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排序方式: 共有239条查询结果,搜索用时 15 毫秒
1.
We present H monochromatic and spectroscopic observations of the sudden disappearance of a dark filament located near the center of the solar disk on October 26, 1989. The event was not associated with the flare activity. The dark filament first disintegrated into two loop-like components, and then each component successively showed ascending motion with a velocity greater than 30 km s–1. Comparison of the H pictures taken before and after the start of this event suggests that the dark filament was originally composed of two magnetic flux loops. 相似文献
2.
Abstract— Enstatite is one of the major constituent minerals in carbonaceous chondrites. Hydrothermal alteration experiments (26 in total) of enstatite were carried out at pH 0, 6, 7, 12, 13, and 14, at temperatures of 100, 200, and 300 °C, and for run durations of 24, 72, 168, and 336 h in order to provide constraints on the aqueous‐alteration conditions of the meteorites. The recovered samples were studied in detail by using powder X‐ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Under acidic and mildly acidic conditions (pH 0, 6), no significant alteration occurred, whereas under neutral to alkaline conditions (pH 7–14), serpentine and saponite formed in various proportions by replacing enstatite. At 300 °C for 168 h, serpentine formed under neutral to moderately alkaline conditions (pH 7, 12), and serpentine and saponite formed as unit cell‐scale coherent intergrowths under highly alkaline conditions (pH 13, 14). The amounts of phyllosilicates have a tendency to increase with increasing pH, temperature, and run duration. There is also a tendency for saponite to form at higher pH and temperature and under longer run‐durations than serpentine. The results indicate that alteration of enstatite is strongly dependent on the experimental conditions, especially pH. They suggest that CM chondrites experienced aqueous alteration under neutral to alkaline conditions, whereas CV and CI chondrites experienced aqueous alteration under more alkaline conditions. The results also suggest that aqueous alteration in CI chondrites occurred at higher temperatures than in CM chondrites, and aqueous alteration in CV chondrites occurred at even higher temperatures than in CI chondrites. 相似文献
3.
4.
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
5.
6.
The outflow from the Sea of Okhotsk to the North Pacific is important in characterising the surface-to-intermediate-depth
water masses in the Pacific Ocean. The two basins are separated by the Kuril Islands with numerous straits, among which the
Bussol and the Kruzenshterna Straits are deeper than 1000 m. The physics governing the transport between the two basins is
complicated, but when the semidiurnal and diurnal tides are subtracted, the observed density and velocity structures across
the Bussol Strait suggest a significant contribution from geostrophic balance. Using a two-layer model with the interface
at 27.5σ
θ
, part of the upper layer transport that is not driven by tides is estimated using two previously unexplored data sets: outputs
from the Ocean General Circulation Model for Earth Simulator (OFES), and historical hydrographic data. The Pacific water flows
into the Sea of Okhotsk through the northeastern straits. The greatest inflow is through the Kruzenshtern Strait, but the
OFES results show that the contributions from other shallower straits are almost half of the Kruzenshtern inflow. Similarly,
the outflow from the Sea of Okhotsk is through the southwestern straits of the Kuril Islands with the largest Bussol Strait
contributing 60% of the total outflow. The OFES and hydrographic estimates agree that the exchange is strongest in February
to March, with an inflow of about −6 to −12 Sv (negative indicates the flow from the North Pacific, 1 Sv = 106 m3s−1), and an outflow from the Sea of Okhotsk of about +8 to +9 Sv (positive indicates the flow from the Sea of Okhotsk), which
is weakest in summer (−3 to +1 Sv through the northeastern straits and +0 to +3 Sv through the southwestern straits). The
estimated seasonal variation is consistent with a simple analytic model driven by the difference in sea surface height between
the two basins. 相似文献
7.
Ryo Sugimoto Akihide Kasai Toshihiro Miyajima Kouichi Fujita 《Journal of Oceanography》2008,64(1):39-48
Temporal changes in nitrogen isotopic composition (δ15N) of the NO3
− pool in the water column below the pycnocline in Ise Bay, Japan were investigated to evaluate the effect of nitrification
on the change in the δ15N in the water column. The δ15N of NO3
− in the lower layers varied from −8.5‰ in May to +8.4‰ in July in response to the development of seasonal hypoxia and conversion
from NH4
+ to NO3
−. The significantly 15N-depleted NO3
− in May most likely arose from nitrification in the water column. The calculated apparent isotopic discrimination for water
column nitrification (ɛnit = δ15Nsubstrate − δ15Nproduct) was 24.5‰, which lies within the range of previous laboratory-based estimates. Though prominent deficits of NO3
− from hypoxic bottom waters due to denitrification were revealed in July, the isotopic discrimination of denitrification in
the sediments was low (ɛdenit = ∼1‰). δ15NNO3 in the hypoxic lower layer mainly reflects the isotopic effect of water column nitrification, given that water column nitrification
is not directly linked with sedimentary denitrification and the effect of sedimentary denitrification on the change in δ15NNO3 is relatively small. 相似文献
8.
9.
High parallelization efficiency in barotropic-mode computation of ocean models based on multi-grid boundary ghost area 总被引:1,自引:0,他引:1
In general, barotropic-mode computation requires the largest communication time in ocean models because of its iterative nature, when parallel computation is performed based on regional partitioning. In this study, reduction in the overhead time included in the communication in the parallel computation of the barotropic mode is considered to achieve a high parallelization efficiency of ocean models. We verify that the reduction in the communication frequency based on the multi-grid boundary ghost area reduces the total communication time. We find that this is because the sum of several kinds of overhead time for communication occupies a fairly large part of the total communication time. We discuss the trade-off between the decrease in communication time and the increase in computation time due to increased boundary area in such cases, leading to a determination of a suitable width of the multi-grid boundary that minimizes the total required time. We also discuss the efficiencies of the one- and two-dimensional partitioning of the model domain, when a multi-grid boundary is used. In general, two-dimensional partitioning is more efficient than one-dimensional for large partitioning numbers. 相似文献
10.
Koji Sugie Kenshi Kuma Satoshi Fujita Satomi Ushizaka Koji Suzuki Tsutomu Ikeda 《Journal of Oceanography》2011,67(2):183-196
We report on the ability for luxury Fe uptake and the potential for growth utilizing intracellular Fe pools for 4 coastal
centric diatom isolates and in situ phytoplankton assemblages, mainly composed of diatoms. Iron uptake of the diatom isolates
and natural phytoplankton assemblages in the Oyashio region during spring blooms were prevented by adding hydroxamate siderophore
desferrioxamine B (DFB). After the addition of DFB, intracellular Fe in the diatom isolates supported 2.4–4.2 cell divisions
with 1.2–2.6 Chl a doublings. The intracellular Fe was primarily used for cell generation rather than Chl a production, leading to a reduction in the Chl a cell quota in the Fe-starved cells with time. The metabolic properties of the Fe-starved cells with their cell morphologies
were different among species or genera. An on-deck incubation experiment also exhibited 1.9 cell divisions and 0.81 Chl a doublings of phytoplankton after the addition of DFB, also indicating the preference of cell generation over Chl a production. A decrease in the level of cellular Chl a, a main light-harvesting pigment in Fe-starved diatoms, may become a superior survival strategy to protect the cells from
high irradiance that can cause photo-oxidative damages through photosynthesis. Such relatively low-Fe with high-light conditions
could often occur in surface waters of the Oyashio region from spring to summer. 相似文献