each land
surface parameter (roughness length, minimum stomatal resistance, soil depth etc.) were provided. Results were quality controlled
and analyzed, focusing on the scatter simulated amongst the models. There were large differences in how the models’ partitioned
available energy between sensible and latent heat. Annually averaged, simulations for the tropical forest ranged by 79 1 3;W m-2 for the sensible heat flux and 80 W m-2 for the latent heat flux. For the grassland, simulations ranged by 34 W m-2 for the sensible heat flux and 27 W m-2 for the latent heat flux. Similarly large differences were found for simulated runoff and soil moisture and at the monthly
time scale. The models’ simulation of annually averaged effective radiative temperature varied with a range, between all the
models, of 1.4 K for tropical forest and 2.2 K for the grassland. The simulation of latent and sensible heat fluxes by a standard
‘bucket’ models was anomalous although this could be corrected by an additional resistance term. These results imply that
the current land surface models do not agree on the land surface climate when the atmospheric forcing and surface parameters
are prescribed. The nature of the experimental design, it being offline and with artificial forcing, generally precludes judgements
concerning the relative quality of any specific model. Although these results were produced de-coupled from a host model,
they do cast doubt on the reliability of land surface schemes. It is therefore a priority to resolve the disparity in the
simulations, understand the reasons behind the scatter and to determine whether this lack of agreement in de-coupled tests
is reproduced in coupled experiments.
Received: 15 October 1997 / Accepted: 22 April 1999 相似文献
2.
H. Soegaard B. Hasholt T. Friborg C. Nordstroem 《Theoretical and Applied Climatology》2001,70(1-4):35-51
Summary Within the framework of the European LAPP-project (Land Arctic Physical Processes) and as part of the Danish Research Council’s
Polar Programme, studies on water- and surface energy balance in NE Greenland were conducted in 1996 and 1997. Eddy correlation
measurements of water vapour and sensible heat fluxes above the three dominant vegetation types: fen, willow snowbed, and
heath were conducted for the entire growing season. This was supplemented by measurements of evaporation from snow covered
areas and from a small pond. The evapotranspiration was found to be relatively high with the maximum from the fen (≈86 mm
per season). For the two other vegetation types the evapotranspiration was less, for heath 61 mm per season, while willow
snowbed had evaporation rates on intermediate level. By use of the Penman-Monteith equation it was possible to estimate the
altitude dependence of the evapotranspiration and calculate the annual evaporation for the whole area to 80 mm per year. By
applying a bucket model the evaporation was found to be in accordance with changes in soil moisture as monitored with TDR.
The observed surface water balance was compared to river discharge, which shows a glacio-nival regime with an early spring
flow (June), determined by the snow melt in the main valley and an July–August maximum determined by melt on higher plateau
areas. When balancing the individual hydrological components an annual deficit of 180 mm was observed, but it was found that
this deficit could be reduced by correcting for aerodynamic and altitude effects on the precipitation. Finally some of the
possible consequences of a global warming is discussed in relation to the water and energy balance in the high-arctic ecosystem.
Received November 1, 1999 Revised May 15, 2000 相似文献
3.
Experimental determination of turbulent fluxes over the heterogeneous LITFASS area: Selected results from the LITFASS-98 experiment 总被引:1,自引:0,他引:1
F. Beyrich S. H. Richter U. Weisensee W. Kohsiek H. Lohse H. A. R. de Bruin Th. Foken M. Göckede F. Berger R. Vogt E. Batchvarova 《Theoretical and Applied Climatology》2002,73(1-2):19-34
Summary ?During the LITFASS-98 experiment, local flux measurements were performed over five different types of underlying surface
(grass, barley, triticale, pine forest, water) in a heterogeneous landscape using eddy covariance and profile techniques over
a three week time period in June, 1998. Estimates of the area-integrated sensible heat flux during daytime were obtained from
continuous measurements with a large aperture scintillometer (LAS) along a 4.7 km path. The calculation of a mean diurnal
cycle of the fluxes during the experiment revealed significant differences between the main land use classes. A land-use weighted
average of the sensible heat flux was found to be in good agreement with the LAS based estimate, which in turn was supported
by other regionally integrated flux estimates from budget considerations and aircraft measurements for a few case studies.
The profiles of turbulent quantities measured along a 99 m-tower significantly deviate from “idealised” profiles measured
over homogeneous terrain. Peculiarities in the profile structure could be attributed to the heterogeneity of the terrain,
namely to the differences in the surface characteristics of the footprint areas for the different tower levels.
Received June 6, 2001; revised January 15, 2002; accepted April 4, 2002 相似文献
4.
Test of a simple two-layer parameterisation to simulate the energy balance and temperature of a snow pack 总被引:3,自引:0,他引:3
Summary Reasonably simple yet realistic modelling schemes simulating the heat and mass balance within a snow pack are required to
provide the necessary boundary conditions for meteorological and hydrological models. An improvement to a one-layer snow energy
balance model (UEB, Tarboton etal., 1995) is proposed to better simulate snow surface and snow pack temperatures and, as a
result, snowmelt. The modified scheme is assessed against measured snow data from the WINTEX field campaign during spring
1997 in northern Finland, and compared with results from a complex multi-layer snow energy balance scheme. The results show
that separation of a one-layer representation into two snow layers and a soil layer enables a more realistic simulation of
soil and snow temperatures as well as of the snow surface temperature. The two-layer and the multi-layer snow schemes yielded
comparable results for internal processes in the snow whenever the simulation was carried out under similar boundary forcing.
The modified scheme is proposed for use as a sub-scheme in meteorological or hydrological models, or as a tool for simulating
spatially-variable snowmelt and the surface energy balance during seasonal snow cover.
Received November 18, 1999 Revised June 17, 2000 相似文献
5.
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
6.
Matthias Mauder Raymond L. Desjardins Ian MacPherson 《Boundary-Layer Meteorology》2008,129(3):431-450
The objective of this study is to produce two-dimensional maps of the sensible and the latent heat fluxes from airborne measurements,
based on the analysis of a flight pattern, called grid flights. A footprint model with along-wind and cross-wind components
was used to project the measured fluxes onto the surface map. The method was applied to measurements over Arctic tundra during
the Mackenzie Area GEWEX (Global Energy and Water Cycle Experiment) Study (MAGS) 1999. The resulting flux estimates were computed
by integration of a wavelet transform, and corrected for long wavelength losses using information from 100 km long regional
runs that were conducted close to the grid flights. The random flux error was estimated based on the flight length that is
represented in each map element, and a map resolution of 3 × 3 km was chosen in order to keep the average random error of
the latent heat flux below 25%. The random error of the sensible heat flux was smaller by a factor of 1.4 on average. An analysis
of airborne flux measurements at different altitudes showed no significant increase of flux estimates for measurement heights
below 90 m. Thus, the fluxes measured at heights between 48 and 64 m were not corrected for vertical flux divergence. The
resulting flux maps provide quantitative two-dimensional estimates of the energy exchange between the surface and the atmosphere
during the snow melt period in an Arctic environment, which are well-suited for calibration and validation of numerical models. 相似文献
7.
Summary An aircraft-based experimental investigation of the atmospheric boundary layer (ABL) structure and of the energy exchange
processes over heterogeneous land surfaces is presented. The measurements are used for the validation of the mesoscale atmospheric
model “Lokal-Modell” (LM) of the German Weather Service with 2.8 km resolution. In addition, high-resolution simulations using
the non-hydrostatic model FOOT3DK with 250 m resolution are performed in order to resolve detailed surface heterogeneities.
Two special observation periods in May 1999 show comparable convective boundary layer (CBL) conditions. For one case study
vertical profiles and area averages of meteorological quantities and energy fluxes are investigated in detail. The measured
net radiation is highly dependent on surface albedo, and the latent heat flux exhibits a strong temporal variability in the
investigation area. A reduction of this variability is possible by aggregation of multiple flight patterns. To calculate surface
fluxes from aircraft measurements at low altitude, turbulent energy fluxes were extrapolated to the ground by the budget method,
which turned out to be well applicable for the sensible heat flux, but not for the latent flux. The development of the ABL
is well captured by the LM simulation. The comparison of spatiotemporal averages shows an underestimation of the observed
net radiation, which is mainly caused by thin low-level clouds in the LM compared to observed scattered CBL clouds. The sensible
heat flux is reproduced very well, while the latent flux is highly overestimated especially above forests. The realistic representation
of surface heterogeneities in the investigation area in the FOOT3DK simulations leads to improvements for the energy fluxes,
but an overestimation of the latent heat flux still persists. A study of upscaling effects yields more structures than the
LM fields when averaged to the same scale, which are partly caused by the non-linear effects of parameter aggregation on the
LM scale. 相似文献
8.
A GCM land surface scheme was used, in off-line mode, to simulate the runoff, latent and sensible heat fluxes for two distinct
Australian catchments using observed atmospheric forcing. The tropical Jardine River catchment is 2500 km2 and has an annual rainfall of 1700 mm y–1 while the Canning River catchment is 540 km2, has a Mediterranean climate (annual rainfall of 800 mm y–1) and is ephemeral for half the year. It was found that the standard version of a land surface scheme developed for a GCM,
and initialised as for incorporation into a GCM, simulated similar latent and sensible heat fluxes compared to a basin-scale
hydrological model (MODHYDROLOG) which was calibrated for each catchment. However, the standard version of the land surface
scheme grossly overestimated the observed peak runoff in the wet Jardine River catchment at the expense of runoff later in
the season. Increasing the soil water storage permitted the land surface scheme to simulate observed runoff quite well, but
led to a different simulation of latent and sensible heat compared to MODHYDROLOG. It is concluded that this 2-layer land
surface scheme was unable to simulate both catchments realistically. The land surface scheme was then extended to a three-layer
model. In terms of runoff, the resulting control simulations with soil depths chosen as for the GCM were better than the best
simulations obtained with the two-layer model. The three-layer model simulated similar latent and sensible heat for both catchments
compared to MODHYDROLOG. Unfortunately, for the ephemeral Canning River catchment, the land surface scheme was unable to time
the observed runoff peak correctly. A tentative conclusion would be that this GCM land surface scheme may be able to simulate
the present day state of some larger and wetter catchments but not catchments with peaky hydrographs and zero flows for part
of the year. This conclusion requires examination with a range of GCM land surface schemes against a range of catchments.
Received: 9 June 1995 / Accepted: 4 April 1996 相似文献
9.
Summary The land surface model SEWAB (Surface Energy and Water Balance) is designed to be coupled to both, atmospheric and hydrological
models. Its application in mid and high latitudes requires the inclusion of freezing and thawing processes within the soil
and the accumulation and ablation of a snow cover. These winter processes are parameterised with a minimum number of empirical
formulations in order to assure reasonable computation times for an application in climate and sensitivity studies yet accounting
for all important processes. Meteorological forcing data and measurements of snow depth, soil temperature and liquid soil
water content at two locations in the mid-west of North America are used to test the model. Generally the simulated snow depth
matches the measurements, remaining differences in snow depth can be explained by uncertainties in snow density, blowing snow
and errors in precipitation measurements. The simulated soil temperature and liquid soil water content compare well with the
measurements, showing the isolating effect of the snow cover.
Received August 25, 2000 Revised January 19, 2001 相似文献
10.
Summary ?Simultaneous flight measurements with the research aircraft Do 128 and the helicopter-borne turbulence probe Helipod were
performed on 18 June 1998 during the LITFASS-98 field experiment. The area-averaged turbulent vertical fluxes of momentum,
sensible, and latent heat were determined on a 15 km × 15 km and a 10 km × 10 km flight pattern, respectively. The flights
were carried out over heterogeneous terrain at different altitudes within a moderately convective boundary layer with Cumulus
clouds.
Co-spectra-analysis demonstrated that the small scale turbulent transport was completely sampled, while the comparatively
small flight patterns were possibly of critical size regarding the large-scale turbulence. The phygoide of the airplane was
identified as a significant peak in some co-spectra. The turbulent fluxes of momentum and sensible heat at 80 m above the
ground showed systematic dependence on the location of the flight legs above the heterogeneous terrain. This was not observed
for the latent heat flux, probably due to the vertical distribution of humidity in the boundary layer.
Statistical error analysis of the fluxes F showed that the systematic statistical error ΔF was one order of magnitude smaller than the standard deviation σ
F
. The difference between area-averaged fluxes derived from simultaneous Helipod and Do 128 measurements was much smaller than
σ
F
, indicating that the systematic statistical error was possibly over-estimated by the usual method.
In the upper half of the boundary layer the airborne-measured sensible heat flux agreed well with windprofiler/RASS data.
A linear fit was the best approximation for the height dependence of all three fluxes. The linear extrapolations of the latent
and sensible heat fluxes to the ground were in good agreement with tower, scintillometer, and averaged ground-station measurements
on various surface types. Systematic discrepancies between airborne and ground-based measurements were not found.
Received June 18, 2001; revised December 21, 2001; accepted June 3, 2002 相似文献
11.
D. Melas T. Persson H. De Bruin S.-E. Gryning E. Batchvarova C. Zerefos 《Theoretical and Applied Climatology》2001,70(1-4):105-116
Summary A mesoscale numerical model, incorporating a land-surface scheme based on Deardorffs’ approach, is used to study the diurnal
variation of the boundary layer structure and surface fluxes during four consecutive days with air temperatures well below
zero, snow covered ground and changing synoptic forcing. Model results are evaluated against in-situ measurements performed
during the WINTEX field campaign held in Sodankyl?, Northern Finland in March 1997. The results show that the land-surface
parameterization employed in the mesoscale model is not able to reproduce the magnitude of the daytime sensible heat fluxes
and especially the pronounced maximum observed in the afternoon. Additional model simulations indicate that this drawback
is to a large extent removed by the implementation of a shading factor in the original Deardorff scheme. The shading factor,
as discussed in Gryning et al. (2001), accounts for the fact that in areas with sparse vegetation and low solar angles, both
typical for the northern boreal forests in wintertime, absorption of direct solar radiation is due to an apparent vegetation
cover which is much greater than the actual one (defined as the portion of the ground covered by vegetation projected vertically).
Moreover, the observed asymmetry in the diurnal variation of the sensible heat flux indicates that there might be a significant
heat storage in the vegetation. The implementation of an objective heat storage scheme in the mesoscale model explains part
of the observed diurnal variation of the sensible heat flux.
Received November 12, 1999 Revised October 4, 2000 相似文献
12.
Jens Bange Thomas Spieß Marcus Herold Frank Beyrich Barbara Hennemuth 《Boundary-Layer Meteorology》2006,121(1):127-151
Turbulent fluxes of sensible and latent heat were measured with the helicopter-borne turbulence probe Helipod over a heterogeneous landscape around the Meteorological Observatory Lindenberg during the STINHO-2 and LITFASS-2003 field experiments. Besides the determination of area-averaged heat fluxes, the analysis focused on different aspects of the response of the turbulent structure of the convective boundary layer (CBL) on the surface heterogeneity. A special flight pattern was designed to study flux profiles both over quasi-homogeneous sub-areas of the study region (representing the major land use types—forest, farmland, water) and over a typical mixture of the different surfaces. Significant differences were found between the heat fluxes over the individual surfaces along flight legs at about 80 m above ground level, in agreement with large-aperture scintillometer measurements. This flux separation was still present during some flights at levels near the middle of the CBL. Different scales for the blending height and horizontal heterogeneity were calculated, but none of them could be identified as a reliable indicator of the mixing state of the lower CBL. With the exception of the flights over water, the latent heat flux measurements generally showed a larger statistical error when compared with the sensible heat flux. Correlation coefficients a nd integral length scales were used to characterise the interplay between the vertical transport of sensible and latent heat, which was found to vary between ‘fairly correlated’ and ‘decoupled’, also depending on the soil moisture conditions. 相似文献
13.
Summary High resolution aircraft observations made along flight tracks over inhomogeneous surface in the late wintertime boreal zone
are described and compared to 2D mesoscale model simulations with surface properties defined at 2 km resolution from maps.
All observations displayed the expected small-scale turbulence. On top of that, the near-surface wind speeds (but not directions)
showed mesoscale variations related to local topography and roughness. Upward (but not downward) SW and LW radiative fluxes
and ground temperature also displayed mesoscale variability; in SW radiation this was clearly due to local albedo changes.
In the sensible heat flux there was strong horizontal variation near the surface in correlation with surface types. The above
observed mesoscale along-track variations were reasonably well represented by the mesoscale model simulation. The track-averaged
observed sensible and latent heat flux profiles were in rough agreement with a mixing length approach, which used the track-averaged
wind, temperature and moisture profiles as input (mimicking a first-order turbulence closure scheme of a GCM).
Received September 20, 1999 Revised January 21, 2000 相似文献
14.
Dongchul Kim Christopher P. Loughner Melanie A. Wetzel Wendy S. Goliff William R. Stockwell 《Journal of Atmospheric Chemistry》2007,57(1):59-71
Photolysis rate parameters depend upon solar actinic flux and chemical species dependent quantum yields and cross sections.
Spectrally resolved measurements of actinic flux should be preferred over flux derived from models for the analysis of field
observations. Actinic flux can be difficult to derive from the irradiance measurements of flat-plate radiometers. It is also
difficult to estimate from models due to uncertainties in the ozone column, aerosol concentrations and distributions, cloud
cover, optical depth and surface albedo. A series of actinic flux measurements were performed at Storm Peak Laboratory (3,210 m
above sea level), Colorado, United States with spectroradiometers during the wintertime (January 07–10, 2004). The site is
relatively remote with a clean atmosphere and during the wintertime the ground is generally covered by fresh snow with a high
albedo. The actinic flux measurements were used to estimate the photolysis rate parameters of ozone, nitrogen dioxide and
formaldehyde. The measured actinic flux and the photolysis rate parameters derived from the flux were compared to calculations
using the Tropospheric Ultraviolet-Visible Model (TUV), version 4.2 (Madronich and Flocke, 1998). The TUV modeled actinic
flux, the measured flux and the photolysis rate parameters derived from them had similar temporal patterns. However there
were significant differences in their magnitude due to uncertainties in the data available to initialize the TUV model and
the calibration of the spectroradiometer. 相似文献
15.
G. Mastrantonio V. Malvestuto S. Argentini T. Georgiadis A. Viola 《Meteorology and Atmospheric Physics》1999,71(1-2):127-132
Summary The development of a convective boundary layer over the Antarctic Plateau is documented by a Doppler minisodar data-set recorded
during a 10 day campaign in January 1997. The vertical velocities associated with thermals do not exceed 1 m/s, while the
depth of the convective layer, usually less than 200 m, never surpasses 300 m. Measurements of momentum flux, sensible heat
flux, wind speed and radiation budget show characteristics that are typical of a convective boundary layer evolution. The
diurnal behaviour of absolute humidity, however, exhibits features that are not expected, e.g. anticorrelation with incoming
net radiation and air temperature.
Received October 30, 1998 Revised May 26, 1999 相似文献
16.
Sven-Erik Gryning Ekaterina Batchvarova H. A. R. De Bruin 《Boundary-Layer Meteorology》2001,99(3):465-488
Measurements carried out in Northern Finland on radiation and turbulent fluxes over a sparse, sub-arctic boreal forest with snow covered ground were analysed. The measurements represent late winter conditions characterised by low solar elevation angles. During the experiment (12–24 March 1997) day and night were about equally long. At low solar elevation angles the forest shades most of the snow surface. Therefore an important part of the radiation never reaches the snow surface but is absorbed by the forest. The sensible heat flux above the forest was fairly large, reaching more than 100 W m-2. The measurements of sensible heat flux within and above the forest revealed that the sensible heat flux from the snow surface is negligible and the sensible heat flux above the forest stems from warming of the trees. A simple model for the surface energy balance of a sparse forest is presented. The model treats the diffuse and direct shortwave (solar) radiation separately. It introduces a factor that accounts for the shading of the ground at low solar elevation angles, and a parameter that deals with the partial transparency of the forest.Input to the model are the direct and diffuse incoming shortwave radiation.Measurements of the global radiation (direct plus diffuse incoming shortwaveradiation) above the forest revealed a considerable attenuation of the globalradiation at low solar elevation. A relation for the atmospheric turbidity asfunction of the solar elevation angle is suggested. The global radiation wassimulated for a three month period. For conditions with a cloud cover of lessthan 7 oktas good agreement between model predictions and measurementswere found. For cloud cover 7 and 8 oktas a considerable spread can beobserved. To apply the proposed energy balance model, the global radiationmust be separated into its diffuse and direct components. We propose a simpleempirical relationship between diffuse shortwave and global radiation asfunction of cloud cover. 相似文献
17.
During slightly unstable but still very close to neutral conditions new results from two previous investigations have shown
a significant increase of sensible and latent heat fluxes over the sea. The vertical heat transport during these conditions
is dominated by detached eddies originating at the top of the boundary layer, bringing relatively cold and dry air to the
surface. This effect can be described in numerical models by either enhanced heat transfer coefficients for sensible and latent
heat (Stanton and Dalton numbers respectively) or with an additional roughness length, added to the original roughness lengths
for heat and humidity. Such new expressions are developed using turbulence measurements from the Baltic Sea valid for wind
speeds up to 14 m s−1. The effect of including the increased heat fluxes is investigated using two different numerical models: a regional three-dimensional
climate model covering northern Europe, and a process-oriented ocean model for the Baltic Sea. During periods of several days,
the latent heat flux can be increased by as much as 100 W m−2. The increase in sensible heat flux is significantly smaller since the process is only of importance in the very near-neutral
regime where the sensible heat flux is very small. The long-term average effect over the Baltic Sea is of the order of several
W m−2. 相似文献
18.
Snow cover on the Tibetan Plateau (TP) has been shown to be essential for the East Asian summer monsoon. In this paper, we demonstrate that tropical cyclone (TC) 04B (1999) in the northern Indian Ocean, which made landfall during the autumn of 1999, may have contributed to climate anomalies over East Asia during the following spring and summer by increasing snow cover on the TP. Observations indicate that snow cover on the TP increased markedly after TC 04B (1999) made landfall in October of 1999. Sensitivity experiments, in which the TC was removed from a numerical model simulation of the initial field, verified that TC 04B (1999) affected the distribution as well as increased the amount of snow on the TP. In addition, the short-term numerical modeling of the climate over the region showed that the positive snow cover anomaly induced negative surface temperature, negative sensible heat flux, positive latent heat flux, and positive soil temperature anomalies over the central and southern TP during the following spring and summer. These climate anomalies over the TP were associated with positive (negative) summer precipitation anomalies over the Yangtze River valley (along the southeastern coast of China). 相似文献
19.
Summary The Bowen Ratio-Energy Balance (BREB) and the aerodynamic method were used to estimate turbulent fluxes of sensible and latent
heat flux over an irrigated agricultural area (IAA) and over two dry agricultural areas (DAA1 and DAA2). These turbulent fluxes
were analysed and particular attention paid to two specific areas. First, a quantitative analysis of sensible and latent heat
fluxes obtained by the BREB method was carried out, taking into account different soil type, vegetation and surface conditions.
The results showed that in IAA latent heat flux was higher than sensible heat flux, except in summer months, while in DAA1
and DAA2, sensible heat flux was higher except in the months when the vegetation was at the stage of maximum development.
Second, sensible and latent heat fluxes estimates from the BREB method were compared with those obtained from the aerodynamic
method. In this comparison factors such as soil type, soil vegetation cover, homogeneity or inhomogeneity of terrain and mesoscale
effects such as orography and wind patterns were taken into account. The results show that in conditions of light wind, the
two methods only concur if the condition of horizontal homogeniety is fulfilled. The influence of inhomogeneity seems to decrease
and agreement between methods improves, if the wind is stronger and the effects of meso and synoptic scales are predominant.
Received May 18, 1999/Revised March 15, 2000 相似文献
20.
Summary ?Progress in technology as well as signal processing has promoted Wind Profiler Radar (WPR) or sodar with RASS additions to become standard tools in profiling of the atmospheric boundary layer. Apart from
these instruments’ basic abilities in profiling mean winds and temperature, this paper will give an emphasis on the profiling
of ABL height as well as the turbulent fluxes of sensible heat and momentum both, with respect to methods as well as with
respect to realization. The special focus will thereby be laid on the demands for vertical profiling, which were defined within
the LITFASS-project of the German Meteorological Service. In the frame of this project, some special measuring campaigns have
been performed where remote-sensing systems were used to assess their abilities in profiling ABL parameters. On the base of
some case studies from these campaigns comparisons are shown, where results from sodar/RASS and WPR/RASS measurements are
compared to measurements from airborne sensor systems and results from numerical models. Regarding turbulent heat fluxes,
we found excellent agreement for remotely-sensed flux profiles from WPR/RASS with both, numerical models and airborne in-situ
measurements. However, as the inherent errors of the remotely-sensed fluxes are in the order of ± 20 ⋯ 30 W/m2 typically, current signal processing does not allow to interpret small-scale vertical structures in the profiles with respect
to surface inhomogeneities yet.
Received June 16, 2001; revised February 20, 2002; accepted May 30, 2002 相似文献