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排序方式: 共有193条查询结果,搜索用时 15 毫秒
1.
Hari Om Vats M. R. Deshpande K. N. Iyer Tetsuro Kondo Takeshi Isobe 《Astrophysics and Space Science》1996,243(1):251-254
This article describes the observations of a type III radio burst observed at 103 MHz simultaneously by the two radio telescopes situated at Rajkot (22.3°N, 70.7°E) and Thaltej (23°N, 72.4°E). This event occurred on September 30, 1993 at about 0430 UT and lasted for only half a minute. The event consisted of several sharp spikes in a group. The rise and fall time of these are comparable, however the peaks of individual spikes varied by a factor of four. The comparison of these observations with the data of solar radio spectrograph HiRAS indicates that this was a metric radio burst giving highest emission at about 103 MHz. 相似文献
2.
Yoichi?ShimadaEmail author Atsushi?Kubokawa Kay?I.?Ohshima 《Journal of Oceanography》2005,61(5):913-920
Recent observations suggest that the annual mean southward transport of the East Sakhalin Current (ESC) is significantly larger
than the annual mean Sverdrup transport. Motivated by this observational result, transport of a western boundary current has
been investigated using a simple numerical model with a western slope. This transport is defined as the instantaneous barotropic
transport integrated from the western boundary to the offshore point where the barotropic velocity vanishes. The model, forced
by seasonally varying wind stress, exhibits an annual mean of the western boundary current transport that is larger than that
of the Sverdrup transport, as observed. The southward transport from October to March in the model nearly equals the instantaneous
Sverdrup transport, while the southward transport from April to September decreases slowly. Although the Sverdrup transport
in July vanishes, the southward transport in summer nearly maintains the annual mean Sverdrup transport, because the barotropic
Rossby wave cannot intrude on the western slope. This summer transport causes the larger annual mean. Although there are some
uncertainties in the estimation of the Sverdrup transport in the Sea of Okhotsk, the seasonal variation of the southward transport
in the model is qualitatively similar to the observations. 相似文献
3.
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
4.
Mesozoic brackish-water bivalve faunas in Japan diversified in three steps: at the beginning of the Early Jurassic, Early and Late Cretaceous. The Hettangian Niranohama Fauna in northeastern Honshu represents the establishment of a heterodont-dominated brackish-water fauna that persisted until the early Late Cretaceous. No similar composition is known from the Triassic. The infauna consists mostly of non-siphonate and some short-siphonate heterodonts, while the epifauna is represented by diverse pteriomorphian families. In the Early Cretaceous Tetori Group in central Honshu, the long-siphonate heterodonts Tetoria (Corbiculidae) and the semi-infaunal soft-bottom oyster Crassostrea appeared. The evolutionary diversification of the latter, known as the most important element of modern brackish-water faunas, may thus originate at that time. In the early Late Cretaceous (Cenomanian) of the Goshoura and Mifune Groups in west Kyushu, several euryhaline deep-burrowing heterodont families, such as Veneridae and Tellinidae, further diversified in the brackish and marine environments. The Late Cretaceous is characterized by massive shell biolithic beds in which large Crassostrea species are common, a feature common for Cenozoic brackish-water faunas. The long-term changes in the composition of the brackish-water faunas in Japan represents thus an evolutionary record, irrespective of the severe physiological and environmental conditions imposed on the highly conservative nature of the fauna. 相似文献
5.
Jule Xiao Yoshio Inouchi Hisao Kumai Shusaku Yoshikawa Yoichi Kondo Tungsheng Liu Zhisheng An 《Quaternary Research》1997,47(3):277-283
The record of the biogenic silica flux (BSF, g cm−2(103yr)−1) in Lake Biwa reflects changes in diatom productivity in the lake and provides information regarding changes in paleoclimatic conditions. The BSF record of Lake Biwa demonstrates five periods over the past ca. 145,000 yr when the BSF values were significantly greater than 7.5 g cm−2(103yr)−1, and five intervals when they were lower. The data imply that paleoclimatic conditions were warmer and wetter from ca. 123,000 to 115,000, 103,000 to 95,000, 88,000 to 72,000, 57,000 to 32,000 yr B.P., and around ca. 6000 yr B.P. when the BSF values were greater, and relatively dry and cold from ca. 141,000 to 123,000 yr B.P. and during intervals between two of the five warm and wet episodes when the BSF values were lower. Time series of the BSF record can be correlated with the record of biogenic silica content in Lake Baikal and the marine oxygen isotope stages 1 through 6. Furthermore, the BSF values varied with much higher amplitude during the last interglaciation than during the last glaciation, probably implying that the diatom productivity in Lake Biwa was likewise more variable and had a larger range under interglacial conditions than under glacial conditions. 相似文献
6.
Yoichi Fukuda Toshihiro Higashi Shuzo Takemoto Maiko Abe Sjafra Dwipa Dendi Surya Kusuma Achmad Andan Koichiro Doi Yuichi Imanishi Giuseppe Arduino 《Journal of Geodynamics》2004,38(3-5):489
For the purposes of the calibration of the superconducting gravimeter (SG) in Bandung and the establishment of the absolute gravity (AG) points, we carried out AG measurements for the first time in Indonesia in November 2002. The measurements in Bandung were conducted between November 15th and 20th by means of a FG5 (#210), and 14,520 effective drops were obtained. The gravity value newly determined at the AG point in Bandung is 977976701.2 μgal (1 μgal = 10−8 ms−2) and the scale factor for the SG is −52.22 μgal/V. We also established another AG point in Yogyakarta near Merapi volcano and carried out AG measurements in Yogyakarta between November 22nd and 26th. The gravity value determined for this station is 978203093.5 μgal. 相似文献
7.
A Simple Single-Layer Urban Canopy Model For Atmospheric Models: Comparison With Multi-Layer And Slab Models 总被引:26,自引:7,他引:26
Hiroyuki Kusaka Hiroaki Kondo Yokihiro Kikegawa Fujio Kimura 《Boundary-Layer Meteorology》2001,101(3):329-358
We developed a simple, single-layer urban canopy model, and comparedit to both multi-layer and slab models. Our single-layer model has thefollowing features: (a) It is a column model of energy and momentumexchange between an urban surface and the atmosphere, (b) it includesthe influence of street canyons, which are parameterized to representthe urban geometry, (c) it includes shadowing from buildings andreflection of radiation, and (d) it estimates both the surfacetemperatures of, and heat fluxes from, three surface types: roof, wall,and road. In the simulation of the single-layer model, the roof washottest during the daytime, but coolest from midnight to early morning.This is consistent with output from the multi-layer model and fieldobservations at a residential area on a clear, summer day. The diurnalvariation of the energy budget from the single-layer model agrees wellwith that from the multi-layer model. Our single-layer model'sperformance is nearly that of a multi-layer model for studyingmesoscale heat islands. Nevertheless, it is simply parameterized,and thus easily included in larger-scale atmospheric models. The slabmodel has the largest nighttime cooling rate of the three models. Toovercome this, it needs more adjustments than for the canopy models. 相似文献
8.
Aerodynamic roughness over an inhomogeneous ground surface 总被引:4,自引:0,他引:4
The aerodynamic roughness parameter z
0 over inhomogeneous ground surfaces, such as cities, rural towns and so on, is determined by analyzing the wind data at AMeDAS observatories in the Tohoku and Kanto districts of Japan, by making use of Rossby number similarity theory. It is found that the aerodynamic roughness parameter is proportional to the average size of the roughness elements.A practical method of estimating the aerodynamic roughness parameter over an extensive area with various inhomogeneities is developed. In this method, the Digital National Land Information data bank is employed. As an example, the roughness parameter distribution around Tsukuba Academic City is presented. 相似文献
9.
Tomohiro Nakamura Takahiro Toyoda Yoichi Ishikawa Toshiyuki Awaji 《Journal of Oceanography》2010,66(1):41-60
A steady quasi-geostrophic 2.5-layer model, forced by both Ekman pumping and a mass source/sink situated at the western boundary
has been constructed to investigate the effect of diapycnal transport due to convection in the Okhotsk Sea and tidal mixing
at the Kuril Straits on the intermediate layer in the North Pacific. The model illustrates a combined effect of the wind-driven
and mass-driven circulations. First, net mass input induces a “barotropic” mode inter-gyre flow along the western boundary
through the dynamical influence of Kelvin waves. This flow creates characteristic curves (geostrophic contours) that facilitate
inter-gyre communication through the western boundary layer from the location of the mass source to the subtropical gyre.
Due to the effect of wind-driven circulation, the offshore part turns eastward into the interior, encircles the outer rim
of the region (which would otherwise be the pool region in the absence of mass input), and then encounters the western boundary.
Eventually, the water fed into the lower layer flows mostly along this path and later flows away to the equatorial region.
Conversely, in the upper layer, water is fed from the equator to the subtropics, and to the subpolar interior region through
the western boundary current. The water then circulates along the outer rim and is absorbed into the mass sink. The model
is controlled mainly by three nondimensional parameters: (1) the ratio of net mass input rate to the maximum Sverdrup transport
(Q/T
Sv
max
), which affects the inter-gyre communication by altering the paths of geostrophic contours, (2) the ratio of a mass input
rate into the lower layer to that in total (Q
2/Q), which controls the vertical structure of the inter-gyre flow, and (3) the measure of the wind forcing effect relative to
the β effect, which determines the horizontal extent of the area influenced by the mass input. The other parameter regimes with
respect to Q/T
Sv
max
and Q
2/Q are also presented. 相似文献
10.
Macroscopic criteria for Green type porous materials with spheroidal voids: application to double porous materials
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Combined effects of matrix plastic compressibility and void shape are investigated for ductile porous materials. To this end, a spheroidal volume containing a confocal spheroidal (prolate or oblate) void subjected to uniform strain rate boundary conditions has been first studied. A Green type matrix is chosen as a prototype for investigating effects of plastic compressibility. This is carried out by using a kinematics limit analysis theory from which a closed‐form expression of the macroscopic criterion is established for the considered class of materials. These results are then extended to ductile porous materials made up of a green matrix containing randomly oriented spheroidal voids. In the framework of a two‐step homogenization procedure, the obtained results are implemented to describe the macroscopic behavior of double porous materials involving spherical voids at the microscale and randomly oriented and distributed spheroidal voids at the mesoscale. For validation purpose, the new derived criteria are assessed and validated by comparing their predictions to available upper bounds and numerical data from literature. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献