共查询到20条相似文献，搜索用时 46 毫秒
1.
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
2.
A. D. Matthias 《Theoretical and Applied Climatology》1990,42(1):3-17
Summary Soil temperature is often inadequately based upon relatively few measurements at widely dispersed locations. Within arid regions, such as the desert southwestern United States, soils, microclimates, and thus soil temperature may be markedly heterogeneous. Because extensive measurement of soil temperature is often not feasible, models are needed that simulate soil temperature based on readily available soil survey and above-ground weather information. This paper describes a simple energy-budget based model for simulating daily mean temperatures within a bare arid land soil. The model requires basic information on soil physical properties, and daily weather data including air temperature, windspeed, rainfall, and solar radiation to calculate daily surface energy budget components and surface temperature. One of two alternative numerical methods is then used to calculated subsurface temperatures. Tests of the model using 1987 daily temperature data from an arid site at Yuma, Arizona resulted in root mean square deviations within 1.4°C between daily modeled and measured temperatures at both 0.05 and 0.10 m depths. Sensitivity analysis showed modeled temperatures at 0.05 m depth to be most sensitive to parameters affecting the surface energy balance such as air temperature and solar radiation. Modeled temperatures at 1.0m depth were relatively more sensitive to initial temperature conditions and to parameters affecting distribution of energy within the profile such as thermal conductivity.With 3 Figures 相似文献
3.
The heat flux density in a non-homogeneous bare loessial soil 总被引：2，自引：0，他引：2
This work describes the relationship between the diurnal patterns of the radiant energy exchange in the atmospheric surface layer and the soil heat flux density of a bare irrigated soil in an arid environment. The measurements show that the soil heat flux density is a large fraction of the net radiation. The soil moisture content has little effect on this fraction but modifies the phase relationship between the net radiation and the soil heat flux density waves. Differences between the thermal regimes of the wet and dry soil appear to be caused by latent heat exchanges rather than changes of the soil thermal properties. The data also show that the variation with depth of the soil thermal properties strongly influences the propagation of the temperature and heat flux density waves in the soil. A heat diffusion theory for non-homogeneous conductors (Lettau, 1962) which enables the thermal properties of the soil to be predicted is tested by comparison with experimental determinations in the field. 相似文献
4.
Micrometeorological models at various scales require ground surface temperature, which may not always be measured in sufficient spatial or temporal detail. There is thus a need for a model that can calculate the surface temperature using only widely available weather data, thermal properties of the ground, and surface properties. The vegetated/permeable surface energy balance (VP-SEB) model introduced here requires no a priori knowledge of soil temperature or moisture at any depth. It combines a two-layer characterization of the soil column following the heat conservation law with a sinusoidal function to estimate deep soil temperature, and a simplified procedure for calculating moisture content. A physically based solution is used for each of the energy balance components allowing VP-SEB to be highly portable. VP-SEB was tested using field data measuring bare loess desert soil in dry weather and following rain events. Modeled hourly surface temperature correlated well with the measured data (r 2 = 0.95 for a whole year), with a root-mean-square error of 2.77 K. The model was used to generate input for a pedestrian thermal comfort study using the Index of Thermal Stress (ITS). The simulation shows that the thermal stress on a pedestrian standing in the sun on a fully paved surface, which may be over 500 W on a warm summer day, may be as much as 100 W lower on a grass surface exposed to the same meteorological conditions. 相似文献
5.
6.
Abstract A physically‐based numerical model was developed to estimate the temporal course of the surface energy flux densities and the soil temperatures in dry and wet bare soils. Aerodynamic heat, vapour and momentum transfer theory was used to calculate the sensible and latent heat flux densities at the surface under diabatic and adiabatic conditions. A finite‐difference solution of the differential equation describing one‐dimensional heat transfer was used to calculate the surface soil heat flux density and soil profile temperatures. The surface temperature was determined iteratively by the simultaneous solution of equations describing radiative, heat and momentum transfer at the surface. The model was tested with measurements from energy balance studies conducted on a dry, sandy soil and a wet, silt loam soil, and was found to predict accurately the surface energy fluxes and soil temperatures over three‐day periods under conditions of potential and negligible evaporation. The sensitivity of the model to uncertainties in the aerodynamic roughness lengths for momentum (z0) and heat (zT) is reported. Values for z0 and Z0/ZT of 0.5 mm and 3.0, respectively, resulted in the best agreement between modelled and measured values of the fluxes and temperatures for both soils. 相似文献
7.
Incorporating organic soil into a global climate model 总被引：3，自引：1，他引：2
Organic matter significantly alters a soil’s thermal and hydraulic properties but is not typically included in land-surface
schemes used in global climate models. This omission has consequences for ground thermal and moisture regimes, particularly
in the high-latitudes where soil carbon content is generally high. Global soil carbon data is used to build a geographically
distributed, profiled soil carbon density dataset for the Community Land Model (CLM). CLM parameterizations for soil thermal
and hydraulic properties are modified to accommodate both mineral and organic soil matter. Offline simulations including organic
soil are characterized by cooler annual mean soil temperatures (up to ∼2.5°C cooler for regions of high soil carbon content).
Cooling is strong in summer due to modulation of early and mid-summer soil heat flux. Winter temperatures are slightly warmer
as organic soils do not cool as efficiently during fall and winter. High porosity and hydraulic conductivity of organic soil
leads to a wetter soil column but with comparatively low surface layer saturation levels and correspondingly low soil evaporation.
When CLM is coupled to the Community Atmosphere Model, the reduced latent heat flux drives deeper boundary layers, associated
reductions in low cloud fraction, and warmer summer air temperatures in the Arctic. Lastly, the insulative properties of organic
soil reduce interannual soil temperature variability, but only marginally. This result suggests that, although the mean soil
temperature cooling will delay the simulated date at which frozen soil begins to thaw, organic matter may provide only limited
insulation from surface warming. 相似文献
8.
利用青藏高原中部玉树隆宝湿地2015年7月-2016年7月的观测资料,分析了土壤冻结、融化前后土壤温、湿度和地表能量收支特征,结果表明：冻土持续时期为12月至次年4月,深层土壤的冻结较浅层土壤滞后,融化过程快于冻结过程,5-40 cm土壤全部冻结历时51 d,全部融化历时19 d。土壤体积含水量年变化幅度达0.6 m3/m3。冻结过程5-40 cm土壤体积含水量下降,融化过程5-10 cm土壤体积含水量升高。土壤冻结之后,感热通量白天的值升高,潜热通量白天的值降低,净辐射和土壤热通量均降低,土壤热通量日变化幅度增大。土壤融化之后,潜热通量、净辐射和土壤热通量白天的值升高。地表反照率、鲍恩比、土壤热导率和土壤热扩散率冻结后增大融化后减小,土壤热容量冻结后减小融化后增大。 相似文献
9.
2008年7—9月中国北方不同下垫面晴空陆面过程特征差异 总被引：4，自引：1，他引：3
采用2008年7—9月观测的中国干旱/半干旱区实验观测协同与集成研究资料,选取了9个下垫面(包括裸地、草地、森林和农田),分析了中国北方不同下垫面以及不同地区同类下垫面的晴空陆面辐射平衡和热量平衡日变化特征差异。结果表明,不同下垫面以及不同地区同类下垫面的地表辐射和能量过程特征差异明显,而这种差异主要源于下垫面的光学特性、水热特性以及局地陆-气系统中可利用水分的不同。在辐射平衡的比较方面,荒漠沙地发射的长波辐射最大,高寒森林的长波辐射最低,农田下垫面发射的长波辐射总体低于草地;荒漠沙地、草地、农田和高寒森林的反射率依次减弱;荒漠沙地、草地、农田、森林下垫面的净辐射依次增大。在能量平衡方面,荒漠区沙地可利用能量大部分(约80%)用于加热大气,约20%消耗于蒸发和加热土壤;草地下垫面可利用能量中用于加热大气的能量比蒸发水分消耗的能量高,但高寒草甸例外;农田下垫面可利用能量的大部分消耗于蒸发,消耗于加热大气的能量不到20%。水含量越高,潜热通量越大,能量闭合率越低,能量过程也更复杂。 相似文献
10.
D.L. Verseghy 《大气与海洋》2013,51(3):435-456
Abstract The performance of two Canadian land surface schemes of widely differing complexity is compared and contrasted in a pair of year‐long simulations using the GCM developed at Atmospheric Environment Service, Canada. The old land surface model incorporates the force‐restore method for soil temperatures and the bucket approximation for soil moisture; the new model, CLASS (Canadian Land Surface Scheme) features three soil layers, an explicitly modelled snow layer, a thermally separate vegetation canopy, and physically‐based calculations of heat and moisture transfers between all of the land surface components and the atmosphere. It was reported in previous papers that compared with observations, the old scheme tends to generate a climate which is characterized by anomalously high precipitation rates and cold temperatures over land. In this paper, by reference to field measurements and to the energy fluxes and temperatures generated by the two models at local scales, the hypotheses earlier postulated as to the underlying reasons for this are validated. The main factor contributing to the climate anomalies observed with the old scheme is found to be its generation of excessive evaporation rates; this is caused by the fact that the evaporation rate is never directly energy‐limited, the fact that the scaling of the evaporation rale with decreasing soil moisture content underestimates the effect of vegetation stomatal resistance, and the fact that the evaporation rate over bare soil depends not on the surface soil moisture, but on the moisture content of whole modelled soil column. The cold surface temperatures are additionally attributed to systematic errors incurred by the forward‐stepping temperature scheme, and to the fact that soils subjected to subzero temperature forcing in the winter are modelling as freezing completely. Finally, the inability of the old scheme to simulate partially frozen soils means that it proves unable to handle either shallow frost penetration at temperature latitudes, or the development of an active layer in permafrost. 相似文献
11.
Michael D. Novak 《Boundary-Layer Meteorology》1991,56(1-2):141-161
A model that couples the surface energy balance equation, a surface hydraulic resistance equation, and the force-restore soil temperature model to a mixed-layer model of the planetary boundary layer is described. The mixed layer is separated from the soil by a relatively thin surface layer and is overlain by a stable free atmosphere with prescribed profiles of potential temperature and water vapour density. The model is in reasonably good agreement with daytime micrometeorological measurements made at a wet bare site at Agassiz, British Columbia, and a desert site at Pampa de La Joya, Peru. The sensitivity of the mixed-layer model to conditions in the free atmosphere, to the parameters describing the growth of the mixed layer, and to surface roughness lengths, surface hydraulic resistance, and windspeed is examined. 相似文献
12.
Eddy-correlation measurements over snow, wet bare soil, and lake water indicate very small vertical ozone fluxes. Adjustments to the small vertical fluxes are needed to take into account the effect of mean Stefan flow associated with evaporation at the surface and the effects of correlation between density variations and vertical wind fluctuations. For snow, the residual resistance calculated for the surface is about 34 s cm-1, indicating that the maximum deposition velocity is abut 0.03 cm s-1. For cold bare soil well saturated with water, the surface resistance is about 10 s cm-1 (maximum deposition velocity of about 0.1 cm s-1). The highest resistances obtained are for transfer to the surface of Lake Michigan, yielding values near 90 s cm-1 for resistance (0.01 cm s-1 for deposition velocity).Work supported by the U.S. Dept. of Energy and the U.S. Environmental Protection Agency. 相似文献
13.
14.
R. Horton K. L. Bristow G. J. Kluitenberg T. J. Sauer 《Theoretical and Applied Climatology》1996,54(1-2):27-37
Summary Crop residues alter the surface properties of soils. Both shortwave albedo and longwave emissivity are affected. These are linked to an effect of residue on surface evaporation and water content. Water content influences soil physical properties and surface energy partitioning. In summary, crop residue acts to soil as clothing acts to skin. Compared to bare soil, crop residues can reduce extremes of heat and mass fluxes at the soil surface. Managing crop residues can result in more favorable agronomic soil conditions. This paper reviews research results of the quantity, quality, architecture, and surface distribution of crop residues on soil surface radiation and energy balances, soil water content, and soil temperature.With 6 Figures 相似文献
15.
基于Radarsat-2 SAR数据反演定西裸露地表土壤水分 总被引：2，自引：0，他引：2
利用Radarsat-2 SAR数据和定西地区野外土钻法及WET仪器观测的土壤水分数据,分析了同极化后向散射系数与不同土层深度土壤水分之间的关系,采用交叉极化(VV/VH)组合模型反演土壤水分并进行对比验证。结果表明:水平、垂直同极化后向散射系数均与10~20 cm土壤含水量相关性最好,相关系数R均为0.74;受地表粗糙度和土壤质地等影响,同极化后向散射系数与0~10 cm土壤水分相关性均较低。交叉极化组合模型的反演值与10~20 cm实测土壤水分相关性较高,R值达0.75,而与0~10 cm和20~30 cm实测值的相关性较低(R值分别为0.47和0.52),但均通过α=0.05的显著性检验;WET仪器实测0~6 cm土壤水分经校正后与反演值的相关系数为0.46(通过α=0.01的显著性检验),校正后的结果有效提高了WET仪器测量精度。交叉极化组合模型可用于裸露地表土壤水分的反演,更适用于提取10~20 cm土壤含水量信息。 相似文献
16.
利用Landsat7ETM＋遥感资料热红外波段定量反演晴空状态下夏季干旱区典型绿洲地表真实温度,运用影像叠加分析、直方图比对、缓冲区分析和空间自相关分析及剖面线分析等方法,分析其热场分布规律。结果表明：绿洲热场分布具有显著正空间自相关特性,Moran’s值为0．5489,Z值为48．44,同时呈现出显著的局部空间集聚现象;就局部而言,在相同热力环境下,由于盐碱地与裸地热容量不同,盐碱地温度低于周边裸地温度,盐碱地平均温度比周边300、900m和1500m缓冲区裸地的平均气温分别低0．59、0．44℃和0．26℃;然而盐碱地大多分布在裸地的高温区中心,且温度变化幅度小,在裸地低温区周围分布较少,所以就整体而言,裸地平均气温低于盐碱地温度,热场分布规律依次为水体温度21．65、耕地温度27．86、林草地温度35．59、城镇温度40．06℃、裸地温度42．07℃。水体、城镇、盐碱地、裸地的温度波动较小,热力景观单一,热场分布均匀,而耕地和林草地的温度梯度大,热力景观复杂多样,热场分布极不均匀,局部热场存在突变现象。绿洲荒漠交错带的面积较大,可以降低荒漠对绿洲的热力侵蚀,对保护绿洲有重要作用。 相似文献
17.
Bulk Formulation of the Surface Heat Flux 总被引：1，自引：1，他引：1
An interpretive literature survey examines different approachesfor applying the bulk aerodynamic formulato predict the surface heat flux. The surface heat flux is often predicted in terms of the surface radiation temperature, which is also used to predict the upward longwave radiation and the heat flux into the soil. In models, the thermal roughness length based on the surface radiation temperature (radiometric roughness length) is often specified to be smaller than the roughness length for momentum for a number of distinct reasons. The definition of the radiometric roughness length depends on the way that the surface temperature is measured, the choice of stability functions and displacement height and inclusion of any additional resistances.Using airborne eddy correlation data collected over eight different sites including bare soil, crops and grassland and several types of forests, the radiometric roughness length is found to vary by orders of magnitude in a manner that is difficult to formulate. Alternatively, we evaluate the approach where the thermal roughness length is equated with the better behaved roughness length for momentum and the corresponding aerodynamic surface temperature is modelled in terms of the surface radiation temperature, solar radiation, and vegetation index. The influence of wind speed and soil moisture on the difference between the aerodynamic and surface radiation temperatures is also examined. 相似文献
18.
An Amplified Signal of Climatic Change in Soil Temperatures during the Last Century at Irkutsk, Russia 总被引：2，自引：1，他引：2
T. Zhang Roger G. Barry D. Gilichinsky S. S. Bykhovets V. A. Sorokovikov Jingping Ye 《Climatic change》2001,49(1-2):41-76
Climatic changes at the Earth's surface propagate slowly downward into theground and modify the ambient ground thermal regime. However, causes of soiltemperature changes in the upper few meters are not well documented. One majorobstacle to understanding the linkage between the soil thermal regime andclimatic change is the lack of long-term observations of soil temperatures andrelated climatic variables. Such measurements were made throughout the formerSoviet Union with some records beginning at the end of the 19th century. Inthis paper, we use records from Irkutsk, Russia, to demonstrate how the soiltemperature responded to climatic changes over the last century. Both airtemperature and precipitation at Irkutsk increased from the late 1890s to the1990s. Changes in air temperature mainly occurred in winter, while changes inprecipitation happened mainly during summer. There was an anti-correlationbetween mean annual air temperature and annual total precipitation, i.e., more(less) precipitation during cold (warm) years. There were no significanttrends of changes in the first day of snow on the ground in autumn, but snowsteadily disappeared earlier in spring, resulting in a reduction of the snowcover duration. A grass-covered soil experiences seasonal freezing for morethan nine months each year and the long-term average maximum depth ofseasonally frozen soils was about 177 cm with a range from 91 cm to 260 cm.The relatively lower soil temperature at shallow depths appears to representthe so-called `thermal offset' in seasonally frozen soils. Changes in meanannual air temperature and soil temperature at 40 cm depth were about the samemagnitude (2.0 °C to 2.5 °C) over the common period of record, but thepatterns of change were substantially different. Mean annual air temperatureincreased slightly until the 1960s, while mean annual soil temperatureincreased steadily throughout the entire period. This leads to the conclusionthat changes in air temperature alone cannot explain the changes in soiltemperatures at this station. Soil temperature actually decreased duringsummer months by up to 4 °C, while air temperature increased slightly.This cooling in the soil may be explained by changes in rainfall and hencesoil moisture during summer due to the effect of a soil moisture feedbackmechanism. While air temperature increased about 4 °C to 6 °C duringwinter, soil temperature increased by up to 9 °C. An increase in snowfallduring early winter (October and November) and early snowmelt in spring mayplay a major role in the increase of soil temperatures through the effects ofinsulation and albedo changes. Due to its relatively higher thermalconductivity compared to unfrozen soils, seasonally frozen ground may enhancethe soil cooling, especially in autumn and winter when thermal gradient isnegative. 相似文献
19.
敦煌荒漠戈壁地区裸土地表反照率参数化研究 总被引：4，自引：1，他引：3
利用敦煌站观测资料,选取其中观测资料完整且连续性好的7个年份每年5～10月的地表净辐射四分量和土壤湿度资料,分析研究了敦煌荒漠戈壁地区裸土地表反照率与太阳高度角和表层土壤含水量之间的关系,结果表明:地表反照率与太阳高度角呈e指数关系,随太阳高度角的增大而减小,当太阳高度角大于40°时,地表反照率趋于稳定。表层土壤含水量的增大可导致地表反照率的减小,地表反照率与5 cm深土壤湿度呈线性关系。另外,建立了敦煌荒漠戈壁地区裸土地表反照率与太阳高度角和表层土壤含水量之间的双因子参数化公式,提出了一种更加适合该地区的地表反照率参数方案,并且选取2002年6～9月的实测资料对拟合的参数化公式进行模拟验证。本文所提出的地表反照率参数化方案能够很好地再现该地区裸土地表反照率的“U”型日变化特征,可准确地模拟出地表反照率的动态变化趋势。基于此参数化方案计算得到的地表反射辐射与实测值基本一致。 相似文献
20.
Measuring the effect of overgrazing in the Sonoran Desert 总被引：4，自引：0，他引：4
Nevin A. Bryant Lee F. Johnson Anthony J. Brazel Robert C. Balling Charles F. Hutchinson Louisa R. Beck 《Climatic change》1990,17(2-3):243-264
Long term overgrazing in Mexico has caused a sharp discontinuity in vegetative cover along the international border in the semi-arid Sonoran Desert. The United States side, protected from overgrazing by the Taylor Act since 1934, exhibits longer, more plentiful grasses and less bare soil than adjoining Mexican lands. Satellite- and ground-based datasets were used in a multi-scale examination of the differential radiative and reflective characteristics of the two regimes. The more exposed Mexican landscape dries more rapidly than the United States following summer convective precipitation. After about three days, depletion of soil moisture evokes a period of higher surface and air temperatures in Mexico. Good correspondence was found between remote and in situ measures of surface temperature and biomass. 相似文献