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排序方式: 共有3491条查询结果,搜索用时 15 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.
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
5.
Erosion of man-made, forestry drainage channels occurs when the plough cuts through the surface peat layer into the underlying erodible mineral soil. A procedure is developed, based on hydraulic considerations, which will allow the drainage engineer to design stable drainage networks in upland forestry plantations. An example design chart is given for an erodible sandy loam type soil. 相似文献
6.
The aim of this interdisciplinary study is to examine a component of the hydrological cycle in Galapagos by characterizing
soil properties. Nine soil profiles were sampled on two islands. Their physical and hydrodynamic properties were analyzed,
along with their mineralogical composition. Two groups of soils were identified, with major differences between them. The
first group consists of soils located in the highlands (>350 m a.s.l.), characterized by low hydraulic conductivity (<10−5 m s−1) and low porosity (<25%). These soils are thick (several meters) and homogeneous without coarse components. Their clay fraction
is considerable and dominated by gibbsite. The second group includes soils located in the low parts of the islands (<300 m
a.s.l.). These soils are characterized by high hydraulic conductivity (>10−3 m s−1) and high porosity (>35%). The structure of these soils is heterogeneous and includes coarse materials. The physical properties
of the soils are in good agreement with the variations of the rainfall according to the elevation, which appears as the main
factor controlling the soil development. The clayey alteration products constrain soils physical and hydrodynamic properties
by reducing the porosity and consequently the permeability and also by increasing water retention. 相似文献
7.
H2O-undersaturated melting experiments of synthesized basalt (SiO2 = 50.7 wt.%, MgO = 8.3 wt.%, Mg# = 60) were conducted at fO2 corresponding to NNO+1 and NNO−1 to clarify the effects of pressure (2–7 kbar) and H2O on fractional crystallization in island arcs. H2O content was ranged from nominally anhydrous to 4.4 wt.%. Differentiation trends, namely the liquid lines of descent, change
sensitively according to pressure-H2O relations. Tholeiitic differentiation trends are reproduced with H2O ≤ ∼2 wt.% in primary magma. With such quantities of H2O, fractional crystallization is controlled by olivine + plagioclase at 2 kbar. Increasing the pressure from 2 to ≥4 kbar
induces early crystallization of orthopyroxene instead of olivine and therefore SiO2 enrichment in the residual melts is suppressed. Increasing H2O (≥ ∼2 wt.% in primary magma) stabilizes clinopyroxene relative to orthopyroxene and/or magnetite. Although the phase relations
and proportions strongly depend on fO2 and H2O content, differentiation trends are always calc-alkaline. 相似文献
8.
Flood hazard delineation combining geomorphological and hydrological methods: an example in the Northern Iberian Peninsula 总被引:2,自引:1,他引:1
Flood mapping requires the combination and integration of geomorphological and hydrological-hydraulic methods; however, despite
this, there is very little scientific literature that compares and validates both methods. Two types of analysis are addressed
in the present article. On the one hand, maps of flood plains have been elaborated using geomorphological evidence and historical
flood data in the mountainous area of northwestern Spain, covering an area of more then 232 km2 of floodplains. On the other hand, a hydrometeorological model has been developed (Clark semidistributed unit hydrograph)
in the Sarria River basin (155 km2, NW Spain). This basin is not gauged, hence the model was subjected to a goodness-of-fit test of its parameter (curve number)
by means of Monte Carlo simulation. The peak flows obtained by means of the hydrological model were used for hydraulic modeling
(one-phase, one-dimensional and steady flow) in a 4 km2 urban stretch of the river bed. The delineation of surface areas affected by floods since 1918, as well as those analyzed
subsequent to the geomorphological study, reveals a high degree of reliability in the delineation of the flooded areas with
frequent recurrence intervals (<50 years). If we compare these flooded surface areas with the estimate obtained by the hydrological-hydraulic
method we can see that the latter method overestimates the extent of the surface water by 144% for very frequent recurrence
intervals (>10 years) and underestimates it as the recurrence interval increases, by up to 80% less floodplain for exceptional
events (>500 years). Finally, a management map is put forth combining the most reliable results available by integrating both
methods.
Originally presented at the Sixth International Conference on Geomorphology. 相似文献
9.
10.
In this study, we investigate two internal wave generation methods in numerical modeling of time-dependent equations for water wave propagation, i.e., delta source function method and source term addition method, the latter of which has been called the line source method in literatures. We derive delta source functions for the Boussinesq-type equations and extended mild-slope equations. By applying the fractional step splitting method, we show that the delta source function method is equivalent to the source term addition method employing the energy velocity. This suggests that the energy velocity should be used rather than the phase velocity for the transport of incident wave energy in the source term addition method. Finally, the performance of the delta source function method is verified by accurately generating nonlinear cnoidal waves as well as linear waves for horizontally one-dimensional cases. 相似文献