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51.
Yutaka Nagata 《Journal of Oceanography》1979,35(1):26-35
The nature of the autocovariance function and power spectrum of time series of spike-array type is discussed. As the spacing of spikes is not easily seen directly in power spectrum, prudence should be exercised in interpreting the gradient spectrum of oceanic fine-structure. We calculated the autocovariance function and lag joint probability density of the record of the vertical profile of the vertical temperature gradient measured in the San Diego Trough. The results obtained support the results of the bispectral analysis in the previous paper (Nagata, 1978) that the predominant length scale of about 5 m has two meanings: spacing of the spikes and wavelength of a sinusoidal wave. The results seem to show the existence of nernal waves having a vertical wavelength the same as the spacing of the spikes or the thickness of the homogeneous layer in the oceanic fine-structure. 相似文献
52.
Tomoharu?SenjyuEmail author Yutaka?Isoda Takafumi?Aramaki Shigeyoshi?Otosaka Shinzo?Fujio Daigo?Yanagimoto Takashi?Suzuki Kenshi?Kuma Kosuke?Mori 《Journal of Oceanography》2005,61(6):1047-1058
Hydrographic observations have revealed detailed structure of the Bottom Water in the Japan Sea. The Yamato Basin Bottom Water
(YBBW) exhibits higher temperatures and lower dissolved oxygen concentrations than those found in the Japan Basin Bottom Water
(JBBW). Both Bottom Waters meet around the boundary region between the Yamato and the Japan Basins, forming a clear benthic
front. The structure of the benthic front suggests an estuary-like water exchange between both Basins, with the inflow from
the Japan Basin passing under the outflow from the Yamato Basin. It is inferred from the property distributions that the JBBW
flowing into the Yamato Basin is entrained by the cyclonic circulation in the basin, and modified to become the YBBW. Vertical
diffusion and thermal balance in the YBBW are examined using a box model. The results show that the effect of geothermal heating
has about 70% of the magnitude of the vertical thermal diffusion and both terms cancel the advection term of the cold JBBW
from the Japan Basin. The box model also estimates the turnover time and vertical diffusivity for the YBBW as 9.1 years and
3.4 × 10−3 m2s− 1, respectively. 相似文献
53.
Stokes' expansion is applied to the internal waves of finite amplitude, which propagate on the interface between two layers of infinite thickness. Stream function, wave profile, phase velocity and mass transport velocity are given in the fifth order approximation. It is shown that (a) phase velocity increases with increase of wave steepness, (b) mass transport appears in the direction of the wave propagation in both layers as in the case of the surface waves, and (c) when the density difference is very small, the wave profile is flattened not only at the troughs but also at the crests. 相似文献
54.
The behavior of the water wedge advancing along the interface between two homogeneous layers is investigated experimentally. The horizontally intruding wedge is strongly influenced by the detailed structure of the interface, even when the interface is sharp enough for its position to be visually determined. Within our experimental range, the intrusion velocity is very slow and depends on the thickness of the interface along which the water wedge intrudes. The wedge length is well described by the relation which is derived using an analogy to the linearly stratified case. The results could be useful for understanding the generation mechanism of the oceanic microstructure. 相似文献
55.
239, 240Pu,137Cs and90Sr concentrations were determined in sea waters from the central and western North Pacific in 1980 and 1982. The results are
consistent with those reported earlier for North Pacific waters. The profiles of90Sr and137Cs show a monotonic decrease with depth, whilst239, 240Pu shows a distinct subsurface maximum at a depth between 400 and 1,000 m.
The calculated inventories of these nuclides significantly exceed the global mean fallout inputs for these latitudes. This
may be due to local fallout input to the ocean at times of large-scale nuclear weapon tests in the equatorial North Pacific.
The existence of measurable amounts of137Cs and239, 240Pu in deep waters suggests that these nuclides are transported by sinking particulate matter from the surface to the deep
ocean. 相似文献
56.
We found a simple function of pH that relates to sea surface temperature (SST, K) and chlorophyll-a (Chl, µg l−1) using measured surface seawater pH, SST and Chl data sets over the North Pacific: pH (total hydrogen scale at 2°C) = 0.01325 SST − 0.0253 Chl + 4.150 (R2 = 0.95, p < 0.0001, n = 483). Moreover, evaluating the seasonal variation of pH based on this algorithm, we compared the measured pH with the predicted pH at the observational time series stations in subpolar and subtropical regions. The average of ΔpH (measured - predicted, n = 52) was 0.006 ± 0.022 pH. Therefore, the combination of SST and Chl can allow us to determine the spatiotemporal distribution of pH over the North Pacific. Using the climatological data sets of SST and Chl with our pH algorithms, we have described the seasonal distributions of pH at 25°C (pH(25)) and pH in situ temperature (pH(T)) over the North Pacific surface water. 相似文献
57.
Yutaka?W.?WatanabeEmail author Hiroshi?Ishida Toshiya?Nakano Naoki?Nagai 《Journal of Oceanography》2005,61(6):1011-1016
Using time series of hydrographic data in the wintertime and summertime obtained along 137°E from 1971 to 2000, we found that
the average contents of nutrients in the surface mixed layer showed linear decreasing trends of 0.001∼0.004 μmol-PO4 l−1 yr−1 and 0.01∼0.04 μmol-NO3 l−1 yr−1 with the decrease of density. The water column Chl-a (CHL) and the net community production (NCP) had also declined by 0.27∼0.48
mg-Chl m−2 yr−1 and 0.08∼0.47 g-C-NCP m−2 yr−1 with a clear oscillation of 20.8±0.8 years. These changes showed a strong negative correlation with the Pacific Decadal Oscillation
Index (PDO) with a time lag of 2 years (R = 0.89 ± 0.02). Considering the recent significant decrease of O2 over the North Pacific subsurface water, these findings suggest that the long-term decreasing trend of surface-deep water
mixing has caused the decrease of marine biological activity in the surface mixed layer with a bidecadal oscillation over
the western North Pacific. 相似文献
58.
On the basis of the model proposed by Matsui and Abe, we will show that two major factors — distance from the Sun and the efficiency of retention of accretional energy — control the early evolution of the terrestrial planets. A diagram of accretional energy versus the optical depth of a proto-atmosphere provides a means to follow the evolutionary track of surface temperature of the terrestrial planets and an explanation for why the third planet in our solar system is an aqua-planet. 相似文献
59.
Changes in the lower limit of mountain permafrost between 1973 and 2004 in the Khumbu Himal, the Nepal Himalayas 总被引:2,自引:0,他引:2
Kotaro Fukui Yoshiyuki Fujii Yutaka Ageta Katsuhiko Asahi 《Global and Planetary Change》2007,55(4):251-256
Because the Khumbu Himal of the Nepal Himalayas lacks long-term climate records from weather stations, mountain permafrost degradation serves as an important indicator of climate warming. In 1973, the permafrost lower limit was estimated to be 5200–5300 m above sea level (ASL) on southern-aspect slopes in this region. Using ground-temperature measurements, we examined the mountain permafrost lower limit on slopes with the same aspect in 2004. The results indicate that the permafrost lower limit was 5400–5500 m ASL in 2004. The permafrost lower limit was estimated to be 5400 to 5500 m on slopes with a southern aspect in the Khumbu Himal in 1991 using seismic reflection soundings. Thus, it is possible that the permafrost lower limit has risen 100–300 m between 1973 and 1991, followed by a stable limit of 5400 to 5500 m over the last decade. An increase in mean annual air temperature of approximately 0.2 to 0.4 °C from the 1970s to the 1990s has indicated a rise in the permafrost lower limit of 40 to 80 m at the Tibetan Plateau. The rise in the mountain permafrost lower limit in the Khumbu Himal exceeds that of the Tibetan Plateau, suggesting the possibility of greater climate warming in the Khumbu Himal. 相似文献
60.
Paleomagnetism of the middle Cretaceous Iritono granite in the Abukuma region, northeast Japan 总被引:1,自引:0,他引:1
Ken-ichi Wakabayashi Hideo Tsunakawa Nobutatsu Mochizuki Yuhji Yamamoto Yutaka Takigami 《Tectonophysics》2006,421(1-2):161-171
We have studied the paleomagnetism of the middle Cretaceous Iritono granite of the Abukuma massif in northeast Japan together with 40Ar–39Ar dating. Paleomagnetic samples were collected from ten sites of the Iritono granite (102 Ma 40Ar–39Ar age) and two sites of its associated gabbroic dikes. The samples were carefully subjected to alternating field and thermal demagnetizations and to rock magnetic analyses. Most of natural remanent magnetizations show mixtures of two components: (1) H component, high coercivity (Bc > 50–90 mT) or high blocking temperature (Tb > 350–560 °C) component and (2) L component, relatively low Bc or low Tb component. H component was obtained from all the 12 sites to give a mean direction of shallow inclination and northwesterly declination (I = 29.9°, D = 311.0°, α95 = 2.7°, N = 12). This direction is different from the geocentric axial dipole field at the present latitude (I = 56.5°) and the typical direction of the Cenozoic remagnetization in northeast Japan. Since rock magnetic properties indicate that the H component of the Iritono granite is carried mainly by magnetite inclusions in plagioclase, this component probably retains a primary one. Thus the shallow inclination indicates that the Abukuma massif was located at a low latitude (16.1 ± 1.6°N) about 100 Ma and then drifted northward by about 20° in latitude. The northwesterly deflection is attributed mostly to the counterclockwise rotation of northeast Japan due to Miocene opening of the Japan Sea. According to this model, the low-pressure and high-temperature (low-P/high-T) metamorphism of the Abukuma massif, which has been well known as a typical location, would have not occurred in the present location. On the other hand, the L component is carried mainly by pyrrhotite and its mean direction shows a moderate inclination and a northwesterly declination (I = 42.8°, D = 311.5°, α95 = 3.3°, N = 9). Since this direction is intermediate between the H component and early Cenozoic remagnetization in northeast Japan, some thermal event would have occurred at lower temperature than pyrrhotite Curie point ( 320 °C) during the middle Cretaceous to early Cenozoic time to have resulted in partial remagnetization. 相似文献