Radiative Feedbacks and Monsoon Circulations: A View from Simplified Models     

Hervé Le Treut  Gilles Bellon 《Pure and Applied Geophysics》2005,162(8-9):1543-1555

The modulation of radiative processes by changes in water vapor and cloudiness is at the origin of important feedbacks which control climate variability as well as climate changes. These feedbacks are especially active in the intertropical area, where it is possible to diagnose a combination of partially compensating positive and negative feedbacks. The characteristics and the strength of those feedbacks is closely associated with the dynamical regimes in which they develop. Reverse changes in dynamical patterns may cause a modulation of the radiative processes. A first approach to these problems is to distinguish between two ascending and subsiding circulation patterns. This bimodality of the circulation is well established in the tropical area, and favors the use of simplified models as an appropriate tool to carry out a first-order quantification of these processes. In particular, this combination of radiative and dynamical feedbacks characterizes the development of the monsoons and their variability. Simple conceptual models can thus serve to characterize some of the factors which will affect the intraseasonal variations of the monsoon.  相似文献   

Photosynthesis-transpiration coupling model at canopy scale in terrestrial ecosystem   总被引：1，自引：0，他引：1  

REN Chuanyou  YU Guirui  WANG Qiufeng  Guan Dexin 《中国科学D辑(英文版)》2005,48(Z1)

At the hypothesis of big leaf, an ecosystem photosynthesis-transpiration coupling cycle model was established by the scaled SMPT-SB model from single leaf to canopy, and model parameterization methods were discussed. Through simulating the canopy light distribution, canopy internal conductance to CO2 can be scaled from single leaf to canopy by integrating to canopy using the relationship between single internal conductance and photosynthetic photon flux density. Using the data observed by eddy covariance method from the Changbai Mountains site of ChinaFLUX, the application of the model at the canopy scale was examined. Under no water stress, the simulated net ecosystem photosynthesis rate fitted with the observed data very well, the slope and R2 of the line regression equation of the observed and simulated values were 0.7977 and 0.8892, respectively (n = 752), and average absolute error was 3.78 μmol CO2 m-2s-1; the slope, R2 and average absolute error of transpiration rate were 0.7314, 0.4355 and 1.60mmol H2O m-2 s-1, respectively (n = 752). The relationship between canopy photosynthesis,transpiration and external environmental conditions was discussed by treating the canopy as a whole and neglecting the comprehensive feedback mechanism within canopy, and it was noted that the precipitation course affected the transpiration rate simulation badly. Compared to the models based on eco-physiological processes, the SMPT-SB model was simple and easy to be used. And it can be used as a basic carbon and water coupling model of soil-plant-atmosphere continuum.  相似文献   

The diurnal and seasonal characteristics of urban heat island variation in Beijing city and surrounding areas and impact factors based on remote sensing satellite data     

ZHANG Jiahua  HOU Yingyu  LI Guicai  YAN Hao  YAO Fengmei 《中国科学D辑(英文版)》2005,48(Z2)

Based on the land surface temperature (LST), the land cover classification map,vegetation coverage, and surface evapotranspiration derived from EOS-MODIS satellite data, and by the use of GIS spatial analytic technique and multivariate statistical analysis method, the urban heat island (UHI) spatial distribution of the diurnal and seasonal variabilities and its driving forces are studied in Beijing city and surrounding areas in 2001. The relationships among UHI distribution and landcover categories, topographic factor, vegetation greenness, and surface evapotranspiration are analyzed. The results indicate that: (i) The significant UHI occur in Beijing city areas in the four seasons due to high heat capacity and multi-reflection of compression building, as well as with special topographic features of its three sides surrounded by mountains,especially in the summer. The UHI spatial distribution is corresponding with the urban geometry structure profile. The LST difference is approximately 4-6℃ between Beijing city and suburb areas, comparatively is 8- 10℃ between Beijing city area and outer suburb area in northwestern regions. (ii) The UHI distribution and intensity in daytime are different from nighttime in Beijing city area, the nighttime UHI is obvious. However, in the daytime, the significant UHI mainly appears in the summer, the autumn takes second place, and the UHI in the winter and the spring seem not obvious. The surface evapotranspiration in suburb areas is larger than that in urban areas in the summer, and high latent heat exchange is evident, which leads to LST difference between city area and suburb area. (iii) The reflection of surface landcover categories is sensitive to the UHI, the correlation between vegetation greenness and UHI shows obviously negative.The scatterplot shows that there is the negative correlation between NDVI and LST (R2 = 0.6481).The results demonstrate that the vegetation greenness is an important factor for reducing the UHI,and large-scale construction of greenbelts can considerably reduce the UHI effect.  相似文献   

Strain accumulation in sand due to cyclic loading: drained triaxial tests     

T. Wichtmann  A. Niemunis  Th. Triantafyllidis   《Soil Dynamics and Earthquake Engineering》2005,25(12):967-979

Our aim is the prediction of the accumulation of strain and/or stress under cyclic loading with many (thousands to millions) cycles and relatively small amplitudes. A high-cycle constitutive model is used for this purpose. Its formulas are based on numerous cyclic tests. This paper describes drained tests with triaxial compression and uniaxial stress cycles. The influence of the strain amplitude, the average stress, the density, the cyclic preloading history and the grain size distribution on the direction and the intensity of strain accumulation is discussed.  相似文献   

Effect of the Mahanadi River on the Development of Storm Surge Along the Orissa Coast of India: A Numerical Study     

S. K. Dube  P. C. Sinha  A. D. Rao  Indu Jain  Neetu Agnihotri 《Pure and Applied Geophysics》2005,162(8-9):1673-1688

River-ocean coupled models are described for the evaluation of the interaction between river discharge and surge development along the Orissa coast of India. The models are used to study the effect of fresh water discharge from the Mahanadi River on the surge response along the Orissa coast due to the October 1999 super cyclone which led to severe flooding of the coastal and delta regions of Orissa. The so-called 1999 Paradip cyclone was one of the most severe cyclones; causing extensive damage to property and loss of lives. The present study emphasizes the impact of the Mahanadi River on overall surge development along the Orissa coast. Therefore, we have developed a location specific fine resolution model for the Orissa coast and coupled it with a one–dimensional river model. The numerical experiments are carried out, both with and without inclusion of fresh water discharge from the river. The bathymetry for the model has been taken from the naval hydrographic charts extending from the south of Orissa to the south of west Bengal. A simple drying scheme has also been included in the model in order to avoid the exposure of land near the coast due to strong negative sea-surface elevations. The simulations with river-ocean coupled models show that the discharge of fresh water carried by the river may modify the surge height in the Bay, especially in the western Bay of Bengal where one of the largest river systems of the east coast of India, the Mahanadi River, joins with the Bay of Bengal. Another dynamic effect of this inlet is the potentially deep inland penetration of the surge originating in the Bay. The model results are in good agreement with the available observations/estimates.  相似文献   

Numerical model of convection in sills     

A. Rozmarynowska  L. Czechowski 《Studia Geophysica et Geodaetica》2005,49(3):383-402

The numerical model of convection in magma sills is developed. The model is based on a full system of equations of fluid dynamics and includes heat transfer, buoyancy effects and diffusion of some minor component (marker). Solidification is treated as a phase transition. The results indicate that there are some qualitative differences between very thin sills with Rayleigh number Ra = 10⁵ and thin sills with Ra = 10⁶. For a basaltic magma the first case corresponds to the thickness of the sills of approximately 30 cm and the second case corresponds to the thickness of 60 cm. In the first case mixing is inefficient and conduction is the dominant form of heat transfer. In the second case mixing is efficient and convection is the dominant form of heat transfer. Some of the results can be scaled for the more viscous magmas in thicker sills.  相似文献   

Study on the Source Parameters of Earthquakes in the Middle Eastern Area of North Tianshan in Xinjiang     

Zhao Cuiping 《中国地震研究》2005,19(4):381-390

INTRODUCTIONThe study of source parameters is usually based oninversionfromobservational seismic waveformdata.Seismic wave affected bygeometric spreading,inelastic attenuation,scatteringandsite effects ofthe mediumontheir way fromsource to station.Therefo…  相似文献   

在卸荷产生拉剪情况下裂隙岩体的力学行为     

吴汉辉  杨转运  刘会 《岩土工程技术》2005,19(5):237-240

据岩体在卸荷情况下的拉剪应力状态,确定了节理岩体的线弹性断裂力学模型。依照此模型,可以得到相对远离裂隙(该位置的点到裂隙中心的距离比裂缝长度大)且受裂隙影响区域内应力、应变和变形方程。这些对评估裂隙岩石变形有重要的参考意义。通过用理论方程的计算结果和卸荷情况下试验观测所得的数据对比,证明该模型应用于实际工程中具有可行性。  相似文献   

采空区二维超声波物理模型实验研究     

赵家福  田钢  石战结  王者江 《吉林大学学报(地球科学版)》2005,(Z1)

由于对资源矿产的过度开采使得矿山地区(尤其是煤矿)出现了采空区,从而引起地表塌陷等地质灾害。为了深入了解地震方法在采空区调查中的应用效果,从超声波物理模型实验研究出发,论述了物理模型的原理和制作,研究了采空区的地震波场特征,并利用W inse is软件对所采集的二维超声波实验数据进行了处理。由叠偏剖面推断的采空区的位置与实际模型相符,从而验证了超声波采空区物理模型试验是有效的、可信的;同时可以为实际探测采空区提供进一步的理论依据。  相似文献   

ASSESSING THE SUITABILITY OF THE EPIC CROP MODEL FOR USE IN THE STUDY OF IMPACTS OF CLIMATE VARIABILITY AND CLIMATE CHANGE IN WEST AFRICA   总被引：1，自引：0，他引：1  

James Adejuwon 《Singapore journal of tropical geography》2005,26(1):44-60

The EPIC (Erosion Productivity Impact Calculator) crop model, developed by scientists of the United States Department of Agriculture (USDA), has been successfully applied to the study of erosion, water pollution, crop growth and production in the US but is yet to be introduced for serious research purposes in other countries or regions. This paper reports on the applicability of the EPIC 8120 crop model for the assessment of the potential impacts of climate variability and climate change on crop productivity in sub‐Saharan West Africa, using Nigeria as the case study. Among the crops whose productivity has been successfully simulated with this model are five of West Africa's staple food crops: maize, millet, sorghum (guinea corn), rice and cassava. Thus, using the model, the sensitivities of maize, sorghum and millet to seasonal rainfall were demonstrated with coefficients of correlation significant at over 98 per cent confidence limits. The validation tests were based on a comparison of the observed and the model‐generated yields of rice and maize. The main problems of validation relate to the multiplicity of crop varieties with contrasting performances under similar field conditions. There are also the difficulties in representing micro‐environments in the model. Thus, some gaps appear between the observed and the simulated yields, arising from data or model deficiencies, or both. Based on the results of the sensitivity and validation tests, the EPIC crop model could be satisfactorily employed in assessing the impacts of and adaptations to climate variability and climate change. Its use for the estimation of production and the assessment of vulnerabilities need to be pursued with further field surveys and field experimentation.  相似文献