Properties of winter mixed layer variability on the shelf-slope region facing the Kuroshio—study of Tosa Bay, southern Japan     

Hiroshi Kuroda  Yuichi Hirota  Takashi Setou  Kazuhiro Aoki  Daisuke Takahashi  Tomowo Watanabe 《Ocean Dynamics》2014,64(1):47-60

To examine the properties of winter mixed layer (ML) variability in the shelf-slope waters facing the Kuroshio, we analyzed historical temperature records and the simulated results of a triply nested high-resolution numerical model. As a candidate of the shelf-slope waters, we focused on Tosa Bay, off the southern Japan. A time series of observed monthly mean ML temperatures and depths in the bay exhibits a remarkable seasonal variation. The period when the ML develops can be divided into two regimes: from September to November, when the sea surface cooling is gradually enhanced, the ML temperature and depth decreases and increases, respectively; from January to March, the ML temperature and depth are kept nearly constant, while the sea surface cooling in January reaches its annual maximum. In the latter regime, variance for the monthly mean ML depth is the largest of the year. To further study the ML properties in the latter regime corresponding to winter, we examined simulated results. It was found that the largest variance for ML depth is attributed to a dominant intramonthly variation. This is related to a submesoscale variation with typical spatial scales of 10–20 km, induced by the Kuroshio and its frontal disturbances. Simulated monthly mean heat balance within the ML showed that heat advection balances with heat flux at the sea surface and entrainment through the ML bottom. Moreover, the monthly mean heat advection is determined mainly by the intramonthly eddy heat advection, suggesting that the high-frequency intramonthly variation related to submesoscale variations contributes significantly to the low-frequency monthly variations of the ML in winter.  相似文献   

Fifteen years progress of the TRITON array in the Western Pacific and Eastern Indian Oceans     

Kentaro Ando  Yoshifumi Kuroda  Yosuke Fujii  Tatsuya Fukuda  Takuya Hasegawa  Takanori Horii  Yasuhisa Ishihara  Yuji Kashino  Yukio Masumoto  Keisuke Mizuno  Motoki Nagura  Iwao Ueki 《Journal of Oceanography》2017,73(4):403-426

The Triangle Trans‐Ocean Buoy Network (TRITON) project by the Japan Agency for Marine-Earth Science and Technology began with deployment in the western tropical Pacific Ocean in 1998 and has shifted to steady, long-term observations since 1999. After on-site inter-comparison with the Autonomous Temperature Line Acquisition System mooring system of the Tropical Atmosphere and Ocean (TAO) array by the National Oceanic and Atmospheric Administration, the TRITON array became the international TAO/TRITON array in 2000 as a key component of the Global Ocean and Climate Observing Systems. The TAO/TRITON array took over from the TAO array, which was developed during the Tropical Ocean and Global Atmosphere program (1985–1994), and replaced the western part of TAO with new additional real-time measurements of salinity and ocean currents. In 2001, two TRITON moorings were deployed in the eastern Indian Ocean for capturing the eastern pole of the Indian Ocean Dipole. From this initiative, the Indian Ocean Observing System (IndOOS) was designed, and the Indian Ocean mooring array (Research Moored Array for Africa–Asian–Australian Monsoon Analysis and Prediction) was developed as a key component of IndOOS. In this paper, 15 years of progress in the TRITON project in the western Pacific and eastern Indian Oceans is reviewed with regards to scientific outcomes, technological development, and collaborations with international and domestic partners. Future directions for sustainable observation in the Pacific and Indian Oceans are also discussed.  相似文献   

Coastal current on the eastern shelf of Hidaka Bay     

Hiroshi Kuroda  Yutaka Isoda  Hidetaka Takeoka  Satoshi Honda 《Journal of Oceanography》2006,62(5):731-744

In order to examine seasonal variation in a coastal current and the dynamics of the current, we carried out a mooring current measurement near the coast on the eastern shelf of Hidaka Bay from December 2002 to July 2003. There seemed to be two current regimes during the observed period; one a southeastward current from December to March, and the other a northwestward current after April. Arrested topographic wave dynamics was used to understand along-shore steady momentum balance at the mooring site. It was found that the friction term was negligible during the former regime, that is, the wind stress term roughly counterbalanced the pressure gradient term. On the other hand, the contribution of each term to the momentum balance was sensitive to the resistance coefficient value during the latter regime. A numerical study showed that wind forcing alone could not reproduce the observed current velocity and momentum balance during the former regime. One possible interpretation of the observed results is superposition of the arrested topographic waves forced by the along-shore wind stress and downstream extension of the Coastal Oyashio. Numerical experiments using combined forcing of the wind stress and an inflow associated with the Coastal Oyashio supported the expected dynamics.  相似文献   

Occurrence characteristics of chaetognath species along the PM transect in the Japan sea during 1972–2002     

Naoki Nagai  Kazuaki Tadokoro  Kazunori Kuroda  Takashige Sugimoto 《Journal of Oceanography》2006,62(5):597-606

A long-term variation in dominant species of chaetognaths in the Tsushima Warm Current was analyzed using samples collected four times a year from 1972 to 2002 by the Maizuru Marine Observatory along the PM transect in the Japan Sea. Of 19 occurring species, 13 subtropical species formed a major portion of the standing stock. Species richness in the study area was similar to that in the East China Sea and the South China Sea. Four species, Sagitta minima, S. nagae, S. enflata, S. elegans dominated in the upper 150 m water column. The most dominant species per season were S. minima in both winter and autumn, S. elegans in spring and S. nagae in summer. Water temperature and salinity ranges of the most frequent occurrence for three dominant species revealed a common tendency in the order of S. nagae > S. minima > S. enflata towards colder temperature and higher salinity. Inter-annual abundance of chaetognath species fluctuated proportionally in response to the warm or cool phases in water temperature. Water temperature was a fundamental factor in regulating distributional occurrence, being more decisive than salinity. Changes of both dominant species and species numbers in relation to the reduced abundance during winter to spring and the subsequent increase during summer to autumn might be caused by specific differences in optimum temperature. Chaetognath species are important as an indicator of water masses and significant for our understanding of changes and evaluations of the Japan Sea ecosystem.  相似文献   

Two Modes of Salinity and Temperature Variation in the Surface Layer of the Pacific Warm Pool     

Kentaro Ando  Yoshifumi Kuroda 《Journal of Oceanography》2002,58(4):599-609

The characteristics of temperature and salinity variation in the Pacific warm pool were investigated using Empirical Orthogonal Function (EOF) analysis on one year's temperature and salinity data in the surface layer (0–50 m) obtained from the Triangle Trans-Ocean Buoy Network (TRITON) buoy array. Two dominant modes of surface temperature and salinity variation were found. One is a positive correlation mode where temperature and salinity were scattered almost parallel to isopycnal lines in a T-S diagram, which has little effect on the density field. The other is a negative correlation mode where temperature and salinity were distributed across isopycnal lines, which has a substantial impact on the density field. In particular, we found that the negative correlation mode at 5°N, 156°E was predominant on a seasonal time scale and contributed to the surface dynamic height variation, and therefore to surface geostrophic current. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Interannual variability of subsurface temperature in summer induced by the Kuroshio over Bungo Channel,Tosa Bay,and Kii Channel,south of Japan     

Hiroshi Kuroda  Manabu Shimizu  Takashi Setou 《Continental Shelf Research》2010

Using historical in situ temperature record, we investigate interannual variability of temperature in summer over Bungo Channel, Tosa Bay, and Kii Channel (hereafter “BTK”), south of Japan. This study aims to reveal the interregional relation of the subsurface temperature variability between the shelf and slope as well as between BTK, and specify the primary cause of the temperature variability in terms of the Kuroshio path. It is shown that 100-m temperature on the slope of BTK is synchronous with each other and highly correlated with coastal sea levels from Kyushu to Kii Peninsula, suggesting that subsurface temperature over the slope varies simultaneously on spatial scales of 400–500 km in the along-slope direction. The 100-m temperature on the slope is also correlated with the near-bottom temperature on the shelf, implying that the near-bottom temperature is determined mainly by the larger-scale variability over the slope. The Kuroshio state in summer of each year is classified into the large meander (LM), non-large meander (NLM), and intermittent larger meander (IM) propagating eastward along the slope. It is found that remarkable temperature increases are accompanied by the IM propagations south of BTK. Temperatures during the IM and LM period are significantly different, the means of which are the highest and lowest, respectively. Temperature during the NLM period with the second highest mean value exhibits the largest variance. Statistical analysis suggests that this variance is related to the Kuroshio axis shift over Izu Ridge between the nearshore and offshore NLM paths.  相似文献   

Time-lapse borehole radar monitoring of an infiltration experiment in the vadose zone     

S. Kuroda  H. Jang  H.J. Kim   《Journal of Applied Geophysics》2009,67(4):361

Ground-penetrating radar (GPR) is an effective tool for imaging the spatial distribution of water content. An artificial groundwater recharge test was conducted in Nagaoka City in Japan, and time-lapse crosshole GPR data were collected to monitor the infiltration process in the vadose zone. Since electromagnetic wave velocities in the vadose zone are largely controlled by variations in water content, an increase in traveltime is interpreted as an increase in saturation. In the test zone, the infiltrated water penetrated downward with an average velocity of about 2.7 m/h. A finite-difference time-domain method using two-dimensional cylindrical coordinates is applied to simulate radargrams associated with the advancing wetting front and to quantify the effects of critical refraction. Standard zero-offset profiling for which all first-arrivals are assumed to be direct waves results in an underestimation of water content in the transition zone above the wetting front. As a result, correct velocity analysis requires identification of first-arriving critically refracted waves from the traveltime profile to accurately determine a water content profile.  相似文献   

Post‐Eocene intensification of deep‐water circulation in the central South Pacific: Micropalaeontological clues from dredged sites along the eastern Manihiki Plateau margin     

Atsushi Ando  Junichiro Kuroda  Reinhard Werner  Kaj Hoernle  Brian T. Huber 《地学学报》2019,31(1):28-38

Reconstruction of early Cenozoic deep‐water circulation is one of the keys to modelling Earth's greenhouse‐to‐icehouse surface evolution, but it has long been hampered by the paucity of information from the central South Pacific. To help overcome this knowledge gap, we present new micropalaeontological data from dredged carbonates (R/V Sonne Expedition SO193) at several eastern volcanic salients of the Manihiki Plateau. Interestingly, despite appreciable longitudinal separations among the dredged sites, ages indicated by the foraminiferal assemblages are consistently around the Middle Eocene (including mixed Turonian [Late Cretaceous]/Eocene at a single site), suggesting widespread post‐Eocene cessation of the pelagic sedimentation. By integrating with independent seismic and chronostratigraphic data (Deep Sea Drilling Project Leg 33) for large‐scale erosion of top‐Eocene–Oligocene sedimentary units on the eastern Manihiki Plateau, our results can be viewed as novel physical evidence for the intensification of central South Pacific deep‐water circulation since the Eocene/Oligocene climatic transition.  相似文献   

Japanese lunar robotics exploration by co-operation with lander and rover     

Takashi Kubota  Yasuharu Kunii  Yoji Kuroda 《Journal of Earth System Science》2005,114(6):777-785

Unmanned mobile robots for surface exploration of the Moon or planets have been extensively studied and developed. A lunar rover is expected to travel safely in a wide area and explore in detail. Japanese lunar robotics exploration is under study to conduct an unmanned geological survey in the vicinity of central peaks of impact craters for investigation of the sub-surface materials. This will give us the key information to study the lunar inner structure and understand the Moon’s origin and evolution as well as to investigate the evolution of magma ocean and later igneous processes. To carry out the geological exploration in the central peak, lander and rover co-operative exploration is proposed. The working group has been conducting feasibility study of advance technologies. This paper addresses an overview of lunar exploration with lander and rover and also enumerates future technologies to be established. The rover R&D group has developed an innovative science micro rover with a new mobility system and a lightweight manipulator. The design and implementation of a science rover for the near future lunar missions requiring long traverses and scientific observations are described and some experimental results are presented.  相似文献   

Crustal structure and tectonics of the Hidaka Collision Zone, Hokkaido (Japan), revealed by vibroseis seismic reflection and gravity surveys     

Kazunori Arita  Takashi Ikawa  Tanio Ito  Akihiko Yamamoto  Matsuhiko Saito  Yasunori Nishida  Hideyuki Satoh  Gaku Kimura  Teruo Watanabe  Takeshi Ikawa  Toru Kuroda 《Tectonophysics》1998,290(3-4):197-210

This study is the first integrated geological and geophysical investigation of the Hidaka Collision Zone in southern Central Hokkaido, Japan, which shows complex collision tectonics with a westward vergence. The Hidaka Collision Zone consists of the Idon'nappu Belt (IB), the Poroshiri Ophiolite Belt (POB) and the Hidaka Metamorphic Belt (HMB) with the Hidaka Belt from west to east. The POB (metamorphosed ophiolites) is overthrust by the HMB (steeply eastward-dipping palaeo-arc crust) along the Hidaka Main Thrust (HMT), and in turn, thrusts over the Idon'nappu Belt (melanges) along the Hidaka Western Thrust (HWT). Seismic reflection and gravity surveys along a 20-km-long traverse across the southern Hidaka Mountains revealed hitherto unknown crustal structures of the collision zone such as listric thrusts, back thrusts, frontal thrust-and-fold structures, and duplex structures. The main findings are as follows. (1) The HMT, which dips steeply at the surface, is a listric fault dipping gently at a depth of 7 km beneath the eastern end of the HMB, and cutting across the lithological boundaries and schistosity of the Hidaka metamorphic rocks. (2) A second reflector is detected 1 km below the HMT reflector. The intervening part between these two reflectors is inferred to be the POB, which is only little exposed at the surface. This inference is supported by the high positive Bouguer anomalies along the Hidaka Mountains. (3) The shallow portion of the IB at the front of the collision zone has a number of NNE-dipping reflectors, indicative of imbricated fold-and-thrust structures. (4) Subhorizontal reflectors at a depth of 14 km are recognized intermittently at both sides of the seismic profile. These reflectors may correspond to the velocity boundary (5.9–6.6 km/s) previously obtained from seismic refraction profiling in the northern Hidaka Mountains. (5) These crustal structures as well as the back thrust found in the eastern end of the traverse represent characteristics of collisional tectonics resulting from the two collisional events since the Early Tertiary.  相似文献