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371.
在“超大城市垂直综合气象观测技术研究及实验”中,利用欧洲中期天气预报中心(ECMWF)的ERA Interim再分析数据集,对2018年北京观象台的地基导航卫星气象观测(GNSS/MET)、探空和微波辐射计观测的水汽总量(PWV)进行了对比分析,结果表明,3种观测和ECMWF模式分析具有较好的相关性,可以较好地监测北京水汽的变化。与ECMWF模式对比,GNSS/MET、探空和微波辐射计的偏差分别为0.54mm、1.94mm、-0.65mm,均方根误差分别为3.55mm、3.60mm、6.08mm;若以探空作为参考,GNSS/MET、ECMWF和微波辐射计的偏差分别为-1.39mm、-1.94mm、-2.58mm,均方根误差为2.85mm、3.59mm、6.79mm。由此可见GNSS/MET、探空和ECMWF模式分析的水汽具有较好的质量。从对比结果看,GNSS/MET在相关性、偏差和均方根误差方面均表现突出,和探空、ECMWF相当,而微波辐射计差别明显,均方根误差最大,但剔除雨日后,资料质量得到提高,表明微波辐射计资料的应用需要注意降水条件,反演算法需在今后进行改进。 相似文献
372.
There exist many fluvio-glacial deposits in the valley of Dadu River,Southwest China,which dates back to the Pleistocene.As some of the deposits are located within the seasonal water fluctuation zone of reservoirs,the seepage of groundwater acts as one of the key factors influencing their stability.Investigation into the sediment properties and permeability is,therefore,crucial for evaluating the sediment stability.In this study,in-situ permeability and sieving tests have been carried out to determine grain size distribution,correlations of permeability and hydraulic gradients,and relations between permeability and sedimentation properties.Test results indicate that the deposits are composed mostly of sands,gravels,cobbles and boulders,and the percentage of fines is less than 5%.The sediments have high densities,low porosities and natural moisture contents.At low hydraulic gradients,the seepage velocity obeys the Darcy’s law,while a nonDarcy permeability is observed with hydraulic gradient exceeding a certain value(about 0.5-0.7).The linear permeability coefficient ranges from 0.003 to 0.009 cm/s.Seepage failure occurs above a threshold between 1.1 and 1.5.The test data fit well with the non-linear permeability equations suggested by Forchheimer and Izbash.The non-Darcy permeability proves to be in accordance with the seepage equation suggested by Izbash with the power ’m’ of about 0.6-0.7.The characteristic grain sizes of the studied deposits are found in a narrow range between 0.024 and 0.031 mm,which is much lower than the effective grain size(d 10). 相似文献
373.
374.
Progress of limnology in China 总被引:1,自引:0,他引:1
The following six aspects in the utilization of lake resources and progress of limnological research in China are described:
1. Expeditions for comprehensive investigation of lakes; 2. Physical limnology; 3. lacustrine sedimentology and paleolimnology;
4. Hydrobiology and ecology; 5. Hydrochemistry and environmental protection; 6. Development and utilization of lake resources.
This paper was published in Chinese inScientia Limnologica Sinica
1 (1): 1–11, 1989. 相似文献
375.
Li-Ping Yang Ling-Hua Wang Jian-Sen He Chuan-Yi Tu Shao-Hua Zhang Lei Zhang Xue-Shang Feng 《天文和天体物理学研究(英文版)》2015,(3):348-362
Superhalo electrons appear to be continuously present in the interplanetary medium, even during very quiet times, with a power-law spectrum at energies above ~2 ke V. Here we numerically investigate the generation of superhalo electrons by magnetic reconnection in the solar wind source region, using magnetohydrodynamics and test particle simulations for both single X-line reconnection and multiple X-line reconnection. We find that the direct current electric field, produced in the magnetic reconnection region, can accelerate electrons from an initial thermal energy of T ~ 105 K up to hundreds of ke V. After acceleration, some of the accelerated electrons, together with the nascent solar wind flow driven by the reconnection, propagate upwards along the newly-opened magnetic field lines into interplanetary space, while the rest move downwards into the lower atmosphere. Similar to the observed superhalo electrons at 1 AU, the flux of upward-traveling accelerated electrons versus energy displays a power-law distribution at ~ 2-100 ke V, f(E) ~ E-δ, with a δ of ~ 1.5- 2.4.For single(multiple) X-line reconnection, the spectrum becomes harder(softer) as the anomalous resistivity parameter α(uniform resistivity η) increases. These modeling results suggest that the acceleration in the solar wind source region may contribute to superhalo electrons. 相似文献
376.
In this paper the question about the space correlation of the fluctuation in helium nuclear reaction diffusion system has been analysed. We have introduced the diffusion term into master equation of the probability distribution function of density. The spectrum of fluctuation waves in helium nuclear reaction system have been obtained. There is a series of waves which described the propagation of the fluctuation moments of the local density. The instability of helium combustion at its beginning for the star which mass satisfyingM<2M
may be related with those increasing fluctuation waves. We also use the bifurcation theory to deal with the partial differential equation of helium nuclear reaction system. The expression of supercritical ordinary bifurcation is obtained. 相似文献
377.
Chuan-Yi Tu 《Solar physics》1971,109(1):149-186
A new solar wind model has been developed by including in the model the Alfvénic fluctuation power spectrum equation proposed by Tu et al. (1984). The basic assumptions of the model are as follows: (1) for heliocentric distances r > 10 R
, the radial variation of the power spectrum of Alfvénic fluctuations is controlled by the spectrum equation (1), (2) for heliocentric distances r < 10 R
, the radial variation of the fluctuation amplitude is determined by the Alfvén wave WKB solution, (3) no energy cascades from the low-frequency boundary of the Alfvénic fluctuation power spectrum into the fluctuation frequency range, and the energy which cascades from the high-energy boundary of the spectrum into the higher frequency range is transported to heat of the solar wind flow. Some solutions of this model which, on one hand, describe the major properties of the Alfvénic fluctuations and the high-speed flow observed by Helios in the space range between 0.3–1 AU and, on the other hand, are consistent with the observational constraints at the coronal base have been obtained under the following conditions: (1) the spectrum index of the fluctuations is near to -1 for almost the whole frequency range at 10 R
, (2) the particle flux density at 1 AU is not greater than 3 × 108 cm–2 s–1, (3) the solution is for spherically-symmetric flow geometry or the solution passes through the outermost of the three critical points of the rapidly diverging flow geometry with f
max = 7. Some solutions passing through the innermost critical point of the rapidly diverging flow geometry with f
max = 7 have been found, however, with too low pressure at the coronal base to compare with the observational constraints. Heat addition or other kind of momentum addition for r < 10 R
is required to modify this model to yield better agreement with observations. A cascade energy flux function which leads to Kolmogorov power law in the high-frequency range of Alfvénic fluctuations is presented in Appendix A. More detailed discussions about the characteristics, the boundary conditions and the solution of the spectrum equation (1) are given in Appendix B.Projects supported by the Science Fund of the Chinese Academy of Sciences. 相似文献
378.
Chenglong Tu Congqiang Liu Timothy A. Quine Matthew William Jones Taoze Liu Longbo Li Wenjing Liu 《中国地球化学学报》2018,37(5):746-757
Intensive soil tillage is a significant factor in soil organic matter decline in cultivated soils. Both cultivation abandonment and foregoing tillage have been encouraged in the past 30 years to reduce greenhouse gas emissions and soil erosion. However, the dynamic processes of soil organic carbon (SOC) in areas of either continuous cultivation or abandonment remain unclear and inconsistent. Our aims were to assess and model the dynamic processes of SOC under continuous tillage and after cultivation abandonment in the black soil of Northeast China. Soil profiles were collected of cultivated or abandoned land with cultivation history of 0–100 years. An isotope mass balance equation was used to calculate the proportion of SOC derived from corn debris (C4) and from natural vegetation (C3) to deduce the dynamic process. Approximately 40% of SOC in the natural surface soil (0–10 cm) was eroded in the first 5 years of cultivation, increasing to about 75% within 40 years, before a slow recovery. C4 above 30 cm soil depth increased by 4.5%–5% or 0.11–0.12 g·kg?1 on average per year under continuous cultivation, while it decreased by approximately 0.34% annually in the surface soil after cultivation abandonment. The increase in the percentage of C4 was fitted to a linear equation with given intercepts in the upper 30 cm of soil in cultivated land. A significant relationship between the change of C4 and time was found only in the surface soil after abandonment of cultivation. These results demonstrate the loss and accumulation of corn-derived SOC in surface black soil of Northeast China under continuous tillage or cultivation abandonment. 相似文献
379.
侯德封同志是我国早期地球化学事业的开创者、组织者和设计师。他于50年代初提出的化学地史及60年代反复强调的核子地质均蕴育了浓厚的地球化学思维。在50年代我国制定12年科学技术发展规划和60年代创办我国第一个地球化学研究机构的过程中,侯老发挥了远见卓识和当机立断的地球化学事业开拓者的关键作用。在领导和组织建国后我国早期的稀有元素地球化学、同位素地球化学和铀钍地球化学科研工作中,侯老是主要的带头人,在学术思想上提出了指导性见解。 相似文献
380.
论述了湛江海洋大学校园树木景观的现状和规划。指出要以园林生态学原则为指导思想建设热带生态园林式校园 相似文献