Estimation of Hourly Solar Radiation at the Surface under Cloudless Conditions on the Tibetan Plateau Using a Simple Radiation Model

In this study, the clear sky hourly global and net solar irradiances at the surface determined using SUNFLUX, a simple parameterization scheme, for three stations （Gaize, Naqu, and Lhasa） on the Tibetan Plateau were evaluated against observation data. Our modeled results agree well with observations. The correlation coefficients between modeled and observed values were 〉 0.99 for all three stations. The relative error of modeled results, in average was 〈 7%, and the root-mean-square variance was 〈 27 W m-2. The solar irradiances in the radiation model were slightly overestimated compared with observation data; there were at least two likely causes. First, the radiative effects of aerosols were not included in the radiation model. Second, solar irradiances determined by thermopile pyranometers include a thermal offset error that causes solar radiation to be slightly underestimated. The solar radiation absorbed by the ozone and water vapor was estimated. The results show that monthly mean solar radiation absorbed by the ozone is 〈 2% of the global solar radiation （〈 14 W m-2）. Solar radiation absorbed by water vapor is stronger in summer than in winter. The maximum amount of monthly mean solar radiation absorbed by water vapor can be up to 13% of the global solar radiation （95 W m-2）. This indicates that water vapor measurements with high precision are very important for precise determination of solar radiation.

Relationship between Net Radiation and Broadband Solar Radiation in the Tibetan Plateau

The characteristics of net radiation （Rn） （0.3-10 μm） in Lhasa and Haibei in the Tibetan Plateau were analyzed based on long-term in-situ measurements of surface radiation data. The monthly average of daily Rn reached a minimum during the winter period followed by an increase until May and then a decline until January. This variation is consistent with solar activity. The annual mean daily total Rn values were 0.92 MJ m^-2 d^-1 and 0.66 MJ m-2 d-1 in Lhasa and Haibei, respectively. A relationship between Rn and broadband solar radiation （Rs） was demonstrated by a good linear correlation at the two sites. Rn can be an accurate estimate from Rs. The estimated Rn values were similar to the observed values, and the relative deviations between the estimates and measurements of Rn were 2.8% and 3.8% in Lhasa and Haibei, respectively. The application of the Rn estimating model to other locations showed that it could provide acceptable estimated Rn values from the Rs data. Furthermore, we analyzed the influence of clouds on Rn by different clear index （Ks）, defined as the ratio of Rs to the extraterrestrial solar irradiance on a horizontal surface. The results indicate that more accurate results are associated with increased cloudy conditions. The influence of the albedo was also considered, but its inclusion in the model resulted in only a slight improvement. Because surface albedo is not usually measured, an expression based solely ou global solar radiation could be of more extensive use.

Dynamic simulation insights into friction weakening effect on rapid long-runout landslides:A case study of the Yigong landslide in the Tibetan Plateau,China

This study proposed a novel friction law dependent on velocity,displacement and normal stress for kinematic analysis of runout process of rapid landslides.The well-known Yigong landslide occurring in the Tibetan Plateau of China was employed as the case,and the derived dynamic friction formula was included into the numerical simulation based on Particle Flow Code.Results showed that the friction decreased quickly from 0.64(the peak)to 0.1(the stead value)during the 5s-period after the sliding initiation,which explained the behavior of rapid movement of the landslide.The monitored balls set at different sections of the mass showed similar variation characteritics regarding the velocity,namely evident increase at the initial phase of the movement,followed by a fluctuation phase and then a stopping one.The peak velocity was more than 100 m/s and most particles had low velocities at 300s after the landslide initiation.The spreading distance of the landslide was calculated at the two-dimension(profile)and three-dimension scale,respectively.Compared with the simulation result without considering friction weakening effect,our results indicated a max distance of about 10 km from the initial unstable position,which fit better with the actual situation.

Comparative analysis of the mass elevation effect and its implication for the treeline between the Tibetan and Bolivian plateaus based on solar radiation

As one of the main non-zonal factors,the mass elevation effect(MEE)has significant impacts on both regional climates and mountain ecological patterns.In recent years,with the development of quantitative techniques and methods,quantitative studies on the MEE and its implication on mountain altitudinal belts have developed rapidly.However,some issues have not been solved yet,such as high errors in spatial temperature estimations and difficulties in the definition and extraction of intramountain base elevation.Moreover,there is still a lack of comparative studies on the MEE and its influence on treelines and snowlines as most studies were conducted on specific mountains or plateaus.To compare the MEE magnitudes of the Tibetan Plateau(TP)and the Bolivian Plateau(BP),we estimated the correspondent air temperatures and simulated the solar radiations based on MODIS surface temperature,station observation,and treeline data.Then,we analyzed the elevation of the 10℃isotherms on the two plateaus,the temperatures at the same elevation,and the solar radiations.According to the mechanism of the MEE and the relationship of solar radiation and treeline,we constructed treeline models for the two plateaus through a stepwise regression analysis by considering several influencing factors of the MEE(e.g.,air temperature and precipitation)and using solar radiation as its proxy.The results showed that:(1)the MEE magnitude on the TP is equivalent to that on the BP although the former is slightly higher than the latter;(2)the MEE strongly influences the highest treelines in the northern and southern hemispheres,which both occur on the two plateaus.Notably,the treeline distribution models based on solar radiation had higher accuracies than those models with parameters of temperature and precipitation(the adjusted R^(2) values were 0.76 for the TP and 0.936 for the BP),indicating that solar radiation can be used to quantify the MEE and its implications on treelines.Overall,the results of this study can serve as a basis for subsequent analyses on the MEE’s impact factors.

Radiation balance and the response of albedo to environmental factors above two alpine ecosystems in the eastern Tibetan Plateau

Understanding the energy balance on the Tibetan Plateau is important for better prediction of global climate change. To characterize the energy balance on the Plateau, we examined the radiation balance and the response of albedo to environmental factors above an alpine meadow and an alpine wetland surfaces in the eastern Tibetan Plateau, using 2014 data. Although our two sites belong to the same climatic background, and are close geographically, the annual incident solar radiation at the alpine meadow site(6,447 MJ/(m2·a)) was about 1.1 times that at the alpine wetland site(6,012 MJ/(m2·a)),due to differences in the cloudiness between our two sites. The alpine meadow and the alpine wetland emitted about 38%and 42%, respectively, of annual incident solar radiation back into atmosphere in the form of net longwave radiation; and they reflected about 22% and 18%, respectively, of the annual incident solar radiation back into atmosphere in the form of shortwave radiation. The annual net radiation was 2,648 and 2,544 MJ/(m2·a) for the alpine meadow site and the alpine wetland site, respectively, accounting for only about 40% of the annual incident solar radiation, significantly lower than the global mean. At 30-min scales, surface albedo exponentially decreases with the increase of the solar elevation angle; and it linearly decreases with the increase of soil-water content for our two sites. But those relationships are significantly influenced by cloudiness and are site-specific.

Effect of solar radiation on net ecosystem CO_2 exchange of alpine meadow on the Tibetan Plateau

On the Tibetan Plateau, the alpine meadow is the most widespread vegetation type. The alpine meadow has a low biological productivity and low vegetation coverage in the growing season. The daytime NEE between the atmosphere and the alpine meadow ecosystem was influenced by solar radiation. To analyze the characteristics of change in NEE and to calculate the parameters related to photosynthesis and respiration in different solar radiation environments, the NEE measurements were taken in Damxung from July to August in 2003, 2004, 2005 and 2006 using the eddy covariance technique. Solar radiation was grouped into three levels according to the net radiation, which was more than 155 W m-2 d-1 on clear days, 144±5 W m-2 d-1 on partly cloudy days and less than 134 W m-2 d-1 on cloudy days. The diurnal relationships between NEE and PAR varied with differences in solar radiation, which was a rectangular hyperbola form on clear days, two different concave curves on partly cloudy days and an irregular triangle form on cloudy days. The mean CO2 absorption rate showed a decreasing trend with increasing solar radiation. The daytime absorption maximum occurred around 10：00 on clear days with an average of slightly less –0.2 mg m-2 d-1, around 11：00 on partly cloudy days with an average of about –0.2 mg m-2 d-1, and around 12：00 on cloudy days with an average of about –0.25 mg m-2 d-1. As solar radiation increased, the Amax and the Q10 decreased. However, the R10 increased and the maximum of the α occurred on partly cloudy days. The optimum net solar radiation was about 134–155 W m-2 d-1, which induced a PAR of about 1800-2000 μmol m-2 s-1 and soil temperature at a depth of 5 cm of about 14℃. Therefore, on the Tibetan Plateau, the alpine meadow ecosystem will have a higher carbon absorption potential while solar radiation decreases in the future.

Review of numerical simulation on the dynamics of Qinghai-Xizang plateau

In recent twenty years, much numerical simulation work has been done on the evolution of Qinghai-Xizang (Tibetan) plateau. In this paper some principal numerical models and results are reviewed and analyzed. The earlier plane stress or plane strain model has much discrepancy with the actual deformation of Qinghai-Xizang plateau, such as the thickening of Tibetan crust and the lateral extrusion of Tibet along strike-slip faults. The thin viscous sheet model and the thin-plate model may simulate the change of the crustal thickness and the deformation pro-duced by gravitational force. It is suitable for studying the large-scale and long-time deformation. The influence of faults on the deformation of Tibetan plateau should be further studied.

THE EFFECTS OF THE PLATEAU'S TOPOGRAPHIC GRADIENT ON ROSSBY WAVES AND ITS NUMERICAL SIMULATION

By using barotropic model equations, this article analyzed the characteristics of Rossby waves, the propaga- tion features of wave energy and the influence of dynamic and thermal effects of the Tibetan Plateau on Rossby waves, and the focus is on discussing the plateau＇s topographic gradient effects on atmospheric Rossby waves. Then based on the WRF3.2 and the NCEP/NCAR FNL reanalysis data, we devised comparative tests of changing the plateau＇s topo- graphic gradient and simulated a process of persistent heavy rain that happened in May 2010 in South China. The re- sults are shown as follows. The Tibetan Platean＇s topography is conducive to the formation of atmospheric Rossby waves, while the platean＇s terrain, its friction and heating effects can all make the atmospheric Rossby waves develop into the planetary waves; The effects of platean＇s north and south slopes on the Rossby wave＇ phase velocity is opposite, and when the slope reached a certain value can the quasi-steady normal fluctuations be generated; Simultaneously, due to the plateau＇s topographic gradient, descending motion appears at the west side of the plateau while ascending motion appears at the east side, and the vertical movement increased with the amplification of topographic gradients. The plateau＇s topographic gradient also obviously amplified the precipitation in South China, and the rainfall area increased with the amplification of topographic gradients and gradually moved from south to north and from west to east, which is conducive to the occurrence and development of convective activities in the downstream areas of the Tibetan Plateau; Moreover, for the plateau＇s dynamic and thermal effects, the Rossby wave＇ propagation shows upstream effects of ener- gy dispersion, so the plateau can then affect the weather in downstream areas. Moreover, the wave group velocity in- creased with the degree of topographic slope.

Influence of mantle convection to the crustal movement pattern in the northeastern margin of the Tibetan Plateau based on numerical simulation

Based on the recent observations about the movement and rheological structure of the lithosphere and deformation pattern of the crust, we developed a three-dimensional finite element model for the northeastern margin of the Tibetan Plateau.The model considered the impacts of both external and internal conditions, including mantle convection, gravitational potential energy and block interactions. We compared the simulated surface movement rates to the observed GPS velocities, and the results revealed that crustal movement gradually decreased toward the edge of the plateau. The factors controlling this pattern are the interactions of adjacent blocks, gravitational potential energy of the plateau, and also mantle convection as well. Additionally,according to the observation that there was an apparent difference between the horizontal movement rate of the lithosphere and convective velocity of the underlying mantle, and also based on the results of seismic anisotropy studies that suggest different strengths and deformation regimes of the lithosphere in different tectonic blocks, we proposed that the impact of mantle convection on the lithosphere may have varied in space, and introduced a parameter named mantle convection intensity factor in numerical simulations. Our simulation results show consistent surface movement rates with GPS observations, which further supports the viewpoint of seismic anisotropy studies, i.e., the degree of coupling between the crust and mantle varies significantly among different blocks.

Characteristics of Solar Radiation and the Impact of Clouds at Yangbajing, Tibet

Yangbajing (YBJ) is located in the Tibetan Plateau, China. The characteristics of solar radiation and its relationship with clouds at YBJ from April 2009 to April 2010 were analyzed in this paper. The annual mean solar radiation was 478.4 W m 2 , and the annual mean transmittance was 0.713. The atmospheric mean trans- mittance of clear skies reaches 0.828 when the solar elevation angle (SEA) is greater than 10 degrees. Comparisons with numerical simulations show that the atmosphere of YBJ is clean. Impacts from atmospheric conditions on solar radiation are similar for clear skies during the year because the standard deviation of transmittance in clear skies was less than 0.05 when the SEA was greater than 10 degrees. It is important to understand the impact of clouds on solar radiation without considering other impact factors. In the last part of this article, the authors analyzed and established a statistical quantitative relationship between surface solar radiation and cloud fraction.

A Modeling Study of the Effects of Anomalous Snow Cover over the Tibetan Plateau upon the South Asian Summer Monsoon

The e?ect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SMMR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo e?ect, which is compensated by weaker upward sensible heat ?ux associated with colder surface temperature, whereas the e?ects of snow melting and evaporation are relatively smaller. The anomalies of surface heat ?uxes can last until June and become unobvious in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May. The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this in?uence is only obvious in early summer and almost disappears in later stages.

Influence of the Tibetan Plateau on the Summer Climate Patterns over Asia in the IAP/LASG SAMIL Model

A series of numerical experiments are carried out by using the Spectral Atmospheric Model of State Key Laboratory of Numerical Modeling Atmospheric Sciences and Geophysical Fluid Dynamics/Institute of Atmospheric Physics （SAMIL） to investigate how the Tibetan Plateau （TP） mechanical and thermal forcing affect the circulation and climate patterns over subtropical Asia. It is shown that, compared to mechanical forcing, the thermal forcing of TP plays a dominant role in determining the large-scale circulation in summer. Both the sensible heating and the latent heating over TP tend to generate a surface cyclonic circulation and a gigantic anticyclonic circulation in the mid- and upper layers, whereas the direct effect of the latter is much more significant. Following a requirement of the time-mean quasi-geostrophic vorticity equation for large-scale air motion in the subtropics, convergent flow and vigorous ascending motion must appear to the east of TP. Hence the summer monsoon in East China is reinforced efficiently by TP. In contrast, the atmosphere to the west of TP is characterized by divergent flow and downward motion, which induces the arid climate in Mid-Asia.

NUMERICAL SIMULATIONS OF HEATING ANOMALY EFFECTS OF TIBETAN PLATEAU ON CIRCULATION IN SUMMER

A 5-layer numerical model with p-σ incorporated coordinate system and primitive equations is used to simulate the effects of heating anomaly at and over the Tibetan(Qinghai-Xizang)Plateau on the circulations in East Asia in sum- mer,The model is described briefly in the text and the results are analysed in somewhat detail.Results show that the sur- face albedo,the drag coefficient,the evaporation rate and the ground temperature all have large influences on the circula- tion near the Plateau and in East Asia.When the heating at the surface increases,the Tibetan high in the upper troposphere intensifies,too.Its area enlarges and its axis tilts to northwest.The upper tropical easterly increase and shifts to north.The southwesterly in the lower troposphere,in consistence,also increases.The cross-equatorial low-lev- el currents along Somali and South India are influenced to increase their speeds while those over North Australia de- crease.The land low over the Asian Continent deepens.Meanwhile the upward motions over the land of east China and over the Indo-China Peninsula intensify and therefore the precipitation over those areas increases.However,along the coastal area of China the upward motions and therefore the precipitation decrease. Atmospheric heat source anomaly has large influence on the circulation,too.Simulated results indicate that heat source anomaly in the lower atmosphere over the Plateau influences the intensity and the position of the monsoon circu- lation while that in the upper atmosphere only affects the intensity.The heating status over the Plateau has slight influ- ence on the westerly jet,north of the Plateau,while it has strong effect on the subtropical jet at the mid and low latitudes.

Impact of Surface Potential Vorticity Density Forcing over the Tibetan Plateau on the South China Extreme Precipitation in January 2008. Part Ⅱ:Numerical Simulation

The surface air convergence on the eastern flank of the Tibetan Plateau (TP) can increase the in situ surface potential vorticity density (PVD). Since the elevated TP intersects with the isentropic surfaces in the lower troposphere, the increased PVD on the eastern flank of TP thus forms a PVD forcing to the intersected isentropic surface in the boundary layer. The influence of surface PVD forcing over the TP on the extreme freezing rain/snow over South China in January 2008 is investigated by using numerical experiments based on the Finite-volume Atmospheric Model of the IAP/LASG (FAMIL). Compared with observations, the simulation results show that, by using a nudging method for assimilating observation data in the initial flow, this model can reasonably reproduce the distribution of precipitation, atmospheric circulation, and PVD propagation over and downstream of the TP during the extreme winter precipitation period. In order to investigate the impact of the increased surface PVD over the TP on the extreme precipitation in South China, a sensitivity experiment with surface PVD reduced over the TP region was performed. Compared with the control experiment, it is found that the precipitation in the TP downstream area, especially in Southeast China, is reduced. The rainband from Guangxi Region to Shandong Province has almost disappeared. In the lower troposphere, the increase of surface PVD over the TP region has generated an anomalous cyclonic circulation over southern China, which plays an important role in increasing southerly wind and the water vapor transport in this area;it also increases the northward negative absolute vorticity advection. In the upper troposphere, the surface PVD generated in eastern TP propagates on isentropic surface along westerly wind and results in positive absolute vorticity advection in the downstream areas. Consequently, due to the development of both ascending motion and water vapor transport in the downstream place of the TP, extremely heavy precipitation occurs over southern China. Thereby, a new mechanism concerning the influence of the increased surface PVD over the eastern TP slopes on the extreme weather event occurring over southern China is revealed.

Numerical simulation of GPS observed clockwise rotation around the eastern Himalayan syntax in the Tibetan Plateau

From Global Position System(GPS) measurements,there is a clockwise rotation around the eastern Himalayan syntax in the Tibetan Plateau.This phenomenon is difficult to be interpreted by simple two-dimensional modeling from a geodynamic point of view.Because of the extremely thick crust and the lower crust with relatively high temperature in the Tibetan Plateau,the lithospheric rheology in Tibet and surrounding areas present a complex structure.In general,the tectonic structure of the Tibetan Plateau consists of brittle upper crust,ductile lower crust,high viscosity lithospheric upper mantle,and low viscosity asthenosphere,the same as the case in many other continental regions.However,the lower crust in the Tibetan Plateau is much more ductile with a lower viscosity than those of its sur-roundings at the same depth,and the effective viscosity is low along the collision fault zone.In this study,we construct a three-dimensional Maxwell visco-elastic model in spherical coordinate system,and simulate the deformation process of the Tibetan Plateau driven by a continuous push from the Indian plate.The results show that the existence of the soft lower crust under the plateau makes the entire plateau uplift as a whole,and the Himalayas and the eastern Himalayan syntax uplift faster.Since the lower crust of surrounding blocks is harder except in the southeastern corner where the high-temperature material is much softer and forms an exit channel for material transfer,after the whole plateau reaches a certain height,the lower crustal and upper mantle material begins to move eastward or southeastward and drag the upper crust to behave same way.Thus,from the macroscopic point of view,a relative rigid motion of the plateau with a clockwise rotation around the eastern Himalayan syntax is developed.

A Numerical Case Study on a Mesoscale Convective System over the Qinghai-Xizang (Tibetan) Plateau

A mesoscale convective system (MCS) developing over the Qinghai-Xizang Plateau on 26 July 1995 is simulated using the fifth version of the Penn State-NCAR nonhydrostatic mesoscale model (MM5). The results obtained are inspiring and are as follows. (1) The model simulates well the largescale conditions in which the MCS concerned is embedded, which are the well-known anticyclonic Qinghai-Xizang Plateau High in the upper layers and the strong thermal forcing in the lower layers. In particular, the model captures the meso-α scale cyclonic vortex associated with the MCS, which can be analyzed in the 500 hPa observational winds; and to some degree, the model reproduces even its meso-β scale substructure similar to satellite images, reflected in the model-simulated 400 hPa rainwater. On the other hand, there are some distinct deficiencies in the simulation; for example, the simulated MCS occurs with a lag of 3 hours and a westward deviation of 3–5° longitude. (2) The structure and evolution of the meso-α scale vortex associated with the MCS are undescribable for upper-air sounding data. The vortex is confined to the lower troposphere under 450 hPa over the plateau and shrinks its extent with height, with a diameter of 4° longitude at 500 hPa. It is within the updraft area, but with an upper-level anticyclone and downdraft over it. The vortex originates over the plateau, and does not form until the mature stage of the MCS. It lasts for 3–6 hours. In its processes of both formation and decay, the change in geopotential height field is prior to that in the wind field. It follows that the vortex is closely associated with the thermal effects over the plateau. (3) A series of sensitivity experiments are conducted to investigate the impact of various surface thermal forcings and other physical processes on the MCS over the plateau. The results indicate that under the background conditions of the upper-level Qinghai-Xizang High, the MCS involved is mainly dominated by the low-level thermal forcing. The simulation described here is a good indication that it may be possible to reproduce the MCS over the plateau under certain large-scale conditions and with the incorporation of proper thermal physics in the lower layers.

A Numerical Investigation on Microphysical Properties of Clouds and Precipitation over the Tibetan Plateau in Summer 2014

In order to improve our understanding of microphysical properties of clouds and precipitation over the Tibetan Plateau (TP), six cloud and precipitation processes with different intensities during the Third Tibetan Plateau Atmospheric Science Experiment (TIPEX-Ⅲ) from 3 July to 25 July 2014 in Naqu region of the TP are investigated by using the high-resolution mesoscale Weather Research and Forecasting (WRF) model. The results show unique properties of summertime clouds and precipitation processes over the TP. The initiation process of clouds is closely associated with strong solar radiative heating in the daytime, and summertime clouds and precipitation show an obvious diurnal variation. Generally, convective clouds would transform into stratiform clouds with an obvious bright band and often produce strong rainfall in midnight. The maximum cloud top can reach more than 15 km above sea level and the velocity of updraft ranges from 10 to 40 m s-1. The simulations show high amount of supercooled water content primarily located between 0 and -20℃ layer in all the six cases. Ice crystals mainly form above the level of -20℃ and even appear above the level of -40℃ within strong convective clouds. Rainwater mostly appears below the melting layer, indicating that its formation mainly depends on the melting process of precipitable ice particles. Snow and graupel particles have the characteristics of high content and deep vertical distribution, showing that the ice phase process is very active in the development of clouds and precipitation. The conversion and formation of hydrometeors and precipitation over the plateau exhibit obvious characteristics. Surface precipitation is mainly formed by the melting of graupel particles. Although the warm cloud microphysical process has less direct contribution to the formation of surface precipitation, it is important for the formation of supercooled raindrops, which are essential for the formation of graupel embryos through heterogeneous freezing process. The growth of graupel particles mainly relies on the riming process with supercooled cloud water and aggregation of snow particles.

INFLUENCES OF DIURNAL CHANGE OF SOLAR RADIATION ON SIMULATED PROPERTIES OF SUMMER MONSOON

Comparative experiments with and without the diurnal change of solar radiation are made in this paper by use of an air-sea coupled 7-layer primitive equation modeling system in a zonal domain between 60°S and 60°N.The results show that the quasi-stationary patterns of the mean monsoon circulations are not evidently affected by the diurnal change of solar radiation.The main influences may come from the land-sea distribution and the orography.However,the inclusion of the diurnal change of solar radiation into the model system may improve the intensities of the simulated monsoon circulations both at the high and the low levels.It can influence the distributive pattern of precipitation to a larger extent.Without the diurnal change,precipitation in the interior of land would decrease and in the coastal regions it would increase.The changes of the soil temperature and the soil moisture are fairly correspondent to that of precipitation.The areas with increasing precipitation and the areas with decreasing precipitation are distributed in the wave form.As to the influences on the monsoon development,the results indicate that the diurnal change of solar radiation can speed up the development of the monsoon in the early stage.Therefore,the inclusion of the diurnal change of solar radiation can make the model equilibrium state to reach earlier.

基于聚光集热和脉动风压的定日镜群模拟研究

太阳辐射量和风荷载会直接影响光热电站的持续发电量。文章根据新疆哈密地区中电淖毛湖光热电站的实际环境情况,建立定日镜群的三维数值模型,对不同季节太阳辐射和迎风仰角下镜群的受热情况及流场特性开展数值模拟,分析获得风在不同入射角下镜面耀斑分布情况和脉动风压系数。结果表明:模拟所得镜群阻力系数和升力系数与相关研究结果较为吻合,验证了所建模型的有效性;不同季节下耀斑的分布规律较为相似,主要取决于太阳方向角的变化;随着风入射角的增大,镜群的尾流区域呈先减小后增大趋势;由于定日镜镜群中的尾流可有效抑制风压,结合镜群的排布方式保证内部的稳定性,其中,正五边形定日镜的中心处保持较低的脉动风压,极大提高了镜面受力均衡性。

基于离散元数值模拟的冰川冰抗剪强度特性及影响因素研究

在现场调研和直剪试验标定的基础上,通过PFC2D数值模拟分析了纯多晶冰、冰岩嵌固体、岩屑冰和碎石冰4类冰川介质的抗剪强度及温度、岩屑含量、碎石含量与粒径的影响,进行了试验验证。结果表明:(1)纯多晶冰沿最大剪应力面产生剪切破坏,冰岩嵌固体沿冰岩接触面发生剪切破坏,破裂面较为平整;而岩屑冰和碎石冰的剪切破坏特征与颗粒含量和粒径有关,破裂面凹凸不平。(2)抗剪强度随着温度的升高而降低,-40~-10℃时基本呈线性下降,而-40℃以下和-10℃以上时影响则更为显著,其中内摩擦角对于温度的响应相比黏聚力更为敏感。(3)抗剪强度随着岩屑或碎石含量的增加而增大,含量从0增加到20%时对内摩擦角的影响较大、对黏聚力的影响较小,而含量从60%增加到80%时对黏聚力的影响比对内摩擦角的影响更为显著,含量20%~60%时两者皆呈线性增大。(4)随着碎石粒径的增大,内摩擦角先增大、后减小,黏聚力则先减小、后增大,碎石粒径12.5mm左右时分别达到最大值和最小值。研究结果对于揭示冰崩机理及灾害防治具有科学价值和现实意义。