The development of three-dimensional current system during a magnetospheric substorm     

K. Kawasaki  C.-I. Meng  Y. Kamide 《Planetary and Space Science》1974,22(11):1471-1484

It is suggested that the pattern of three-dimensional substorm current circuit varies significantly even during the lifetime of a single substorm. This gives rise to quite complex time variations of the magnetic field at low latitude stations even for relatively isolated substorms. To verify this, three-dimensional current models with time dependent spatial variations are used to simulate one type of complex low-latitude “substorm signature”. It is shown that the utmost care should be exercised in determining different substorm phases on the basis of such a signature. The results indicate also that, in certain longitudes in the evening sector, one should expect distinct differences in characteristics between positive bays observed on the ground and at the synchronous distance.  相似文献   

Isotopic tracers for water masses in the coastal region of eastern Hokkaido     

Sachiko Oguma  Tsuneo Ono  Akira Kusaka  Hiromi Kasai  Yasuhiro Kawasaki  Tomonori Azumaya 《Journal of Oceanography》2008,64(4):525-539

In this study we used two stable isotopes, δ¹³C and δ¹⁸O, for water mass classification in the coastal region off eastern Hokkaido. δ¹³C* values, which were corrected for the biological effect, and δ ¹⁸O values up to 300 m depth suggested that the isotopic character of the onshore and offshore water in the southern Okhotsk Sea, the Nemuro Strait and the western North Pacific could be explained by the mixing of three source waters: the Oyashio water (OYW), Soya Warm Current water (SWCW) and East Sakhalin Current water (ESCW). In summer, δ ¹³C*-δ ¹⁸O plots indicated mixing between SWCW from the southern Okhotsk Sea and OYW in the Pacific coast of southeastern Hokkaido, while temperature-salinity plots of the onshore water showed minimal difference from the offshore OYW. In winter, on the other hand, the mixed water of ESCW and OYW (or SWCW) appeared in the Pacific coastal region, distributed as cold, low salinity onshore water. Finally, we estimated mixing ratios of OYW, SWCW and ESCW in the coastal region of western North Pacific using their mean values of δ ¹³C* and δ ¹⁸O as endmembers. These results suggest seasonal and yearly changes of water mass combination en route from the southern Okhotsk Sea to the western North Pacific.  相似文献   

Enhanced chlorophyll associated with island-induced cyclonic eddies in the eastern channel of the Tsushima Straits     

Goh Onitsuka  Akihiko Morimoto  Tetsutaro Takikawa  Atsushi Watanabe  Masatoshi Moku  Yutaka Yoshikawa  Tetsuo Yanagi 《Estuarine, Coastal and Shelf Science》2009,81(3):401-408

The relationship between island-induced cyclonic eddies and chlorophyll a (chl-a) was investigated using field data and satellite images in the eastern channel of the Tsushima Straits. The maximum chl-a concentration around the leeward eddy of the Tsushima Islands was two or three times greater than that of outside the eddy. Two different mechanisms of chl-a enhancement associated with island-induced cyclonic eddies were found in the post-bloom periods. In summer, when nutrients were depleted in the surface layer, eddy pumping increased the nutrient supply in the euphotic zone, resulting in enhanced chl-a around the shallow thermocline near the eddy core. In late autumn, when the mixed layer deepened over the euphotic zone, the mixed layer depth became shallow due to the doming effect of the cyclonic eddy, therefore, the improved irradiance condition led to an increase in the chl-a concentration in the surface mixed layer. Nighttime satellite visible images showed a number of fishing vessels in the lee region of the Tsushima Islands, implying that the enhanced phytoplankton biomass may have resulted in good feeding conditions for fishes and squids in the Tsushima Straits.  相似文献   

Seasonal variation of horizontal material transport through the eastern channel of the Tsushima Straits   总被引：2，自引：2，他引：0  

Akihiko Morimoto  Tetsutaro Takikawa  Goh Onitsuka  Atsushi Watanabe  Masatoshi Moku  Tetsuo Yanagi 《Journal of Oceanography》2009,65(1):61-71

We conducted hydrographic observations ten times in the Tsushima Strait to reveal seasonal variations of horizontal material transports such as of heat, freshwater, chlorophyll a, and dissolved inorganic nitrogen (DIN) and phosphorus (DIP) through the eastern channel of the Tsushima Strait (ECTS). The volume, freshwater, and heat transport results are of nearly the same order as results reported in previous studies. The annual mean DIN and DIP transports of 3.59 kmol/s and 0.29 kmol/s are large relative to those of the Changjiang and the Taiwan Strait and are horizontally transported through the ECTS. Nutrient transports are high in July–August and October and low in April and November. Increased nutrient transports in July–August and October are due to the appearance of a cold saline water mass in the bottom layer of the ECTS. Changes in DIN transports in summer and autumn, which account for two-thirds of the total annual DIN transport, would have a large effect on the nitrogen budget and biological productivity in the Tsushima Warm Current region.  相似文献   

Recursive computation of mutual potential between two polyhedra     

Masatoshi Hirabayashi  Daniel J. Scheeres 《Celestial Mechanics and Dynamical Astronomy》2013,117(3):245-262

Recursive computation of mutual potential, force, and torque between two polyhedra is studied. Based on formulations by Werner and Scheeres (Celest Mech Dyn Astron 91:337–349, 2005) and Fahnestock and Scheeres (Celest Mech Dyn Astron 96:317–339, 2006) who applied the Legendre polynomial expansion to gravity interactions and expressed each order term by a shape-dependent part and a shape-independent part, this paper generalizes the computation of each order term, giving recursive relations of the shape-dependent part. To consider the potential, force, and torque, we introduce three tensors. This method is applicable to any multi-body systems. Finally, we implement this recursive computation to simulate the dynamics of a two rigid-body system that consists of two equal-sized parallelepipeds.  相似文献   

Reminiscences of a Japanese Contemporary     

Masatoshi Kitamura 《Astrophysics and Space Science》2005,296(1-4):33-41

It was in 1936 when a young Czech student of age 22 came to Japan through Siberia for participating in the solar eclipse expedition. Since then, he had visited us 13 times until 1993 (when he passed away). At each visit his lectures were vivid for us and had strong impact on the audience. Needless to say, it was the late Professor Zdeněk Kopal. In this brief presentation first I reveal my reminiscences of our common time in Manchester and Japan as a contemporary, and second I make some remarks on my activities for the Japanese Official Development Assistance (ODA) for astronomy in developing countries, in a similar way like Professor Kopal contributed in later years to the development of astronomy mainly in middle-east countries.  相似文献   

A note on the DP-2variation     

S.-I. Akasofu  F. Yasuhara  K. Kawasaki   《Planetary and Space Science》1973,21(12):2232-2238

It is shown that a significant part, if not all, of the DP-2 variation can reasonably be explained by the combined effect of the equatorward expansion of the permanent S_q^p current system and its enhancement. Both phenomena are now found to be controlled by the northsouth component of interplanetary magnetic field. Thus, it is concluded that the DP-2 variation arises from a modulation of the permanently existing S_q^p current system by the interplanetary magnetic field, rather than by an intermittent growth of a particular type of current system.  相似文献   

Short-period interplanetary and polar magnetic field variations     

K. Kawasaki  F. Yasuhara  S.-I. Akasofu 《Planetary and Space Science》1973,21(10):1743-1755

It is shown that the dependence of the variations of vertical component of the polar cap magnetic field on the sector structure (actually, the azimuthal or Y component) of the interplanetary magnetic field as first discovered by Svalgaard (1968) and Mansurov (1969) extends to variations as brief as 1 hr or even less. The relation between sector structure dependent variations and substorm fields as indicated by the southward-directed component of the interplanetary magnetic field is investigated by comparing brief variations over selected intervals of time. The independence of the variations of the polar cap vertical and horizontal components suggests that there are at least two different current systems which produce brief variations in the polar cap. One of the current systems is related to the substonn field; the other is strongly seasonally dependent and is confined to the dayside sector of the Earth.  相似文献   

IGU Working Group on “tropical climatology and human settlements”     

Masatoshi M. Yoshino 《GeoJournal》1981,5(2):179-181

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Book reviews     

Richard M. Hammer  Masatoshi M. Yoshino  K. Cehak 《GeoJournal》1979,3(2):222-224

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