Evolution and decay of a warm-core ring within the western subarctic gyre of the North Pacific,as observed by profiling floats     

Sachihiko Itoh  Yugo Shimizu  Shin-ichi Ito  Ichiro Yasuda 《Journal of Oceanography》2011,67(3):281-293

This study investigated temporal variations in the vertical structure and water properties of a warm-core ring that migrated into the western subarctic gyre of the North Pacific, based on analyses of temperature and salinity data derived from two profiling floats, together with shipboard and satellite observation data. The floats were initially deployed into cold and fresh Oyashio water in September 2003, and were entrained into a warm-core ring in October 2003, remaining within the ring until detrainment in December 2004. Drastic cooling and freshening of the upper core water of the ring were observed during the above entrainment of the floats with cold and fresh water into the ring, whereas moderate variations in structure and water properties were observed during a quasi-isolated phase from November 2003 to November 2004 when the ring did not experience major interactions with ambient hydrographic features. The upper part of the core water (upper core), with relatively warm/saline water above 26.6 σ _θ , was under the influence of the atmosphere in winter via the formation of a deep mixed layer exceeding 300 dB, and had a prominent pycnostad below the seasonal pycnocline from spring to autumn. In contrast, the lower core, with relatively cold and fresh water below 26.6 σ _θ , was not ventilated throughout the observation period. Isopycnal surfaces showed a shoaling trend of about 50 dB/year during the quasi-isolated phase, suggesting viscous decay over a timescale of several years. Markedly cold and thick water was also frequently observed within the ring, indicating the intrusion of water from the Sea of Okhotsk.  相似文献   

Sunspot Bright Points     

Debi Prasad Choudhary  Toshifumi Shimizu 《Solar physics》2013,288(1):171-190

We used the flux-calibrated images from the Broad-band Filter Imager and Stokes Polarimeter data obtained with the Solar Optical Telescope onboard the Hinode spacecraft to study the properties of bright points in and around sunspots. The selected bright points are smaller in diameter than 150 km with contrasts exceeding about 3 % in the ratio of sunspot images obtained with the G-band (430.5 nm) and Ca ii H (396.85 nm) filters. The bright points are classified as umbral dot, peripheral umbral dot, penumbral grains, and G-band bright point depending on their location. The bright points are preferentially located around the penumbral boundary and in the fast decaying parts of the umbra. The color temperature of the bright points is in the range of 4600 K to 6600 K with cooler ones located in the central part of the umbra. The temperature increases as a function of distance from the center outward. The G-band, CN-band (388.35 nm), and Ca ii H fluxes of the bright points as a function of their blue-band (450.55 nm) brightness increase continuously in a nonlinear fashion unlike their red (668.4 nm) and green (555.05 nm) counterparts. This is consistent with a model in which the localized heating of the flux tube depletes the molecular concentration, resulting in the reduced opacity that leads to the exposition of deeper and hotter layers. The light curve of the bright points shows that the enhanced brightness at these locations lasts for about 15 to 60 min with the least contrast for the points outside the sunspot. The umbral dots near the penumbral boundary are associated with elongated filamentary structures. The spectropolarimeter observations show that the filling factor decreases as the G-band brightness increases. We discuss the results using the model in which the G-band bright points are produced in the cluster of flux tubes that a sunspot consists of.  相似文献   

Evapotranspiration and runoff in a forest watershed,western Japan     

A. Shimizu  T. Shimizu  Y. Miyabuchi  Y. Ogawa 《水文研究》2003,17(15):3125-3139

A Note has been published for this article in Hydrological Processes 18(4) 2004, 825. Both water and heat balances were studied in a conifer plantation watershed in south‐west Japan, within the warm‐temperate East Asia monsoon area. Forest cover in the watershed consists mainly of Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa) plantations. Precipitation and runoff have been observed since 1991, so evapotranspiration can be compared with the water balance. Two meteorological observation towers were built to monitor evapotranspiration in the watershed. The annual average precipitation, amount of runoff and losses were 2166, 1243 and 923 mm, respectively. The evapotranspiration (latent heat flux) agreed well with the water balance losses. The average annual evapotranspiration at the tower built in the centre of the watershed was 902 mm; evapotranspiration at the other tower, further upslope, was 875 mm. The observed evapotranspiration was 39% to 40% of the average precipitation (2166 mm). The mean net radiation was c. 2·6 GJ m^?2 year^?1, and is considered a representative value of the net radiation (Rn) in coniferous plantations in this region. This region is classified in the humid zone based on the ratio of net radiation (Rn) to the energy required to evaporate the rainfall (λR). The mean annual evaporation of canopy‐intercepted water was 356 mm or about 15% of the average precipitation. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

The structure of cometary atmospheres     

Mikio Shimizu 《Astrophysics and Space Science》1976,40(2):243-251

The distributions of various kinds of molecular ions in the atmospheres of new and old comets made up from dirty ice of the second kind (H₂O ice and hydrate clathrates of CO and N₂) have been computed at various heliocentric distances, by taking into account photoionization, ionmolecular reactions, electron-ion recombinations, and some transport effects. The results have been compared with observations and other computations. It is argued that dirty ice of the second kind model will impose a restriction on the theory of the origin of the solar system.  相似文献   

Oxygen isotopic anomaly and solar nebular photochemistry     

Y. Kitamura  M. Shimizu 《Earth, Moon, and Planets》1983,29(2):199-202

At the cool periphery of the solar nebula, oxygen could photochemically be formed from water. The mixing of¹⁷O and¹⁸O enriched by the self-shielding effect of¹⁶O₂ to the dust grain melted by the shock waves there would explain the oxygen isotopic anomaly in the high-temperature mineral of the carbonaceous meteorites.  相似文献   

Comparison of toxicity between populations of Gonyaulax tamarensis of eastern North American waters     

Lucie Maranda  Donald M. Anderson  Yuzuru Shimizu 《Estuarine, Coastal and Shelf Science》1985,21(3):401-410

Isolates of the dinoflagellate Gonyaulax tamarensis were established from benthic cysts or motile cells collected along the north-western Atlantic coast from the Bay of Fundy to Long Island. All clones were grown under the same conditions and assayed in a blind test for toxin content and composition. Differences in toxin content (μmouse unit per cell) spanning two orders of magnitude were found, with decreasing toxicity from north to south. Some isolates had undetectable toxin levels. The low toxicity of southern strains of G. tamarensis may explain the historical absence of paralytic shellfish poisoning (PSP) in areas where cysts and motile cells have been reported. The cause of the observed geographic pattern is unknown, but is does suggest that there may be an environmentally-determined southern limit to the regional PSP problem.Qualitative data on the toxin composition of some clones indicate that saxitoxin, neosaxitoxin and gonyautoxins -II, -III and -IV are generally present. A more quantitative approach (i.e. one which examines each isolate for all of the 12 Gonyaulax toxins) is needed to fully utilize the potential of toxin composition in discriminating between strains.  相似文献   

Buoyancy-driven perturbations in a rapidly rotating,electrically conducting fluid: part I – flow and magnetic field     

David E. Loper  Arnaud Chulliat  Hisayoshi Shimizu 《地球物理与天体物理流体动力学》2013,107(6):429-469

The steady velocity, perturbation pressure and perturbation magnetic field, driven by an isolated buoyant parcel of Gaussian shape in a rapidly rotating, unconfined, incompressible electrically conducting fluid in the presence of an imposed uniform magnetic field, are obtained by means of the Fourier transform in the limit of small Ekman number. Lorentz and inertial forces are neglected. The solution requires at most evaluation of a single integral and is found in closed form in some spatial regions. The solution has structure on two disparate scales: on the scale of the buoyant parcel and on the scale of the Taylor column, which is elongated in the direction of the rotation axis. The detailed structures of the flow and pressure depend linearly on the relative orientation of gravity and rotation, with the solution for arbitrary orientation being a linear combination of two limiting cases in which these vectors are colinear (polar case) and perpendicular (equatorial case). The perturbation magnetic field depends additionally on the relative orientation of the imposed magnetic field, and three limiting cases of interest are presented in which gravity and rotation are colinear (polar–toroidal case), gravity and imposed field are colinear (equatorial–radial case) and all three are mutually perpendicular (equatorial–toroidal case). Visualization and analysis of the velocity and perturbation magnetic field vectors are facilitated by dividing these vector fields into geostrophic and ageostrophic protions. In all cases, the geostrophic and ageostrophic portions have different structure on the Taylor-column scale. The buoyancy force is balanced by a pressure force in the polar case and by a flux of momentum in the equatorial case. The pressure force and momentum flux do not decay in strength with increasing axial distance. Far from the parcel, the axial mass flux varies as the inverse one-third power of distance from the parcel. The velocity has a single geostrophic vortex in the polar case and two vortices in the equatorial case. The perturbation magnetic field has two, four and one geostrophic vortices in the polar–toroidal, equatorial–radial and equatorial–toroidal cases, respectively. To facilitate comparison of the present results with numerical simulations carried out in a finite domain, a set of boundary conditions are developed, with may be applied at a finite distance from the parcel.  相似文献   

Field measurement and modeling of near-bed sediment transport processes with fluid mud layer in Tokyo Bay     

Nakagawa  Yasuyuki  Nadaoka  Kazuo  Yagi  Hiroshi  Ariji  Ryuichi  Yoneyama  Haruo  Shirai  Kazuhiro 《Ocean Dynamics》2012,62(10):1535-1544

Tokyo Bay is one of the estuaries in Japan with a high population of almost 26 million people in the basin area. One of the major concerns for the environment in this water area is the decreasing ecosystem functions including the deterioration of water and sediment qualities caused by various anthropogenic activities. Since the bottom sediments around almost the entire area of the inner bay consist of fine materials with a high organic content, which cause the deterioration of water quality through processes such as hypoxia, an understanding of the fine sediment dynamics in the Bay is crucial for an environmental assessment of the water area. This paper proposes a model for the key processes of fine sediment dynamics, which reflects field data about muddy bed structures and their dynamics obtained during the monitoring campaign in 2007. One of the specific features of the sediment in the Bay at present is the persistent existence of fluid mud layers (water content over 300 %) with a thickness of around a few decimeters, which might be caused by deposition of abundant organic particles due to eutrophication. The present study shows that diffusion flux model delivers quite reliable results for estimating erosion flux from the top of fluid mud layers after calibrating the model parameter against the time series data of vertical flux measured by an acoustic Doppler velocimeter system. This study also derives analytical solutions, based on the Bingham fluid concept, of advection flux in the fluid mud layer on which external shear stress force is applied.

  相似文献   

Aturoidea (Nautilida) from the Upper Cretaceous Sada limestone in Shimanto City, Kochi Prefecture, Japan     

Yasuyuki Tsujino  Hirohide Iwata 《Cretaceous Research》2009,30(4):911-916

The first specimen of Aturoidea to be recorded in East Asia has been found in the Upper Cretaceous Sada limestone in Shimanto City, Kochi Prefecture, Japan. The specimen is one of the few representatives from the Upper Cretaceous, along with species known from Libya, Angola, and India. The specimen is very similar to A. mathewsonni from the Paleocene deposits in California. However, we describe the specimen as A. cf. mathewsonni, as it slightly differs from A. mathewsonni in the shape of the lateral lobe of the suture. The finding reveals that Aturoidea had already lived in waters around East Asia in the Late Cretaceous.  相似文献   

Polarization Calibration of the Solar Optical Telescope onboard Hinode     

K. Ichimoto  B. Lites  D. Elmore  Y. Suematsu  S. Tsuneta  Y. Katsukawa  T. Shimizu  R. Shine  T. Tarbell  A. Title  J. Kiyohara  K. Shinoda  G. Card  A. Lecinski  K. Streander  M. Nakagiri  M. Miyashita  M. Noguchi  C. Hoffmann  T. Cruz 《Solar physics》2008,249(2):233-261

The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector magnetic fields on the Sun through precise spectropolarimetry of solar spectral lines with a spatial resolution of 0.2 – 0.3 arcsec. A photometric accuracy of 10⁻³ is achieved and, after the polarization calibration, any artificial polarization from crosstalk among Stokes parameters is required to be suppressed below the level of the statistical noise over the SOT’s field of view. This goal was achieved by the highly optimized design of the SOT as a polarimeter, extensive analyses and testing of optical elements, and an end-to-end calibration test of the entire system. In this paper we review both the approach adopted to realize the high-precision polarimeter of the SOT and its final polarization characteristics.  相似文献