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排序方式: 共有7236条查询结果,搜索用时 180 毫秒
1.
Tomoki Oda Tomohiro Egusa Nobuhito Ohte Norifumi Hotta Nobuaki Tanaka Mark B. Green Masakazu Suzuki 《水文研究》2021,35(5):e14177
Understanding changes in evapotranspiration during forest regrowth is essential to predict changes of stream runoff and recovery after forest cutting. Canopy interception (Ic) is an important component of evapotranspiration, however Ic changes and the impact on stream runoff during regrowth after cutting remains unclear due to limited observations. The objective of this study was to examine the effects of Ic changes on long-term stream runoff in a regrowth Japanese cedar and Japanese cypress forest following clear-cutting. This study was conducted in two 1-ha paired headwater catchments at Fukuroyamasawa Experimental Watershed in Japan. The catchments were 100% covered by Japanese coniferous plantation forest, one of which was 100% clear-cut in 1999 when the forest was 70 years old. In the treated catchment, annual runoff increased by 301 mm/year (14% of precipitation) the year following clear-cutting, and remained 185 mm/year (7.9% of precipitation) higher in the young regrowth forest for 12–14 years compared to the estimated runoff assuming no clear-cutting. The Ic change was −358 mm/year (17% of precipitation) after cutting and was −168 mm/year (6.7% of precipitation) in the 12–14 years old regrowth forest compared to the observed Ic during the pre-cutting period. Stream runoff increased in all seasons, and the Ic change was the main fraction of evapotranspiration change in all seasons throughout the observation period. These results suggest that the change in Ic accounted for most of the runoff response following forest cutting and the subsequent runoff recovery in this coniferous forest. 相似文献
2.
A short summary of recent progress in measuring and understanding turbulence during magnetic reconnection in laboratory plasmas
is given. Magnetic reconnection is considered as a primary process to dissipate magnetic energy in laboratory and astrophysical
plasmas. A central question concerns why the observed reconnection rates are much faster than predictions made by classical
theories, such as the Sweet–Parker model based on MHD with classical Spitzer resistivity. Often, the local resistivity is
conjectured to be enhanced by turbulence to accelerate reconnection rates either in the context of the Sweet–Parker model
or by facilitating setup of the Pestchek model. Measurements at a dedicated laboratory experiment, called MRX or Magnetic
Reconnection Experiment, have indicated existence of strong electromagnetic turbulence in current sheets undergoing fast reconnection.
The origin of the turbulence has been identified as right-hand polarized whistler waves, propagating obliquely to the reconnecting
field, with a phase velocity comparable to the relative drift velocity. These waves are consistent with an obliquely propagating
electromagnetic lower-hybrid drift instability driven by drift speeds large compared to the Alfven speed in high-beta plasmas.
Interestingly, this instability may explain electromagnetic turbulence also observed in collisionless shocks, which are common
in energetic astrophysical phenomena. 相似文献
3.
滇西动态重力网的分形特征及空间分辨力 总被引:1,自引:1,他引:0
贾民育 《大地测量与地球动力学》1996,(4)
介绍了用分形学描述地球物理观测网非均匀分布和联合应用分形特征与Shannon定理确定最佳网格距的方法。研究了滇西动态重力网的分形特征,它的分形维Df=1.27,最佳网格距r0=28km。讨论了1986年至1994年间网区发生的8次Ms>5.0级地震前重力场变化的可信性,指出这些变化的波长均大于100km,至少2倍于网的最小空间分辨力,因而是可信的 相似文献
4.
Tidal effects on temperature front in the Yellow Sea 总被引:5,自引:0,他引:5
Temperature front (TF) is one of the important features in the Yellow Sea, which forms in spring, thrives in summer, and fades
in autumn as thermocline declines. TF intensity ⋎S
T
⋎ is defined to describe the distribution of TF. Based on the MASNUM wave-tide-circulation coupled model, temperature distribution
in the Yellow Sea was simulated with and without tidal effects. Along 36°N, distribution of TF from the simulated results
are compared with the observations, and a quantitative analysis is introduced to evaluate the tidal effects on the forming
and maintaining processes of the TF. Tidal mixing and the circulation structure adapting to it are the main causes of the
TF.
Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No.
49736190). 相似文献
5.
介绍了基于STC89C516RD+单片机的实验开发平台的硬件电路设计、ISP编程、软件开发实例及系统的抗干扰措施.为帮助学生学习单片机技术,同时也为有经验者开发和调试产品打下基础. 相似文献
6.
Wang Yanhui 《水文研究》1992,6(2):241-251
Black locust (Robina pseudoacacia) has become one of the most important shelter species in the loess area of northwest China. This paper summarizes recent research concerning its hydrological influence, including canopy interception, litter absorption capacity, its effect on rainfall kinetic energy, infiltration rates, surface runoff, soil moisture, and evapotranspiration, and its role in soil conservation. Several predictive models are listed. on the basis of existing results, optimum characteristics for an effective plantation are defined, and problems requiring further research are identified. 相似文献
7.
Integrated approach for identification of potential groundwater zones in Seethanagaram Mandal of Vizianagaram District,Andhra Pradesh,India 总被引:1,自引:0,他引:1
Identifying a good site for groundwater exploration in hard rock terrain is a challenging task. In hard rocks, groundwater
occurs in secondary porosity developed due to weathering, fracturing, faulting, etc., which is highly variable within short
distance and contributing to near-surface inhomogeneity. In such situations topographic, hydrogeological and geomorphological
features provide useful clues for the selection of suitable sites.
Initially, based on satellite imagery, topographical, geomorphological and hydrogeological features, an area of about 149
km2 was demarcated as a promising zone for groundwater exploration in the hard rock tract of Seethanagaram Mandal, Vizianagaram
District, Andhra Pradesh, India. A total of 50 Vertical Electrical Soundings (VES) were carried out using Wenner electrode
configuration. An interactive interpretation of the VES data sharpened the information inferred from geomorphological and
hydrogeological reconnaissance. Ten sites were recommended for drilling. Drilling with Down-The-Hole Hammer (DTH) was carried
out at the recommended sites down to 50 to 70 m depths. The interpreted VES results matched well with the drilled bore well
lithologs. The yields of bore wells vary from 900 to 9000 liters per hour (lph). 相似文献
8.
煤岩对压裂裂缝长期导流能力影响的实验研究 总被引:7,自引:0,他引:7
煤层中一般都伴有煤层气,通过压裂可以将煤层气释放出来,一方面能够获得清洁能源,另一方面可以提高煤田的安全开采。煤岩层自身特点决定了其在压裂中应用的实验评价方法及结论应具有特殊性,本文主要针对煤层气井的煤岩层压裂裂缝长期导流能力进行实验评价研究。实验表明,与砂岩地层不同,煤岩的硬度较小,压裂中支撑剂嵌入情况较严重;煤岩易破碎,碎屑颗粒充填到支撑剂中;同时支撑剂存在破碎及吸附伤害等,多种作用导致支撑裂缝的导流能力降低。实验中,以煤岩层闭合压力为一个重要的参数,实验对比分析了在不同闭合压力下,铺砂浓度、支撑剂粒径、支撑剂种类及组合的选择、支撑剂颗粒的破碎与嵌入、压裂液残渣等因素对煤岩层导流能力的影响。本文的实验结论为,嵌入对煤岩层支撑裂缝的导流能力伤害很大,加大铺砂浓度、采用低破碎率支撑剂、降低压裂液伤害能在一定程度上提高煤层裂缝的导流能力,但影响程度随闭合压力的增加而逐渐降低。本文所得出的结论对今后煤层气的开发及设计施工具有一定的指导意义。 相似文献
9.
Application of MODFLOW and geographic information system to groundwater flow simulation in North China Plain, China 总被引:2,自引:0,他引:2
Shiqin Wang Jingli Shao Xianfang Song Yongbo Zhang Zhibin Huo Xiaoyuan Zhou 《Environmental Geology》2008,55(7):1449-1462
MODFLOW is a groundwater modeling program. It can be compiled and remedied according to the practical applications. Because
of its structure and fixed data format, MODFLOW can be integrated with Geographic Information Systems (GIS) technology for
water resource management. The North China Plain (NCP), which is the politic, economic and cultural center of China, is facing
with water resources shortage and water pollution. Groundwater is the main water resource for industrial, agricultural and
domestic usage. It is necessary to evaluate the groundwater resources of the NCP as an entire aquifer system. With the development
of computer and internet information technology it is also necessary to integrate the groundwater model with the GIS technology.
Because the geological and hydrogeological data in the NCP was mainly in MAPGIS format, the powerful function of GIS of disposing
of and analyzing spatial data and computer languages such as Visual C and Visual Basic were used to define the relationship
between the original data and model data. After analyzing the geological and hydrogeological conditions of the NCP, the groundwater
flow numerical simulation modeling was constructed with MODFLOW. On the basis of GIS, a dynamic evaluation system for groundwater
resources under the internet circumstance was completed. During the process of constructing the groundwater model, a water
budget was analyzed, which showed a negative budget in the NCP. The simulation period was from 1 January 2002 to 31 December
2003. During this period, the total recharge of the groundwater system was 49,374 × 106 m3 and the total discharge was 56,530 × 106 m3 the budget deficit was −7,156 × 106 m3. In this integrated system, the original data including graphs and attribution data could be stored in the database. When
the process of evaluating and predicting groundwater flow was started, these data were transformed into files that the core
program of MODFLOW could read. The calculated water level and drawdown could be displayed and reviewed online. 相似文献
10.
Ibticem Chamtouri Habib Abida Hafedh Khanfir Salem Bouri 《Environmental Geology》2008,55(5):1123-1133
Groundwater in Sfax City (Tunisia) has been known since the beginning of the century for its deterioration in quality, as
a result of wastewater recharge into the aquifer. An average value of 12 × 106 m3 of untreated wastewater reaches the groundwater aquifer each year. This would result not only in a chemical and biological
contamination of the groundwater, but also in an increase of the aquifer piezometric level. Quantitative impacts were evaluated
by examining the groundwater piezometric level at 57 surface wells and piezometers. The survey showed that, during the last
two decades, the groundwater level was ever increasing in the urban area with values reaching 7 m in part; and decreasing
in Sidi Abid (agricultural area) with values exceeding −3 m. Groundwater samples for chemical and microbial analysis were
collected from 41 wells spread throughout the study area. Results showed significantly elevated levels of sodium, chlorides,
nitrates and coliform bacteria all over the urban area. High levels (NO3: 56–254 mg/l; Na >1,500 mg/l; Coliforms >30/100 ml) can be related to more densely populated areas with a higher density
of pit latrine and recharge wells. Alternatively results showed a very variable chemical composition of groundwater, e.g.
electrical conductivity ranges from 4,040 to19,620 μs/cm and the dry residual varies between 1.4 and 14 g/l with concentrations
increasing downstream. Furthermore a softening of groundwater in Set Ezzit (highly populated sector) was observed. 相似文献