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陆面过程模式是气候模式和天气模式的核心组成部分之一.在土壤—植被—大气耦合模式(Soil-PlantAtmosphere Model,SPAM)的基础上,发展了新一代北京大学陆面过程模式PKULM(Peking University Land Model).本文首先介绍了PKULM的辐射传输、湍流输送、光合作用、土壤水热输送等过程的参数化方案;采用隐式迭代计算框架,发展并应用了一个快速的线性方程组求解算法,提高了模式计算稳定性;提出并使用了二分搜索算法计算气孔阻抗,避免了CLM(Community Land Model)等使用的迭代方法在干旱区不稳定的情况,提高了模式的适用性;采用水势为基础的土壤水分扩散方程,使模式能够模拟土壤饱和区的水分输送过程,为进一步与水文过程模式耦合奠定了基础;还发展了一个地表积水与径流过程的机理模型,提高了模式对地表水分平衡过程的模拟能力;最后,使用"中国西北干旱区陆—气相互作用观测试验"平凉站的资料对模式进行了检验并与NOAH(National Center for Environmental Prediction,Oregon State University,Air Force,and Hydrology Lab model)陆面过程模式的模拟结果进行了比较,结果表明PKULM能够较好地模拟西北半干旱区农田下垫面地气交换过程. 相似文献
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为了研究实验变形失稳过程中的应变场快速调整阶段和岩石结构破坏过程中的复杂变形场,将高速、高分辨率、多通道的应变观测技术引入构造物理实验,搭建了用以观测瞬态变形场的多通道动态应变观测系统,形成了16Bit分辨率、96通道、3.4kHz采样速度、1με分辨率且连续记录的应变观测系统。通过观测断层失稳过程高速滑动阶段和裂纹扩展过程的力学场时空变化,发现断层粘滑失稳过程的演化具有3个特征阶段:预滑动阶段、高频震荡阶段和低频调整止滑阶段。每个阶段的持续时间、应变速率、频率特性、振幅等都具有自身特点;三维断层扩展模型的实验结果显示,岩桥区断层贯通是一个快速过程,先多点局部扩展,后跳跃式连接。在断层贯通之后,样品整体崩垮之前,存在一个相对稳定的阶段,持续时间为几十ms。多通道动态应变观测系统填补了在地震模拟与岩石力学实验中应变观测频带的空缺,可以获得高密度、高精度的动态应变场,进一步研究瞬态应变场演化与应变波时空过程,为理解从缓慢递进变形到突发失稳释放过程提供了技术支持。 相似文献
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永登5.8级地震孕育发生过程中的断层形变与重力场动态图象特征s 总被引：3，自引：0，他引：3
初步研究了1995年7月22日甘肃永登5.8级地震孕育发生过程中的断层形变异常和重力场、垂直形变场动态演化特征．孕震过程中近源区有3处断层形变呈,,相变化异常,外围区1993年以来先后有10余处场地断层形变出现台阶、突跳等异常．流动重力监测到震前出现的高值异常区、同震效应及震后恢复正常的演变过程等．资料反映了孕震过程中近源区断层运动由准线性走向非线性的过程,重力场变化由孕育、发震过程的非均匀态走向震后的准均匀态的演化过程,较强地震的孕育发生与区域应力应变场的动态演化密切相关．还简要总结了作者对这次地震中短期预报试验的经验教训． 相似文献
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SWAT modeling with uncertainty and cluster analyses of tillage impacts on hydrological processes 总被引：3，自引：2，他引：1
Gangsheng Wang Michael E. Barber Shulin Chen Joan Q. Wu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(2):225-238
The impacts of tillage practices, majorly conventional tillage (CT) and no-till (NT), on soil hydraulic properties have been studied in recent decades. In this paper, we incorporated an auto-calibration algorithm into the Soil and Water Assessment Tool (SWAT) model and calibrated the model at eight field sites with soil water content (SWC) observations in the Pataha Creek Watershed, WA, USA. The Green–Ampt method in SWAT was chosen to determine infiltration and surface runoff. Parameter uncertainty was quantified by “relatively optimal” parameter sets filtered by a critical objective function value. Cluster analysis was adopted to obtain equal-sized parameter sets for each site and to compare parameter sets between tillage practices. The centers of these clusters were employed as a sample of parameter values. The clustered parameter sets were then used in scenario analysis to examine the impacts of cropland tillage practices on lateral flow, runoff and evapotranspiration (ET). The model parameters (e.g., soil hydraulic properties) were significantly different between CT and NT. In particular, higher bulk density, larger available water capacity, and higher effective hydraulic conductivity were found for NT than for CT. SWCs at three depths of the NT sites were significantly higher than those of CT sites, which could be attributed to tillage practices. However, higher available water capacity at NT sites indicated that the NT soil had a higher capacity to hold water. Thus the mean net changes in SWC during a year were not significantly different between CT and NT. The statistically different model parameters neither resulted in statistical differences in annual outputs (e.g., runoff and ET) nor substantial differences in monthly outputs. Our study indicates that the tillage impacts on hydrological processes are site-specific and scale-dependent. 相似文献
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Ana L. Londero Jean P. G. Minella Fabio J. A. Schneider Dinis Deuschle Danrlei Menezes Olivier Evrard Madalena Boeni Gustavo H. Merten 《水文研究》2021,35(3):e14094
No-till (NT) is a conservation system that improves the hydrological regime of agricultural slopes by providing greater surface protection and benefits to the physical and hydrological properties of soils. However, the isolated use of NT is not enough to control runoff and its associated degradation processes. Therefore, this study aimed to evaluate the runoff of agricultural slopes under NT under different runoff control conditions by monitoring 63 rainfall events in two 2.4-ha zero-order catchments and 27 rainfall events in four 0.6-ha macroplots. The catchments are paired and similar in terms of the type of soil and relief, but different regarding the presence of terraces. The macroplots have different soil and crop management systems. By using monitoring techniques, the hyetographs and hydrographs revealed the influence of the different types of management on the catchments and macroplots and allowed rainfall characteristics, runoff volume, runoff coefficients, water infiltration, peak runoff, response times, and curve number to be analysed. The terraces positively affected the NT and controlled runoff and related variables, in addition to infiltration significantly increasing and runoff reducing in the terraced catchment. All the hydrological information assessed pointed to the positive effects provided by the presence of the terraces. The results in the macroplots showed that high amounts of phytomass and/or chiselling do not control runoff and its correlated variables in medium and high magnitude events. The study concludes by underlining the need for additional measures to control runoff (terraces), even in areas under NT and with high phytomass production. Additionally, the study emphasizes the importance of monitoring at the catchment scale to better understand the hydrological behaviour of agricultural areas and provide the necessary parameters to effectively control runoff. 相似文献
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In October 1965 and February 1966, 55 Young-pits were installed in tropical Northern Territory (NT) and temperate New South Wales (NSW). Pits were monitored in 1968, 1971 and 1974; also, for the NT only, in 1988. In each region, half of the pits are on weathered granite, and half on sandstone. Local relief is 30m or less, and slopes are up to 20°. Annual rainfall is evenly distributed in the NSW sites (800 mm a−1), but is confined to the five to six month wet season in NT (1200 mm a−1). Six pits suffered external disturbance and so were not analysed. Analysis of 160 rods in 49 undisturbed pits shows: (1) vectorial movement generally not downslope parallel to the ground surface, but dominated by a vertically downward component; (2) significant uphill and vertically upward components of movement for many rods; (3) a weak correlation between total movement and sine of slope; (4) rapid movement during 1965-68, and slow movement thereafter; (5) significantly higher creep rates on the NT granites than on all other sites, perhaps because mound-building termites are especially active there. We conclude that our data do not support soil creep models which assume that all movement is downslope and slope-parallel. Repeated long-term measurements are essential to distinguish long-term creep rates from the short-term effects of disturbance. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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Observed reduction in recent sea ice areal extent and thickness has focused attention on the fact that the Arctic marine system appears to be responding to global‐scale climate variability and change. Passive microwave remote‐sensing data are the primary source underpinning these reports, yet problems remain in geophysical inversion of information on ice type and concentration. Uncertainty in sea‐ice concentration (SIC) retrievals is highest in the summer and fall, when water occurs in liquid phase within the snow–sea‐ice system. Of particular scientific interest is the timing and rate of new ice formation due to the control that this form of sea ice has on mass, energy and gas fluxes across the ocean–sea‐ice–atmosphere interface. In this paper we examine the critical fall freeze‐up period using in situ data from a ship‐based and aerial survey programme known as the Canadian Arctic Shelf Exchange study combined with microwave and optical Earth observations data. Results show that: (1) the overall physical conditions observed from aerial survey photography were well matched with coincident moderate‐resolution imaging spectroradiometer data and Radarsat ScanSAR imagery; (2) the shortwave albedo was linearly related to old ice concentration derived from survey photography; (3) the three SSM/I SIC algorithms (NASA Team (NT), NASA Team 2 (NT2), and Bootstrap (BT)) showed considerable discrepancies in pixel‐scale comparison with the Radarsat ScanSAR SICs well calibrated by the aerial survey data. The major causes of the discrepancies are attributed to (1) the inherent inability to detect the new thin ice in the NT and BT algorithms, (2) mismatches of the thin‐ice tie point of the NT2 algorithm, and (3) sub‐pixel ambiguity between the thin ice and the mixture of open water and sea ice. These results suggest the need for finer resolution of passive microwave sensors, such as AMSR‐E, to improve the precision of the SSM/I SIC algorithms in the marginal ice zone during early fall freeze‐up. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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根据第７代ＩＧＲＦ模型,计算并绘制了１９００-２０００年（时间间隔为５ａ）非偶极子磁场的全球分布,计算和分析了各个磁异常中心位置和强度的变化,东亚正磁异常、大洋洲负磁异常、南大西洋正磁异常、非洲负磁异常和北美洲正磁异常是分布范围广、异常强度大的５个磁异常。南大西洋正磁异常是强度最大的磁异常。在２０世纪９０年代以前,东亚正磁异常的强度位居第２位,９０年代以后,非洲负磁异常的强度（绝对值）超过东亚正磁异常,成为第２大磁异常。磁异常强度增长最快的是非洲负磁异常、南大西洋正磁异常和大洋洲负磁异常。南大西洋正磁异常和非洲负磁异常是磁异常中心位置变化最快的两个磁异常。 相似文献
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María Concepcin Ramos Evangelina Pareja‐Snchez Daniel Plaza‐Bonilla Carlos Cantero‐Martínez Jorge Lampurlans 《水文研究》2019,33(15):2095-2109
The main objective of this research was to analyse the effect of soil management on soil sealing and on soil water content under contrasting tillage practices and its influence on corn yield. The experimental research was carried out in a field cultivated with irrigated corn differentiated into three zones representing a gradient of soil texture (Z1, Z2, and Z3, i.e., increasingly coarser). Two plots under different soil management practices (conventional intensive tillage, CT, and no‐tillage, NT) were selected in each zone. The susceptibility to sealing of each soil and the steady infiltration rates were evaluated in the laboratory subjecting the soils to rainfall simulation applied at an intensity of 25 mm h?1. In addition, soil porosity under each treatment was quantified. Soil water content (0–90 cm depth) was determined gravimetrically at the beginning and the end of the growing cycle and at the surface (0–5 cm) during three growing seasons and continuously at two depths (5–15 and 50–60 cm) during the last growing cycle. Soil water content was simulated using the SIMPEL model, which was calibrated for the experimental conditions. Corn yield and above‐ground biomass were also analysed. Significant differences in soil sealing among zones, with decreasing soil sealing for coarser textures, and treatments were observed with infiltration rates that were near twice in NT than in CT, being the effect of soil cover significant in the reduction of soil detachment and soil losses. NT showed higher soil water content than CT, especially in the surface layers. Above‐ground biomass production was smaller in CT than in NT, and in the areas with higher sealing susceptibility was 30% to 45% smaller than in other zones, reaching the smallest values in Z1. A similar reduction in corn yield was observed between treatments being smaller in CT than in NT. No‐tillage has been confirmed as an effective technique that benefits soil physical properties as well as crop yields in relation to CT, being its impact greater in soils susceptible to sealing. 相似文献
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地面磁共振是一种新的地球物理探测方法,能够通过探测地下水中氢质子丰度获取地下水含量、孔隙度等水文地质信息.然而,磁共振信号甚为微弱,仅达到纳伏级(10~(-9)V),极易受到噪声干扰.其中,尖峰噪声对磁共振信号影响最为严重,亟待研究有效的噪声抑制方法.小波多尺度分解硬阈值是近两年国际磁共振领域专家提出的尖峰噪声有效消除方法,但硬阈值算法设定阈值的固有缺陷会引发信号震荡,出现伪吉布斯效应,导致信号损失.基于此,本文提出压缩小波变换(Synchrosqueezing Wavelet Transform,SWT)和非线性國值处理(Nonlinear Thresholding,NT)算法联合消除磁共振信号尖峰噪声干扰.首先选择Morlet小波作为基小波,使得信号与噪声数据具有更高的时频集中性,利于尖峰噪声消除.其次,基于压缩小波系数进行非线性处理,可以弥补利用硬阈值和软阈值进行噪声消除时所引起的信号损失.仿真数据和实际数据结果表明,SWT联合NT方法可以利用单次采集数据有效消除尖峰噪声干扰并还原信号.本文提出的消噪方法将为磁共振数据后续反演解释,如多指数弛豫反演,奠定坚实的基础. 相似文献