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1.
我国黄土高原地区地处夏季风边缘,分布在气候和生态过渡带,气候环境的空间差异很大,对陆面能量的空间分布格局影响非常显著.然而,由于受该地区陆面过程观测站点较少的局限,对整个黄土高原区域陆面能量的空间分布规律及其影响机制的认识十分有限.在对CLM模式模拟的陆面能量平衡分量资料进行试验验证的基础上,利用CLM模式模拟的近30年黄土高原地区陆面能量平衡分量资料,分析了该地区近30年平均陆面能量平衡分量的空间变化特征以及与最干燥年和最湿润年的差异,研究了陆面能量平衡分量空间分布与经、纬度和海拔高度等地理因素及降水和气温等气候因子之间的关系.发现,黄土高原地区陆面能量平衡分量空间差异非常显著,地表净辐射和感热通量由南至北增加,潜热通量和土壤热通量从东南向西北减少;空间最干格点和最湿格点之间的地表感热、潜热和土壤热通量几乎相差1倍左右,地表能量分配由最干格点的感热通量主导转变为最湿格点的感热和潜热平分秋色;年际干湿波动对地表能量平衡分量的影响也相当显著,对感热和潜热通量的改变幅度最大接近30%.而且,经纬度和海拔高度等地理因素及温度和降水等气候要素均与陆面能量平衡分量空间分布有一定的相关性,但地表净辐射与海拔高度和纬度的关系更密切,感热通量与降水和纬度的关系更密切,而潜热和土壤热通量只与降水的关系比较密切. 相似文献
2.
大量近地层观测试验表明,利用涡动相关法观测的湍流通量小于近地层可利用能量,即近地层能量是不闭合的,这种不闭合度一般为20%甚至更高.而陆面过程模式是基于地气间能量平衡建立,并且模式中的湍流边界层参数化方案通常根据实际观测的湍流通量来确定,因此能量不闭合必将对陆面过程模式造成一定的影响.本文利用2007年春季SACOL站的近地层观测资料,依据能量守恒将能量不闭合中的残余能量通过波文比分配到观测的湍流通量中,即修正涡动相关法观测的湍流通量使得近地层能量达到平衡;之后分别利用观测和修正的湍流通量,建立了能量不闭合和闭合情形下的湍流参数化方案,借助陆面过程模式SHAW,通过数值模拟和对比分析方法考察近地层能量闭合度对陆面过程模式的影响.研究结果表明近地层能量闭合对陆面过程模式有显著的影响:在陆面过程数值模拟中,当应用近地层能量不闭合的湍流通量形成的湍流参数化方案时,陆面过程模式会明显高估地表长波辐射及土壤温度;但当应用修正湍流通量使得近地层能量达到闭合形成的湍流参数化方案后,在不改变任何地表土壤物理生化属性的情况下,陆面过程模式能较好地模拟地表长波辐射和土壤温度. 相似文献
3.
黄土高原半干旱草地生长季干湿时段环境因子对陆面水、热交换的影响 总被引：1，自引：0，他引：1
《中国科学:地球科学》2015,(8)
利用黄土高原陆面过程观测试验研究(LOPEX)资料,分析了榆中半干旱草地生长季主要干湿时段陆面水、热过程的差异及环境因子的影响特征.研究发现,干湿时段陆面温、湿特征变化差异明显,干旱时段日平均归一化温度垂直分布结构整体"前倾",湿润时段则呈"后倾"状;干旱时段,20 cm以上浅层土壤是温度的活跃层,干湿时段土壤中热量的传递速率明显不同.干旱时段H/Rn和LE/Rn与5 cm土壤温度之间满足线性关系;湿润时段H/Rn和LE/Rn与5 cm土壤温度为非线性关系,日尺度上陆面水、热交换趋势发生转变的临界土壤温度为16℃.干旱时段H/Rn和LE/Rn与土壤含水量之间满足线性规律;湿润时段H/Rn和LE/Rn与5 cm土壤含水量之间呈非线性变化,0.21 m3 m?3是日尺度上陆面水、热交换趋势发生转变的临界点.干旱时段,饱和水汽压差小于0.7 k Pa时,H/Rn随饱和水汽压差的增大而增大,LE/Rn随饱和水汽压差的增大而减小,而当饱和水汽压差大于0.7 k Pa时,H/Rn和LE/Rn均趋于常数;湿润时段,H/Rn随饱和水汽压差的增大而增大,LE/Rn随饱和水汽压差的增大而减小.上述特征直接体现了陆面环境因子的差异在水、热交换过程中的作用,也间接反映了云降水过程对陆面水、热交换过程的影响. 相似文献
4.
沙漠地区植被稀疏、干旱少雨,其陆面物理过程具有与全球其它地区显著不同的特点.本文利用巴丹吉林沙漠观测资料,分析和计算了地表反照率、比辐射率、粗糙度和土壤热容量、热传导系数等关键陆面过程参数,建立了适合于沙漠地区的陆面过程模式DLSM (Desert Land Surface Model),并与NOAH陆面过程模式的模拟结果和观测资料进行了比较.结果表明:巴丹吉林沙漠地表反照率为0.273,比辐射率为0.950,地表粗糙度为1.55×10-3 m,土壤热容量和热扩散系数分别为1.08×106 J·m-3·K-1和3.34×10-7 m2·s.辐射传输、感热输送和土壤热传导过程是影响沙漠地区地表能量平衡的主要物理过程.通过对这三种过程的准确模拟检验,DLSM能够较准确地模拟巴丹吉林沙漠地气能量交换特征;短波辐射、长波辐射和感热通量的模拟结果与观测值间的标准差分别为7.98,6.14,33.9 W·m-2,与NOAH陆面过程模式的7.98,7.72,46.6 W·m-2的结果接近.地表反照率是沙漠地区最重要的陆面过程参数,地表反照率增大5%,向上短波辐射通量随之增加5%,感热通量则减小2.8%.本文研究结果对丰富陆面过程参数化方案,改进全球陆面过程模式、气候模式具有参考意义. 相似文献
5.
大气边界层是地球大气重要物理特征之一.干旱气候背景下的大气边界层特征与人们以往对典型大气边界层的认识有很大不同,其形成机制也比较特殊.本文利用冬、夏两季典型时段在极端干旱区敦煌开展的大气边界层和陆面过程综合观测试验,对大气边界层厚度与净辐射、地-气温差和感热通量等陆面热力因素的日变化特征进行了对比分析,研究了大气边界层的发展和维持衰退过程与陆面热力和动力过程的关系,发现发展过程消耗的能量要比维持衰退过程高得多,而且进入残余层后对流边界层发展对陆面热力作用更敏感,发展也更迅速.风速的动力作用对大气边界层发展也有一定的影响,尤其对冬季稳定大气边界层影响较大.极强的陆面热力作用是我国干旱区形成深厚大气边界层的主导因素. 相似文献
6.
利用“我国西北干旱区陆－气相互作用观测试验"在敦煌双墩子戈壁站取得的观测资料及最近的一些研究成果对陆面模式中反照率、相似性函数及地表粗糙度(动量粗糙度，标量粗糙度)3个方面的参数化方案进行了改进，然后对一次典型降水过程的陆面特征及近地层的风、温、湿进行了模拟.结果表明：改进的模式能对降水条件下的干旱区陆面特征进行较好的模拟，其中对辐射、地表温度的模拟相当好，而对能量的模拟虽然还有要改进的地方，但总体结果令人满意；另外改进后的模式对近地层的温度和湿度的模拟也有明显的改善. 相似文献
7.
数值差分格式及格点设置对土壤温度模拟结果的影响 总被引：2，自引：2，他引：0
土壤温度是反映气候系统和生态系统能量循环的重要地球物理学参量,土壤温度的模拟精度直接影响着气候系统模式以及陆面物理过程模式的模拟结果.为了提高模式对土壤温度的模拟能力,本文利用土壤热扩散方程的傅里叶解析解定量研究了差分方案、格点设置以及时间步长对土壤温度模拟结果的影响;提出了一种优化的格点设置方案,并利用巴丹吉林沙漠观测数据检验了该方案的性能.研究结果表明:三种差分方案中,显式方案的模拟误差最小,Crank-Nicolson方案其次,隐式方案的模拟误差最大;每一种格点设置方案均存在一个使模拟结果误差最小的最优化时间步长;常用格点设置方案的最优化时间步长为5358 s,最小标准差为0.156 K,优化方案的最优化时间步长为1694 s,最小标准差为0.0465 K;取时间步长为1800 s时,采用常用格点设置方案,巴丹吉林沙漠10 cm深度土壤温度模拟结果的标准差为1.61 K,而采用优化方案,模拟结果的标准差降至0.21 K,改进效果明显. 相似文献
8.
地球重力场季节和年际变化主要来源于地球表层大气、海洋和陆地各系统间水的质量交换,由GRACE重力卫星探测地球重力场变化所反映陆地水储量的改变主要来自降雨、土壤蒸发蒸腾、河流输运以及向地下深层的渗透等过程．本研究利用陆面过程模式CLM3．5以及基于本征正交分解的集合四维变分同化方法PODEn4DVar,构建能够同化GRACE卫星重力场的陆面水文同化系统LDAS．G,实现对地球重力场所反映的大尺度陆地水储量变化在时间及垂直方向各分量的分解,并对垂直方向的水文变量进行同化,从而更好地估计陆面水循环要素变化并实现其监测．利用LDAS．G同化系统进行理想试验以及针对中国区域所进行的同化试验表明该同化系统能够改善对陆面水文要素变化的模拟,对大尺度陆面水文循环监测研究具有重要意义． 相似文献
9.
针对陆上三分量地震资料去噪处理中面临的面波噪声能量强、有效信号能量弱、转换波与面波主频叠置、非矢量保真处理等问题,本文基于多分量数据中有效信号与强面波噪声在极化属性、振幅能量、视速度三方面的特征差异,提出了一种时频域压制多分量数据强面波的去噪方法,并设计了相应的矢量滤波器。该方法利用小波变换将地震信号变换到时频域,并基于时频域瞬时极化率公式计算出各点极化率参数,然后根据面波视速度划分出有效信号区和面波噪声区,并据此对有效信号进行能量均值统计,最后联合极化率、能量、频率特征对噪声识别和分频、分区压制。理论模型和实际资料处理验证了本文方法的正确性和有效性,为解决低信噪比陆上多分量资料面波压制提供了又一种有效手段。 相似文献
10.
复杂多变的陆地表微波比辐射率,造成陆面上星载微波观测反演大气参数较为困难,也使得许多卫星微波资料不易同化应用到数值模式,因此迫切需要提供准确可靠的陆面微波地表比辐射率信息.随着卫星观测技术的迅速发展,利用丰富的星载被动微波观测直接反演陆面微波比辐射率成为一种主要手段.国外针对星载微波成像仪和微波垂直探测器开展较为系统的陆面微波比辐射率研究,建立不同类型的地表比辐射率反演方法,开发地表比辐射率参数化方法并应用于辐射资料同化.对于卫星观测反演陆面微波比辐射率存在的问题,开展了评估分析和方法订正.国内利用卫星观测也开展了一些陆面微波比辐射率研究工作,尚需要系统、综合的提炼.对于地表特征复杂的中国地区,还需要评估认识不同陆面微波比辐射率反演方法在我国适用情况,需要增强陆面微波比辐射率数据质量的认识以及业务应用. 相似文献
11.
Spatial distribution of surface energy fluxes over the Loess Plateau in China and its relationship with climate and the environment 总被引：1，自引：0，他引：1
Qiang Zhang Liang Zhang Jing Huang LiYang Zhang WenYu Wang Sha Sha 《中国科学:地球科学(英文版)》2014,57(9):2135-2147
China's Loess Plateau is located at the edge of the Asian summer monsoon in a transition zone of climate and ecology. In the Loess Plateau, climate and environments change along with space, which has an obvious impact on the spatial distribution of surface energy fluxes. Because of scarce land-surface observation sites and short observation time in this area, previous studies have failed to fully understand the land-surface energy balance characteristics over the entire the Loess Plateau and their effect mechanisms. In this paper, we first test the simulation ability of the Community Land Model(CLM) model by comparing its simulated data with observed data. Based on the simulation data for the Loess Plateau over the past thirty years, we then analyze the spatial distribution of surface energy fluxes and compare the pattern differences between the area averages for the driest year and wettest year. Furthermore, we analyze the relationship between the spatial distribution of the components of the surface energy balance with longitude, latitude, altitude, precipitation and temperature. The main results are as follows: the spatial distribution of surface energy fluxes are significantly different, with the surface net radiation and sensible heat flux increasing from south to north and latent heat flux and soil heat flux decreasing from southeast to northwest. The sensible heat flux at the driest point is nearly twice as high as that at the wettest point, whereas the latent heat flux and soil heat flux at the driest point are half as much as that at the wettest point. The impact of variations of annual precipitation on the components of the surface energy balance is also obvious, and the maximum magnitude of the changes to the sensible heat flux and latent heat flux is nearly 30%. To a certain extent, geographical factors(including longitude, latitude, and altitude) and climate factors(including temperature and precipitation) affect the surface energy fluxes. However, the surface net radiation is more closely related to latitude and altitude, sensible heat flux is more closely related to the monsoon rainfall and latitude, and latent heat flux and soil heat flux are more closely related to the monsoon rainfall. 相似文献
12.
Freezing and thawing processes at the soil surface play an important role in determining the nature of Tibetan land and atmosphere interactions. In this study, land surface water and heat exchanges under different freezing and thawing conditions over the central Tibetan Plateau were investigated using observations from the Coordinated Enhanced Observing Period/Asia‐Australia Monsoon Project on the Tibetan Plateau, and the Simultaneous Heat and Water Model. During the freezing and thawing stages, significant diurnal variation of soil temperature resulted in a diurnal cycle of unfrozen water content at the surface. Radiation and energy components and evapotranspiration averaged over four freeze/thaw stages also changed diurnally. On average, the surface albedo (0·68) during the completely frozen stage was sharply higher than those during the freezing, thawing, and completely thawed stages due to the snow cover. The Bowen ratios were 3·1 and 2·5 in the freezing and thawing stages, respectively, but the ratio was only 0·5 in the completely thawed stage. Latent heat flux displayed distinctly better correlation with unfrozen soil water content during the freezing and thawing stages than during the completely frozen and thawed stages. This implies that the diurnal cycle of unfrozen soil water, resulting from diurnal freeze/thaw cycles at the surface, has a significant impact on latent heat flux. A surface energy imbalance problem was encountered, and the possible sources of error were analysed. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
13.
On the relationship between environmental aridization of the Loess Plateau and soil water in loess 总被引：6，自引：0，他引：6
The similarity between loess palaeo- environment and geographic distribution of modem bioclimatic zones is taken as a starting
point; the relationship between the environmental aridization and soil water in loess ia discussed from the point view of
the soil water energy status and their soil water physical characteristics of modem lcessial soils on the Loess Plateau. The
soil water content becomes less and less from southeast to northwest, which not only provides favorable conditions for dust
production by wind of loess origin, but also reveals that there is obviously a directional change in the environmental drought
intensity of the Loess Plateau.
Project supported by the key pmject (KZ951-B1-211) of ecological and environmental study of the Chinese Academy of Sciences 相似文献
14.
15.
This study aims to quantify the contribution of land use/cover change (LUCC) during the last three decades to climate change conditions in eastern China. The effects of farmland expansion in Northeast China, grassland degradation in Northwest China, and deforestation in South China were simulated using the Weather Research and Forecasting (WRF) model in addition to the latest actual land cover datasets. The simulated results show that when forestland is converted to farmland, the air temperature decreased owing to an increase in surface albedo in Northeast China. The climatic effect of grassland degradation on the Loess Plateau was insignificant because of the negligible difference in albedo between grassland and cropland. In South China, deforestation generally led to a decrease in temperature. Furthermore, the temperature decrease caused by the increase in albedo counteracted the warming effects of the evapotranspiration decrease, so the summer temperature change was not significant in South China. Excluding the effects of urbanization in the North China Plain, the LUCC effects across the entire region of East China presented an overall cooling trend. However, the variation in temperature scale and magnitude was less in summer than that in winter. This result is due mainly to the cooling caused by the increase in albedo offset partly by the increase in temperature caused by the decrease in evaporation in summer. Summer precipitation showed a trend of increasing–decreasing–increasing from southeast to northwest after LUCC, which was induced mainly by the decrease in surface roughness and cyclone circulations appearing northwest of Northeast China, in the middle of the Loess Plateau, and in Yunnan province at 700 hPa after forests were converted into farmland. All results will be instructive for understanding the influence of LUCC on regional climate and future land planning in practice. 相似文献
16.
Based on important factors that affect soil moisture spatial distribution, such as the slope gradients, land use, vegetation
cover, and surface water diffusion characteristics together with field measurements of soil moisture data obtained from the
surface soil under different land use structures, a soil moisture spatial distribution model was established. The diffusion
degree coefficient of surface water for different vegetations was estimated from soil moisture values obtained from field
measurements. The model can be solved using the finite unit method. The soil moisture spatial distribution on the hill slopes
in the Loess Plateau were simulated by the model. A comparison of the simulated values with measurement data shows that the
model is a good fit. 相似文献
17.
Feedbacks between vegetation restoration and local precipitation over the Loess Plateau in China 总被引：1，自引：0，他引：1
《中国科学:地球科学(英文版)》2021,(6)
The implementation of large-scale vegetation restoration over the Chinese Loess Plateau has achieved clear improvements in vegetation fraction, as evidenced by large areas of slopes and plains being restored to grassland or forest.However, such large-scale vegetation restoration has altered land-atmosphere exchanges of water and energy, as the land surface characteristics have changed. These variations could affect regional climate, especially local precipitation. Quantitatively evaluating this feedback is an important scientific question in hydrometeorology. This study constructs a coupled land-atmosphere model incorporating vegetation dynamics, and analyzes the spatio-temporal changes of different land use types and land surface parameters over the Loess Plateau. By considering the impacts of vegetation restoration on the water-energy cycle and on land-atmosphere interactions, we quantified the feedback effect of vegetation restoration on local precipitation across the Loess Plateau, and discussed the important underlying processes. To achieve a quantitative evaluation, we designed two simulation experiments, comprising a real scenario with vegetation restoration and a hypothetical scenario without vegetation restoration.These enabled a comparison and analysis of the net impact of vegetation restoration on local precipitation. The results show that vegetation restoration had a positive effect on local precipitation over the Loess Plateau. Observations show that precipitation on the Loess Plateau increased significantly, at a rate of 7.84 mm yr~(-2), from 2000 to 2015. The simulations show that the contribution of large-scale vegetation restoration to the precipitation increase was about 37.4%, while external atmospheric circulation changes beyond the Loess Plateau contributed the other 62.6%. The average annual precipitation under the vegetation restoration scenario over the Loess Plateau was 12.4% higher than that under the scenario without vegetation restoration. The above research results have important theoretical and practical significance for the ecological protection and optimal development of the Loess Plateau, as well as the sustainable management of vegetation restoration. 相似文献
18.
Reed M. Maxwell Fotini Katopodes Chow Stefan J. Kollet 《Advances in water resources》2007,30(12):2447-2466
This study combines a variably-saturated groundwater flow model and a mesoscale atmospheric model to examine the effects of soil moisture heterogeneity on atmospheric boundary layer processes. This parallel, integrated model can simulate spatial variations in land-surface forcing driven by three-dimensional (3D) atmospheric and subsurface components. The development of atmospheric flow is studied in a series of idealized test cases with different initial soil moisture distributions generated by an offline spin-up procedure or interpolated from a coarse-resolution dataset. These test cases are performed with both the fully-coupled model (which includes 3D groundwater flow and surface water routing) and the uncoupled atmospheric model. The effects of the different soil moisture initializations and lateral subsurface and surface water flow are seen in the differences in atmospheric evolution over a 36-h period. The fully-coupled model maintains a realistic topographically-driven soil moisture distribution, while the uncoupled atmospheric model does not. Furthermore, the coupled model shows spatial and temporal correlations between surface and lower atmospheric variables and water table depth. These correlations are particularly strong during times when the land-surface temperatures trigger shifts in wind behavior, such as during early morning surface heating. 相似文献
19.
《中国科学:地球科学(英文版)》2015,(3)
Assume that an oasis and its surrounding desert consist of an isolated system without mass and energy exchange with the outer environment.The characteristics of oasis evolution have been explored under the condition of system energy conservation.The results show that oasis evolves with two equilibrium states.The first equilibrium suggests a stable expansive and an unstable degraded oasis whereas the second equilibrium indicates a stable shrink and an unstable increase of the oasis area.If one equilibrium state is unstable,the components of the isolated system(oasis and desert) would tend to be no energy exchange and they each reach to energy balance respectively.Oasis would maintain its initial area in this case.Further analyses point out that the two equilibrium states have completely different characteristics.In the first equilibrium state,a higher vegetation albedo,lower soil albedo and larger canopy resistance,and direr soil both contribute to the oasis area expansion,accompanying an excessive large desert soil and vegetation canopy temperature difference(SCTD).In the second equilibrium state,however,a lower vegetation albedo,higher soil albedo and small canopy resistance,and wetter soil benefit the oasis area to stay near its initial value,following a moderate SCTD.The convergent trajectories of the initial values in phase space are influenced by the separatrices of the equilibrium points.Higher temperature is an advantage factor for initial values convergent to the oasis expansion solution. 相似文献
20.
《水文科学杂志》2013,58(6):1079-1093
Abstract A time series analysis of 152 VV-polarized Advanced Synthetic Aperture Radar (ASAR) Wide Swath Mode (WSM) images collected over the central part of the Tibetan Plateau is presented for the period from April 2005 to September 2007. The signatures of a grassland and a wetland are studied to identify the impact of three land-surface states on the backscatter (σ°). The considered land-surface states are soil moisture, soil temperature and vegetation biomass represented by Système Pour l'Observation de la Terre (SPOT) Normalized Difference Vegetation Index (NDVI). Comparison of the σ° time series with these land-surface states via a multivariate regression shows that the grassland σ° are well represented by the soil moisture dynamics, while the wetland σ° also has a strong correlation with soil temperature. Further, we found that the contribution of the NDVI to the explanation of the temporal σ° variability is limited for both the grassland and wetland. 相似文献