Spectral similarity between scalars at very low frequencies in the unstable atmospheric surface layer over the Tibetan plateau   总被引：1，自引：7，他引：1  

Jun Asanuma  Ichiro Tamagawa  Hirohiko Ishikawa  Yaoming Ma  Taiichi Hayashi  Yongqiang Qi  Jiemin Wang 《Boundary-Layer Meteorology》2007,122(1):85-103

Similarity between temperature and water vapour was investigated in the Fourier domain by using their coherency spectra, defined as the correlation coefficient between their Fourier modes, and the relative efficiency of their vertical transport. The class-averaged values of these indices were computed from the turbulence measurements over sparse grasslands on the Tibetan plateau during the intensive observations of GEWEX (Global Energy and Water Experiment) Asian Monsoon Experiment (GAME). It was found that the energy-containing eddies at scales up to 100z (z being height) are characterised by well-maintained similarity between these scalars. The scalars are highly correlated with each other, and their transport efficiencies are almost equal within this scale range. In contrast, similarity was not always maintained at scales larger than 1000z. Detailed analyses showed that this breakdown of similarity occurs occasionally or sporadically, suggesting that it is caused by events whose average return period is not much smaller than the current averaging time, i.e. 30 min. We speculate that entrainment of drier and warmer air at the top of the atmospheric boundary layer caused the scalar dissimilarity at this scale range.  相似文献   

The Kinematics, Physical Condition and Magnetic Field of the W3 Irs5 Region     

Hiroshi Imai  Anuj P. Sarma 《Astrophysics and Space Science》2005,295(1-2):71-75

We have independently investigated water masers associated with the star-forming region W3 IRS5 with the VLBA. Imai et al., found that the maser 3-D motions exhibit outflows, which likely originate from two of the hyper-compact HII regions in this source. Sarma et al., have detected the Zeeman effect in water masers toward W3 IRS5 and measured line-of-sight magnetic field strengths of between 14 and 42 mG. The directions of maser linear polarization are well aligned in the whole maser region and perpendicular to the estimated magnetic field. These polarimetric results are consistent with an hourglass model of the magnetic field in W3 IRS5. Imai et al., also have analyzed the microstructures found in the individual maser features (1AU), which exhibit the fractal fashion and express turbulence on very small scales. Together, we have demonstrated that observations of water masers enable us to comprehensively enhance our understanding of the early stages of the formation of massive stars in clusters.  相似文献   

Nitrogen and phosphorus distributions across the thermohaline front in Kii Channel in winter     

Ichiro Yuasa  Eisuke Hashimoto  Hideki Ueshima 《Journal of Oceanography》1993,49(4):407-424

We have studied nitrogen and phosphorus distributions across the thermohaline front in Kii Channel in winter by using engine-cooling sea water of a ferry boat. On Dec. 1986 and Jan. 1987, differences of PO₄–P and DIN across the front are recognized. Especially in the latter case, differences of nutrients concentrations across the front are very obvious. But differences of nutrients across the front on Feb. 1986, Feb. and Mar. 1987 are not obvious. Inspite of winter,Akashiwo had happened in Osaka Bay, nutrients mostly have already been utilized by phytoplankton in inner part of Osaka Bay. Consequently, differences of nutrients concentrations across the front are nearly zero.  相似文献   

Errata: Structure of Subsurface Intrusion of the Oyashio Water into the Kuroshio Extension and Formation Process of the North Pacific Intermediate Water     

Kuniaki Okuda  Ichiro Yasuda  Yutaka Hiroe  Yugo Shimizu 《Journal of Oceanography》2001,57(4):495-497

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Absolute Volume Transports of the Oyashio Referred to Moored Current Meter Data Crossing the OICE     

Kazuyuki Uehara  Shin-Ichi Ito  Hideo Miyake  Ichiro Yasuda  Yugo Shimizu  Tomowo Watanabe 《Journal of Oceanography》2004,60(2):397-409

During November 2000–June 2002, both direct current measurements from deployment of a line of five moorings and repeated CTD observations were conducted along the Oyashio Intensive observation line off Cape Erimo (OICE). All the moorings were installed above the inshore-side slope of the Kuril-Kamchatka Trench. Before calculating the absolute volume transports, we compared vertical velocity differences of relative geostrophic velocities with those of the measured velocities. Since both the vertical velocity differences concerned with the middle three moorings were in good agreement, the flows above the continental slope are considered to be in thermal wind balance. We therefore used the current meter data of these three moorings, selected among all five moorings, to estimate the absolute volume transports of the Oyashio referred to the current meter data. As a result, we estimated that the southwestward absolute volume transports in 0–1000 db are 0.5–12.8 × 10⁶ m³/sec and the largest transport is obtained in winter, January 2001. The Oyashio absolute transports in January 2001, crossing the OICE between 42°N and 41°15′ N from the surface to near the bottom above the continental slope, is estimated to be at least 31 × 10⁶ m³/sec. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Two-dimensional asymmetric vortex merger: Contour dynamics experiment   总被引：1，自引：0，他引：1  

Ichiro Yasuda  Glenn R. Flierl 《Journal of Oceanography》1995,51(2):145-170

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Characteristics of SSH Anomaly Based on TOPEX/POSEIDON Altimetry and in situ Measured Velocity and Transport of Oyashio on OICE     

Shin-Ichi Ito  Kazuyuki Uehara  Takashi Miyao  Hideo Miyake  Ichiro Yasuda  Tomowo Watanabe  Yugo Shimizu 《Journal of Oceanography》2004,60(2):425-437

An observation line along the TOPEX/POSEIDON (T/P) ground track 060 was set to estimate the Oyashio transport. We call this line the OICE (Oyashio Intensive observation line off-Cape Erimo) along which we have been conducting repeated hydrographic observations and maintaining mooring systems. T/P derived sea surface height anomaly (SSHA) was compared with velocity and transport on OICE. Although the decorrelation scale of SSHA was estimated at about 80–110 km in the Oyashio region, the SSHA also contains horizontal, small-scale noise, which was eliminated using a Gaussian filter. In the comparison between the SSHA difference across two selected points and the subsurface velocity measured by a moored Acoustic Doppler Current Profiler (ADCP), the highest correlation (0.92) appeared when the smoothing scale was set at 30 km with the two points as near as possible. For the transport in the Oyashio region, the geostrophic transport between 39°30′ N and 42°N was compared with the SSHA difference across the same two points. In this case the highest correlations (0.79, 0.88 and 0.93) occurred when the smoothing scale was set at 38, 6 and 9 km for reference levels of 1000, 2000 and 3000 db, respectively. The annual mean transport was estimated as 9.46 Sv in the 3000 db reference case. The Oyashio transport time series was derived from the T/P SSHA data, and the transports are smaller than that estimated from the Sverdrup balance in 1994–1996 and larger than that in 1997–2000. This difference is consistent with baroclinic response to wind stress field. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Simulation of Formation and Spreading of Salinity Minimum Associated with NPIW Using a High-Resolution Model     

Hiroshi Ishizaki  Ichiro Ishikawa 《Journal of Oceanography》2002,58(2):463-485

A series of numerical experiments were conducted with a high-resolution (eddy-permitting) North Pacific model to simulate the formation and spreading of the salinity minimum associated with the North Pacific Intermediate Water (NPIW). It was found that two factors are required to simulate a realistic configuration of the salinity minimum: a realistic wind stress field and small-scale disturbances. The NCEP reanalyzed wind stress data lead to better results than the Hellerman and Rosenstein wind stress data, due to the closer location of the simulated Oyashio and Kuroshio at the western boundary. Small-scale disturbances formed by relaxing computational diffusivity included in the advection scheme promote the large-scale isopycnal mixing between the Oyashio and Kuroshio waters, simulating a realistic configuration of the salinity minimum. A detailed analysis of the Oyashio water transport was carried out on the final three-year data of the experiment with reduced computational diffusivity. Simulated transport of the Kuroshio Extension in the intermediate layer is generally smaller than the observed value, while those of the Oyashio and the flow at the subarctic front are comparable to the observed levels. In the Oyashio-Kuroshio interfrontal zone the zonally integrated southward transport of the Oyashio water (140-155°E) is borne by the eddy activity, though the time-mean flow reveals the existence of a coastal Oyashio intrusion. In the eastern part (155°E-180°) the zonally integrated transport of the Oyashio water indicates a southward peak at the southern edge of the Kuroshio Extension, which corresponds to the branching of the recirculating flow from the Kuroshio Extension.  相似文献   

Dynamics of the Kuroshio large meander     

Ichiro Yasuda  Jong -Hwan Yoon  Nobuo Suginohara 《Journal of Oceanography》1985,41(4):259-273

The bimodality of the Kuroshio path is studied numerically with a barotropic inflow-outflow model. The dynamics that determines the path depends on the Rossby number,Ro (proportional to inlet velocity) and the Reynolds number (representing effects of viscosity). At lowRo (<Ro ₁) only a meander path occurs, while at highRo(Ro ₂) only a straight path is developed. Between these critical values (Ro ₁RoRo₂) either of the two paths can occur (multiple states), and the choice of path is determined by its history. Increase (decrease) inRo acrossRo ₂ (Ro ₁) leads to catastrophic transition from one path to the other. In the intermediate range (Ro ₁RoRo₂), the straight path is conditionally unstable to finite amplitude disturbances, and abrupt changes to the meander path take place. Absolute vorticity is almost conserved along the meander path, while along the straight path it is dissipated in large amount near the coast. At low Re, the flow tends to a viscous flow, and steady states are obtained. At highRe, time variations with different periods for the meander and straight paths become dominant. Intermittent transitions from one state to the other without any changes of external parameters are found at intermediateRo and at highRe.  相似文献   

Fluid Inclusion and Stable Isotope Study at the Southeastern Martabe Deposit: Purnama,Barani and Horas Ore Bodies,North Sumatra,Indonesia          下载免费PDF全文

Stephanie Saing  Ryohei Takahashi  Akira Imai 《Resource Geology》2016,66(2):127-148

The Martabe Au–Ag deposit, North Sumatra Province, Indonesia, is a high sulfidation epithermal deposit, which is hosted by Neogene sandstone, siltstone, volcanic breccia, and andesite to basaltic andesite of Angkola Formation. The deposit consists of six ore bodies that occurred as silicified massive ore (enargite–luzonite–pyrite–tetrahedrite–tellurides), quartz veins (tetrahedrite–galena–sphalerite–chalcopyrite), banded sulfide veins (pyrite–tetrahedrite–sphalerite–galena) and cavity filling. All ore bodies are controlled by N–S and NW–SE trending faults. The Barani and Horas ore bodies are located in the southeast of the Purnama ore body. Fluid inclusion microthermometry, and alunite‐pyrite and barite‐pyrite pairs sulfur isotopic geothermometry show slightly different formation temperatures among the ore bodies. Formation temperature and salinity of fluid inclusions of the Purnama ore body range from 200 to 260 C and from 6 to 8 wt.% NaCl equivalent, respectively. Formation temperature and salinity of fluid inclusions of the Barani ore body range from 200 to 220 °C and from 0 to 2.5 wt.% NaCl equivalent and those of the Horas ore body range from 240 to 275 °C and from 2 to 3 wt.% NaCl equivalent, respectively. The Barani and Horas ore bodies are less silicified and sulfides are less abundant than the Purnama ore body. A relationship between enthalpy and chloride content indicates mixing of hot saline fluids with cooler dilute fluids during the mineralization of each of the ore bodies. The δ¹⁸O values of quartz samples from the southeast ore bodies exhibit a wide range from +4.2 to +12.9‰ with an average value of +7.0‰. The δ¹⁸O values of H₂O estimated from δ¹⁸O values of quartz, barite and calcite confirm the oxygen isotopic shift to near meteoric water trend, which support the incorporation of meteoric water. Salinity of the fluid inclusions decrease from >5 wt.% NaCl equivalent in the Purnama ore body to <3 wt.% NaCl equivalent in the Barani ore body, indicating different fluid systems during mineralization. The δ³⁴S values of sulfide and sulfate in Purnama range from ? 4.2 to +5.5‰ and from +1.2 to +26.7‰, those in the Barani range from ? 4.3 to +26.4‰ and from +3.9 to +18.5‰ and those in the Horas ore body range from ? 11.8 to +3.5‰ and from +1.4 to +25.7‰, respectively. The δ³⁴S of total bulk sulfur in southeastern ore bodies (Σδ³⁴S) was estimated to be approximately +6‰. The estimated sulfur fugacity during formation of the Purnama and Horas ore bodies is relatively high. It was between 10^?4.8 and 10^?10.8 atm at 220 to 260 °C. Tellurium fugacity was between 10^?7.8 and 10^?9.5 atm at 260 °C and between 10^?9 and 10^?10.6 atm at 220 °C in the Purnama ore body. The Barani ore body was formed at lower fS₂, lower than about 10^?14 atm at 200 to 220 °C based on the presence of arsenopyrite and pyrrhotite in the early stage, and between 10^?14 and 10^?12 atm based on the existence of enargite and tennantite in the last stage. © 2016 The Society of Resource Geology  相似文献