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1.
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
2.
Accurately representing complex land-surface processes balancing complexity and realism remains one challenge that the weather
modelling community is facing nowadays. In this study, a photosynthesis-based Gas-exchange Evapotranspiration Model (GEM)
is integrated into the Noah land-surface model replacing the traditional Jarvis scheme for estimating the canopy resistance
and transpiration. Using 18-month simulations from the High Resolution Land Data Assimilation System (HRLDAS), the impact
of the photosynthesis-based approach on the simulated canopy resistance, surface heat fluxes, soil moisture, and soil temperature
over different vegetation types is evaluated using data from the Atmospheric Radiation Measurement (ARM) site, Oklahoma Mesonet,
2002 International H2O Project (IHOP_2002), and three Ameriflux sites. Incorporation of GEM into Noah improves the surface energy fluxes as well
as the associated diurnal cycle of soil moisture and soil temperature during both wet and dry periods. An analysis of midday,
average canopy resistance shows similar day-to-day trends in the model fields as seen in observed patterns. Bias and standard
deviation analyses for soil temperature and surface fluxes show that GEM responds somewhat better than the Jarvis scheme,
mainly because the Jarvis approach relies on a parametrised minimum canopy resistance and meteorological variables such as
air temperature and incident radiation. The analyses suggest that adding a photosynthesis-based transpiration scheme such
as GEM improves the ability of the land-data assimilation system to simulate evaporation and transpiration under a range of
soil and vegetation conditions. 相似文献
3.
Xiaodong Xie Xiaoxian Huang Tijian Wang Mengmeng Li Shu Li Pulong Chen 《Acta Meteorologica Sinica》2018,32(3):456-468
Carbon dioxide (CO2) is an important greenhouse gas that influences regional climate through disturbing the earth’s energy balance. The CO2 concentrations are usually prescribed homogenously in most climate models and the spatiotemporal variations of CO2 are neglected. To address this issue, a regional climate model (RegCM4) is modified to investigate the non-homogeneous distribution of CO2 and its effects on regional longwave radiation flux and temperature in East Asia. One-year simulation is performed with prescribed surface CO2 fluxes that include fossil fuel emission, biomass burning, air–sea exchange, and terrestrial biosphere flux. Two numerical experiments (one using constant prescribed CO2 concentrations in the radiation scheme and the other using the simulated CO2 concentrations that are spatially non-homogeneous) are conducted to assess the impact of non-homogeneous CO2 on the regional longwave radiation flux and temperature. Comparison of CO2 concentrations from the model with the observations from the GLOBALVIEW-CO2 network suggests that the model can well capture the spatiotemporal patterns of CO2 concentrations. Generally, high CO2 mixing ratios appear in the heavily industrialized eastern China in cold seasons, which probably relates to intensive human activities. The accommodation of non-homogeneous CO2 concentrations in the radiative transfer scheme leads to an annual mean change of–0.12 W m–2 in total sky surface upward longwave flux in East Asia. The experiment with non-homogeneous CO2 tends to yield a warmer lower troposphere. Surface temperature exhibits a maximum difference in summertime, ranging from–4.18 K to 3.88 K, when compared to its homogeneous counterpart. Our results indicate that the spatial and temporal distributions of CO2 have a considerable impact on regional longwave radiation flux and temperature, and should be taken into account in future climate modeling. 相似文献
4.
Estimates of anthropogenic CO<Subscript>2</Subscript> uptake in a global ocean model 总被引:2,自引:0,他引:2
A global ocean general circulation model (L30T63) is employed to study the uptake and distribution
of anthropogenic CO2 in the ocean. A subgrid-scale mixing scheme called GM90 is used in the model. There are
two main GM90 parameters including isopycnal diffusivity and skew (thickness) diffusivity. Sensitivities of
the ocean circulation and the redistribution of dissolved anthropogenic CO2 to these two parameters are
examined. Two runs estimate the global oceanic anthropogenic CO2 uptake to be 1.64 and 1.73 Pg C yr-1
for the 1990s, and that the global ocean contained 86.8 and 92.7 Pg C of anthropogenic CO2 at the end of 1994,
respectively. Both the total inventory and uptake from our model are smaller than the data-based estimates.
In this presentation, the vertical distributions of anthropogenic CO2 at three meridional sections are
discussed and compared with the available data-based estimates. The inventory in the individual basins is
also calculated. Use of large isopycnal diffusivity can generally improve the simulated results, including
the exchange flux, the vertical distribution patterns, inventory, storage, etc. In terms of comparison of
the vertical distributions and column inventory, we find that the total inventory in the Pacific Ocean
obtained from our model is in good agreement with the data-based estimate, but a large difference exists
in the Atlantic Ocean, particularly in the South Atlantic. The main reasons are weak vertical mixing and
that our model generates small exchange fluxes of anthropogenic CO2 in the Southern Ocean. Improvement in
the simulation of the vertical transport and sea ice in the Southern Ocean is important in future work. 相似文献
5.
Penélope Serrano-Ortiz Andrew S. Kowalski Francisco Domingo Borja Ruiz Lucas Alados-Arboledas 《Boundary-Layer Meteorology》2008,126(2):209-218
Errors in the estimation of CO2 surface exchange by open-path eddy covariance, introduced during the removal of density terms [Webb et al. Quart J Roy Meteorol
Soc 106:85–100, (1980) - WPL], can happen both because of errors in energy fluxes [Liu et al. Boundary-Layer Meteorol 120:65–85,
(2006)] but also because of inaccuracies in other terms included in the density corrections, most notably due to measurements
of absolute CO2 density (ρ
c
). Equations are derived to examine the propagation of all errors through the WPL algorithm. For an open-path eddy covariance
system operating in the Sierra de Gádor in south-east Spain, examples are presented of the inability of an unattended, open-path infrared gas analyzer (IRGA) to
reliably report ρ
c
and the need for additional instrumentation to determine calibration corrections. A sensitivity analysis shows that relatively
large and systematic errors in net ecosystem exchange (NEE) can result from uncertainties in ρ
c
in a semi-arid climate with large sensible heat fluxes (H
s
) and (wet) mineral deposition. When ρc is underestimated by 5% due to lens contamination, this implies a 13% overestimation of monthly CO2 uptake. 相似文献
6.
Joe Kidston Christian Brümmer T. Andrew Black Kai Morgenstern Zoran Nesic J. Harry McCaughey Alan G. Barr 《Boundary-Layer Meteorology》2010,136(2):193-218
Components of the surface energy balance of a mature boreal jack pine forest and a jack pine clearcut were analysed to determine
the causes of the imbalance that is commonly observed in micrometeorological measurements. At the clearcut site (HJP02), a
significant portion of the imbalance was caused by: (i) the overestimation of net radiation (R
n
) due to the inclusion of the tower in the field of view of the downward facing radiometers, and (ii) the underestimation
of the latent heat flux (λE) due to the damping of high frequency fluctuations in the water vapour mixing ratio by the sample tube of the closed-path
infrared gas analyzer. Loss of low-frequency covariance induced by insufficient averaging time as well as systematic advection
of fluxes away from the eddy-covariance (EC) tower were discounted as significant issues. Spatial and temporal distributions
of the total surface-layer heat flux (T), i.e. the sum of sensible heat flux (H) and λE, were well behaved and differences between the relative magnitudes of the turbulent fluxes for several investigated energy
balance closure (C) classes were observed. Therefore, it can be assumed that micrometeorological processes that affected all turbulent fluxes
similarly did not cause the variation in C. Turbulent fluxes measured at the clearcut site should not be forced to close the energy balance. However, at the mature
forest site (OJP), loss of low-frequency covariance contributed significantly to the systematic imbalance when a 30-min averaging
time was used, but the application of averaging times that were long enough to capture all of the low-frequency covariance
was inadequate to resolve all of the high-frequency covariance. Although we found qualitative similarity between T and the net ecosystem exchange (NEE) of carbon dioxide (CO2), forcing T to closure while retaining the Bowen ratio and applying the same factor to CO2 fluxes (F
C
) cannot be generally recommended since it remains uncertain to what extent long wavelength contributions affect the relationship
between T, F
C
and C. 相似文献
7.
Xingxia Kou Xiangjun Tian Meigen Zhang Zhen Peng Xiaoling Zhang 《Acta Meteorologica Sinica》2017,31(5):834-851
A regional surface carbon dioxide (CO2) flux inversion system, the Tan-Tracker-Region, was developed by incorporating an assimilation scheme into the Community Multiscale Air Quality (CMAQ) regional chemical transport model to resolve fine-scale CO2 variability over East Asia. The proper orthogonal decomposition-based ensemble four-dimensional variational data assimilation approach (POD-4DVar) is the core algorithm for the joint assimilation framework, and simultaneous assimilations of CO2 concentrations and surface CO2 fluxes are applied to help reduce the uncertainty in initial CO2 concentrations. A persistence dynamical model was developed to describe the evolution of the surface CO2 fluxes and help avoid the “signal-to-noise” problem; thus, CO2 fluxes could be estimated as a whole at the model grid scale, with better use of observation information. The performance of the regional inversion system was evaluated through a group of single-observation-based observing system simulation experiments (OSSEs). The results of the experiments suggest that a reliable performance of Tan-Tracker-Region is dependent on certain assimilation parameter choices, for example, an optimized window length of approximately 3 h, an ensemble size of approximately 100, and a covariance localization radius of approximately 320 km. This is probably due to the strong diurnal variation and spatial heterogeneity in the fine-scale CMAQ simulation, which could affect the performance of the regional inversion system. In addition, because all observations can be artificially obtained in OSSEs, the performance of Tan-Tracker-Region was further evaluated through different densities of the artificial observation network in different CO2 flux situations. The results indicate that more observation sites would be useful to systematically improve the estimation of CO2 concentration and flux in large areas over the model domain. The work presented here forms a foundation for future research in which a thorough estimation of CO2 flux variability over East Asia could be performed with the regional inversion system. 相似文献
8.
Land-surface heterogeneity effects on the subgrid scale of regional climate and numerical weather prediction models are of vital interest for the energy and mass exchange between the surface and the atmospheric boundary layer. High-resolution numerical model simulations can be used to quantify these effects, and are a tool used to obtain area-averaged surface fluxes over heterogeneous land surfaces. We present high-resolution model simulations for the LITFASS area near Berlin during the LITFASS-2003 experiment, which were carried out using the non-hydrostatic model FOOT3DK of the University of Köln with horizontal resolutions of 1 km and 250 m. The LITFASS-2003 experimental dataset is used for comparison. The screen level quantities show good quality for the simulated pressure, temperature, humidity and wind speed and direction. Averaged over the four week experimental period, simulated surface energy fluxes at land stations show a small bias for the turbulent heat fluxes and an underestimation of the net radiation caused by excessive cloudiness in the simulations. For eight selected days with low cloud amounts, the net radiation bias is close to zero, but the sensible heat flux shows a strong positive bias. Large differences are found for latent heat fluxes over a lake, which are partly due to local effects on the measurements, but an additional problem seems to be the overestimation of the turbulent exchange under stable conditions in the daytime internal boundary layer over the lake. In the area average over the LITFASS area of 20 × 20 km2, again a strong positive bias of 70 W m?2 for the sensible heat is present. For the low soil moisture conditions during June 2003, the simulation of the turbulent heat fluxes is sensitive to variations in the soil type and its hydrological properties. Under these conditions, the supply of ground water to the lowest soil layer should be accounted for. Different area-averaging methods are tested. The experimental set-up of the LITFASS-2003 experiment is found to be well suited for the computation of area-averaged turbulent heat fluxes. 相似文献
9.
Otávio C. Acevedo Osvaldo L. L. Moraes David R. Fitzjarrald Ricardo K. Sakai Larry Mahrt 《Boundary-Layer Meteorology》2007,125(1):49-61
Turbulent fluxes obtained using the conventional eddy covariance approach result in erratic results with large time fluctuations
in extremely stable conditions. This can limit efforts to estimate components of the nocturnal energy budget and respiratory
CO2 fluxes. Well-organized fluxes that show a clear dependence on turbulent intensity were obtained when multiresolution decomposition
was used to estimate turbulent exchanges. CO2, heat and water vapour fluxes were observed at a site in the eastern Amazon basin that had been cleared for agricultural
purposes. Temporal scales of the carbon transfer were determined and shown to be similar to those of latent heat, but as much
as three times larger than those of sensible heat. CO2 eddy diffusivities at the temporal scales on which most of the vertical CO2 exchange occurs are shown to be 50 times larger than the eddy diffusivity for heat. A process associated with the vertical
scale of the scalar accumulation layer is suggested to explain these different scales and turbulent diffusivities of carbon
and sensible heat transfer. For an appreciable range of turbulence intensities, the observed vertical turbulent carbon exchange
is insufficient to account for the locally respired CO2 estimated independently. Evidence that shallow drainage currents may account for this is given. 相似文献
10.
土壤水分条件对内蒙古典型草原水汽和二氧化碳通量的影响研究 总被引:1,自引:1,他引:0
本文基于2007年和2008年生长季内蒙古羊草和大针茅草原湍流观测资料,分析了两种典型草原下垫面生长季的不同土壤水分条件下水汽和二氧化碳通量交换特征及其控制因子。主要结果如下:(1)在植被生长峰值期,日尺度上,干旱条件下土壤湿度是潜热通量的主要控制因子,而土壤水分条件较好时潜热通量主要受净辐射控制。(2)与大针茅草原相比,羊草草原叶面积指数较大,水分条件较好时,其潜热通量平均值更大,CO2吸收能力更强,吸收CO2更多;但在土壤水分胁迫出现时,羊草草原叶面的气孔闭合度急剧增加,大针茅草原的潜热通量、和CO2吸收反而更大,表现出更为耐旱的植被特性。(3)地表导度可以用来解释土壤水分条件对羊草和大针茅草原碳水通量的影响。 相似文献
11.
In the context of CO2 surface exchange estimation, an analysis combining the basic principles of diffusion and scalar conservation shows that the
mixing ratio is the appropriate variable both for defining the (eddy covariance) turbulent flux and also for expressing the
relationship between the turbulent flux and surface exchange in boundary-layer budget equations. Other scalar intensity variables
sometimes chosen, both the CO2 density and molar fraction, are susceptible to the influence of surface exchange of heat and water vapour. The application
of a hypsometric analysis to the boundary-layer “control volume” below the tower measurement height reveals flaws in previously
applied approaches: (a) incompressibility cannot be assumed to simplify mass conservation (the budget in terms of CO2 density); (b) compressibility alone makes the analysis of mass conservation vulnerable to uncertainties associated with resultant
non-zero vertical velocities too small to measure or model over real terrain; and (c) the WPL (Webb et al. (1980) Quart J
Roy Meteorol Soc 106:85–100) “zero dry air flux” assumption is invalidated except at the surface boundary. Nevertheless, the
definition and removal of the WPL terms do not hinge upon this last assumption, and so the turbulent CO2 flux can be accurately determined by eddy covariance using gas analysers of either open- or closed-path design. An appendix
discusses the necessary assumptions and appropriate interpretations for deriving the WPL terms. 相似文献
12.
Surface turbulent flux measurements over the Loess Plateau for a semi-arid climate change study 总被引:2,自引:0,他引:2
In order to provide high quality data for climate change studies, the data quality of turbulent flux measurements at the station
of SACOL (Semi-Arid Climate & Environment Observatory of Lanzhou University), which is located on a semi-arid grassland over
the Loess Plateau in China, has been analyzed in detail. The effects of different procedures of the flux corrections on CO2, momentum, and latent and sensible heat fluxes were assessed. The result showed that coordinate rotation has a great influence
on the momentum flux but little on scalar fluxes. For coordinate rotation using the planar fit method, different regression
planes should be determined for different wind direction sectors due to the heterogeneous nature of the ground surface. Sonic
temperature correction decreased the sensible heat flux by about 9%, while WPL correction (correction for density fluctuations)
increased the latent heat flux by about 10%. WPL correction is also particularly important for CO2 fluxes. Other procedures of flux corrections, such as the time delay correction and frequency response correction, do not
significantly influence the turbulent fluxes. Furthermore, quality tests on stationarity and turbulence development conditions
were discussed. Parameterizations of integral turbulent characteristics (ITC) were tested and a specific parameterization
scheme was provided for SACOL. The ITC test on turbulence development conditions was suggested to be applied only for the
vertical velocity. The combined results of the quality tests showed that about 62%–65% of the total data were of high quality
for the latent heat flux and CO2 flux, and as much as about 76% for the sensible heat flux. For the momentum flux, however, only about 35% of the data were
of high quality. 相似文献
13.
An urban canopy model is developed for use in mesoscale meteorological and environmental modelling. The urban geometry is
composed of simple homogeneous buildings characterized by the canyon aspect ratio (h/w) as well as the canyon vegetation characterized by the leaf aspect ratio (σ
l
) and leaf area density profile. Five energy exchanging surfaces (roof, wall, road, leaf, soil) are considered in the model,
and energy conservation relations are applied to each component. In addition, the temperature and specific humidity of canopy
air are predicted without the assumption of thermal equilibrium. For radiative transfer within the canyon, multiple reflections
for shortwave radiation and one reflection for longwave radiation are considered, while the shadowing and absorption of radiation
due to the canyon vegetation are computed by using the transmissivity and the leaf area density profile function. The model
is evaluated using field measurements in Vancouver, British Columbia and Marseille, France. Results show that the model quite
well simulates the observations of surface temperatures, canopy air temperature and specific humidity, momentum flux, net
radiation, and energy partitioning into turbulent fluxes and storage heat flux. Sensitivity tests show that the canyon vegetation
has a large influence not only on surface temperatures but also on the partitioning of sensible and latent heat fluxes. In
addition, the surface energy balance can be affected by soil moisture content and leaf area index as well as the fraction
of vegetation. These results suggest that a proper parameterization of the canyon vegetation is prerequisite for urban modelling. 相似文献
14.
Interpreting CO<Subscript>2</Subscript> Fluxes Over a Suburban Lawn: The Influence of Traffic Emissions 总被引:1,自引:0,他引:1
Turf-grass lawns are ubiquitous in the United States. However direct measurements of land–atmosphere fluxes using the eddy-covariance
method above lawn ecosystems are challenging due to the typically small dimensions of lawns and the heterogeneity of land
use in an urbanised landscape. Given their typically small patch sizes, there is the potential that CO2 fluxes measured above turf-grass lawns may be influenced by nearby CO2 sources such as passing traffic. In this study, we report on two years of eddy-covariance flux measurements above a 1.5 ha
turf-grass lawn in which we assess the contribution of nearby traffic emissions to the measured CO2 flux. We use winter data when the vegetation was dormant to develop an empirical estimate of the traffic effect on the measured
CO2 fluxes, based on a parametrised version of a three-dimensional Lagrangian footprint model and continuous traffic count data.
The CO2 budget of the ecosystem was adjusted by 135gCm−2 in 2007 and by 134gCm−2 in 2008 to determine the natural flux, even though the road crossed the footprint only at its far edge. We show that bottom-up
flux estimates based on CO2 emission factors of the passing vehicles, combined with the crosswind-integrated footprint at the distance of the road, agreed
very well with the empirical estimate of the traffic contribution that we derived from the eddy-covariance measurements. The
approach we developed may be useful for other sites where investigators plan to make eddy-covariance measurements on small
patches within heterogeneous landscapes where there are significant contrasts in flux rates. However, we caution that the
modelling approach is empirical and will need to be adapted individually to each site. 相似文献
15.
M. Wedler R. Geyer B. Heindl S. Hahn J. D. Tenhunen 《Theoretical and Applied Climatology》1996,53(1-3):145-156
Summary During the Hartheim experiment (HartX) 1992, conducted in the Upper Rhine Valley, Germany, we estimated water vapor flux from the understory by several methods as reported in Wedler et al. (this issue). We also examined the photosynthetic gas exchange of the dominant understory speciesBrachypodium pinnatum, Carex alba, andCarex flacca at the leaf level with an CO2/H2O porometer. A mechanisticallybased leaf gas exchange model was parameterized for these understory species and validated via the measured diurnal courses of carbon dioxide exchange. Leaf CO2 gas exchange was scaled-up to patch- and then to stand-level utilizing the leaf gas exchange model as a component of the canopy light interception/energy balance model GAS-FLUX, and by further considering variation in vegetation patch-type distribution, patch-specific spatial structure, patch-type leaf area index, and microclimate beneath the tree canopy.At patch-level,C. alba exhibited the lowest net CO2 uptake of ca. 75 mmol m–2 d–1 due to a low leaf-level photosynthetic capacity, whereas net CO2 fixation ofB. pinnatum- andC. flacca-patches was approx. 178 and 184 mmol m–2 d–1, respectively. Highest CO2 uptake was estimated for mixed patches whereB. pinnatum grew together with the sedge speciesC. alba orC. flacca. Scaling-up of leaf gas exchange to stand level resulted in an estimated average rate of total CO2 fixation by the graminoid understory patches of approximately 93 mmol m–2 d–1 during the HartX period. The conservative gas exchange behavior ofC. alba at Hartheim and its apparent success in space capture seems to affect overall functioning of this pine forest ecosystem by limiting understory CO2 uptake. The CO2 uptake by the understory is approximately 20% of stand total CO2 uptake. CO2 uptake fluxes mirror the relative differences in water loss from the understory and crown layer during the HartX period. Comparative measurements indicate that understory vegetation in spruce and pine forests is not greatly different from that of other low-statured natural ecosystems such as tundra or marshes under high light conditions, although CO2 capture by the understory at Hartheim is at the low extreme of the estimates, apparently due to the success ofC. alba.
With 6 Figures 相似文献
16.
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
17.
Expedition data obtained in the coastal-shelf zone of the East Siberian Sea in September 2003, 2004, and 2008 are generalized.
Studies of carbonate system in water and CO2 fluxes between ocean and atmosphere in this region confirmed that it was reasonable to divide the water area studied into
two biogeochemical provinces and that the ecosystem of its coastal part is mainly of a heterotrophic nature. In different
years, the extent of water supersaturation in carbon dioxide in the East Siberian Sea and the area of the CO2 release significantly changed. Geographic localization of the atmosphere action centers over the Arctic and their intensity
were main determining factors; that told both on the formation of a basic character of the atmospheric and hydrological processes
and on the dynamics of the CO2 exchange between water and air. 相似文献
18.
Dennis Baldocchi 《Boundary-Layer Meteorology》1992,61(1-2):113-144
An integrated canopy micrometeorological model is described for calculating CO2, water vapor and sensible heat exchange rates and scalar concentration profiles over and within a crop canopy. The integrated model employs a Lagrangian random walk algorithm to calculate turbulent diffusion. The integrated model extends previous Lagrangian modelling efforts by employing biochemical, physiological and micrometeorological principles to evaluate vegetative sources and sinks. Model simulations of water vapor, CO2 and sensible heat flux densities are tested against measurements made over a soybean canopy, while calculations of scalar profiles are tested against measurements made above and within the canopy. The model simulates energy and mass fluxes and scalar profiles above the canopy successfully. On the other hand, model calculations of scalar profiles inside the canopy do not match measurements.The tested Lagrangian model is also used to evaluate simpler modelling schemes, as needed for regional and global applications. Simple, half-order closure modelling schemes (which assume a constant scalar profile in the canopy) do not yield large errors in the computation of latent heat (LE) and CO2 (F
c
) flux densities. Small errors occur because the source-sink formulation of LE andF
c are relatively insensitive to changes in scalar concentrations and the scalar gradients are small. On the other hand, complicated modelling frames may be needed to calculate sensible heat flux densities; the source-sink formulation of sensible heat is closely coupled to the within-canopy air temperature profile. 相似文献
19.
Mesoscale surface turbulent fluxes over a complex terrain surrounded by oceans have been investigated using a 3-D numerical mesoscale model, under conditions with and without synoptic flows. The study indicated that under synoptically calm condition, the allocation and intensity of mesoscale surface turbulent fluxes (MSTFs) were greatly impacted by the thermally forced mesoscale circulation (TFMC) over mesoscale heterogeneous landscape. The max-imum values of sensible (Hs) and latent (LE) heat fluxes were located over the convergent zones and considerably im-pacted by the soil wetness (M), but did not depend strongly on the atmospheric background thermal stability (β0). The simulated results suggested that the sensible heat flux was closely proportional to the square of wind speed in the surface layer. By the action of synoptic flow, the allocation of LE was shifted to downwind, its intensity increased. 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