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71.
72.
1948-2009年塔里木盆地空中水汽输送时空分布特征 总被引:3,自引:2,他引:1
利用1948-2009年美国NCEP/NCAR的逐月再分析资料(2.5°×2.5°),分析了塔里木地区大气中不同层次水平和垂直方向的水汽输入、输出和收支情况及其变化趋势.结果表明:1)塔里木盆地上空水平方向为水汽汇,且纬向贡献大于经向,垂直方向水汽主要由下层向中上层输送;2)水汽的水平和垂直净收支均具有季节性变化,且夏季辐合为主,冬季辐散为主;3)水汽的水平和垂直输送都表现为较一致的年际变化,且均在1970年代中后期出现了较明显的年代际突变;4)在1978年到2003年全球变暖明显的时段内,水平方向水汽净输入量呈减少趋势,垂直方向呈增加趋势.可以认为,在气候变化背景下,全球变暖加速了水循环,但同时改变了纬向的热力差异,导致塔里木盆地局地水循环的加速,以及经向水汽净输入量的减少. 相似文献
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74.
Net primary productivity(NPP) is the most important index that represents the structure and function of the ecosystem.NPP can be simulated by dynamic global vegetation models(DGVM),which are designed to represent vegetation dynamics relative to environmental change.This study simulated the NPP of China's ecosystems based on the DGVM Integrated Biosphere Simulator(IBIS) with data on climate,soil,and topography.The applicability of IBIS in the NPP simulation of China's terrestrial ecosystems was verified first.Comparison with other relevant studies indicates that the range and mean value of simulations are generally within the limits of observations;the overall pattern and total annual NPP are close to the simulations conducted with other models.The simulations are also close to the NPP estimations based on remote sensing.Validation proved that IBIS can be utilized in the large-scale simulation of NPP in China's natural ecosystem.We then simulated NPP with climate change data from 1961 to 2005,when warming was particularly striking.The following are the results of the simulation.(1) Total NPP varied from 3.61 GtC/yr to 4.24 GtC/yr in the past 45 years and exhibited minimal significant linear increase or decrease.(2) Regional differences in the increase or decrease in NPP were large but exhibited an insignificant overall linear trend.NPP declined in most parts of eastern and central China,especially in the Loess Plateau.(3) Similar to the fluctuation law of annual NPP,seasonal NPP also displayed an insignificant increase or decrease;the trend line was within the general level.(4) The regional differences in seasonal NPP changes were large.NPP declined in spring,summer,and autumn in the Loess Plateau but increased in most parts of the Tibetan Plateau. 相似文献
75.
Junhong Bai Qingqing Zhao Junjing Wang Qiongqiong Lu Xiaofei Ye Zhaoqin Gao 《中国地理科学(英文版)》2014,24(3):279-286
Little information is available on denitrification potential of marsh soils in natural saline-alkaline wetlands. The denitrification potentials of an open wetland in the floodplain(Erbaifangzi wetland) and a closed wetland(Fulaowenpao wetland) in backwater areas in Jilin Province of Northeast China were monitored by an anaerobic incubation at 30℃ for 25 days. Our results showed that the relative denitrification index(RDI) increased gradually with incubation time, and showed a rapid increase in the first 5 days of incubation. The RDI values declined quickly from surface soils to subsurface soils and then kept a small change in deeper soils along soil profiles over the incubation time. Denitrification proceeded much faster in the top 20 cm soils of open wetland than in the closed wetland, whereas no significant differences in RDI values were observed in deeper soils between both wetlands. The RDIs were significantly negatively correlated with bulk density and sand content, while a significantly positive correlation with clay content, soil organic matter, total nitrogen and phosphorous. The maximum net NO–3-N loss through denitrification in 1 m depth were higher in the open wetland than the closed wetland with higher soil pH values. Future research should be focused on understanding the influencing mechanisms of soil alkalinity. 相似文献
76.
北京一次大暴雨的水汽收支和微物理过程数值分析 总被引:1,自引:1,他引:0
利用NCEP1°×1°再分析资料和常规气象观测资料,使用WRF模式对2012年7月21日发生在北京地区的一次特大暴雨天气过程进行数值模拟。在模拟结果的基础上,分析了此次暴雨过程的形势演变和水汽条件,并分别计算了暴雨发生过程中北京全市范围内的水汽输送、水汽收支、大气可降水量和空中各相态水物质的量值大小、空间分布情况及其相互转化关系。结果发现:这次降水主要受高空槽、低涡和地面切变线的影响。有东南、西南两条水汽输送通道,计算区域上空水汽收支变化与地面雨强的演变对应很好。中低层持续而强烈的水汽净输入,为暴雨的发生发展提供了很好的水汽条件。北京各站点大气可降水量普遍超过历史极值,反映了降水的极端性。降水发展不同阶段,云内微物理过程存在差异,降水量初期以暖雨为主,降雨量不大,之后冷雨过程增强,降水量迅速增大。 相似文献
77.
The Soil Moisture and Net Primary Production Affected by CO_2 and Climate Change Using a Coupled Model 下载免费PDF全文
In this paper, a coupled model was used to estimate the responses of soil moisture and net primary production of vegetation (NPP) to increasing atmospheric CO2 concentration and climate change. The analysis uses three experiments simulated by the second-generation Earth System Model (CanESM2) of the Canadian Centre for Climate Modelling and Analysis (CCCma), which are part of the phase 5 of the Coupled Model Intercomparison Project (CMIP5). The authors focus on the magnitude and evolution of responses in soil moisture and NPP using simulations modeled by CanESM, in which the individual effects of increasing CO2 concentration and climate change and their combined effect are separately accounted for. When considering only the single effect of climate change, the soil moisture and NPP have a linear trend of 0.03 kg m^-2 yr^-1 and-0.14 gC m^- 2 yr^-2, respec- tively. However, such a reduction in the global NPP results from the decrease of NPP at lower latitudes and in the Southern Hemisphere, although increased NPP has been shown in high northern latitudes. The largest negative trend is located in the Amazon basin at -1.79 gC m^-2 yr^-2. For the individual effect of increasing CO2 concentration, both soil moisture and NPP show increases, with an elevated linear trend of 0.02 kg m^-2 yr^-1 and 0.84 gC m^-2 yr^-2, respectively. Most regions show an increasing NPP, except Alaska. For the combined effect of increasing atmospheric CO2 and climate change, the increased soil moisture and NPP exhibit a linear trend of 0.04 kg m^2 yr^-1 and 0.83 gC m^2 yr^-2 at a global scale. In the Amazon basin, the higher reduction in soil moisture is illustrated by the model, with a linear trend of-0.39 kg m^-2 yr^-1, for the combined effect. Such a change in soil moisture is caused by a weakened Walker circulation simulated by this coupled model, compared with the single effect of increasing CO2 concentration (experiment M2), and a consequence of the reduction in NPP is also shown in this area, with a linear trend of- 相似文献
78.
《Atmósfera》2014,27(3):305-315
Hourly averaged net all-wave radiation data spanning a complete three-year period (2010-2012) at a meteorological station located inside the Obafemi Awolowo University campus in Ile-Ife (7.52° N, 4.52° E), Nigeria is presented in this study to investigate its diurnal and seasonal variations. Using a high-sensitivity four-component net radiometer, the data represents so far the most consistent and detailed information available for a tropical location in West Africa. From the dataset, hourly maxima of the net radiation occurred at 14:00 LT (GMT + 1), whose values increased considerably from 337.6 ± 146.4 Wm−2 in July, which is the peak of the wet season, to 441.7 ± 82.4 Wm−2 in March, the end of the dry season. April and October, both of which mark the beginning and end of the raining season at Ile-Ife have recorded the highest values of 584.7 and 612.2 Wm−2, respectively. There was strong intra/inter-seasonal variation observed in the monthly mean values of the net radiation due mainly to the fluctuations in cloudiness and humidity. In the study area, the data indicated a net radiative heating taking place at the surface, whose annual trend follows a bimodal distribution. The present data supports the results published in earlier studies by other authors. 相似文献
79.
80.
In this article, we investigate the main parameters that influence the propagation of a fluid‐driven fracture in a poroelastoplastic continuum. These parameters include the cohesive zone, the stress anisotropy, and the pore pressure field. The fracture is driven in a permeable porous domain that corresponds to weak formation by pumping of an incompressible viscous fluid at the fracture inlet under plane strain conditions. Rock deformation is modeled with the Mohr–Coulomb yield criterion with associative flow rule. Fluid flow in the fracture is modeled by the lubrication theory. The movement of the pore fluid in the surrounding medium is assumed to obey the Darcy law and is of the same nature as the fracturing fluid. The cohesive zone approach is used as the fracture propagation criterion. The problem is modeled numerically with the finite element method to obtain the solution for the fracture length, the fracture opening, and the propagation pressure as a function of the time and distance from the pumping inlet. It is demonstrated that the plastic yielding that is associated with the rock dilation in an elastoplastic saturated porous continuum is significantly affected by the cohesive zone characteristics, the stress anisotropy, and the pore pressure field. These influences result in larger fracture profiles and propagation pressures due to the larger plastic zones that are developing during the fracture propagation. Furthermore, it is also found that the diffusion process that is a major mechanism in hydraulic fracture operations influences further the obtained results on the fracture dimensions, plastic yielding, and fluid pressures. These findings may explain partially the discrepancies in net pressures between field measurements and conventional model predictions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献