Cross-Validation of Open-Path and Closed-Path Eddy-Covariance Techniques for Observing Methane Fluxes     

Hiroki Iwata  Yoshiko Kosugi  Keisuke Ono  Masayoshi Mano  Ayaka Sakabe  Akira Miyata  Kenshi Takahashi 《Boundary-Layer Meteorology》2014,151(1):95-118

Methane ( ${\mathrm {CH}}_{4}$ ) fluxes observed with the eddy-covariance technique using an open-path ${\mathrm {CH}}_{4}$ analyzer and a closed-path ${\mathrm {CH}}_{4}$ analyzer in a rice paddy field were evaluated with an emphasis on the flux correction methodology. A comparison of the fluxes obtained by the analyzers revealed that both the open-path and closed-path techniques were reliable, provided that appropriate corrections were applied. For the open-path approach, the influence of fluctuations in air density and the line shape variation in laser absorption spectroscopy (hereafter, spectroscopic effect) was significant, and the relative importance of these corrections would increase when observing small ${\mathrm {CH}}_{4}$ fluxes. A new procedure proposed by Li-Cor Inc. enabled us to accurately adjust for these effects. The high-frequency loss of the open-path ${\mathrm {CH}}_{4}$ analyzer was relatively large (11 % of the uncorrected covariance) at an observation height of 2.5 m above the canopy owing to its longer physical path length, and this correction should be carefully applied before correcting for the influence of fluctuations in air density and the spectroscopic effect. Uncorrected ${\mathrm {CH}}_{4}$ fluxes observed with the closed-path analyzer were substantially underestimated (37 %) due to high-frequency loss because an undersized pump was used in the observation. Both the bandpass and transfer function approaches successfully corrected this flux loss. Careful determination of the bandpass frequency range or the transfer function and the cospectral model is required for the accurate calculation of ${\mathrm {CH}}_{4}$ fluxes with the closed-path technique.  相似文献   

Observation of Interactions and Eruptions of Two Filaments     

Jiangtao Su  Yu Liu  Hiroki Kurokawa  Xinjie Mao  Shangbin Yang  Hongqi Zhang  Haimin Wang 《Solar physics》2007,242(1-2):53-63

We present new observations of the interactions of two close, but distinct, Hα filaments and their successive eruptions on 5 November 1998. The magnetic fields of the filaments are both of the sinistral type. The interactions between the two filaments were initiated mainly by an active filament of one of them. Before the filament eruptions, two dark plasma ejections and chromospheric brightenings were observed. They indicate that possible magnetic reconnection had occurred between the two filaments. During the first filament eruption, salient dark mass motions transferring from the left erupting filament into the right one were observed. The right filament erupted 40 minutes later. This second filament eruption may have been the result of a loss of stability owing to the sudden mass injection from the left filament. Based on the Hα observations, we have created a sketch for understanding the interactions between two filaments and accompanying activities. The traditional theory of filament merger requires that the filaments share the same filament channel and that the reconnection occurs between the two heads, as simulated by DeVore, Antiochos, and Aulanier (Astrophys. J. 629, 1122, 2005; 646, 1349, 2006). Our interpretation is that the external bodily magnetic reconnection between flux ropes of the same chirality is another possible way for two filament bodies to coalesce. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.  相似文献   

The height of Hα flare emitting region     

Hiroki Kurokawa 《Solar physics》1983,86(1-2):195-196

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Surface water chemistry and nitrate pollution in Shimabara,Nagasaki, Japan     

Hiroki Amano  Kei Nakagawa  Ronny Berndtsson 《Environmental Earth Sciences》2018,77(9):354

Groundwater is a finite resource that is threatened by pollution all over the world. Shimabara City, Nagasaki, Japan, uses groundwater for its main water supply. During recent years, the city has experienced severe nitrate pollution in its groundwater. For better understanding of origin and impact of the pollution, chemical effects and surface–groundwater interactions need to be examined. For this purpose, we developed a methodology that builds on joint geochemical analyses and advanced statistical treatment. Water samples were collected at 42 sampling points in Shimabara including a part of Unzen City. Spatial distribution of water chemistry constituents was assessed by describing Stiff and Piper diagrams using major ions concentrations. The nitrate (NO₃?+?NO₂–N) concentration in 45% of water samples exceeded permissible Japanese drinking level of 10 mg L^??1. Most of the samples showed Ca–HCO₃ or Ca–(NO₃?+?SO₄) water types. Some samples were classified into characteristic water types such as Na–Cl, (Na?+?K)–HCO₃, (Na?+?K)–(SO₄?+?NO₃), and Ca–Cl. Thus, results indicated salt water intrusion from the sea and anthropogenic pollution. At the upstream of Nishi River, although water chemistry was characterized as Ca–HCO₃, ion concentrations were higher than those of other rivers. This is probably an effect of disinfection in livestock farming using slaked lime. Positive correlation between NO₃^? and SO₄^2?, Mg²⁺, Ca²⁺, Na⁺, K⁺, and Cl^? (r?=?0.32–0.64) is evidence that nitrate pollution sources are chemical fertilizers and livestock waste. Principal component analysis showed that chemistry of water samples can be explained by three main components (PCs). PC1 depicts general ion concentration. PC2 and PC3 share influence from chemical fertilizer and livestock waste. Cluster analyses grouped water samples into four main clusters. One of these is the general river chemistry mainly affected by PC1. The others reflect anthropogenic activities and are identified by the combination of the three PCs.  相似文献   

Sea‐cliff retreat and shore platform widening: steady‐state equilibrium?     

Mark E. Dickson  Hiroki Ogawa  Paul S. Kench  Andrew Hutchinson 《地球表面变化过程与地形》2013,38(9):1046-1048

We challenge the notion of steady‐state equilibrium in the context of progressive cliff retreat on micro‐tidal coasts. Ocean waves break at or close to the abrupt seaward edge of near‐horizontal shore platforms and then rapidly lose height due to turbulence and friction. Conceptual models assume that wave height decays exponentially with distance from the platform edge, and that the platform edge does not erode under stable sea‐level. These assumptions combine to a steady‐state view of Holocene cliff retreat. We argue that this model is not generally applicable. Recent data show that: (1) exponential decay in wave height is not the most appropriate conceptual model of wave decay; (2) by solely considering wave energy at gravity wave frequencies the steady‐state model neglects a possible formative role for infragravity waves. Here we draw attention to possible mechanisms through which infragravity waves may drive cliff retreat over much greater distances (and longer timescales) than imaginable under the established conceptual model. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Variations in fraction of absorbed photosynthetically active radiation and comparisons with MODIS data in burned black spruce forests of interior Alaska     

Hiroki Iwata  Masahito Ueyama  Chie Iwama  Yoshinobu Harazono 《Polar Science》2013,7(2):113-124

Absorption of photosynthetically active radiation (PAR) by vegetation was observed in two burned black spruce forests, one and seven years after wildfire, in interior Alaska along with several vegetation properties. This study considered PAR absorption by mosses by examining the relationship between PAR transmittance and fractional coverage of green vegetation. Our results suggest that mosses absorbed a considerable fraction of incoming PAR in the burned forests, which cannot be neglected in evaluating the fraction of absorbed PAR (FPAR). The relationships between FPAR and vegetation indices revealed that enhanced vegetation index (EVI) may be suitable for expressing the spatial and temporal variation of FPAR, regardless of stand age after wildfire. The comparison between the observed in situ FPAR and FPAR derived from Moderate Resolution Imaging Spectroradiometer (MODIS FPAR) clearly showed that MODIS FPAR was highly overestimated. The most likely reason for the overestimation was identified as misclassification of land cover type. The current regional estimation of photosynthesis in boreal region based on the light-use efficiency approach and MODIS FPAR is probably overestimated, and an accurate distribution of FPAR is desired for clarifying the regional carbon exchange in boreal forests.  相似文献   

Structural changes of synthetic opal by heat treatment   总被引：1，自引：0，他引：1  

Akane Arasuna  Masayuki Okuno  Hiroki Okudera  Tomoyuki Mizukami  Shoji Arai  Shin’ichi Katayama  Mikio Koyano  Nobuaki Ito 《Physics and Chemistry of Minerals》2013,40(9):747-755

The structural changes of synthetic opal by heat treatment up to 1,400 °C were investigated using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared and Raman spectroscopies. The results indicate that the dehydration and condensation of silanol in opal are very important factors in the structural evolution of heat-treated synthetic opal. Synthetic opal releases water molecules and silanols by heat treatment up to 400 °C, where the dehydration of silanol may lead to the condensation of a new Si–O–Si network comprising a four-membered ring structure of SiO₄ tetrahedra, even at 400 °C. Above 600 °C, water molecules are lost and the opal surface and internal silanol molecules are completely dehydrated by heat effect, and the medium-temperature range structure of opal may begin to thermally reconstruct to six-membered rings of SiO₄ tetrahedra. Above 1,000 °C, the opal structure almost approaches that of silica glass with an average structure of six-membered rings. Above 1,200 °C, the opal changes to low-cristobalite; however, minor evidence of low-tridymite stacking was evident after heat treatment at 1,400 °C.  相似文献   

A new climatology of the Okhotsk Sea derived from the FERHRI database     

Hiroki Uehara  Andrey A. Kruts  Yuriy N. Volkov  Tomohiro Nakamura  Tsuneo Ono  Humio Mitsudera 《Journal of Oceanography》2012,68(6):869-886

This paper introduces a new hydrographic climatology of the Okhotsk Sea; this climatology was constructed from the Far Eastern Regional Hydrometeorological Research Institute (FERHRI) database. The FERHRI database has a volume of data three to five times larger than the data used in previous studies because unpublished Russian observation data have been included in the FERHRI database. After removing erroneous data from the database by pertinent quality control methods, the climatology for 1/4°?×?1/4° grids is produced by applying objective analysis procedures. Features similar to those in previous studies are seen in the intermediate layers in the Okhotsk Sea, whereas our climatology provides values that fill in gaps in previous climatologies. It is obvious from the monthly climatologies that temperature and salinity distributions evolve in accordance with seasonal variations in the Eastern Sakhalin Current and inflow from the North Pacific. We also reconstructed climatologies for the winter mixed layer and dense shelf water from data obtained from the temperature minimum waters identified as the remnants of these two layers. Free access to the 1°?×?1° versions of all climatologies constructed in this study is available through the website.  相似文献   

Comparison of the soil physical properties and hydrological processes in two different forest type catchments   总被引：1，自引：0，他引：1  

Zhang  Chuan  Yan  Haofang  Takase  Keiji  Oue  Hiroki 《Water Resources》2016,43(1):225-237

Water Resources - Soil physical properties and hydrological processes were analyzed in two experimental catchments with different forest types: one catchment is covered mostly with conifer type...  相似文献   

Geotechnical sealing material for coastal disposal facility for soils and wastes contaminated by radioactive cesium     

Takashi Tsuchida  Hiroki Murakami  Ooki Kurihara  A. M. R. G. Athapaththu  Yuichi Tanaka  Kazuhiko Ueno 《Marine Georesources & Geotechnology》2017,35(4):481-495

Safe disposal of wastes produced due to the process of decontamination in and around Fukushima No. 1 nuclear power plant is an urgent requirement. The purpose of this study was to develop a sealing material which can be used as an engineered barrier for a final disposal facility for the soils and wastes contaminated by radioactive cesium. The analyses conducted based on 4-m-thick sealing layer revealed that the hydraulic conductivity of the sealing material needs to be kept below 5.0?×?10^?10?m/s to avoid the seepage of contaminants below the environmentally safe limits. Sealing material was developed using marine clay–bentonite mixture and the engineering characteristics were examined. The results of laboratory experiments showed that, with the addition of bentonite, the hydraulic conductivity equal to or less than 5.0?×?10^?10?m/s was achieved when the effective consolidation stress is equal to or more than 27?kPa. From the tests for adsorption properties for cesium, it was found that the sealing material showed the significant capacity of adsorption for cesium in seawater. It was concluded that the construction of waste disposal facility on the sandy seafloor is feasible using the sealing layer proposed in this study.  相似文献