Comparison of Kuroshio surface velocities derived from satellite altimeter and drifting buoy data   总被引：2，自引：0，他引：2  

Hiroshi Uchida  Shiro Imawaki  Jian-Hwa Hu 《Journal of Oceanography》1998,54(1):115-122

Sea-surface geostrophic velocities for the Kuroshio region calculated from TOPEX/POSEIDON altimetry data together within situ oceanographic data are compared with surface velocities derived from drifting buoy trajectories. The geostrophic velocities agree well with the observed velocities, suggesting that the Kuroshio surface layer is essentially in geostrophic balance, within measurement error. The comparison is improved a little when the centrifugal acceleration is taken into account. The observed velocities are divided into the temporal mean and fluctuation components, and the partitioning of velocities between these two components is examined. For the Kuroshio region, most of the fluctuation components of the velocities derived from drifting buoys are found to be positive. This result suggests that Eulerian mean velocities for the Kuroshio region estimated from drifting buoy data tend to be larger than actual means, due to the buoy’s tendency to sample preferentially in the high-velocity Kuroshio.  相似文献   

Energetics and Dynamics of an Impulsive Flare on March 10, 2001     

Ramesh Chandra  Rajmal Jain  Wahab Uddin  Keiji Yoshimura  Takeo Kosugi  Taro Sakao  Anita Joshi  M. R. Deshpande 《Solar physics》2006,239(1-2):239-256

We present Hα observations from ARIES (Nainital) of a compact and impulsive solar flare that occurred on March 10, 2001 and which was associated with a CME. We have also analyzed HXT, SXT/Yohkoh observations as well as radio observations from the Nobeyama Radio Observatory to derive the energetics and dynamics of this impulsive flare. We coalign the Hα, SXR, HXR, MW, and magnetogram images within the instrumental spatial-resolution limit. We detect a single HXR source in this flare, which is found spatially associated with one of the Hα bright kernels. The unusual feature of HXR and Hα sources, observed for the first time, is the rotation during the impulsive phase in a clockwise direction. We propose that the rotation may be due to asymmetric progress of the magnetic reconnection site or may be due to the change of the peak point of the electric field. In MW emission we found two sources. The main source is at the main flare site and another is in the southwest direction. It appears that the remote source is formed by the impact of accelerated energetic electrons from the main flare site. From the spatial correlation of multiwavelength images of the different sources, we conclude that this flare has a three-legged structure.  相似文献   

Elastic wave velocity monitoring as an emerging technique for rainfall-induced landslide prediction     

Yulong Chen  Muhammad Irfan  Taro Uchimura  Guanwen Cheng  Wen Nie 《Landslides》2018,15(6):1155-1172

Landslides are recurring phenomena causing damages to private property, public facilities, and human lives. The need for an affordable instrumentation that can be used to provide an early warning of slope instability to enable the evacuation of vulnerable people, and timely repair and maintenance of critical infrastructure is self-evident. A new emerging technique that correlates soil moisture changes and deformations in slope surface by means of elastic wave propagation in soil was developed. This approach quantifies elastic wave propagation as wave velocity. To verify its applicability, a series of fixed and varied slope model tests, as well as a large scale model test, were conducted. Analysis of the results has established that the elastic wave velocity continuously decreases in response of moisture content and deformation, and there was a distinct surge in the decrease rate of wave velocity with failure initiation, soil deformation was thus envisaged to have more significant effect on elastic wave velocity than water content. It is proposed that a warning be issued at switch of wave velocity decrease rate. Based on these observations, expected operation of the elastic wave velocity monitoring system for landslide prediction in the field application is presented. Consequently, we conclude that the elastic wave velocity monitoring technique has the potential to contribute to landslide prediction.  相似文献   

Mechanism and future risk of slope instability induced by extreme rainfall event in Izu Oshima Island,Japan     

Towhata  Ikuo  Goto  Satoshi  Goto  Shigeru  Akima  Takeshi  Tanaka  Junya  Uchimura  Taro  Wang  Gonghui  Yamaguchi  Hiroshi  Aoyama  Shogo 《Natural Hazards》2021,105(1):501-530

Natural Hazards - A volcanic slope in Izu Oshima Island in Japan experienced a profound rain-induced disaster in October 2013. Since this slope had been stable for centuries except for minor...  相似文献   

Latitudinal distribution of soil CO2 efflux and temperature along the Dalton Highway,Alaska   总被引：1，自引：1，他引：0  

Yongwon Kim  Seong-Deog Kim  Hiroyuki Enomoto  Keiji Kushida  Miyuki Kondoh  Masao Uchida 《Polar Science》2013,7(2):162-173

In this paper, we investigate spatial variations in soil CO₂ efflux and carbon dynamics across five sites located between 65.5°N and 69.0°N in tundra and boreal forest biomes of Alaska. Growing and winter mean CO₂ effluxes for the period 2006–2010 were 261 ± 124 (Coefficients of Variation: 48%) and 71 ± 42 (CV: 59%) gCO₂/m², respectively. This indicates that winter CO₂ efflux contributed 24% of the annual CO₂ efflux over the period of measurement. In tundra and boreal biomes, tussock is an important source of carbon efflux to the atmosphere, and contributes 3.4 times more than other vegetation types. To ensure that representativeness of soil CO₂ efflux was determined, 36 sample points were used at each site during the growing season, so that the experimental mean fell within ±20% of the full sample mean at 80% and 90% confidence levels. We found that soil CO₂ efflux was directly proportional to the seasonal mean soil temperature, but inversely proportional to the seasonal mean soil moisture level, rather than to the elevation-corrected July air temperature. This suggests that the seasonal mean soil temperature is the dominant control on the latitudinal distribution of soil CO₂ efflux in the high-latitude ecosystems of Alaska.  相似文献   

C2/c pyroxene phenocrysts from three potassic series in the Neogene alkaline volcanics, NE Turkey: their crystal chemistry with petrogenetic significance as an indicator of P–T conditions     

Faruk Aydin  Richard M. Thompson  Orhan Karsli  Hinako Uchida  Jason B. Burt  Robert T. Downs 《Contributions to Mineralogy and Petrology》2009,158(1):131-147

Chemical and structural data are reported for C2/c pyroxene phenocrysts collected from three potassic series (Group A: basanite-tephrite, Group B: tephrite-phonolitic tephrite, Group C: alkaline basalt-trachybasalt) of the Neogene alkaline volcanics (NAVs) in northeastern Turkey, in order to investigate the evolution of the magmatic plumbing system and the location of magma chamber(s) with crystallization conditions. The rock series hosting the clinopyroxene phenocrysts show generally porphyritic texture and have a variable phenocryst-rich nature (20–58%), with phenocryst assemblages characterized by cpx ± ol ± plag ± foid ± amp ± bio. The clinopyroxene phenocrysts can be chemically classified as Ti- and Fe³⁺-rich Al-diopsides for Groups A and B (AB-cpxs) and Ti- and Fe³⁺-poor Al-diopsides for Group C (C-cpxs). They have poorly variable composition, clustering in the diopside field. Structurally, the diopside groups have nearly similar a (ranging from 9.73 to 9.75 ?), V _cell (437.2–440.9 ?³), and 〈beta〉 angle values (106.01°–106.23°), but some differences in polyhedral parameters and geometries of the AB-cpxs and C-cpxs have been observed. For example, the AB-cpxs are characterized by larger c (5.27–5.30 vs. 5.25–5.28 ?), V _T (2.27–2.30 vs. 2.23–2.28 ?³), and V _M2 (25.53–25.72 vs. 25.41–25.59 ?³) values and smaller b (8.87–8.88 vs. 8.88–8.91 ?) and V _M1 (11.49–11.63 vs. 11.64–11.83 ?³) values with respect to the C-cpxs. In addition, the AB-cpxs show higher values of V _M2/V _M1 (2.20–2.23) due to large V _M2 and small V _M1 compared to the V _M2/V _M1 ratios of the C-cpxs (<2.19). Such differences in the crystal structure of the AB-cpxs and C-cpxs from the NAVs are partly related to different crystallization pressures, but mostly related to variation in melt composition and, possibly, the influence of other crystallizing mineral phases. In particular, R(M2-O1) and R(M1-O2) (i.e. bond lengths) differences in the clinopyroxenes of different groups support the presence of evolved host rocks with different alkaline character (i.e. silica-undersaturated Groups A–B and silica-saturated Group C). Based on the cpx-geothermobarometry, the crystallization pressures for the C-cpxs are lower than 4.5 kbars, but the AB-cpxs have relatively high-pressure values (5.6–10.6 kbars), suggesting that the AB-cpxs crystallized in higher pressure environments. The relatively higher crystallization temperatures of the AB-cpxs also indicate higher cooling rates. The P–T estimates suggest that the source regions of the clinopyroxene phenocrysts from the NAVs were crustal magma chambers in a closed plumbing system at a moderate- to low-pressure regime.  相似文献   

Search for weak white-light flares by time-wise photographic cancellation     

Yutaka Uchida  Hugh Hudson 《Solar physics》1972,26(2):414-417

This study proposes as a working hypothesis that small white-light flares accompany all major (proton) flare events and suggests a new method for systematically finding these patches of white-light emission. The new technique consists of the time-wise application of the photographic cancellation method to detect small time-varying features around the time of the impulsive phase of a flare.  相似文献   

Equilibrium configuration of the magnetosphere of a star loaded with accreted magnetized mass     

Yutaka Uchida  B. C. Low 《Journal of Astrophysics and Astronomy》1981,2(4):405-419

Equilibrium configuration of the magnetosphere of a star loaded by the gravitationally accreted plasma having its own magnetic field is investigated. Axisymmetry around the star’s magnetic axis is assumed for simplicity. It is seen that two distinct configurations appear for the cases of parallel and antiparallel magnetic field of the accreted plasma with respect to the star’s magnetic moment. If the external field is antiparallel to the star’s magnetic moment, the stellar magnetosphere is confined within a spherical region surrounded by the external field with a separatric surface between them. This is an extension of the case of the spherical accretion of non-magnetic plasma dealt with thus far in connection with the mass accretion by the degenerate stars in X-ray binaries. It is noticed that the mass slides down along the field lines to the point closest to the star and is stratified hydrostatically in equilibrium to form a disk in the equatorial plane. The mass loading compresses the sphere as a whole in this case. If, on the other hand, the external field is parallel to the star’s magnetic moment, there appears a ring of magnetic neutral point in the equatorial plane. Polar field is open and extends to infinity while the low-latitude field is closed and faces the external field of opposite polarity across the neutral point. The increase of the loaded mass in this case causes a shrink of the closed field region, and the open polar flux is increased. Therefore, the transition between equilibria with small and large amount of the loaded mass requires the reconnection of magnetic lines of force, and the reconnection of the flux through the magnetic neutral ring is proposed as the mechanism of the steady or the intermittent mass leakage like the ones postulated for some X-ray bursters. Visiting Scientist supported by the Japan Society for the Promotion of Sciences.  相似文献   

Time variation of the spectrum of Gyro-synchrotron emission from the Sun     

Tatsuo Takakura  Yutaka Uchida  Keizo Kai 《Solar physics》1968,4(1):45-57

The emission spectra and their time variations of gyro-synchrotron emission from an ensemble of energetic electrons are computed for some initial power-law distributions of the electron energies N()d= ^– with =2 or 4. The spectra and decay curves of the emission are compared with solar microwave bursts in order to separately estimate the magnetic field H and . From a limited number of observations, we have 3 and H 10³ gauss for the microwave impulsive bursts, and 2 and H (500–1000) gauss for the microwave type-IV bursts.  相似文献   

The Fourier transform of controlled-source time-domain electromagnetic data by smooth spectrum inversion   总被引：1，自引：0，他引：1  

Yuji Mitsuhata  Toshihiro Uchida  Yutaka Murakami  Hiroshi Amano 《Geophysical Journal International》2001,144(1):123-135

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