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1.
The Met Office Hadley Centre Unified Model (HadAM3) with the tiled version of the Met Office Surface Exchange Scheme (MOSES2) land surface scheme is used to assess the impact of a comprehensive imposed vegetation annual cycle on global climate and hydrology. Two 25-year numerical experiments are completed: the first with structural vegetation characteristics (Leaf Area Index, LAI, canopy height, canopy water capacity, canopy heat capacity, albedo) held at annual mean values, the second with realistic seasonally varying vegetation characteristics. It is found that the seasonalities of latent heat flux and surface temperature are widely affected. The difference in latent heat flux between experiments is proportional to the difference in LAI. Summer growing season surface temperatures are between 1 and 4 K lower in the phenology experiment over a majority of grid points with a significant vegetation annual cycle. During winter, midlatitude surface temperatures are also cooler due to brighter surface albedo over low LAI surfaces whereas during the dry season in the tropics, characterized by dormant vegetation, surface temperatures are slightly warmer due to reduced transpiration. Precipitation is not as systematically affected as surface temperature by a vegetation annual cycle, but enhanced growing season precipitation rates are seen in regions where the latent heat flux (evaporation) difference is large. Differences between experiments in evapotranspiration, soil moisture storage, the timing of soil thaw, and canopy interception generate regional perturbations to surface and sub-surface runoff annual cycles in the model. 相似文献
2.
Sang-Hyun Lee 《Boundary-Layer Meteorology》2011,140(2):315-342
The vegetated urban canopy model (VUCM), which includes parametrizations of urban physical processes for artificial surfaces
and vegetated areas in an integrated system, has been further developed by including physical processes associated with grass-covered
surfaces in urban pervious surfaces and the photosynthesis effects of urban vegetation. Using measurements made from three
urban/suburban sites during the BUBBLE field campaign in 2002, the model’s performance in modelling surface fluxes (momentum
flux, net radiation, sensible and latent heat fluxes and storage heat flux) and canopy air conditions (canopy air temperature
and specific humidity) was critically evaluated for the non-precipitation and the precipitation days. The observed surface
fluxes at the urban/suburban sites were significantly altered by precipitation as well as urban vegetation. Especially, the
storage heat at urban surfaces and underlying substrates varied drastically depending on weather conditions while having an
important role in the formation of a nocturnal urban surface layer. Unlike the nighttime canopy air temperature that was largely
affected by the storage-heat release, the daytime canopy air conditions were highly influenced by the vertical turbulent exchange
with the overlying atmosphere. The VUCM well reproduced these observed features in surface fluxes and canopy air conditions
at all sites while performing well for both the non-precipitation and the precipitation days. The newly implemented parametrizations
clearly improved the model’s performance in the simulation of sensible and latent heat fluxes at the sites, more noticeably
at the suburban site where the vegetated area fraction is the largest among the sites. Sensitivity analyses for model input
parameters in VUCM elucidated the relative importance of the morphological, aerodynamic, hydrological and radiative/thermal
properties in modelling urban surface fluxes and canopy air conditions for daytime and nighttime periods. These results suggest
that the VUCM has great potential for urban atmospheric numerical modelling for a range of cities and weather conditions in
addition to having a better physical basis in the representation of urban vegetated areas and associated physical processes. 相似文献
3.
Valéry Masson 《Boundary-Layer Meteorology》2000,94(3):357-397
An urban surface scheme for atmospheric mesoscale models ispresented. A generalization of local canyon geometry isdefined instead of the usual bare soil formulation currently usedto represent cities in atmospheric models. This allows refinement ofthe radiative budgets as well as momentum, turbulent heat and ground fluxes.The scheme is aimed to be as general as possible, in order to representany city in the world, for any time or weather condition(heat island cooling by night, urban wake, water evaporation after rainfalland snow effects).Two main parts of the scheme are validated against published data.Firstly, it is shown that the evolution of the model-predictedfluxes during a night with calm winds is satisfactory, considering both the longwave budget and the surface temperatures. Secondly, the original shortwave scheme is tested off-line and compared to the effective albedoof a canyon scale model. These two validations show that the radiative energy input to the urban surface model is realistic.Sensitivity tests of the model are performed for one-yearsimulation periods, for both oceanic and continental climates. The scheme has the ability to retrieve, without ad hoc assumptions, the diurnal hysteresis between the turbulent heat flux and ground heat flux. It reproduces the damping of the daytime turbulent heat flux by the heat storage flux observed in city centres. The latent heat flux is negligible on average,but can be large when short time scales are considered (especially afterrainfall). It also suggests that in densely built areas, domesticheating can overwhelm the net radiation, and supply a continuous turbulentheat flux towards the atmosphere. This becomes very important inwinter for continental climates. Finally, a comparison with a vegetation scheme shows that the suburban environment can be represented with a bare soil formulation for large temporal or spatial averages (typical of globalclimatic studies), but that a surface scheme dedicated to the urban surface is necessary when smaller scales are considered: town meteorological forecasts, mesoscale or local studies. 相似文献
4.
Study on Effects of Building Morphology on Urban Boundary Layer Using an Urban Canopy Model 
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下载免费PDF全文 An urban canopy model is incorporated into the Nanjing University Regional Boundary Layer Model. Temperature simulated by the urban canopy model is in better agreement with the observation, especially in the night time, than that simulated by the traditional slab model. The coupled model is used to study the effects of building morphology on urban boundary layer and meteorological environment by changing urban area, building height, and building density.It is found that when the urban area is expanded, the urban boundary layer heat flux, thermal turbulence, and the turbulent momentum flux and kinetic energy all increase or enhance, causing the surface air temperature to rise up. The stability of urban atmospheric stratification is affected to different extent at different times of the day.When the building height goes up, the aerodynamic roughness height, zero plane displacement height of urban area, and ratio of building height to street width all increase. Therefore, the increase in building height results in the decrease of the surface heat flux, urban surface temperature, mean wind speed, and turbulent kinetic energy in daytime. While at night, as more heat storage is released by higher buildings, thermal turbulence is more active and surface heat flux increases, leading to a higher urban temperature.As the building density increases, the aerodynamic roughness height of urban area decreases, and the effect of urban canopy on radiation strengthens. The increase of building density results in the decrease in urban surface heat flux, momentum flux, and air temperature, the increase in mean wind speed, and the weakening of turbulence in the daytime. While at night, the urban temperature increases due to the release of more heat storage. 相似文献
5.
The Mellor–Yamada–Nakanishi–Niino (MYNN) planetary boundary-layer (PBL) scheme is a second-order turbulence closure model that is an improved version of the Mellor–Yamada scheme based on large-eddy simulation data. It simulates PBL structure and evolution well, particularly over the ocean surface. However, when used with various underlying surfaces in China, the scheme overestimates the turbulent momentum flux and the sensible heat flux. Based on observations of surface fluxes in China, we attempt to improve the MYNN model by modifying the parameters and representation of the turbulence scale. Closure constants and empirical expressions in the diagnostic equation are chosen first, and an additional component of the turbulent heat flux is considered in the potential temperature prognostic equation to improve the surface heat-flux modelling. The modified MYNN scheme is incorporated into a three-dimensional mesoscale model and is evaluated using various underlying surface observations. Amelioration of the surface turbulent fluxes is confirmed at five observational sites in China over different land-use types. 相似文献
6.
应用城市冠层模式研究建筑物形态对城市边界层的影响 总被引：5，自引：1，他引：4
文中将城市冠层模式耦合到南京大学城市尺度边界层模式中,通过模拟对比发现,耦合模式对城市地区气温模拟结果更接近于观测值,尤其是对城市地区夜间气温模拟的改进.运用改进耦合模式通过多个敏感性试验的模拟,从城市面积扩张、建筑物高度增加、建筑物分布密度变化等角度研究城市建筑物三维几何形态变化对城市边界层及城市气象环境的影响,试验结果表明:(1)城市面积扩张使得城市下垫面的热通量增大,热力湍流活动增强,动量通量输送增强,城市湍能增大,湍流扩散系数变大,城市气温升高,且对不同时刻城市区域大气层结稳定度均有不同程度的影响.(2)建筑物高度增加增大了城市下垫面的粗糙度和零平面位移.同时也增大了城市街渠高宽比.城市建筑物越高,白天城市地区地表热通量越小,城市上空大气温度越低,平均风速减小,湍能减小;夜间由于高大建筑物释放储热比低矮建筑物要多,其热力湍流相对活跃,地表热通量增大,使得城市区域气温较高.(3)建筑物密度增大,会减小城市下垫面的粗糙度同时增强街渠对辐射的影响.建筑物密度增大在白天会减小地表热通量和动量通量,使城市气温降低,平均风速增大,城市湍流活动能力减弱;夜间城市释放较多储热使得气温较高. 相似文献
7.
B. Offerle C. S. B. Grimmond K. Fortuniak K. Kłysik T. R. Oke 《Theoretical and Applied Climatology》2006,84(1-3):103-115
Summary Energy fluxes have been measured over an area near the centre of the city of Łódź, Poland, since November 2000. The site was
selected because the building style (surface cover and morphology) is typical of European cities, yet distinct from the majority
of cities where energy balance observations have been studied thus far. The multi-year dataset permits consideration of temporal
changes in energy balance partitioning over a wide range of seasonal and synoptic conditions and of the role of heat storage
and anthropogenic fluxes in the energy balance. Partitioning of net radiation into the turbulent fluxes is consistent in the
two years, with the largest differences occurring due to differing precipitation. The monthly ensemble diurnal cycles of the
turbulent fluxes over the two years are similar. The largest differences occur during the July–September period, and are attributable
to greater net radiation and lower rainfall in 2002. The latent heat flux accounts for approximately 40% of the turbulent
heat transfer on an annual basis. The average daily daytime Bowen ratio and its variability are slightly reduced during the
summer (growing) season. Anthropogenic heat is a significant input to the urban energy balance in the winter. The fluxes observed
in this study are consistent with results from other urban sites. 相似文献
8.
The Atmospheric Boundary Layer Over Baltic Sea Ice 总被引：4，自引：0，他引：4
A new parametrization for the surface energy balance of urban areas is presented. It is shown that this new method can represent some of the important urban phenomena, such as an urban heat island and the occurrence of a near-neutral nocturnal boundary layer with associated positive turbulent heat fluxes, unlike the traditional method for representing urban areas within operational numerical weather prediction (NWP) models. The basis of the new parametrization is simple and can be applied easily within an operational NWP model. Also, it has no additional computational expense compared to the traditional scheme and is hence applicable for operational forecasting requirements. The results show that the errors for London within the Met Office operational mesoscale model have been significantly reduced since the new scheme was introduced. The bias and root-mean-square (rms) errors have been approximately halved, with the rms error now similar to the model as a whole. The results also show that a seasonal cycle still exists in the model errors, but it is suggested that this may be caused by anthropogenic heat sources that are neglected in the urban scheme.The British Crowns right to retain a non-exclusive royalty-free license in and to any copyright is acknowledged. 相似文献
9.
From September 2006 to September 2007, the intersite variability of turbulence characteristics and turbulent heat fluxes was analysed at two urban stations in Essen, Germany. One site was situated within an urban residential setting while the other was located at the border of an urban park and suburban/urban residential housing. Therefore, the surroundings at both sites contributing to surface–atmosphere exchange differed in terms of surface cover and surface morphology. During the 1-year measurement period, 19% of data were characterised by stable atmospheric stratification. Since observations of urban turbulence characteristics under stable stratification are scarce, so far, this work adds additional input to this discussion. Turbulence characteristics, i.e. normalised standard deviations of wind components, were in agreement to empirical fits from other urban observations under both instable and stable atmospheric stratification. However, differences in magnitude of turbulence characteristics between sites were observable. Comparison of turbulent heat fluxes indicated typical urban features in the site located in the urban setting with increased surface heating and higher surface heat fluxes by about 30%. Also the temporal evolution of heat fluxes on the diurnal course was affected. Differences in momentum flux were of minor magnitude with about 6% variation on average between sites. Findings indicate that multiple urban flux measurements within one city may be characterised by general similarities in terms of turbulent characteristics but are still significantly influenced by differences in the surface cover of the flux footprint. 相似文献
10.
Two surface layer parameterization schemes along with five planetary boundary layer (PBL) schemes in the Weather Research and Forecasting model (WRF) are analyzed in order to evaluate the performance of the WRF model in simulating the surface variables and turbulent fluxes over an Indian sub-continent region. These surface layer schemes are based on the fifth-generation Pennsylvania State University—National Center for Atmospheric Research Mesoscale Model (MM5) parameterization; (a) Old MM5 scheme having Businger-Dyer similarity functions and (b) revised MM5 scheme utilizing the functions that are valid for full ranges of atmospheric stabilities. The study suggests that each PBL scheme can reproduce the diurnal variation of 2 m temperature, momentum flux and sensible heat flux irrespective of the surface layer scheme used for the simulations. However, a comparison of model-simulated values of surface variables and turbulent fluxes with observed values suggests that each PBL scheme is found to systematically over-estimate the nocturnal 2 m temperature and 10 m wind speed with both the revised and old schemes during stable conditions. 相似文献
11.
R. A. Spronken-Smith M. Kossmann P. Zawar-Reza 《Theoretical and Applied Climatology》2006,84(1-3):137-149
Summary Typical observations of surface energy fluxes in urban areas usually employ the eddy covariance approach with measurements
from a tower at a height well above the roughness elements. Net radiation and the turbulent fluxes are directly measured,
the anthropogenic flux may be estimated and the storage flux is calculated as an energy balance residual. This paper reports
both measurement and modelling of energy fluxes during wintertime in suburban areas of Christchurch, New Zealand. Under settled
anticyclonic conditions, a strong inversion can occur over the city which severely restricts turbulent mixing. Even after
sunrise the turbulent fluxes are small, and if one assumes advection is negligible, this means the storage flux increases
in importance to very high levels. This paper suggests that these high storage rates are physically unrealistic for this environment.
Rather, it is likely that some energy, which is assumed to be dissipated as heat storage, is more likely lost through mesoscale
advection or attributed to errors caused by unsuitable measurement techniques under conditions with low friction velocity.
However, even these two processes cannot fully account for flux loss. A full study is recommended to resolve this issue and
meanwhile, caution is advised when applying current research methodology to estimate storage fluxes in urban areas in stable
wintertime conditions. 相似文献
12.
MM5模式中城市冠层参数化方案的设计及其数值试验 总被引：15，自引：5，他引：15
文中在综合国外一些较先进的中尺度模式城市作用参数化方案的基础上 ,从城市下垫面结构对城市边界层大气作用的物理机制及实际应用两方面出发 ,对城市下垫面结构和人为活动等因素对边界层结构的影响及中尺度模式中城市化作用的合理体现等问题进行了较全面的考虑 ,改进和设计出能够较全面、细致地描述城市结构对大气边界层动力、热力结构的影响 ,且适合中尺度模式结构特点的城市冠层参数化方案 (UCP) ,并实现了其与MM5模式的耦合。进行了耦合后的UCP方案及采用原城市作用方案的MM5模式对BECAPEX试验期间北京地区气象条件多重嵌套细尺度进行了模拟试验 ,并与观测结果对比 ,结果表明 :相比于MM 5模式中原有表示城市作用的参数化方案来讲 ,设计的UCP方案在很大程度上提高了MM 5模式对城市边界层热力和动力结构的模拟能力。 相似文献
13.
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
14.
Simultaneous energy balance observations at a rural and a suburban site in Vancouver, B.C. during the summer of 1983 are presented. The study is a follow-up to that conducted in 1980. Many of the 1980 results were unexpected and the present study seeks to assess their representativeness. The net radiant, turbulent sensible, and rural soil heat flux densities were measured directly. The suburban heat storage was parameterized and the turbulent latent heat flux densities were resolved as residuals in the energy balances. The 1983 average diurnal energy partitioning for both sites was typical of those quoted in the literature, suggesting that the 1980 results represent an extreme case. Suburban-rural differences showed the suburban area to have a 4% increase in net radiation, a 51% increase in turbulent sensible heat, and a 46% decrease in turbulent latent heat flux density. The values of the average daytime Bowen ratio were 0.46 and 1.28 for the rural and suburban areas, respectively. The sensible heat flux density exhibited relatively large values in the late afternoon and remained directed upward on many summer evenings. Large day-to-day variability in the relative magnitude of the suburban turbulent fluxes may have been due to synoptic influences. In this environment, the turbulent surface and mixed layers are closely coupled because of the low aerodynamic resistance over the rough surface. 相似文献
15.
16.
We examine the performance of several methods to estimate meteorological inputs for modelling dispersion in urban areas during
convective conditions. Sensible heat flux, surface friction velocity and turbulent velocities are estimated from measurements
of mean wind speed and the standard deviation of temperature fluctuations at a single level on a tower at two suburban sites
and at one urban site in Riverside, California. These estimates are compared with observations made at these sites during
a field study conducted in 2007. The sensible heat flux is overestimated in the urban area, while it is underestimated at
a suburban site when temperature fluctuations are used in the free convection formulation to estimate heat flux. The bias
in heat flux estimates can be reduced through a correction that depends on stability. It turns out that the bias in heat flux
estimates has a minor effect on the prediction of surface friction velocity and turbulent velocities. Estimates of sensible
heat flux, surface friction velocity and turbulent velocities are sensitive to estimates of aerodynamic roughness length,
and we suggest estimating the aerodynamic roughness length through detailed micrometeorological measurements made during a
limited field study. An examination of the impact of the uncertainty in estimating surface micrometeorology on concentrations
indicates that, at small distances from a surface release, ground-level concentrations computed using estimates of heat flux
and surface friction compare well with the those based on observed values: the bias is small and the 95% confidence interval
of the ratio of the two concentrations is 1.7. However, at distances much larger than the Obukhov length, this confidence
interval is close to 2.3 because errors in both friction velocity and heat flux affect plume spread. Finally, we show that
using measurements of temperature fluctuations in estimating heat flux is an improvement on that based on the surface energy
balance, even when net radiation measurements are available. 相似文献
17.
S. Weber 《Theoretical and Applied Climatology》2006,83(1-4):169-179
Summary This study concentrates on measurements of ground heat fluxes within a porous urban ballast layer that were conducted from
June to September 2002 at the goods station in Osnabrück, Germany. To account for the limitation of accurately installing
sensors within the heterogeneous and porous ballast bulk, the heat fluxes were calculated from four different methods to compare
their variability, dynamics and shortcomings. Ground heat fluxes were gathered from 1) a heat flux plate with the inclusion
of heat storage between the soil surface and the heat flux plate, 2) temperature gradient measurements with correction for
heat storage, 3) temperature gradient measurements with a modelled surface temperature and a laboratory derived thermal conductivity,
4) as residual from the surface energy balance equation. The results show a distinct deviation of the four methods for absolute
values of the ground heat flux as well as for temporal dynamics on the diurnal cycle. As indicated by the temporal dynamics
of the ground heat flux times series and a simple error analysis of the four methods, the most plausible estimates for an
urban application in a heterogeneous ballast layer were obtained by temperature gradient measurements between the surface
and −0.05 m. Overall, the results indicate that accurate ground heat flux measurements in urban applications still prove difficult
to acquire. 相似文献
18.
Adrie F. G. Jacobs Bert G. Heusinkveld Albert A. M. Holtslag 《Boundary-Layer Meteorology》2008,126(1):125-136
Observations for May and August, 2005, from a long-term grassland meteorological station situated in central Netherlands were
used to evaluate the closure of the surface energy budget. We compute all possible enthalpy changes, such as the grass cover
heat storage, dew water heat storage, air mass heat storage and the photosynthesis energy flux, over an averaging time interval.
In addition, the soil heat flux was estimated using a harmonic analysis technique to obtain a more accurate assessment of
the surface soil heat flux. By doing so, a closure of 96% was obtained. The harmonic analysis technique appears to improve
closure by 9%, the photosynthesis for 3% and the rest of the storage terms for a 3% improvement of the energy budget closure.
For calm nights (friction velocity u
* < 0.1 m s−1) when the eddy covariance technique is unreliable for measurement of the vertical turbulent fluxes, the inclusion of a scheme
that calculates dew fluxes improves the energy budget closure significantly. 相似文献
19.
Thomas Loridan Fredrik Lindberg Oriol Jorba Simone Kotthaus Susanne Grossman-Clarke C. S. B. Grimmond 《Boundary-Layer Meteorology》2013,147(3):493-523
The parameterization of surface heat-flux variability in urban areas relies on adequate representation of surface characteristics. Given the horizontal resolutions (e.g. $\approx $ 0.1–1 km) currently used in numerical weather prediction (NWP) models, properties of the urban surface (e.g. vegetated/built surfaces, street-canyon geometries) often have large spatial variability. Here, a new approach based on Urban Zones to characterize Energy partitioning (UZE) is tested within a NWP model (Weather Research and Forecasting model; WRF v3.2.1) for Greater London. The urban land-surface scheme is the Noah/Single-Layer Urban Canopy Model (SLUCM). Detailed surface information (horizontal resolution 1 km) in central London shows that the UZE offers better characterization of surface properties and their variability compared to default WRF-SLUCM input parameters. In situ observations of the surface energy fluxes and near-surface meteorological variables are used to select the radiation and turbulence parameterization schemes and to evaluate the land-surface scheme and choice of surface parameters. For radiative fluxes, improved performance (e.g. $>$ 25 W m $^{-2}$ root-mean-square error reduction for the net radiation) is attained with UZE parameters compared to the WRF v3.2.1 default for all three methods from the simplest to the most detailed. The UZE-based spatial fluxes reproduce a priori expectations of greater energy storage and less evaporation in the dense city centre compared to the residential surroundings. Problems in Noah/SLUCM partitioning of energy between the daytime turbulent fluxes are identified with the overestimation of the turbulent sensible heat and underestimation of the turbulent latent heat fluxes. 相似文献
20.
The impact of new land surface physics on the GCM simulation of climate and climate sensitivity 总被引：16，自引：4，他引：12
P. M. Cox R. A. Betts C. B. Bunton R. L. H. Essery P. R. Rowntree J. Smith 《Climate Dynamics》1999,15(3):183-203
Recent improvements to the Hadley Centre climate model include the introduction of a new land surface scheme called “MOSES”
(Met Office Surface Exchange Scheme). MOSES is built on the previous scheme, but incorporates in addition an interactive plant
photosynthesis and conductance module, and a new soil thermodynamics scheme which simulates the freezing and melting of soil
water, and takes account of the dependence of soil thermal characteristics on the frozen and unfrozen components. The impact
of these new features is demonstrated by comparing 1×CO2 and 2×CO2 climate simulations carried out using the old (UKMO) and new (MOSES) land surface schemes. MOSES is found to improve the
simulation of current climate. Soil water freezing tends to warm the high-latitude land in the northern Hemisphere during
autumn and winter, whilst the increased soil water availability in MOSES alleviates a spurious summer drying in the mid-latitudes.
The interactive canopy conductance responds directly to CO2, supressing transpiration as the concentration increases and producing a significant enhancement of the warming due to the
radiative effects of CO2 alone.
Received: 16 March 1998 / Accepted: 4 August 1998 相似文献