Efficiency of neutrino-induced radio measurements to inspect local areas of Enceladus

The Cassini probe observed a young and smooth surface around the south pole of Enceladus, while around the north pole the surface was found to be relatively old and inactive (Porco, C.C. et al. [2006]. Science 311, 1393–1401). This heterogeneous surface implies that the ice thickness of Enceladus is not uniform between the north and south polar regions. Determining the thickness of the icy layer is important to confirm the existence of an internal ocean as well as to reveal the heating mechanism of Enceladus. We show that the measurement of radio waves induced by cosmic neutrinos can be an effective method to constrain the ice thickness of a localized area where conventional gravity or electromagnetic field measurements cannot be used. This method could be used to constrain the thickness of the icy layer on Enceladus even if the ice is a few tens of kilometers thick, measuring over a period of several years, which greatly exceeds the ability of radar sounding, and hence could be used in future orbiter missions.     

Hydrodynamic equations of differentially rotating stellar systems and the velocity ellipsoid

Anisotropic hydrodynamic equations for differentially rotating collisionless stellar systems are derived. These equations can describe the evolution of the systems in a time span longer than their rotation periods.As a by-product of derivation of hydrodynamic equations, the well-known relation that the ratio of the principal axes of the velocity ellipse in a differentially rotating stellar disk is [B/(B-A)]^1/2 is re-found if the system is in a purely circular rotation, whereA andB are the Oort's constants. In addition, we find a systematic mean motion superposed on a purely circular differential rotation makes the directions of axes of the velocity ellipse deviate from the radial and the transverse direction. The observed deviation of directions of axes in our neighbourhood in the Galaxy can be explained if in the mean motion superposed on a purely circular differential rotatin the gas of stars near us is compressed in the radial direction or rarefied in the transverse directions, with irregularities of the order of 5 km/sec in amplitude of velocity and 1 kpc in size. These magnitudes of irregularities agree with those actually observed or with those anticipated from other theoretical considerations.     

Free-air anomalies in the western Pacific from the viewpoint of wave number spectrum

Free-air anomalies in the western Pacific consist of the two groups of wavelengths 200–500 km and longer than 1,000 km. This is the reason why the patterns of short wavelength geoidal undulation and those of free-air anomalies in the western Pacific look alike with earch other. The gravity anomalies of shorter wavelengths can be explained by tectonics related with thickness of the lithosphere. Positive free-air anomalies of longer wavelengths may be explained by relics of the subsided lithosphere.     

Variability of Upper Ocean Heat Balance in the Shikoku Basin during the Ocean Mixed Layer Experiment (OMLET)

The heat balance of the surface layer in the vicinity of the former Ocean Weather Station “Tango” (OWS-T; 29°N, 135°E), where a large amount of heat is transported by the Kuroshio and transferred to the atmosphere, was studied by during Ocean Mixed Layer Experiment (OMLET) as an oceanographic component of the Japanese World Climate Research Program (1987–1991). Temperature and velocity in the upper ocean measured using a surface moored buoy system deployed by the Ocean Research Institute, the University of Tokyo, in total 668 days of four time series namely the periods of April 1988–November 1988 (OMELET-88), August 1989–February 1990 (OMLET-89), April 1990–September 1990 (OMLET-901) and September 1990–January 1991 (OMLET-902). We have analyzed the moored buoy data of the upper 100 m for the latter three time series (OMLET-89, -901 and -902) and here we discuss the heat balance of the upper 100 m, in combination with surface heat flux and oceanographic data provided by the Japan Meteorological Agency. A large fluctuation of oceanic heat convergence/divergence of 200–300 W/m² in amplitude with predominant period of 20–30 days occurred in the first half of OMLET-89 period, which was just the early stage in the formation process of a large meander path of the Kuroshio. A large amount of heat convergence of 71 and 79 W/m² on average was detected in observation period of OMLET-89 and -901, respectively. During OMLET-902, relatively small heat convergence of 13 W/m² was obtained. It is suggested that these variations of oceanic heat convergence in this region were closely related to the fluctuation of the Kuroshio axis to the south of Japan. This revised version was published online in July 2006 with corrections to the Cover Date.     

Observation of temperature and velocity in the coastal water off Kuala Terengganu,Malaysia

Mooring observation of current and temperature was made at 17.8 m layer of 19 m depth about 8 km east to Kuala Terengganu, Peninsular Malaysia. Harmonic analysis was applied to tidal currents for 30 days in September 1993, and to the tides observed at Chendering. The K1 tide was the largest both in tidal currents and the tides. Daily mean temperature, currents, sea level, and winds were analyzed from September 1993 to May 1994. Northeast Monsoon from December to February caused sea level rise of 50 cm and temperature lowering of 1°C.     

Active strike–slip faulting and macroscopically nonrigid deformation of volcanic rocks in central Japan inferred from a paleomagnetic study

Detailed paleomagnetic investigation of a pyroclastic flow deposit has clarified the deformation mode around an active fault. In central Japan, the early Quaternary Nyukawa Pyroclastic Flow Deposit is cut by the active dextral Enako fault. Activity level of the fault is evaluated on the basis of geological and geomorphological surveys. Then, paleomagnetic samples are collected from 22 sites at exposures located on a lineament that is adjoining and parallel to the Enako fault. Stable thermoremanent magnetization (TRM) of the pyroclastic deposit is isolated through progressive thermal and/or alternating field demagnetization tests. Untilted site-mean directions of the TRMs simultaneously acquired during initial cooling indicate significant clockwise vertical-axis rotation. The lineament was then activated with right-lateral motions through the early Quaternary. Together with the late Quaternary activities along the adjoining Enako fault evaluated by our study, the present result exemplifies a migration of active segments within a fault system during the Quaternary. Paleomagnetic directions on the strike–slip fault are not concordant with uniform deformation predicted by the model of rotation of rigid blocks aligned on a master fault, but suggestive of a periodic deformation as a result of intense fracturing and differential rotation of blocks bounded by nested parallel faults.     

Geochemistry of gas hydrate accumulation offshore NE Sakhalin Island (the Sea of Okhotsk): results from the KOMEX-2002 cruise

Geochemical properties of gas hydrate accumulation associated with an active gas vent on the continental slope offshore northeast Sakhalin Island in the Sea of Okhotsk have been investigated. The pore water chemistry data suggest that the gas hydrates (GHs) were formed in an environment of upward-migrating fluid combined with a mechanism of pore water segregation. The upward infiltration of water enriched mainly by Cl^– and K⁺ species appears to occur on the background of earlier diagenesis processes within the gas vent sediments. The GHs were formed from water with chlorinity ranging from 530 to 570 mM. The ¹⁸O and D of GH water varied from –1.4 to –1.8 and from –13 to –18, respectively, representing a mix of seawater and infiltrating fluid water. A complex interaction of pore water, water of ascending fluid and segregated pore water during hydrate formation is also supported by water content measurements and observed gas hydrate structure. The direction of segregated water is opposite to upward fluid migration. Decreasing activity of the gas vent is inferred by comparing the present top of the recovered hydrate layer with previous observations.     

Photographic monitoring system for observing heavy free-falling objects: Multi-stage design packages of radioactive waste

In the consideration of safety it is required that packages containing radioactive wastes when dumped at sea should keep their integrity and retain their contents until they reach the seabed. Packages containing simulated radioactive wastes (non-radioactive) were tested by a free-fall method at depthsca. 4,300 m in an area for dumping industrial waste off Shikoku Island. Since the weight of the largest package was 4,300 kg, special attention was paid to the connection of a buoyancy system with mooring rope. Descent and ascent velocities of the free-fall system were calculated prior to the experiment. A free-fall experiment with an extremely heavy object, heavier than ever previously reported, was accomplished without trouble by using the free-fall system. Recovery of a camera, flash-light, and other components was successful in each of the three experiments. Successive photographing of the package during descent was made and its integrity was observed using the photographs taken by the recovered camera. The packages remained intact during descent and at least for a short time after arrival on the seabed.