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排序方式: 共有286条查询结果,搜索用时 15 毫秒
1.
2.
Irvine WM Friberg P Hjalmarson A Ishikawa S Kaifu N Kawaguchi K Madden SC Matthews HE Ohishi M Saito S Suzuki H Thaddeus P Turner BE Yamamoto S Ziurys LM 《The Astrophysical journal》1988,334(2):L107-L111
We report the astronomical identification of the cyanomethyl radical, CH2CN, the heaviest nonlinear molecular radical to be identified in interstellar clouds. The complex fine and hyperfine structures of the lowest rotational transitions at about 20.12 and 40.24 GHz are resolved in TMC-1, where the abundance appears to be about 5 x 10(-9) relative to that of H2. This is significantly greater than the observed abundance of CH3CN (methyl cyanide) in TMC-1. In Sgr B2 the hyperfine structure is blended in the higher frequency transitions at 40, 80, and 100 GHz, although the spin-rotation doubling is clearly evident. Preliminary searches in other sources indicate that the distribution of CH2CN is similar to that for such carbon chain species as HC3N or C4H. 相似文献
3.
Abyssal currents along the northern periphery of the Shikoku Basin south of Japan were measured by current meters moored off Cape Daio-zaki, Cape Shiono-misaki and Cape Ashizuri-misaki and on the eastern foot of the northernmost part of the Kyushu-Palau Ridge. Total length of observation off Cape Shiono-misaki was about five years including the periods of the Kuroshio large meander and no meander. Analyses of current data show:
- Mean currents with a magnitude of 5–10 cm sec?1 were observed during the whole observation period at all of current meters which were set 400 m above the sea bottom that was deeper than 4,500 m. The mean current for each current meter was parallel to the local bottom contour arond each station and was toward a direction looking the Nankai Trough (a trough located along the northern end of the Shikoku Basin) to the left.
- At each station located above the shelf toe off Cape Daio-zaki and off Cape Shiono-misaki and on the foot of the Kyushu-Palau Ridge, the mean current increases with depth (a bottomward intensification of the mean current), and the vertical extent of the mean current is estimated to be about 2,000 m above the sea bottom.
- At a station located at 2,600 m depth on the continental slope off Cape Shiono-misaki, no bottom-ward intensification of currents was observed.
4.
Radiocarbon and total carbonate data were obtained near the 1973 GEOSECS stations in the North Pacific along 30°N and along 175°E between 1993 and 1994. In these stations, we estimated radiocarbon originating from atomic bomb tests using tritium, trichlorofluoromethane and silicate contents. The average penetration depth of bomb radiocarbon during the two decades has deepened from 900 m to 1300 m. Bomb radiocarbon inventories above the average value for the whole North Pacific were found widely in the western subtropical region around 30°N both in the 1970s and 1990s, and its area in the 1990s was broader than that in the 1970s. In most of the North Pacific, while the bomb radiocarbon has decreased above 25.4, the bomb radiocarbon flux below 25.4 was over 1 × 1012 atom m-2yr-1 in the subtropical region around 30°N. In the tropical area south of 20°N, the bomb radiocarbon inventory below 25.4 increased from zero to over 10 × 1012 atom m-2 during the last three decades. These distributions suggest that the bomb radiocarbon removed from the surface is currently accumulated with bomb 14C flux of over 1 × 1012 atom m-2yr-1 below 25.4 in the subtropical region, mainly by advection from the higher latitude, and that part of the accumulated bomb 14C gradually spread southward with about 30 years. 相似文献
5.
Ichiro Ishikawa Shigeaki Aoki Ryo Furue Nobuo Suginohara 《Journal of Oceanography》1996,52(5):617-632
In recognition that similarity in the density balance leads to resemblance in circulation between the two-dimensional non-rotating and three-dimensional rotating systems which have similar density stratification, we investigate convection induced by cooling at one side wall and heating at the sea surface by using a two-dimensional non-rotating model as idealized representation for the deep Pacific circulation. In the model, various vertical profiles are taken for the side wall cooling, which are assumed to correspond to the density structure of the Anatarctic Circumpolar Current. In a small diffusivity range, two important features are found to be robust against change in the vertical profile of the side wall cooling. One is that the density stratification is horizontally almost uniform. The other is that the balance in the density equation between the vertical advection and the vertical diffusion holds in the interior. Consequently, the vertical density balance, together with the equation of continuity, determines the circulation pattern for the prescribed vertical profile of the side wall cooling. The multi-layered meridional flow, which is expected to exist in the deep Pacific, is shown to form for certain vertical profiles of the side wall cooling. 相似文献
6.
Tetsuo Yanagi Koji Ishikawa Koh-ichi Inoue Satoshi Susami 《Journal of Oceanography》1995,51(2):225-238
The detailed flow structure around a tical front in Hiuchi-Nada, Japan was observed with the use of ADCP (Acoustic Doppler Current Profiler). The surface convergence region is observed at the transition zone between vertically well mixed area and the stratified area. The surface divergence regions exist next to the surface convergence region. The strong downward current is estimated in the middle layer just below the surface convergence region. The maximum surface convergence and the maximum downward velocity in the middle layer are 1.0×10–4 s–1 and 0.12 cm s–1, respectively. 相似文献
7.
Simulation of Formation and Spreading of Salinity Minimum Associated with NPIW Using a High-Resolution Model 总被引:1,自引:2,他引:1
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.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
High quality CTD data were collected in the north of the Shikoku Basin where an abyssal boundary current has been observed through direct current measurements. Analyses of hydrographic data showed:
- Colder and saltier water (heavier water) compared to surrounding waters is found above the continental shelf-toe and the eastern flank of the Kyushu-Palau Ridge where the existence of the abyssal boundary current has been expected. The heavier water has a horizontal extent of about 50 km.
- The heavier water has the vertical scale of 2000 m from the sea bottom, and is associated with a thermal wind shear which enhances a component of the flow toward a direction looking the Nankai Trough (a trough located along the northern end of the Shikoku Basin) to the left in the abyss. The assumed “level of no motion” at about 2500 m depth gives the geostrophically estimated current in a good agreement with the directly measured current.
9.
Effects of the presence of a circumpolar region on buoyancy-driven circulation are investigated by using an idealized numerical ocean model. Comparison of circulation and meridional density (heat) transport is made between a closed ocean and an ocean with a cyclic gap near its southern boundary. The presence of the circumpolar region leads to disconnection of the meridional overturning across the circumpolar region. And the circumpolar eastward flow reaches the bottom of the ocean. It is essential for this that the pycnocline is deeper than the bottom of the gap. Since the amount of the mass transported northward must return southward at the levels deeper than the bottom of the cyclic gap, the weak stratification, hence weak vertical geostrophic shear, at the deeper levels leads to inactive communication across the circumpolar region. Meridional heat transport across the circumpolar region is made mainly by horizontal diffusion for the ocean with the cyclic gap, while the contribution of the advection is dominant for the closed ocean. Sensitivity of meridional heat transport to change in horizontal diffusivity is studied. The meridional heat transport for the ocean with the cyclic gap is more sensitive than for the closed ocean. The change in heat transport occurs not only in the circumpolar region but also in the rest of the ocean. It is suggested that subgrid scale phenomena, especially mesoscale eddies, in the circumpolar region controls the whole ocean to a great extent. 相似文献
10.
State Estimation of the North Pacific Ocean by a Four-Dimensional Variational Data Assimilation Experiment 总被引:1,自引:0,他引:1
Toshiyuki Awaji Shuhei Masuda Yoichi Ishikawa Nozomi Sugiura Takahiro Toyoda Tomohiro Nakamura 《Journal of Oceanography》2003,59(6):931-943
A four-dimensional variational data assimilation system has been applied to an experiment to describe the dynamic state of
the North Pacific Ocean. A synthesis of available observational records and a sophisticated ocean general circulation model
produces a dynamically consistent dataset, which, in contrast to the nudging approach, provides realistic features of the
seasonally-varying ocean circulation with no artificial sources/sinks for temperature and salinity fields. This new dataset
enables us to estimate heat and water mass transports in addition to the qualification of water mass formation and movement
processes. A sensitivity experiment on our assimilation system reveals that the origin of the North Pacific Intermediate Water
can be traced back to the Sea of Okhotsk and the Bering Sea in the subarctic region and to the subtropical Kuroshio region
further south. These results demonstrate that our data assimilation system is a very powerful tool for the identification
and characterization of ocean variabilities and for our understanding of the dynamic state of ocean circulation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献