利用区域尺度气象模式模拟黑河地区地表能量通量的研究

应用中尺度区域模式RAMS (the regional atmospheric model system), 在40余组不同参数的条件下模拟中国干旱半干旱黑河地区的地表能量通量和土壤温度特征, 并以此探索模式在干旱半干旱地区的适用性。为了证明模拟结果的准确性和模式的稳定性, 模拟连续运行30天, 其中包含晴好和阴雨的天气过程。模拟结果表明: 即使使用较为可靠的NECP再分析气压层资料和实地探测资料, 进行初始场和参数的输入, RAMS的默认设置也很难较为合理地反演出地表能量通量, 只有合理地调整好其土壤特征参数, RAMS才能得到与实测资料符合得较好的结果。土壤特征参数对模拟结果影响较大, 影响因子的重要性依次为: 土壤含水量、 土壤层总厚度、 土壤温度。     

WRF/NCAR模拟的夏季长三角城市群区域多城市热岛和地表能量平衡

利用一个包含城市冠层效应的区域模式(WRF/NCAR),对长三角特大城市群的夏季气候效应进行了5 a(2003—2007年)高分辨数值模拟,通过长三角地区有无城市的对比试验分析,重点分析了城市群所造成的多城市热岛和地表能量平衡及其日变化特征。结果表明:城市化会导致显著的地表升温,但昼夜不同的升温幅度造成城市地表温度日较差的降低,以及部分郊区日较差增加;城市化也减小城市近地面风速,但沿海城市升温造成的热力差异,增大白天的海风并降低夜间的陆风。同时大范围城市群的热岛能够显著降低低层气压,导致部分海面风速持续的增加;城市下垫面具有很小的潜热通量,但感热通量和热存储量较大,白天的热岛逐渐增加,并在日落前达到最大,夜间热岛基本维持,但在日出前后迅速减弱;较大的入射短波辐射、较小的向下长波辐射和较低的10 m风速能够减弱白天的热岛,而增强夜间的热岛,并且使热岛峰值从17时延后至20时出现;反之亦然。     

Influence of heterogeneous land surfaces on surface energy and mass fluxes

Summary Land-surface heterogeneity affects surface energy fluxes. The magnitudes of selected land-surface influences are quantified by comparing observations with model simulations of the FIFE (First ISLSCP Field Experiment) domain. Several plausible heterogeneous and homogeneous initial and boundary conditions are examined, although soilmoisture variability is emphasized. It turns out that simple spatial averages of surface variation produced biased flux values. Simulated maximum latent-heat fluxes were approximately 30 to 40 W m^–2 higher, and air temperatures 0.4 °C lower (at noon), when computations were initialized with spatially averaged soil-moisture and leaf-area-index fields. The planetary boundary layer (PBL) height and turbulent exchanges were lower as well. It additionally was observed that (largely due to the nonlinear relationship between initial soil-moisture availability and the evapotranspiration rate), real latent-heat flux can be substantially less than simulated latent-heat flux using models initialized with spatially averaged soil-moisture fields. Differences between real and simulated fluxes also vary with the resolution at which real soil-moisture heterogeneity is discretized.With 8 Figures     

Modelling surface energy fluxes and temperatures in dry and wet bare soils

Abstract

A physically‐based numerical model was developed to estimate the temporal course of the surface energy flux densities and the soil temperatures in dry and wet bare soils. Aerodynamic heat, vapour and momentum transfer theory was used to calculate the sensible and latent heat flux densities at the surface under diabatic and adiabatic conditions. A finite‐difference solution of the differential equation describing one‐dimensional heat transfer was used to calculate the surface soil heat flux density and soil profile temperatures. The surface temperature was determined iteratively by the simultaneous solution of equations describing radiative, heat and momentum transfer at the surface. The model was tested with measurements from energy balance studies conducted on a dry, sandy soil and a wet, silt loam soil, and was found to predict accurately the surface energy fluxes and soil temperatures over three‐day periods under conditions of potential and negligible evaporation. The sensitivity of the model to uncertainties in the aerodynamic roughness lengths for momentum (z₀) and heat (z_T) is reported. Values for z₀ and Z₀/Z_T of 0.5 mm and 3.0, respectively, resulted in the best agreement between modelled and measured values of the fluxes and temperatures for both soils.     

基于WRF模式的京津冀地区地表大气CO2浓度的模拟研究

在“双碳”目标背景下,从国家层面到地方层面,区域、城市、行业企业都在制定和实施双碳目标行动计划。CO₂模拟因其客观性和高时空分辨率等优势,在城市碳排放研究中深受重视。本研究以京津冀地区为研究区域,采用Picarro仪器高精度观测的2019—2020年CO₂数据,利用WRF模式进行CO₂传输模拟,分析了CO₂浓度变化的季节特征,评估了模式在城区中心、城郊及背景3个观测站点的模拟效果,并对边界层高度及化石燃料碳排放等可能影响CO₂浓度的因素进行了研究。3个观测站点分别为北京中国科学院大气物理研究所325 m气象塔观测站(北京站)、河北香河观测站(香河站)和上甸子区域本底观测站(上甸子站)。模拟结果表明：上甸子站优于香河站,香河站优于北京站,在冬季尤其明显;CO₂浓度的高值区主要分布在城区、电厂和工业区,尤其是唐山、石家庄和邯郸地区,大量交通、工业排放导致CO₂浓度明显上升,且高值区的范围在冬季最大;就日平均变化和日变化而言,边界层高度与C...     

Influences on surface energy fluxes in simulated present and doubled CO2 climates

The surface energy fluxes simulated by the CSIRO9 Mark 1 GCM for present and doubled CO₂ conditions are analyzed. On the global scale the climatological flux fields are similar to those from four GCMs studied previously. A diagnostic calculation is used to provide estimates of the radiative forcing by the GCM atmosphere. For 1 × CO₂, in the global and annual mean, cloud produces a net cooling at the surface of 31 W m^–2. The clear-sky longwave surface greenhouse effect is 311 W m^–2, while the corresponding shortwave term is –79 W m^–2. As for the other GCM results, the CSIRO9 CO₂ surface warming (global mean 4.8°C) is closely related to the increased downward longwave radiation (LW ). Global mean net cloud forcing changes little. The contrast in warming between land and ocean, largely due to the increase in evaporative cooling (E) over ocean, is highlighted. In order to further the understanding of influences on the fluxes, simple physically based linear models are developed using multiple regression. Applied to both 1 × CO₂ and CO₂ December–February mean tropical fields from CSIRO9, the linear models quite accurately (3–5 W m^–2 for 1 × CO₂ and 2–3 W m^–2 for CO₂) relate LW and net shortwave radiation to temperature, surface albedo, the water vapor column, and cloud. The linear models provide alternative estimates of radiative forcing terms to those from the diagnostic calculation. Tropical mean cloud forcings are compared. Over land, E is well correlated with soil moisture, and sensible heat with air-surface temperature difference. However an attempt to relate the spatial variation of LWt within the tropics to that of the nonflux fields had little success. Regional changes in surface temperature are not linearly related to, for instance, changes in cloud or soil moisture.     

Computation of vertical total energy fluxes in a moist atmosphere

This paper examines the computation of surface-level vertical fluxes of total energy in a moist atmosphere. A flux equation is derived which includes the enthalpy of water, the temperature dependence of the latent heat of condensation and variable moisture composition of air. The complete formulation requires keeping track of liquid water fluxes. However, if this is not possible, then the total energy flux is best approximated by neglecting the enthalpy of all net fluxes of water substance. An important finding is that sensible heat fluxes derived using a moist specific heat at constant pressure are not compatible with usual formulations of latent heat unless the net vapor flux is neglected.     

The atmospheric energy budget and implications for surface fluxes and ocean heat transports

Comprehensive diagnostic comparisons and evaluations have been carried out with the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and European Centre for Medium Range Weather Forecasts (ECMWF) reanalyses of the vertically integrated atmospheric energy budgets. For 1979 to 1993 the focus is on the monthly means of the divergence of the atmospheric energy transports. For February 1985 to April 1989, when there are reliable top-of-the-atmosphere (TOA) radiation data from the Earth Radiation Budget Experiment (ERBE), the implied monthly mean surface fluxes are derived and compared with those from the assimilating models and from the Comprehensive Ocean Atmosphere Data Set (COADS), both locally and zonally integrated, to deduce the implied ocean meridional heat transports. While broadscale aspects and some details of both the divergence of atmospheric energy and the surface flux climatological means are reproducible, especially in the zonal means, differences are also readily apparent. Systematic differences are typically ∼20 W m⁻². The evaluation highlights the poor results over land. Land imbalances indicate local errors in the divergence of the atmospheric energy transports for monthly means on scales of 500 km (T31) of 30 W m⁻² in both reanalyses and ∼50 W m⁻² in areas of high topography and over Antarctica for NCEP/NCAR. Over the oceans in the extratropics, the monthly mean anomaly time series of the vertically integrated total energy divergence from the two reanalyses correspond reasonably well, with correlations exceeding 0.7. A common monthly mean climate signal of about 40 W m⁻² is inferred along with local errors of 25 to 30 W m⁻² in most extratropical regions. Except for large scales, there is no useful common signal in the tropics, and reproducibility is especially poor in regions of active convection and where stratocumulus prevails. Although time series of monthly anomalies of surface bulk fluxes from the two models and COADS agree very well over the northern extratropical oceans, the total fields all contain large systematic biases which make them unsuitable for determining ocean heat transports. TOA biases in absorbed shortwave, outgoing longwave and net radiation from both reanalysis models are substantial (>20 W m⁻² in the tropics) and indicate that clouds are a primary source of problems in the model fluxes, both at the surface and the TOA. Time series of monthly COADS surface fluxes are shown to be unreliable south of about 20^∘N where there are fewer than 25 observations per 5^∘ square per month. Only the derived surface fluxes give reasonable implied meridional ocean heat transports. Received: 21 March 2000 / Accepted: 21 June 2000     

Estimation of areally-averaged surface fluxes

The concept of blending height is used to estimate areally averaged surface fluxes of momentum and heat in a stratified, horizontally inhomogeneous surface-layer flow. This concept is based on the assumption that at sufficiently large heights above a heterogeneous surface, subsequent surface modifications will not be recognizable in the flow individually, but overall flux and mean profiles will represent the surface condition of a large area. The height at which the flow becomes approximately independent of horizontal position is called blending height according to Wieringa (1986).Here, it is proposed to classify the ground surface in a surface-layer grid box of a larger-scale model into several land-use categories. Surface momentum and heat fluxes should be estimated for each category at the blending height. The grid-averaged surface fluxes are to be obtained by the average of surface fluxes on each land-use surface weighted by its fractional area. The postulate of computing the surface fluxes at the blending height leads to a new formulation of turbulent transfer coefficients.The proposed parameterization has been tested by employing a small-scale numerical model as a surface-layer grid box of a hypothesized larger-scale model. Several quite different flow configurations have been studied in order to investigate the performance of the new parameterization. Generally, the relative errors of estimated averaged surface fluxes are found to be well within ±10%.     

Influence of irrigated agriculture on diurnal surface energy and water fluxes, surface climate, and atmospheric circulation in California

The impact of land use change on regional climate can be substantial but also is variable in space and time. Past observational and modeling work suggests that in a ‘Mediterranean’ climate such as in California’s Central Valley, the impact of irrigated agriculture can be large in the dry season but negligible in the wet season due to seasonal variation in surface energy partitioning. Here we report further analysis of regional climate model simulations showing that diurnal variation in the impact of irrigated agriculture on climate similarly reflects variation in surface energy partitioning, as well as smaller changes in net radiation. With conversion of natural vegetation to irrigated agriculture, statistically significant decreases of 4–8?K at 2?m occurred at midday June–September, and small decreases of ~1?K occurred in winter months only in relatively dry years. This corresponded to reduced sensible heat flux of 100–350?W?m^?2 and increased latent heat fluxes of 200–450?W?m^?2 at the same times and in the same months. We also observed decreases of up to 1,500?m in boundary layer height at midday in summer months, and marginally significant reductions in surface zonal wind speed in July and August at 19:00 PST. The large decrease in daytime temperature due to shifts in energy partitioning overwhelmed any temperature increase related to the reduced zonal sea breeze. Such changes in climate and atmospheric dynamics from conversion to (or away from) irrigated agriculture could have important implications for regional air quality in California’s Central Valley.     

Comparative measurements of the energy fluxes over a pine forest

During the summer of 1974, simultaneous heat flux measurements were made over a pine forest in three ways:

1. Using the Bowen ratio - Energy Budget technique, with the Bowen ratio estimated from temperature and humidity profiles measured with two pairs of wet-and dry-bulb thermometers at six levels.
2. Using the Bowen ratio - Energy Budget technique, with the Bowen ratio estimated from temperature and humidity measurements using pairs of wet-and dry-bulb thermometers mechanically interchanged every ten minutes.
3. Using the Eddy Correlation - Energy Budget technique, with a direct measurement of the sensible heat flux made by a simple eddy correlation apparatus.

Methods (b) and (c) are shown to give similar results apart from a systematic difference of about 25% in the measured sensible heat flux. This corresponds to an underestimate of the sensible heat flux by the eddy correlation apparatus. Although sometimes consistent with the other two methods, on occasions method (a) gave results which were significantly different from both (b) and (c). When differences occurred, they tended to be systematic and persistent over individual days; but they could change magnitude and sign if the particular sensors used at each level in the profile were rearranged. The experimental program used to collect these and previous data involved the rearrangement of sensors on a regular (two day) time scale. It is shown that, when averaged over several such rearrangements, method (a) produces median values of surface resistance which are more in keeping with those produced by the other methods. This is taken to imply that data previously gathered in this way can be used to produce physically reasonable results providing they are averaged over several days. On the basis of the results presented, recommendations are made on future experimental work in forest micrometeorology.     

Dependence of Indian monsoon rainfall on moisture fluxes across the Arabian Sea and the impact of coupled model sea surface temperature biases

The Arabian Sea is an important moisture source for Indian monsoon rainfall. The skill of climate models in simulating the monsoon and its variability varies widely, while Arabian Sea cold sea surface temperature (SST) biases are common in coupled models and may therefore influence the monsoon and its sensitivity to climate change. We examine the relationship between monsoon rainfall, moisture fluxes and Arabian Sea SST in observations and climate model simulations. Observational analysis shows strong monsoons depend on moisture fluxes across the Arabian Sea, however detecting consistent signals with contemporaneous summer SST anomalies is complicated in the observed system by air/sea coupling and large-scale induced variability such as the El Ni?o-Southern Oscillation feeding back onto the monsoon through development of the Somali Jet. Comparison of HadGEM3 coupled and atmosphere-only configurations suggests coupled model cold SST biases significantly reduce monsoon rainfall. Idealised atmosphere-only experiments show that the weakened monsoon can be mainly attributed to systematic Arabian Sea cold SST biases during summer and their impact on the monsoon-moisture relationship. The impact of large cold SST biases on atmospheric moisture content over the Arabian Sea, and also the subsequent reduced latent heat release over India, dominates over any enhancement in the land-sea temperature gradient and results in changes to the mean state. We hypothesize that a cold base state will result in underestimation of the impact of larger projected Arabian Sea SST changes in future climate, suggesting that Arabian Sea biases should be a clear target for model development.     

Spatial variability of energy fluxes in suburban terrain

Energy fluxes over an area of homogeneous suburban residential land-use in Vancouver, B.C., Canada are shown to vary by up to 25–40% within horizontal scales on the order of 10²–10³ m. Previously, variability of this magnitude has been expected to occur only at larger scales, between land-use zones or as urban-rural differences. In view of these findings, it is recognized that microadvective interaction between surface types at small scales may be important and can affect the energy balance even at larger scales. The present study discusses the small-scale spatial variability of energy fluxes and shows that it varies greatly for each term in the surface energy balance.Net radiation shows a relatively conservative behaviour (via albedo-surface temperature feedback) with little spatial variability. The turbulent fluxes (measured by eddy correlation at 28 m height), on the other hand, show a link between their temporal and spatial variability as the result of a temporally shifting source area which contains varying combinations of surface cover (using the dynamical source area concept of Schmid and Oke, 1990). As a result, part of the measured temporal variation is attributable to spatial differences in surface cover. Anthropogenic heat flux and storage heat flux (both modelled using a high resolution surface data-base) exhibit temporally varying spatial distributions. Their spatial pattern, however, is governed by nested scales of urban morphology (blocks, streets, properties, etc.). These differences in the source of variability between each component flux suggest a difficulty in the interpretation of the energy balance over urban areas, unless each term is spatially-averaged over the principal morphological units occurring in the area.     

Eddy-correlation measurements of sensible heat fluxes over a grass surface

Direct measurements of sensible heat fluxes were conducted over a grass surface at Ladner, British Columbia, using yaw-sphere-thermometer eddy-correlation systems. The results show that for half-hour averaging periods, there is no phase-lag between sensible heat and net radiation flux densities. Field comparison of two yaw-sphere-thermometer systems gave good and consistent agreement. At a height of 2 m above ground and a horizontal crosswind separation of 1.5 m, less than 5% variability was noted in the measured heat fluxes. For a 19-m horizontal separation, the variability was less than 20%. The aridity index (α) advanced by Priestley and Taylor (1972), is shown to be a potentially useful climatic indicator.     

近地面层湍流通量观测误差的比较

本文根据误差理论分析并比较了在近地面层内各种间接确定湍流通量方法的观测误差。空气动力学法由于采用不同的通用函数将造成很大的误差。H扣除法确定潜热通量,当Bowen比较小时误差较小,Bowen比B>1之后误差随B的增大迅速增长。在相同的观测条件下间接法确定湍流通量以Bowen比法和组合法误差最小,实例计算表明组合法的精度最高。     

Southern hemisphere energy fluxes from analyses with special respect to the Weddell Sea region (antarctica)

Summary Meridional eddy transports of sensible heat and zonal momentum caused by transient and stationary waves are computed from Australian operational analyses. The southward sensible heat flux by transient waves is largest in the midlatitudes, where cyclones are responsible for the heat exchange. The flux decreases towards the Weddell Sea. The transport by stationary waves reaches remarkable values locally in the tropics and off the Antarctic coasts. The transport of zonal momentum is mostly accomplished by transient eddies. Zonal averages, horizontal distributions and fluxes along single latitudes are shown.With 12 Figures     

The effect of topography and sea surface temperature on heavy snowfall in the Yeongdong region: A case study with high resolution WRF simulation

An analysis of the heavy snowfall that occurred on 11?C14 February 2011 in the Yeongdong region along the eastern coast is presented. Relevant characteristics based on observation and model simulations are discussed with a focus on the times of maximum snowfall in Gangneung (GN) and Daegwallyong (DG). This event was considered part of the typical snowfall pattern that frequently occurs in the Yeongdong region due to the prevailing northeasterly flow. The control simulation using the high resolution Weather Research and Forecasting (WRF) model (1 km × 1 km) showed reasonable performance in capturing the spatial distribution and temporal evolution of precipitation. The area of precipitation maxima appeared to propagate from the plain coastal region further into the inland mountainous region, in relation to the location of convergence zone. In addition, a series of sensitivity experiments were performed to investigate the effect of topography and sea surface temperature (SST) on the formation of heavy snowfall. The change of topography tended to modulate the topographically induced mechanical flow, and thereby modify the precipitation distribution, which highlights the importance of an elaborate representation of the topography. On the other hand, the sensitivity experiment to prescribe positive (negative) SST forcing shows the enhanced (suppressed) precipitation amount due to the change of the sensible and latent heat fluxes.     

Divergence of turbulent fluxes in the surface layer: case of a coastal city

This study quantifies the processes that take place in the layer between the mean building height and the measurement level of an energy balance micrometeorological tower located in the dense old core of a coastal European city. The contributions of storage, vertical advection, horizontal advection and radiative divergence for heat are evaluated with the available measurements and with a three-dimensional, high-resolution meteorological simulation that had been evaluated against observations. The study focused on a summer period characterized by sea-breeze flows that affect the city. In this specific configuration, it appears that the horizontal advection is the dominant term. During the afternoon when the sea breeze is well established, correction of the sensible heat flux with horizontal heat advection increases the measured sensible heat flux up to 100 W m⁻². For latent heat flux, the horizontal moisture advection converted to equivalent latent heat flux suggests a decrease of 50 W m⁻². The simulation reproduces well the temporal evolution and magnitude of these terms.