Scientific role of ACA for low-mass star-formation study     

Shigehisa Takakuwa  Daisuke Iono  Baltasar Vila-Vilaro  Tomohiko Sekiguchi  Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):169-173

We discuss the scientific role of the Atacama Compact Array (ACA), the Japanese contribution to the ALMA project, for low-mass star-formation study. Our recent observations of several low-mass protostellar envelopes in the submillimeter CS (J=7–6) and HCN (J=4–3) lines with the SMA and ASTE have revealed that these submillimeter emissions are more extended than ∼2000 AU and show different velocity structures from those traced by millimeter lines. These results suggest the importance of taking short-spacing informations the ACA can offer. Our comprehensive imaging simulations of these protostellar envelopes, as well as prestellar cores and debris disks, unprecedentedly demonstrate the scientific importance of ACA.  相似文献   

Asteroids approaching the Earth from directions around the Sun     

Syuzo Isobe  Makoto Yoshikawa 《Earth, Moon, and Planets》1996,72(1-3):263-266

We have estimated close asteroid encounters with the Earth by numerical integrations of a system with the Sun, 9 planets, and 188 near-earth-asteroids during the period 1994–4600. Asteroids approach the Earth from directions within 30? around the Sun in more than 20% of encounters with the closest distance less than 0.01 AU. Since ground-based observations cannot detect these objects, we should develop space-borne and/or lunar observatories in a short time to allow enough warning time before a catastrophic collision.  相似文献   

Seasonality of the Kuroshio Transport Revealed in a Kuroshio Assimilation System   总被引：2，自引：2，他引：2  

Atsuhiko Isobe  Masafumi Kamachi  Yukio Masumoto  Hiroshi Uchida  Tsurane Kuragano 《Journal of Oceanography》2004,60(2):321-328

The seasonal variation of the Kuroshio transport south of Japan has been investigated using the results of an assimilation model. Annual and semiannual variations of the transport and dynamic depth anomaly are reconstructed by CEOF (complex orthogonal empirical function) analysis. In the basin west of the Izu-Ogasawara Ridge, the annual component of the variation propagates westward with the phase speed of the long Rossby wave associated with the first baroclinic mode. The variation also shows a similar tendency to that reproduced in a wind-driven, two-layer model with a ridge. This suggests that the annual variation revealed in the assimilation model is associated with the baroclinic first mode of motion excited above the Izu-Ogasawara Ridge. Furthermore, it is found that both the semiannual component and the annual component are important members determining the seasonal variation of the Kuroshio transport south of Japan. The semiannual component is revealed as a double gyre pattern in the basin west of the Izu-Ogasawara Ridge. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Reliability of ADCP data detided with a numerical model on the East China Sea shelf   总被引：2，自引：0，他引：2  

Atsuhiko Isobe  Takahiro Kuramitsu  Hirotaka Nozaki  Pil-Hun Chang 《Journal of Oceanography》2007,63(1):135-141

The reliability of a numerical tide model for detiding acoustic Doppler current profiler (ADCP) data is examined on the East China Sea shelf. The process is adopted for the ADCP data obtained on 12–13 May 2003. The ocean model accompanied by the most precise harmonic constants available to public is used to compute external tides. The root mean square difference is less than 10 cm/s between the detided currents and those using the least squares method, and so the detiding process using the numerical model is available to detect the East China Sea shelf circulation faster than this speed.  相似文献   

Operational Data Assimilation System for the Kuroshio South of Japan: Reanalysis and Validation   总被引：3，自引：5，他引：3  

Masafumi Kamachi  Tsurane Kuragano  Hiroshi Ichikawa  Hirohiko Nakamura  Ayako Nishina  Atsuhiko Isobe  Daisuke Ambe  Masazumi Arai  Noriaki Gohda  Satoshi Sugimoto  Kumi Yoshita  Toshiyuki Sakurai  Francesco Uboldi 《Journal of Oceanography》2004,60(2):303-312

We describe an operational ocean data assimilation system for the Kuroshio and its validation using a nine-year reanalysis (historical run from 1993 to 2001) dataset of upper-ocean state estimation in the North Pacific. The horizontal structure of volume transport of the Ryukyu Current System (RCS) is shown from the reanalysis: The RCS is connected to the flow of the subtropical gyre, and its volume transport gradually increases from south-east of Okinawa (5–10 Sv) to the east of Amami-Ohshima Island (20 Sv). Comparing the reanalysis with independent observations on the southeast slope of the Amami-Ohshima Island indicates that the root mean square differences (RMSDs) are 0.076 (0.037) m/s in the period of December 1998 to November 1999 (November 1999 to November 2000) respectively. The reanalysis field has a bias (3.1 Sv) of the volume transport of the RCS and the RMSD (3.5 Sv) which is larger than the observed variability (2.81 Sv). Surface velocity and the Kuroshio axis south of Japan are also examined. Comparison of the reanalysis and ADCP data gave maximum RMSD of 0.749 (0.271) m/s in the strong (weak) current regions, respectively. The annual mean value of the axis error is 19 km in 1998. The RMSD of the error is at most 50 km, in 294 cases in the observation period, which is smaller than the observed root mean square variability of the axis (64 km). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Seasonal variation of the vertically averaged flow caused by the Jebar effect in the Tsushima Strait   总被引：1，自引：0，他引：1  

Isobe  Atsuhiko 《Journal of Oceanography》1994,50(6):617-633

The seasonal variation in the barotropic mode of motion caused by joint effect of the baroclinicity and bottom relief (Jebar effect) in the Tsushima Strait is investigated with the use of the diagnostic numerical model in this study. The Jebar effect in the Tsushima Strait is mainly caused by the intrusion of the Bottom Cold Water along the Korean coast in summer. This Jebar effect along the Korean coast locally supplies the negative vorticity in situ, and it forces the coastal current to be intensified. In summer, the volume transport of the Tsushima Warm Current entering the Tsushima Strait is biassed to the western part of the strait comparing with the flow pattern calculated in winter.  相似文献   

The Circulation in the Upper and Intermediate Layers of the South China Sea   总被引：4，自引：0，他引：4  

Atsuhiko Isobe  Takaya Namba 《Journal of Oceanography》2001,57(1):93-104

The circulation in the basin of the South China Sea is reproduced using a four-layer numerical model. Current fields in the second (upper) and third (intermediate) layers are emphasized. Three eddies coexist in the upper layer in summer. The circulation pattern in this layer is similar to that in the first (surface) layer. In winter, a cyclonic circulation occupies the entire basin of the South China Sea in the upper layer as in the surface layer. On the other hand, the circulation pattern in the intermediate layer is fairly different from that in upper two layers especially in winter. A double-gyre pattern appears in the intermediate layer during winter. The pattern is caused by the propagation of the baroclinic Rossby wave of the second mode. This wave is excited at onset of the winter monsoon wind. Such circulation pattern well explains the observed salinity distribution in the intermediate layer. Although the double-gyre pattern in the intermediate layer is revealed even in summer in this model, it is restricted in the western part of the basin. Besides, its current speed is small compared to that in winter.  相似文献   

Low-Frequency Temperature Variability at Fukue Island Located Southwest of the Tsushima Straits     

Atsuyoshi Manda  Atsuhiko Isobe  Kouichi Omura  Yusaku Kyozuka 《Journal of Oceanography》2000,56(2):141-152

Sea surface temperature (SST) and sea surface salinity variations at Fukue Island (located southwest of the Tsushima Straits) were investigated. In spring, low-frequency SST fluctuations with periods of 10–20 days predominate. Synthetic analysis of in situ observation and satellite infrared image reveals that these SST fluctuations are caused by movement of mixed warm water masses which have a temperature intermediate between those of the Kuroshio and the East China Sea (ECS) shelf waters. Since these fluctuations do not correspond with those in the Tsushima Straits, it is indicated that these water masses can hardly pass the Tsushima Straits while retaining their original water properties. In July, SST fluctuations with a period of several days are also found at Fukue Island. Since these SST fluctuations show an opposite correspondence with its salinity fluctuations and a good correspondence with the SST fluctuations at Okinoshima in the Tsushima Straits, it is inferred that warm and low-salinity water originated from the ECS shelf water causes these fluctuations and intrudes into the Tsushima Straits.  相似文献   

Japanese 0.5 m AND 1.0 m telescopes for near-earth asteroid observations     

Syuzo Isobe  Japan Spaceguard Association 《Astrophysics and Space Science》2000,273(1-4):121-126

To make detection andfollow-up observations of near-earth asteroids (NEOs), a new project tobuild 0.5 m and 1.0 m telescopes has been started with a support of theScience and Technology Agency in Japan. These are the first telescopesdesigned from its beginning to dedicate specifically to the NEOobservations and are expected to be one of the most efficient telescopesfor the NEO observations.It is expected to obtain several ten giga-bytedata per one clear night. Such large numbers of data are able to sharewith international groups. These sharing activities will contribute 1)for us to obtain data of asteroid with the lowest level of signal, and2) for those groups to study how to reduce astronomical data.  相似文献   

Light Pollution and its Energy Loss   总被引：3，自引：0，他引：3  

S.I. Isobe  S. Hamamura 《Astrophysics and Space Science》2000,273(1-4):289-294

Data obtained by US DMSP satellites were analyzed to obtain light energyin order to monitor light pollution at different countries. Light detectedby the satellites is one ejected to space and is not mostly used toilluminate objects to be seen. This light is energy loss and produce lightpollution for astronomical observation. We should reduce such energy lossand light pollution.  相似文献