Effectivity of dissolved SF6 tracer for clarification of rainfall–runoff processes in a forested headwater catchment     

Koichi Sakakibara  Maki Tsujimura  Sho Iwagami  Yutaro Sato  Kosuke Nagano  Yuichi Onda 《水文研究》2019,33(6):892-904

Understanding rainfall‐runoff processes is crucial for prevention and prediction of water‐related natural disasters. Sulfur hexafluoride (SF₆) is a potential tracer, but few researches have applied it for rainfall‐runoff process studies. We observed multiple tracers including SF₆ in spring water at 1‐ to 2‐hr intervals during rainstorm events to investigate the effectivity of SF₆ tracer in rainfall–runoff studies through the clarification of rainfall–runoff process. The target spring is a perennial spring in a forested headwater catchment with an area of 0.045 km² in Fukushima, Japan. The relationship between the SF₆ concentration in spring water and the spring discharge volume was negative trend; the SF₆ concentration in spring water becomes low as the spring discharge volume increases especially during rainstorms. The hydrograph separation using SF₆ and chloride ion tracers was applied for determining the contribution of principal sources on rainfall–runoff water. It suggested more than 60% contribution of bedrock groundwater at the rainfall peak and high percentage contribution continued even in the hydrograph recession phase. Based on observed low SF₆ concentration in groundwater after heavy rainfall, the replacement of groundwater near the spring with bedrock groundwater is indicated as a mechanism for water discharge with low SF₆ concentration during rainfall events. Consequently, rainstorm events play an important role as triggers in discharging water stored in the deeper subsurface area. In addition, SF₆ tracer is concluded as one of the strongest tracers for examining rainfall–runoff process studies. And, therefore, this study provided new insights into the dynamics of groundwater and its responses to rainfall in terms of SF₆ concentration variance in water in headwater regions.  相似文献   

Geometric Dependence of the Scalar Transfer Efficiency over Rough Surfaces     

Naoki Ikegaya  Aya Hagishima  Jun Tanimoto  Yudai Tanaka  Ken-ichi Narita  Sheikh Ahmad Zaki 《Boundary-Layer Meteorology》2012,143(2):357-377

We performed a series of wind-tunnel experiments under neutral conditions in order to create a comprehensive database of scalar transfer coefficients for street surfaces using regular block arrays representing an urban environment. The objective is to clarify the geometric dependence of scalar transfer phenomena on rough surfaces. In addition, the datasets we have obtained are necessary to improve the modelling of scalar transfer used for computational simulations of urban environments; further, we can validate the results obtained by numerical simulations. We estimated the scalar transfer coefficients using the salinity method. The various configurations of the block arrays were designed to be similar to those used in a previous experiment to determine the total drag force acting on arrays. Our results are summarized as follows: first, the results for cubical arrays showed that the transfer coefficients for staggered and square layouts varied with the roughness packing density. The results for the staggered layout showed the possibility that the mixing effect of air can be enhanced for the mid-range values of the packing density. Secondly, the transfer coefficients for arrays with blocks of non-uniform heights were smaller than those for arrays with blocks of uniform height under conditions of low packing density; however, as the packing density increased, the opposite tendency was observed. Thirdly, the randomness of rotation angles of the blocks in the array led to increasing values of the transfer coefficients under sparse packing density conditions when compared with those for cubical arrays.  相似文献   

Particulate PAHs levels at Mt. Halla site in Jeju Island, Korea: Regional background levels in northeast Asia     

Ji Yi Lee  Yong Pyo Kim  Naoki Kaneyasu  Hidetoshi Kumata  Chang-Hee Kang   《Atmospheric Research》2008,90(1):91-98

The levels of PM.25 PAHs at Mt. Halla site, Jeju Island, a background site in Korea were observed between March 1999 and March 2002. A seasonal variation was observed for the particulate PAHs concentrations with high levels during cold season similar to Gosan, a nearby coastal background site, due to the seasonal variations of fossil fuel usage in Asia. The total average concentration of ambient particulate PAHs was 404 ± 579 pg m^− 3, about one order lower than the ambient level at Gosan. However, the ratios of the anthropogenic inorganic ion concentrations between Mt. Halla and Gosan were smaller, 1.5 for non sea-salt (nss) sulfate and 2.7 for nitrate. Two possible explanations for these characteristics are (1) two sites measured different air parcels and/or (2) the effect of local emissions were different at two sites. Based on the Bep/BaP ratio result, upper air wind direction data, backward trajectory analysis, and LIDAR measurement data at Gosan, it was found that the degree of the effects of local emissions to the sampling sites be the major reason for the different PAHs levels at two sites though, in some cases, the air parcels arriving at Mt. Halla were different from those arriving at Gosan. For secondary aerosol such as nss sulfate, the lower concentration difference indicates both site are affected by regional transport. It points that the measurement result for directly emitted species such as PAHs at Gosan might be significantly influenced by local emissions.  相似文献   

Meteorological influences of SST anomaly over the East Asian marginal sea on subpolar and polar regions: A case of an extratropical cyclone on 5–8 November 2006     

Ami Ueda  Masaru Yamamoto  Naoki Hirose 《Polar Science》2011,5(1):1-10

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Physiological acclimation by phytoplankton explains observed changes in Si and N uptake rates during the SERIES iron-enrichment experiment     

S. Lan Smith  Naoki Yoshie  Yasuhiro Yamanaka 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(3):394-408

During the SERIES iron-enrichment experiment in the eastern subarctic Pacific, after addition of iron and its subsequent depletion, the Si:N drawdown ratio increased at approximately the time that diatoms became iron limited. Laboratory studies have reported that this results from a decrease in the rate of N uptake together with a more moderate decrease in the rate of Si uptake for iron-limited cultures compared to iron-replete cultures. However, for SERIES Boyd et al. (Limnol. Oceanogr. 50 (2005)) reported an unexplained increase in the rate of Si uptake at the onset of iron limitation and suggested that studies of nutrient uptake kinetics should be undertaken in search of an explanation. We compare the classic Michealis–Menten (MM) kinetics to the recently developed optimal uptake (OU) kinetics (the SPONGE: Smith and Yamanaka. Limnol. Oceanogr. 52 (2007)) within a variable-composition model, which employs cell quotas for each relevant nutrient, applied to the multi-element (C, N, Si, Fe) dynamics during SERIES. Using the Monte Carlo Markov Chain, we fit two versions of the model (differing only in the equations for nutrient uptake) to the available data for nutrient concentrations, chlorophyll, biogenic silica and particulate organic carbon and specific growth rates.With either uptake kinetics, the model reproduces observed concentrations well for nutrients and somewhat less well for chlorophyll. The different uptake kinetics yield greater differences in modeled elemental composition of phytoplankton and biomass of phytoplankton and zooplankton, which are not directly constrained by data. MM kinetics cannot reproduce the observed increase in Si uptake rate as a function of the decreasing trend in concentration of silicic acid, and it predicts Si limitation throughout nearly all of the experiment after iron-fertilization. In contrast, OU kinetics reproduces the increase in Si uptake rate and matches the observation-based estimate for the timing of the return to iron limitation. The key assumption of the SPONGE, that uptake rates of all nutrients depend on physiological acclimation by phytoplankton as a function of the ambient concentration of the growth-limiting nutrient, was originally formulated for modeling chemostat experiments. We show that it also agrees with the observations from this field experiment and provides an explanation for the increases in Si uptake rate and Si:N drawdown ratio.  相似文献   

Long-term operation of the Laser Interferometer Space Antenna and Galactic close white dwarf binaries     

Naoki Seto 《Monthly notices of the Royal Astronomical Society》2002,333(2):469-474

The binary confusion noise spectrum in the Laser Interferometer Space Antenna ( LISA ) band depends strongly on the observational period and abundance of Galactic close white dwarf binaries (CWDBs). We have investigated how the number of the resolved Galactic CWDBs varies with the operation period of LISA , and found that the resolved number would typically grow by a factor of 5 when the operation period increases from 1 to 10 yr. We have also made a similar estimation for the number of CWDBs, the chirp signal of which can be measured using matched filtering analysis.  相似文献   

Hydrological control of dissolved organic carbon dynamics in a forested headwater catchment,Kiryu Experimental Watershed,Japan     

Masatoshi Kawasaki  Nobuhito Ohte  Naoki Kabeya  Masanori Katsuyama 《水文研究》2008,22(3):429-442

To evaluate the influence of hydrological processes on dissolved organic carbon (DOC) dynamics in a forested headwater catchment, DOC concentration was observed along the flow path from rainfall to stream water via throughfall, soil water, groundwater, and spring water for 4 years, and DOC flux through the catchment was calculated. The spatial and temporal variations in DOC concentration and flux were compared with physical hydrological observations and the mean residence time of water. In the upslope soil layer, DOC concentrations were not significantly correlated with water fluxes, suggesting that DOC concentrations were not strictly controlled by water fluxes. In the upslope perennial groundwater, DOC concentration was affected by the change in the amount of microbial degradation of DOC produced by changes in the mean residence time of water. In stream water, the temporal variation in DOC concentration was usually affected by changes in DOC concentration of the inflow component via vertical infiltration from above the perennial groundwater. During dry periods, however, the component from inflow via vertical infiltration was negligible and DOC in the upslope perennial groundwater became the major component of stream water DOC. The temporal variation in stream water DOC concentration during baseflow was affected by rainfall patterns over several preceding months. Therefore, records of rainfall over several preceding months are one of the most important factors for predicting changes in DOC concentration on a catchment scale. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

The effects of the tidal force on shear instabilities in the dust layer of the solar nebula     

Naoki Ishitsu  Minoru Sekiya 《Icarus》2003,165(1):181-194

The linear analysis of the instability due to vertical shear in the dust layer of the solar nebula is performed. The following assumptions are adopted throughout this paper: (1) The self-gravity of the dust layer is neglected. (2) One fluid model is adopted, where the dust aggregates have the same velocity with the gas due to strong coupling by the drag force. (3) The gas is incompressible. The calculations with both the Coriolis and the tidal forces show that the tidal force has a stabilizing effect. The tidal force causes the radial shear in the disk. This radial shear changes the wave number of the mode which is at first unstable, and the mode is eventually stabilized. Thus the behavior of the mode is divided into two stages: (1) the first growth of the unstable mode which is similar to the results without the tidal force, and (2) the subsequent stabilization due to an increase of the wave number by the radial shear. If the midplane dust/gas density ratio is smaller than 2, the stabilization occurs before the unstable mode grows largely. On the other hand, the mode grows faster by one hundred orders of magnitude, if this ratio is larger than 20. Because the critical density of the gravitational instability is a few hundreds times as large as the gas density, the hydrodynamic instability investigated in this paper grows largely before the onset of the gravitational instability. It is expected that the hydrodynamic instability develops turbulence in the dust layer and the dust aggregates are stirred up to prevent from settling further. The formation of planetesimals through the gravitational instabilities is difficult to occur as long as the dust/gas surface density ratio is equal to that for the solar abundance. On the other hand, the shear instability is suppressed and the planetesimal formation through the gravitational instability may occur, if dust/gas surface density ratio is hundreds times as large as that for the solar abundance.  相似文献   

Properties of cluster satellites in hydrodynamical simulations     

Giuseppe Tormen  Lauro Moscardini  Naoki Yoshida † 《Monthly notices of the Royal Astronomical Society》2004,350(4):1397-1408

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Reproduction of the giant jellyfish, <Emphasis Type="Italic">Nemopilema nomurai</Emphasis> (Scyphozoa: Rhizostomeae), in 2006–2008 as peripherally-transported populations     

Naoki Iguchi  Hye Eun Lee  Won Duk Yoon  Suam Kim 《Ocean Science Journal》2010,45(2):129-138

This study investigated the sexual maturation process, release of spermatozoa or eggs and oocyte diameter of the rhizostomid medusae Nemopilema nomurai using samples collected from August 2006 to June 2008 from the waters around Korea and Japan, including peripheral areas outside the species’ usual habitat. Immature medusae were observed from June to October only in the western sector of the study area. The onset of spermatozoa and egg release occurred in September and October, respectively, and peaked in December and January. Medusae migrated eastward from source areas with the Tsushima Warm Current, where they formed gametes and spawned. Peak position and maximum oocyte diameter increased as the gonads developed according to the size-frequency distribution of oocytes. No fertilized eggs or embryos were found in the gonads. The correlation was analyzed with bell diameter, maximum oocyte diameter, sampling date, surface water temperature and gonad color to estimate which environmental factors and maturation indices were related to the maturation stage of females. Maturation stage correlated well with maximum oocyte diameter, which correlated negatively with surface water temperature. There was no significant correlation between bell diameter and maturation stage. Therefore, bell diameter was inappropriate for determining maturation index. Sex could not be distinguished clearly by gonad color. However, light pink gonads were more prevalent in males and various deep colors such as orange and brown were more frequent in female medusae.  相似文献