Physical properties and isotopic characteristics of landfast sea ice around the North Water (NOW) Polynya region     

Toshiyuki Kawamura  Kunio Shirasawa  Kunio Kobinata 《大气与海洋》2013,51(3):173-182

Abstract

An ice core sampling program was conducted during the North Water (NOW) Polynya Project 1998 Experiment in northern Baffin Bay during April‐May 1998. The physical properties of snow and sea ice as well as the microstructure and stable isotopic composition of first‐year landfast sea ice near the polynya were investigated. The thickness of sea ice at the sampling sites ranged between 147 and 194 cm with thinner snow cover during the period between mid‐April and late May. The ice was characterized as typical first‐year landfast sea ice, being composed of a thin granular ice layer at the top and an underlying columnar ice layer towards the bottom of the ice. The samples obtained at a site closer to the ice edge of the polynya contained a thin granular ice layer originating from frazil ice near the ice bottom. Formation of frazil ice was considered to be caused by turbulent processes induced by winds, waves and currents forced from the polynya and also mixing with water masses produced at the polynya.  相似文献   

Molecular line mapping of the giant molecular cloud associated with RCW 106 – II. Column density and dynamical state of the clumps     

T. Wong  E. F. Ladd  D. Brisbin  M. G. Burton  I. Bains  M. R. Cunningham  N. Lo  P. A. Jones  K. L. Thomas  S. N. Longmore  A. Vigan  B. Mookerjea  C. Kramer  Y. Fukui  A. Kawamura 《Monthly notices of the Royal Astronomical Society》2008,386(2):1069-1084

We present a fully sampled C¹⁸O (1–0) map towards the southern giant molecular cloud (GMC) associated with the H  ii region RCW 106, and use it in combination with previous ¹³CO (1–0) mapping to estimate the gas column density as a function of position and velocity. We find localized regions of significant ¹³CO optical depth in the northern part of the cloud, with several of the high-opacity clouds in this region likely associated with a limb-brightened shell around the H  ii region G333.6−0.2. Optical depth corrections broaden the distribution of column densities in the cloud, yielding a lognormal distribution as predicted by simulations of turbulence. Decomposing the ¹³CO and C¹⁸O data cubes into clumps, we find relatively weak correlations between size and linewidth, and a more sensitive dependence of luminosity on size than would be predicted by a constant average column density. The clump mass spectrum has a slope near −1.7, consistent with previous studies. The most massive clumps appear to have gravitational binding energies well in excess of virial equilibrium; we discuss possible explanations, which include magnetic support and neglect of time-varying surface terms in the virial theorem. Unlike molecular clouds as a whole, the clumps within the RCW 106 GMC, while elongated, appear to show random orientations with respect to the Galactic plane.  相似文献   

Calibration and validation of the ocean color version-3 product from ADEOS OCTS     

Masanobu Shimada  Hiromi Oaku  Yasushi Mitomi  Hiroshi Murakami  Akira Mukaida  Yasuhisa Nakamura  Joji Ishizaka  Hiroshi Kawamura  Tasuku Tanaka  Motoaki Kishino  Hajime Fukushima 《Journal of Oceanography》1998,54(5):401-416

We present calibration and validation results of the OCTS’s ocean color version-3 product, which mainly consists of the chlorophyll-a concentration (Chl-a) and the normalized water-leaving radiance (_nL_w). First, OCTS was calibrated for the inter-detector sensitivity difference, offset, and absolute sensitivity using external calibration source. It was also vicariously calibrated using in-situ measurements for water (Chl-a and_nL_w) and atmosphere (optical thickness), which were acquired synchronously with OCTS under cloud-free conditions. Second, the product was validated using selected 17 in-situ Chl-a and 11 in-situ_nL_w measurements. We confirmed that Chl-a was estimated with an accuracy of 68% for Chl-a less than 2 mg/m³, and_nL_w from 94% (band 2) to 128% (band 4). Geometric accuracy was improved to 1.3 km. Stripes were significantly reduced by modifying the detector normalization factor as a function of input radiance.  相似文献   

Experimental study on the bidirectional inelastic deformation capacity of U‐shaped steel dampers for seismic isolated buildings          下载免费PDF全文

Diana Ene  Shoichi Kishiki  Satoshi Yamada  Yu Jiao  Yoshinao Konishi  Masao Terashima  Norihisa Kawamura 《地震工程与结构动力学》2016,45(2):173-192

Hysteretic dampers are used to dissipate earthquake‐induced energy in base‐isolated structures by acquiring inelastic deformations, rendering their hysteretic behavior of vital importance. The present paper focuses on investigating the behavior of U‐shaped steel dampers under bidirectional loading; this is significantly different from their corresponding uniaxial behavior. Two main sets of loading tests on full‐scale specimens are conducted in this regard: (i) quasi‐static tests with simple histories and (ii) dynamic tests with realistic loading histories. Based on the results obtained in the quasi‐static tests, an interaction curve that accounts for the reduction of the cyclic deformation capacity is proposed. However, the fidelity of this relation must be assessed under loading conditions similar to those of a seismically isolated structure subjected to an earthquake, which represents the goal of the second set of tests. The results of the dynamic tests validate the proposed interaction curve for estimating the deformation capacity of U‐shaped steel dampers under bidirectional loading. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Spatio-temporal analysis of recent groundwater-level trends in the Red River Delta, Vietnam     

Duong Du Bui  Akira Kawamura  Thanh Ngoc Tong  Hideo Amaguchi  Naoko Nakagawa 《Hydrogeology Journal》2012,20(8):1635-1650

A groundwater-monitoring network has been in operation in the Red River Delta, Vietnam, since 1995. Trends in groundwater level (1995?C2009) in 57 wells in the Holocene unconfined aquifer and 63 wells in the Pleistocene confined aquifer were determined by applying the non-parametric Mann-Kendall trend test and Sen??s slope estimator. At each well, 17 time series (e.g. annual, seasonal, monthly), computed from the original data, were analyzed. Analysis of the annual groundwater-level means revealed that 35?% of the wells in the unconfined aquifer showed downward trends, while about 21?% showed upward trends. On the other hand, confined-aquifer groundwater levels experienced downward trends in almost all locations. Spatial distributions of trends indicated that the strongly declining trends (>0.3?m/year) were mainly found in urban areas around Hanoi where there is intensive abstraction of groundwater. Although the trend results for most of the 17 time series at a given well were quite similar, different trend patterns were detected in several. The findings reflect unsustainable groundwater development and the importance of maintaining groundwater monitoring and a database in the Delta, particularly in urban areas.  相似文献   

Empirical ocean-color algorithms to retrieve chlorophyll-a, total suspended matter, and colored dissolved organic matter absorption coefficient in the Yellow and East China Seas   总被引：4，自引：1，他引：3  

Eko Siswanto  Junwu Tang  Hisashi Yamaguchi  Yu-Hwan Ahn  Joji Ishizaka  Sinjae Yoo  Sang-Woo Kim  Yoko Kiyomoto  Keiko Yamada  Connie Chiang  Hiroshi Kawamura 《Journal of Oceanography》2011,67(5):627-650

A bio-optical dataset collected during the 1998?C2007 period in the Yellow and East China Seas (YECS) was used to provide alternative empirical ocean-color algorithms in the retrieval of chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) absorption coefficients at 440 nm (ag₄₄₀). Assuming that remote-sensing reflectance (Rrs) could be retrieved accurately, empirical algorithms for T_Chl (regionally tuned Tassan??s Chl-a algorithm) in case-1 waters (T_Chl2i in case-2 waters), T_TSM (regionally tuned Tassan??s TSM algorithm), and T_ag440 or C_ag440 (regionally tuned Tassan??s or Carder??s ag₄₄₀ algorithm) were able to retrieve Chl-a, TSM, and ag₄₄₀ with uncertainties as high as 35, 46, and 35%, respectively. Applying the standard SeaWiFS Rrs, T_Chl was not viable in the eastern part of the YECS, which was associated with an inaccurate SeaWiFS Rrs retrieval because of improper atmospheric correction. T_Chl behaved better than other algorithms in the turbid case-2 waters, although overestimation was still observed. To retrieve more reliable Chl-a estimates with standard SeaWiFS Rrs in turbid water (a proxy for case-2 waters), we modified T_Chl for data with SeaWiFS normalized water-leaving radiance at 555 nm (nLw₅₅₅) > 2 mW cm^?2 ??m^?1 sr^?1 (T_Chl2s). Finally, with standard SeaWiFS Rrs, we recommend switching algorithms from T_Chl2s (for case-2 waters) to MOC_Chl (SeaWiFS-modified NASA OC4v4 standard algorithm for case-1 waters) for retrieving Chl-a, which resulted in uncertainties as high as 49%. To retrieve TSM and ag₄₄₀ using SeaWiFS Rrs, we recommend empirical algorithms for T_TSM (pre-SeaWiFS-modified form) and MT_ag440 or MC_ag440 (SeaWiFS Rrs-modified forms of T_ag440 or C_ag440). These could retrieve with uncertainties as high as 82 and 52%, respectively.  相似文献   

Improved Estimates of Wide-Ranging Sea Surface Temperature from GMS S-VISSR Data   总被引：1，自引：0，他引：1  

Shuichi Tanahashi  Hiroshi Kawamura  Toshihiko Matsuura  Tomoyuki Takahashi  Hiroyuki Yusa 《Journal of Oceanography》2000,56(3):345-358

We have developed an algorithm to estimate the wide-ranging Sea Surface Temperature (SST) data from the GMS-5 (Geostationary Meteorological Satellite) S-VISSR (Stretched-Visible Infrared Spin Scan Radiometer). Better SST estimates are realized by averaging the temporal variation of the VISSR calibration table and decreasing noise of the split-window terms using a spatial filter. The effects of the satellite zenith angle were examined in detail for better estimates, and VISSR-derived SSTs with root-mean-square (rms) error of 0.8 K were achieved using a new algorithm. The accuracy of SST estimates has been improved by using the temporal-spatial average of the split-window terms. Using the new techniques, we demonstrate that the hourly wide-ranging SST image data can be used to study the daily variations of SSTs in the Northern and Southern Pacific Oceans.  相似文献   

Mid-chain ketocarboxylic acids in the remote marine atmosphere: Distribution patterns and possible formation mechanisms     

Kimitaka Kawamura  R. B. Gagosian 《Journal of Atmospheric Chemistry》1990,11(1-2):107-122

In remote marine aerosol samples collected from the North Pacific ocean, Enewetak Atoll, American Samoa, and New Zealand, series of mid-chain ketocarboxylic acids in the range of C₆-C₁₈ were detected. All the positional isomers, except for the 2-oxo and 3-oxo species, were detected for major ketoacid families (e.g. C₉, C₁₁ and C₁₃). Higher ketoacid concentrations (up to 19 ng/m³) were obtained in the northern North Pacific aerosol samples, which generally showed an odd carbon-numbered predominance with 5-oxoundecanoic acid being the major species. By contrast, lower concentrations were obtained in the lower-latitude or subtropical aerosol samples, where even carbon-numbered ketoacids were relatively abundant.The distribution patterns of the odd carbon-numbered ketoacids could not be explained by the primary emissions from source materials including terrestrial higher plants, soil particles, and ocean surfaces. We consider that the isomeric ketocarboxylic acids are produced in the atmosphere by the photochemical oxidation of semi-volatile monocarboxylic acids, which are counterparts of the oxidative degradation of unsaturated fatty acids emitted from seawater surfaces. Atmospheric production of the ketoacids is seemingly enhanced in the northern North Pacific, probably due to an enhanced primary productivity.  相似文献   

Accuracies of NOAA/NESDIS sea surface temperature estimation technique in the oceans around Japan     

F. Sakaida  H. Kawamura 《Journal of Oceanography》1992,48(3):345-351

We have examined accuracies of nine nighttime National Oceanic and Atmospheric Administration/National Environmental Satellite, Data and Information Service (NOAA/NESDIS) equations for SST estimation using the Advanced Very High Resolution Radiometer (AVHRR)/NOAA-11 dataset produced by Sakaida and Kawamura (1992). Among the nine equations, the revised triple-window CPSST algorithm gives the smallest rms error, which is 0.38°C. The dual-window MCSST algorithm gives the largest rms error 0.56°C. Rms errors of the other algorithms are smaller than 0.5°C.  相似文献   

Seasonal Variation of Space/Time Statistics of Short-Term Sea Surface Temperature Variability in the Kuroshio Region   总被引：1，自引：0，他引：1  

Kohtaro?HosodaEmail author  Hiroshi?Kawamura 《Journal of Oceanography》2005,61(4):709-720

Spatial and temporal scales of sea surface temperature (SST) variations in the Kuroshio region have been investigated using a satellite-based one-year merged SST product. Targeting short-term variations with temporal scales of less than a year, decorrelation scales, which are defined as the e-folding scale of SST variability, have been derived as functions of regional positions and calendar months. We assumed that the autocorrelation function of SST has anisotropic Gaussian characteristics in the space-time domain. Resultant spatial and temporal decorrelation scales range from 1 to 3° and 2 to 3 days, respectively. They are strongly inhomogeneous, anisotropic and time-dependent. These characteristics are attributed to the oceanic and atmospheric disturbances. Spatial decorrelation scales are determined mainly by strong atmospheric forcing in the study region. In the area with dominant atmospheric forcing, the spatial scales are larger than those in the other regions. Those in the regions with dynamical oceanographic disturbances are as small as 1°. Signal-to-noise ratios are also large where the atmospheric forcing is strong, while they are small where the oceanic signals are active.  相似文献