Effect of the variation in the lower tropospheric temperature on the wind onset of the Indian summer monsoon     

Kenji Taniguchi  Devraj Rajan  Toshio Koike 《Meteorology and Atmospheric Physics》2010,106(1-2):75-94

There is a large thermal contrast between the Arabian Peninsula and India (Δθ _AI) at the mature stage of the Indian summer monsoon (ISM). The forming process of Δθ _AI is investigated analyzing various datasets. It forms earlier in the lower troposphere than in the middle and upper layers. The potential temperature in the lower troposphere over the west coast of India (θ _IW) abruptly decreases in advance of the rapid enhancement of the westerly wind over the Arabian Sea corresponding to the ISM onset. Such a process was observed for all the target years and the rapid decrease in θ _IW could trigger the ISM onset. The decrease in θ _IW had two patterns. In one case, cooler air is brought by the strong winds around a cyclone over the Arabian Sea. In another case, θ _IW decreases gradually by a synergy of a southwesterly wind over the Arabian Sea and the enlargement of Δθ _AI.  相似文献   

Tectonic architecture through Landsat-7 ETM+/SRTM DEM-derived lineaments and relationship to the hydrogeologic setting in Siwa region, NW Egypt   总被引：2，自引：0，他引：2  

Alaa Masoud  Katsuaki Koike 《Journal of African Earth Sciences》2006,45(4-5):467-477

Fracture zones on the Earth’s surface are important elements in the understanding of plate motion forces, the dynamics of the subsurface fluid flow, and earthquake distributions. However, good exposures of these features are always lacking in arid regions, characterized by flat topography and where sand dunes extensively cover the terrain. During field surveys these conditions, in many cases, hinder the proper characterization of such features. Therefore, an approach that identifies the regional fractures as lineaments on remotely-sensed images or shaded digital terrain models, with its large scale synoptic coverage, could be promising.In the present work, a segment tracing algorithm (STA), for lineament detection from Landsat-7 Enhanced Thematic Mapper Plus (ETM+) imagery, and the data from the Shuttle Radar Topographic Mission (SRTM) 30 m digital elevation model (DEM), has been applied in the Siwa region, located in the northwest of the Western Desert of Egypt. The objectives are to analyze the spatial variation in orientation of the detected linear features and its relation to the hydrogeologic setting in the area and the underlying geology, and to evaluate the performance of the algorithm applied to the ETM+ and the DEM data.Detailed structural analysis and better understanding of the tectonic evolution of the area could provide useful tools for hydrologists for reliable groundwater management and development planning. The results obtained have been evaluated by the structural analysis of the area and field observations. Four major vertical fracture zones were detected corresponding to two conjugate sets of strike-slip faults that governed the surface, and subsurface environments of the lakes in the region, and these correlate well with the regional tectonics.  相似文献   

Study of the structure of silica film by infrared spectroscopy and electron diffraction analyses     

Tomonari Morioka  Seiji Kimura  Noritoshi Tsuda  Chihiro Kaito  Yoshio Saito  & Chiyoe Koike 《Monthly notices of the Royal Astronomical Society》1998,299(1):78-82

Amorphous silicon oxide films have been studied on the basis of electron diffraction (ED) analyses and infrared (IR) spectroscopy in order to elucidate the relationship between the structures. After the heat treatment of the film in air at 300 and 500°C, the ED pattern showed halo rings, and the IR spectra clearly changed. Intensity analysis of the ED pattern provided evidence for the structural change of the amorphous film. It was concluded that the spectral changes in the ranges of 9.2–10.2, 12.5–13.5 and 19.5–22.5 μm were the result of phase transitions of the microcrystallites of α-cristobalite to β-cristobalite, and α- or β-quartz. Astrophysical implications have been discussed.  相似文献   

Surface Flux Parameterization in the Tibetan Plateau   总被引：9，自引：1，他引：9  

Kun Yang  Toshio Koike  Dawen Yang 《Boundary-Layer Meteorology》2003,106(2):245-262

This study investigates some basic aspects related to surface-flux parameterization in the Tibetan Plateau, based on the measurement at three sites. These sites are essentially flat and covered by very sparse and short grasses in the monsoon season. The main contributions include: (1) an optimization technique is proposed to estimate aerodynamic roughness length based on wind and temperature profiles. The approach is not sensitive to random measurement errors if the number of data samples is large enough. The optimized values reasonably vary with surface characteristics. (2) At the three sites, kB^-1 (the logarithm of the ratio of aerodynamic roughness length to thermal roughness length) experiences seasonal and diurnal variations in addition to a dependence on surface types. The mean values for the individual sites vary over a range of 2.7 to 6.4 with large standard deviations. (3) A formula for estimatingthe value of kB^-1 isproposed to account for the effect of seasonal variation of aerodynamic roughness length and diurnal variation of surface temperature. With the formula, the flux parameterization with surface temperature estimates sensible heat flux better than profile parameterization for all the sites.  相似文献   

Characterizing Content Distributions of Impurities in a Limestone Mine Using a Feedforward Neural Network     

Koike  Katsuaki  Matsuda  Setsuro 《Natural Resources Research》2003,12(3):209-222

The factors determining the suitability of limestone for industrial use and its commercial value are the amounts of calcium oxide (CaO) and impurities. From 244 sample points in 18 drillhole sites in a limestone mine, southwestern Japan, data on four impurity elements, SiO₂, Fe₂O₃, MnO, and P₂O₅ were collected. It generally is difficult to estimate spatial distributions of these contents, because most of the limestone bodies in Japan are located in the accretionary complex lithologies of Paleozoic and Mesozoic age. Because the spatial correlations of content data are not clearly shown by variogram analysis, a feedforward neural network was applied to estimate the content distributions. The network structure consists of three layers: input, middle, and output. The input layer has 17 neurons and the output layer four. Three neurons in the input layer correspond with x, y, z coordinates of a sample point and the others are rock types such as crystalline and conglomeratic limestones, and fossil types related to the geologic age of the limestone. Four neurons in the output layer correspond to the amounts of SiO₂, Fe₂O₃, MnO, and P₂O₅. Numbers of neurons in the middle layer and training data differ with each estimation point to avoid the overfitting of the network. We could detect several important characteristics of the three-dimensional content distributions through the network such as a continuity of low content zones of SiO₂ along a Lower Permian fossil zone trending NE-SW, and low-quality zones located in depths shallower than 50 m. The capability of the neural network-based method compared with the geostatistical method is demonstrated from the viewpoints of estimation errors and spatial characteristics of multivariate data. To evaluate the uncertainty of estimates, a method that draws several outputs by changing coordinates slightly from the target point and inputting them to the same trained network is proposed. Uncertainty differs with impurity elements, and is not based on just the spatial arrangement of data points.  相似文献   

Species and concentrations of selenium and nutrients in Tanabe Bay during red tide due toGymnodinium nagasakiense     

Yuichi Koike  Yuzuru Nakaguchi  Keizo Hiraki  Terufumi Takeuchi  Tomoyoshi Kokubo  Takashi Ishimaru 《Journal of Oceanography》1993,49(6):641-656

A red tide due toGymnodinium nagasakiense was observed in August 1988 in Tanabe Bay, Wakayama Prefecture, Japan. The maximum cell concentration ofG. nagasakiense reached 1×10⁵ cells ml^–1 at the surface water. From May to September 1988, the following were monitored: water temperature, salinity, chlorophylla, D.O., dissolved nutrients (NO₂–N, NO₃–N, NH₄–N, PO₄–P DON, DOP), particulate nutrients (PON, POP) and three dissolved selenium species [Se(IV), Se(VI), Organic Se]. Dissolved inorganic nitrogen (NO₃–N, NH₄–N) decreased but PON, POP, DON, DOP and inorganic phosphate increased at the peak of the bloom. The concentration of organic selenium increased up to the bloom initiation period which started on 5 July, and then the concentration of Se(IV) increased as the concentration of organic selenium decreased at the peak of the bloom (3 August). The strong relationship was found between the concentration of Se(IV) and the cell concentration ofG. nagasakiense (r ²=0.98). The Se(IV) requirement ofG. nagasakiense was 2.89×10^–17 moles cell^–1, which was agreed well with 4.4×10^–17 moles cell^–1 found in a laboratory experiment onG. nagasakiense using selenium spiked artificial sea water medium. The average ratio of Se(IV) to dissolved inorganic nitrogen (DIN) during the red tide bloom was 11441, the ratio of Se(IV) to DIN at the surface with the maximum cell concentration ofG. nagasakiense of 1×10⁵ cells ml^–1 was 1137. These results suggested that selenium may play an important role in red tide outbreak ofG. nagasakiense.  相似文献   

N₂O Production, Nitrification and Denitrification in an Estuarine Sediment   总被引：1，自引：0，他引：1  

T. Usui  I. Koike  N. Ogura 《Estuarine, Coastal and Shelf Science》2001,52(6):769

The mechanisms regulating N₂O production in an estuarine sediment (Tama Estuary, Japan) were studied by comparing the change in N₂O production with those in nitrification and denitrification using an experimental continuous-flow sediment–water system with¹⁵N tracer (¹⁵N-NO−3 addition). From Feburary to May, both nitrification and denitrification in the sediment increased (246 to 716 μmol N m⁻² h⁻¹and 214 to 1260 μmol N m⁻² h⁻¹, respectively), while benthic N₂O evolution decreased slightly (1560 to 1250 nmol N m⁻² h⁻¹). Apparent diffusion coefficients of inorganic nitrogen compounds and O₂at the sediment–water interface, calculated from the respective concentration gradients and benthic fluxes, were close to the molecular diffusion coefficients (0·68–2·0 times) in February. However, they increased to 8·8–52 times in May except for that of NO−2, suggesting that the enhanced NO−3 and O₂supply from the overlying water by benthic irrigation likely stimulated nitrification and denitrification. Since the progress of anoxic condition by the rise of temperature from February to May (9 to 16 °C) presumably accelerated N₂O production through nitrification, the observed decrease in sedimentary N₂O production seems to be attributed to the decrease in N₂O production/occurrence of its consumption by denitrification. In addition to the activities of both nitrification and denitrification, the change in N₂O metabolism during denitrification by the balance between total demand of the electron acceptor and supply of NO−3+NO−2 can be an important factor regulating N₂O production in nearshore sediments.  相似文献   

Balloon-Borne Optical Counter for in Situ Aerosol Measurements     

T. Sugita  Y. Kondo  M. Koike  M. Kanada  N. Toriyama  H. Nakajima  T. Deshler  R. Imasu 《Journal of Atmospheric Chemistry》1999,32(1):183-204

A new balloon-borne optical particle counter has been developed to make in situ measurements of stratospheric aerosols. The intensity of light scattered at 60° from the forward direction by individual particles is measured. Aerosol number concentrations in seven size channels can be inferred. The counter has been calibrated using polystyrene and polyvinyl toluene latex spheres. There is good agreement between measured and calculated individual pulse intensities for aerosol with radii from 0.16 to 2.6 µm. The size resolution is limited by broadening of the pulse count/pulse height spectrum, arising mainly from the photoelectron statistics of photomultipliers. Stratospheric aerosol measurements have been made using this instrument at Kiruna (68°N, 21°E), Sweden, in February 1995, and at Aire sur l'Adour (44°N, 0°W), France, in 1992, 1993, and 1994. The uncertainties in the measurements are discussed. The retrieved aerosol concentrations and size distributions are presented, and shown to be broadly consistent with measurements made by the University of Wyoming optical particle counter.  相似文献   

GAME-TIBET青藏高原云和降水综合观测概况及初步结果   总被引：13，自引：7，他引：6  

刘黎平  楚荣忠  宋新民  周筠君  冯锦明  陈成品  张彤  S.Shimizu  K.Ueno  T.Koike  H.Fujii  H.Yamada  Y.Aoi  T.Ueno  J.Horikomi  M.Kajikawa  R Shirooka  J.Teshima 《高原气象》1999,18(3):441-450

对中日合作青藏高原能量水分循环试验项目中云和降水的多普勒雷达观测使用的气象观测仪器和获取的资料等情况进行了总结,并给出了那曲地区水的日变化,不同 雨量计测量降水的对比分析,风速对测量降水影响,多普勒雷达资料的个例分析及云的数值模拟的等初步结果。  相似文献   

On Structure and Temporal Variation of the Bifurcation Current off the Kii Peninsula   总被引：1，自引：0，他引：1  

Makoto Uchida  Junichi Takeuchi  Yoshitaka Morikawa  Youichi Maekawa  Osamu Momose  Takashi Koike  Yutaka Nagata 《Journal of Oceanography》2000,56(1):17-30

The Kii Bifurcation Current is often found along the southwest coast of the Kii Peninsula, and its frequency of occurrence reaches about 70% in the period from 1988 to 1996 (Takeuchi et al., 1998a). In order to clarify the structure and short-period variability of the Kii Bifurcation Current, detailed observations were made four times on board the R/V Seisui-maru of Mie University on October 29–31, 1996, on June 24–26, 1997, October 14–16, 1997, and December 3–4, 1997. The measured horizontal structure of the Kii Bifurcation Current indicates that the eastern portion of the Current (eastward flow near Cape Shionomisaki) consists of a part of the current zone of the Kuroshio. It is shown that the current structure, including the Kii Bifurcation Current in the vicinity of Cape Shionomisaki, is stable when the Kuroshio is flowing in a stationary straight path, but that the current structure is considerably changed when small-scale eddies pass by the cape. Such short-period variation can be monitored by using the daily variation of the sea level difference between Kushimoto and Uragami. In particular, in the case of October 29–31, 1996, when an eminent small-scale eddy passed by Cape Shionomisaki, and when the Kuroshio axis tentatively moved southwards about 50 km apart from the coast, the Kii Bifurcation Current seems to have disappeared.  相似文献