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Two lysimeters with the same dimensions were provided, and filled with the same loam clay. On the soil surface of one lysimeter, grass was planted to compare the hydrologic response of the grassed lysimeter with that of the other bare soil lysimeter.
About half of the runoff from the bare soil lysimeter occurred as overland flow, the rest being groundwater flow. Overland flow scarcely occurred from the grassed lysimeter. Grass roots that developed deep into the soil layer play an important role in increasing the infiltration rate as well as in drying the soil uniformly throughout the soil layer by evapotranspiration, preparing for high infiltration and large rainwater storage for the subsequent rainfall event. Accordingly, the total loss by evapotranspiration from the grassed soil amounts to almost twice that from the bare soil.
For an evaporation- and evapotranspiration-prohibited experiment, the recession characteristics from a saturation state showed similar features for the bare and grassed soils, indicating the same microstructure of high moisture reservability for both soils.
The well-developed grass root system reformed the soil structure considerably to produce the seemingly contradicting characteristics of high moisture conductivity and high moisture reservability; i.e. a high infiltration rate and prolonged groundwater discharge.
Finally, the importance of the initial soil moisture in the rainfall-runoff process, rainfall loss and runoff ratio is stressed. 相似文献
3.
Measurements of size-separated aerosol number concentrations at Midagahara (altitude, 1,930 m), on the western slope of Mt. Tateyama near the coast of the Japan Sea, were performed each autumn from 2006 to 2011. High number concentrations of particles larger than 2 μm were frequently seen in 2006 and 2009 when the influence of Asian dust might have been significant. The pH and the ratio of Ca2+ to total ions were high in the rainwater bulk sampled when high number concentrations of coarse particles were observed. The mean pH of rainwater during the autumn in 2006 was significantly higher than that in 2007 and 2008. Acidic species might have been neutralized by the Asian dust particles. Dust particles may highly affect the natural environment, such as forest ecosystems, at high elevations during seasons without snow cover. 相似文献
4.
Oleg V. Melnichenko Nikolai A. Maximenko Niklas Schneider Hideharu Sasaki 《Ocean Dynamics》2010,60(3):653-666
Recently, prominent jet-like features of the ocean circulation, called striations, with a meridional scale of O(300–500 ;km)
and extending for thousands of kilometers in length, have been detected in satellite and in situ observations and in high-resolution numerical models. In this paper, we study quasi-stationary striations, which are best
seen in the multi-year time-averaged velocity fields. Using 1993–2002 mean dynamic ocean topography, satellite altimeter observations,
and output of the Ocean General Circulation Model for the Earth Simulator, the dynamics of the quasi-stationary striations
in the eastern parts of the subtropical North and South Pacific are examined by assessing individual terms in the time-averaged
equations of relative and potential vorticity. While non-linear effects are found to be essential in the dynamics of the striations,
rejecting some linear hypotheses forwarded in the earlier studies, the relevance of the Rhines mechanism is not confirmed.
Eddy flux does not act as a relative vorticity source for the striations. Using the potential vorticity (PV) diagnostics,
we show that the time-mean PV is not conserved along the time-mean streamlines, and on the scale of the striations these changes
in PV are largely induced by the eddy flux of layer thickness. The fact that eddy fluxes contribute to the striations’ time-mean
PV budget suggests that the striations are not a kinematical artifact of time-averaging of westward-propagating eddies. 相似文献
5.
Interannual-to-decadal variations in the subtropical countercurrent (STCC) and low potential vorticity (PV) water and their
relations in the North Pacific Ocean are investigated on the basis of a 60-year-long hindcast integration of an eddy-resolving
ocean general circulation model. Although vertically coherent variations are dominant for STCC interannual variability, a
correlation analysis shows that an intensified STCC vertical shear accompanies lower PV than usual to the north on 25.5- to
26.1-σθ isopycnal surfaces, and intensified meridional density gradient in subsurface layers, consistent with Kubokawa’s theory (J
Phys Oceanogr 29:1314–1333, 1999). The low-PV signals appear at least 2 years before peaks of STCC, propagating southwestward from the subduction region. 相似文献
6.
Seasonal variations of the Hawaiian Lee Countercurrent induced by the meridional migration of the trade winds 总被引：1，自引：0，他引：1
Hideharu Sasaki Shang-Ping Xie Bunmei Taguchi Masami Nonaka Yukio Masumoto 《Ocean Dynamics》2010,60(3):705-715
Seasonal variations of the Hawaiian Lee Countercurrent (HLCC) are investigated using satellite observations of sea surface
height and wind stress as well as eddy-resolving ocean model simulations. The HLCC is strong from summer to winter and weak
in spring between the dateline and the Hawaiian Islands. In response to the seasonal migration of the northeast trade winds
in the meridional direction, the wind curl dipole lee of Hawaii varies in strength, exciting westward-propagating Rossby waves.
The analyses of both observations and simulations show that the propagation of Rossby waves south of the HLCC, driven by the
southern pole of the wind curl dipole in the lee of the islands, contributes the most to the seasonal variations of the HLCC.
Unlike the wind-driven seasonal variations, our analysis suggests that other mechanisms such as mode water intrusion or air–sea
interaction may cause the interannual variations of the HLCC. 相似文献
7.
Hideharu Kurita Makoto Yokohari Jay Bolthouse 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):147-159
Geografisk Tidsskrift—Danish Journal of Geography 109(2):147–159, 2009 The increasingly global reach of industrial agricultural production has progressively distanced consumers and producers. Not surprisingly, opposition to the global food system commonly seeks to re-localize agriculture by cutting the distance between agricultural production and consumption. Analysis of potential foodsheds can provide an important basis upon which to recover local systems of production and consumption. Here, we examine the potential for municipal and micro-level foodsheds in the greater Tokyo mega-region. Similar to other large cities in Asia, the urban fringe of Tokyo has extensive areas of mixed urban and agricultural land-uses which are often seen as problematic, but which may have many merits from the standpoint of sustainable foodsheds. Indeed, our results indicate that many areas on the urban fringe of the Tokyo mega-region bear potential to meet demand for both rice and vegetables within their borders. Moreover, many people could meet their food needs within a short distance of their residence. These results demonstrate the need to examine the potential for micro-level foodsheds on the urban fringe. 相似文献
8.
Iskhaq Iskandar Hideharu Sasaki Yoshikazu Sasai Yukio Masumoto Keisuke Mizuno 《Ocean Dynamics》2010,60(3):731-742
An eddy-resolving coupled physical–biological model is used to study the effect of cyclonic eddy in enhancing offshore chlorophyll-a (Chl-a) bloom in the southeastern tropical Indian Ocean during boreal summer–fall 2006. The results demonstrate that the offshore
Chl-a blooms are markedly coincident with the high eddy kinetic energy. Moreover, the vertical variations in Chl-a, nitrate, temperature, and mixed-layer depth (MLD) strongly imply that the cyclonic eddies induce surface Chl-a bloom through the injection of nutrient-rich water into the upper layer. Interestingly, we found that the surface bloom only
occurs when the deep Chl-a maximum is located within the MLD. On the other hand, the response of subsurface Chl-a to the eddy pumping is remarkable, although it is hardly observable at the surface. 相似文献
9.
Regionality and seasonality of submesoscale and mesoscale turbulence in the North Pacific Ocean 总被引：1，自引：0，他引：1
The kinetic energy (KE) seasonality has been revealed by satellite altimeters in many oceanic regions. Question about the mechanisms that trigger this seasonality is still challenging. We address this question through the comparison of two numerical simulations. The first one, with a 1/10° horizontal grid spacing, 54 vertical levels, represents dynamics of physical scales larger than 50 km. The second one, with a 1/30° grid spacing, 100 vertical levels, takes into account the dynamics of physical scales down to 16 km. Comparison clearly emphasizes in the whole North Pacific Ocean, not only a significant KE increase by a factor up to three, but also the emergence of seasonal variability when the scale range 16–50 km (called submesoscales in this study) is taken into account. But the mechanisms explaining these KE changes display strong regional contrasts. In high KE regions, such the Kuroshio Extension and the western and eastern subtropics, frontal mixed-layer instabilities appear to be the main mechanism for the emergence of submesoscales in winter. Subsequent inverse kinetic energy cascade leads to the KE seasonality of larger scales. In other regions, in particular in subarctic regions, results suggest that the KE seasonality is principally produced by larger-scale instabilities with typical scales of 100 km and not so much by smaller-scale mixed-layer instabilities. Using arguments from geostrophic turbulence, the submesoscale impact in these regions is assumed to strengthen mesoscale eddies that become more coherent and not quickly dissipated, leading to a KE increase. 相似文献
10.
Ocean Dynamics - In the power spectrum, the upper and deep parts of the Kuroshio Extension have distinctly different peaks. The former peaks around 200 days, while the latter is mainly at the... 相似文献