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1.
Near inertial motion excited by wind change in a margin of the Typhoon 9019   总被引：1，自引：0，他引：1  
An excitation of inertial oscillation in the upper layer east of course of Typhoon 9019 was fortuitously observed at three surface buoys deployed during the Ocean Mixed Layer Experiment (OMLET). The observed inertial oscillation was compared with wind fluctuation measured at Ocean Weather Station T (29°N, 135°E) which was placed at the center of a triangle with three vertexes occupied by the respective surface buoys. Inertial oscillation is effectively excited in the mixed layer at the eastern margin of the typhoon by a rapid decrease of wind rather than by prevailing strong wind. It is shown by means of a least square deviation that the inertial oscillation observed in the mixed layer has a period of 23.9 hours shorter than the local inertial period of 24.7 hours. This shorter period suggests that the inertial oscillation has the finite velocities of phase and group as an inertial internal wave. A theoretically obtained ratio of vertical component of group velocity to that of phase velocity, approximately agrees with observed value. The inertial internal wave is excited by fluctuation of divergence with near inertial period in the mixed layer.  相似文献   
2.
Archeological evidence of Pacific salmon in Hokkaido is reviewed and compared with results from western North America. Salmon remains have been found at 24 sites in Hokkaido from the Early Jomon Period to the Ainu Period (6000–100 years ago). Fish remains at three archeological sites in the Kushiro River basin indicated that Pacific salmon (Oncorhynchus spp.) were distributed and utilized from 6000 years ago. The present Kushiro Wetland was formerly covered with seawater and called the Paleo Kushiro Bay 5000–6000 years ago. Based on the molluscan fossil fauna, seawater temperature at Paleo Kushiro Bay was about 5°C warmer than at present. Warmer conditions for salmon in Kushiro 5000–6000 years ago corresponded with the poor conditions for salmon in the Columbia River basin 6000–7000 years ago. If the future global warming is similar to the conditions that prevailed 5000–6000 years ago, the southern limit of salmon distribution will shift northwards and the salmon production will decrease. However, they will not disappear from either Hokkaido or southwestern North America.  相似文献   
3.
The characteristics of the Kuroshio axis south of Kyushu, which meanders almost sinusoidally, are clarified in relation to the large meander of the Kuroshio by analyzing water temperature data during 1961–95 and sea level during 1984–95. The shape of the Kuroshio axis south of Kyushu is classified into three categories of small, medium, and large amplitude of meander. The small amplitude category occupies more than a half of the large-meander (LM) period, while the medium amplitude category takes up more than a half of the non-large-meander (NLM) period. Therefore, the amplitude and, in turn, the curvature of the Kuroshio axis is smaller on average during the LM period than the NLM period. The mean Kuroshio axis during the LM period is located farther north at every longitude south of Kyushu than during the NLM period, with a slight difference west of the Tokara Islands and a large difference to the east. A northward shift of the Kuroshio axis in particular east of the Tokara Islands induces small amplitude and curvature of the meandering shape during the LM period. During the NLM period, the meandering shape and position south of Kyushu change little with Kuroshio volume transport. In the LM formation stage, the variation of the Kuroshio axis is small west of the Tokara Islands but large to the east due to a small meander of the Kuroshio. In the LM decay stage, the Kuroshio meanders greatly south of Kyushu and is located stably near the coast southeast of Kyushu. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
4.
Ocean Science Journal - We evaluated the influence of areas with dissimilar upwelling intensity along the Humboldt Current System on the morphological variation of the economically important sea...  相似文献   
5.
Properties of the index of position of the Kuroshio axis in the Tokara Strait, named the Kuroshio position index (KPI), were examined using sea-level data during 1984–92. The index is KPI=(X+M x )/(Y+M y whereX(Y) is the anomaly of sea-level difference of Nakanoshima (Naze) minus Nishinoomote from the 1984–92 meanM x (M y ). The correlation with the latitude of the Kuroshio axis in the Tokara Strait concluded that the KPI withM x /M y =0.83 and realisticM y (100±40 cm) best indicates the position of the Kuroshio axis in the strait. The KPI withM x =83 cm andM y =100 cm was newly called the KPI as the best index. Using daily values of this KPI, the relation between the position of the Kuroshio in the strait and the large meander of the Kuroshio shown by Kawabe (1995) was confirmed and studied in detail. A large meander forms (ends) 3.3 (5.1) months after a northward (southward) shift of the Kuroshio in the Tokara Strait. Yet, a temporary southward shift with a duration of ten to twenty days does not finish the large-meander (LM) path. At the LM formation, a small meander southeast of Kyushu begins to move eastward associated with the northward shift. The processes of LM formation and decay are started by the meridional move of the Kuroshio axis in the Tokara Strait. The Kuroshio axis at the FES line during the LM path is located farther north by 7 latitude than that during the non-large-meander (NLM) path. The latitude during the LM formation (decay) stage is a little higher (lower) than that during the LM (NLM) period, though the Kuroshio still takes an NLM (LM) path.  相似文献   
6.
During the strong warm El Niño (EN) that occurred in 1997/98, Independence Bay (14°S, Peru) showed a ca. 10 °C increase in surface temperatures, higher oxygen concentrations, and clearer water due to decreased phytoplankton concentrations. Under these quasi-tropical conditions, many benthic species suffered (e.g. macroalgae, portunid crabs, and polychaetes) while others benefited (e.g. scallop, sea stars, and sea urchins). The most obvious change was the strong recruitment success and subsequent proliferation of the scallop Argopecten purpuratus, whose biomass increased fiftyfold. To understand these changes, steady-state models of the bay ecosystem trophic structure were constructed and compared for a normal upwelling year (1996) and during an EN (1998), and longer-term dynamics (1996–2003) were explored based on time series of catch and biomass using Ecopath with Ecosim (EwE) software. Model inputs were based on surveys and landings data collected by the Instituto del Mar del Perú (IMARPE). Results indicate that while ecosystem size (total throughput) is reduced by 18% during EN, mainly as a result of decreased total primary production, benthic biomass remains largely unchanged despite considerable shifts in the dominant benthic taxa (e.g. scallops replace polychaetes as secondary consumers). Under normal upwelling conditions, predation by snails and crabs utilize the production of their prey almost completely, resulting in more efficient energy flow to higher trophic levels than occurs during EN. However during EN, the proliferation of the scallop A. purpuratus combined with decreased phytoplankton increased the proportion of directly utilized primary production, while exports and flows to detritus are reduced. The simulations suggest that the main cause for the scallop outburst and for the reduction in crab and macroalgae biomass was a direct temperature effect, whereas other changes are partially explained by trophic interactions. The simulations suggest that bottom-up effects largely control the system.  相似文献   
7.
A seasonal scale field observation extending over a period of 82?days was conducted in Urauchi Bay on Kami-Koshiki Island, to record meteotsunami events, disastrous secondary oscillations locally known as ??abiki.?? The bay has an elongated T-shape topography with a narrow mouth opening westward to the East China Sea. The area has suffered the effects of meteotsunami causing flooding in residential area and damage to fishing fleets and facilities. A comprehensive observation system for sea level, ocean currents and barometric pressure was deployed to cover the regions within and offshore from Urauchi Bay and the open sea near the island of Mejima in the East China Sea. Vigorous meteotsunami events, where the total height exceeded 150?cm, were observed over five-day periods during the observation period. One or two hours prior to the arrival of meteotsunami events at Kami-Koshiki Island, abrupt 1?C2?hPa pressure changes were observed at the Mejima observation site. Pressure disturbances were found to travel eastward or northeastward. The propagation speed was found to nearly coincide with that of ocean long waves over the East China Sea, and as a result, resonant coupling should be anticipated. The incoming long waves were also amplified by geometric resonance with eigen oscillations inherent in the T-shape topography of Urauchi Bay.  相似文献   
8.
A time series of surface geostrophic velocity is developed using satellite altimetry data during 1992–2010 for a track across the Kuroshio southeast of Kyushu, Japan. The temporal mean geostrophic velocity is estimated by combining the along-track sea level anomaly and shipboard ADCP data. This approximately 6-km resolution dataset is successful in representing the Kuroshio cross-current structure and temporal variation of the Kuroshio current-axis position during 2000–2010. The authors use this dataset to examine the winter Kuroshio path destabilization phenomenon. Its seasonal features are characterized as follows: the velocity shear on the inshore side of the Kuroshio becomes stronger and the Kuroshio path state becomes unstable from the summer to winter. This evidence is consistent with the hypothetical mechanism governing the destabilization phenomenon discussed in a previous study. Furthermore, the interannual amplitude modulation of the seasonality is examined in relation to interannual variations in the winter northerly wind over the northern Okinawa Trough and the Pacific Decadal Oscillation (PDO) index. The destabilization phenomenon appears 15 times in the period 2000–2010. Ten cases are related to local wind effects, and 7 of these are also connected with the PDO index. This is probably because the winter northerly wind over the northern Okinawa Trough is regulated by the PDO signal in interannual time-scales. Only 4 cases are related to the PDO index, but their driving mechanism remains uncertain.  相似文献   
9.
A numerical method, which combines the boundary element method (BEM) and the volume of the fluid method (VOF method), has been presented to solve wave–structure interactions; the intense wave motion at the proximity of the structure is modeled by the VOF method and the rest of the fluid region is modeled by the BEM. The combined method can considerably reduce the time-consuming VOF domain, and thus practically makes it possible to apply the VOF method for random wave calculations, in which long time computations are usually required to obtain statistically meaningful results, and therefore the use of the single-VOF model often becomes prohibitive in terms of computational time and storage memories. A VOF model CADMAS-SURF, which is based on SMAC scheme and had been constructed by a number of VOF researchers in coastal engineering in Japan, is used in the combined BEM–VOF model. The two-way coupling treatment, which enables us to deal with bidirectional wave propagations, which was originally given for the SOLA-VOF model by Yan et al. (2003a) and later improved by Kim et al. (2007), was modified for the SMAC scheme. The coupling treatments are described in detail in the paper. The validity of the combined BEM–VOF model was investigated by comparing the numerical results with the theoretical results for the propagations of Stokes 5th order waves and random waves.  相似文献   
10.
The bottom currents in the Challenger Deep, the deepest in the world, were measured with super-deep current meters moored at 11°22′ N and 142°35′ E, where the depth is 10915 m. Three current meters were set at 9687 m, 10489 m and 10890 m at the station in the center of the Challenger Deep for 442 days from 1 August 1995 to 16 October 1996. Although rotor revolutions in 60 minutes of recording interval were zero for 37.5% of the time, the maximum current at the deepest layer of 10890 m was 8.1 cm s−1, being composed of tidal currents, inertia motion and long period variations. Two current meters were set at 6608 m and 7009 m at a station 24.9 km north of the center for 443 days from 31 July 1995 to 16 October 1996, and two current meters at 6214 m and 6615 m at a station 40.9 km south of the center for 441 days from 2 August 1995 to 16 October 1996. The mean flow at 7009 m depth at the northern station was 0.7 cm s−1 to 240°T, and that at 6615 m depth at the southern station was 0.5 cm s−1 to 267°T. A westward mean flow prevailed at the stations, and no cyclonic circulation with mean flows of the opposite directions was observed in the Mariana Trench at a longitude of 142°35′ E. Power spectra of daily mean currents showed three spectral peaks at periods of 100 days, 28–32 days and 14–15 days. The peak at 100 day period was common to the power spectra.  相似文献   
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