Experimental study on internal waves in a stratified shear flow

This paper describes experiments on interfacial phenomena in a stratified shear flow having a sharp velocity shear at a density interface. The interface was visualized in vertical cross-section using dye, and the flow pattern was traced using aluminum powder. Two kinds of internal waves with different phase velocities and wave profiles were observed. They are here named p(positive)-waves and n(negative)-waves, respectively. By means of a two-dimensional visualization technique, the following facts have been confirmed regarding these waves. (1) The two kinds of waves propagate in the opposite direction relative to a system moving with the mean velocity at the interface, and their dispersion relations approximately agree with the two solutions of interfacial waves in a two-layer system of a linear basic shear flow. (2) The p-wave has sharp crests and flat troughs, and the n-wave has the reverse of this. This difference in wave profile is due to the finite amplitude effect. (3) Phase velocity of each wave lies within the range of the mean velocity profile, so that a critical layer exists and each wave has a “cat's eye” flow pattern in the vicinity of the critical layer, when observed in a system moving with the phase velocity. Consequently, these two waves are symmetrical with respect to the interface. The mechanisms of generation of these waves, and the entrainment process are discussed. It is inferred that when the “cat's eye” flow pattern is distorted and a stagnation point approaches the interface, entrainment in the form of a stretched wisp from the lower to the upper layer occurs for the p-wave, and from the upper to the lower layer for the n-wave.     

Analysis of year-to-year variation of water temperature along the coast of the Japan sea

Mean monthly records of coastal sea surface temperature data (CSST) obtained from stations along the Japanese coasts of the Japan Sea and from those in the related seas for the period 1941–1984 were analyzed by using various methods of time series analysis, for the purpose of clarifying the nature of the year-to-year variations of the state of the Japan Sea. The year-to-year variations in the Japan Sea were found to be closely related to those in the East China Sea and in the western North Pacific. Specific results are as follows. (1) A sudden cooling in the early 1960's occurred in the southern stations of the Japan Sea and continued to the end of the analyzed data. (2) Variations, with about a 6-year periodicity, were observed at most stations, and were especially dominant in the southern stations of the Japan Sea (3) These variations could be traced back to the Kuroshio region of the East China Sea. (4) Variations, with about a 10-year periodicity, were also observed in the northern stations of the Japan Sea.     

CS,C34S,and CH3OH observations of the molecular cloud associated with NGC 7538

CS(J=1–0), C³⁴S(J=1–0), and CH₃OH(1₀–0₀A and E) emission lines in the core region of molecular cloud associated with NGC 7538 have been surveyed at angular resolution of 33. Distribution of CS column density shows two prominent peaks. Both blue and red wings in CS line are most prominent at 30 northwest of IRS 11.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.This work was carried out under the common use observation program at the Nobeyama Radio Observatory (NRO). NRO, a branch of the Tokyo Astronomical Observatory, University of Tokyo, is a cosmic radio observing facility open to outside users.     

A method of simultaneous analysis of wind and temperature profile data over the water surface by use of the method of least squares

Priestley’s 1959 discussion concerning the estimations of momentum flux and of heat flux from profile observations of wind and temperature, stating that the closeness of the curve fitting is deceptive, is first critically re-examined. Then a method is proposed to estimate vertical flux of momentum and heat over the water surface, from the combined data of of wind speed and temperature are assumed to have similar log-linear profiles, and the most probable profiles are determined by applying the method of least squares simultaneously to wind and temperature data. Consequently, the most probable values of vertical flux of momentum and heat may be estimated to satisfy as much as possible observed data of both wind and temperature simultaneously. The coefficient of the linear term of the log-linear profile, which is treated as an indeterminate coefficient in this method, may be determined from each observed data as a function of stability length. By tentatively applying the method to Rider’s 1954 data it is found that the coefficient shows a characteristic behavior with the stability length.     

Mineralogical and geochemical study of a newly discovered mafic granulite, northwest China: Implications for tectonic evolution of the Altay Orogenic Belt

Abstract A mafic granulite body was newly discovered in the Altay Orogenic Belt, northwest China. The rocks comprise a suite of coarse‐grained and fine‐grained granulites. Orthopyroxenes (hypersthenes) in the rocks have high X_Mg and low Al₂O₃ contents, whereas clinopyroxenes have low TiO₂ and Al₂O₃ contents. Amphiboles and biotites have a high Mg/(Mg + Fe²⁺) ratio and low contents of F and Cl. The peak metamorphic pressure–temperature (P–T) conditions are estimated as 750–780°C and 6–7 kbar, and retrograde P–T conditions are in the range of 590–620°C and 2.3–3.7 kbar, indicating significant decompression. Metamorphic reactions and P–T estimates define a clockwise P–T path. Geochemically, the rocks are high in Mg/(Mg + Fe) and Al₂O₃, depleted in U, Th, K and Rb, and characterized by light rare earth element enrichment and a weak positive Eu anomaly. The Altay mafic granulite shows depleted Nb, P and Ti contents in the mid‐oceanic ridge basalt normalized spider diagram. The geochemical characteristics suggest that the protolith of the Altay mafic granulite was calc‐alkaline basalt and andesite with an island‐arc affinity. The rock has a high ¹⁴³Nd/¹⁴⁴Nd ratio with ?Nd(0) > 0, indicating derivation from a mantle‐depleted source. In the present study, a two‐stage model for the evolution of the Altay mafic granulite is proposed: an early stage in which calc‐alkaline basalt and andesite with island‐arc affinity were subducted into a deeper level of the crust and subjected to granulite‐facies metamorphism generating the mafic granulite, followed by the later stage exhumation of the system into the upper crust by the late Paleozoic thrusting.     

Velocity variation of the Kuroshio during formation of the small meander south of Kyûshû

Historical GEK data provided by JODC is analyzed to investigate the characteristic variation in velocity of the Kuroshio, with special reference to the formation of small meanders south of Kyûshû. It is found that, during or prior to the period of small meander formation, there is a tendency for an abrupt increase in the current velocity west of Yaku-Shima (Yaku-Island), representing an increase in the main current intensity upstream. Also, there are apparent time lags in the variation in current velocity along the path of the Kuroshio between the upstream and the downstream regions of the small meander area. Namely, it is apparent that the increase in Kuroshio velocity in the Satsunan Strait procedes that offshore of Shikoku during the period of the small meander formation, by the order of one month. These results indicate that a nonlinear effect due to the increase in current velocity is a possible cause of the generation of small meanders.     

Lithological and physical properties of core samples from the Sagara oil field: Oil occurrence in Sagara core samples

Abstract   A drilling and coring investigation of the Sagara oil field, central Honshu, Japan, was conducted to contribute to the understanding of hydrocarbon migration processes in a forearc basin. Core samples were analyzed to determine lithology, physical properties (specifically gas permeability) and the characteristics of oil occurrence. Gas permeability values greater than approximately 10⁻¹¹ m² constitute the basic precondition for any lithology to serve as a potential fluid conduit or reservoir in the Sagara oil field. Cores recovered from the 200.6-m-deep borehole were primarily composed of alternating siltstone, sandstone and conglomerate, all of which are correlated to the late Miocene Sagara Group. Both sandstone and conglomerate can be classified into two types, carbonate-cemented and poorly to non-cemented, based on matrix material characteristics. Oil stains are generally absent in the former lithology and more common in the latter. Variations in physical properties with respect to gas permeability values are directly related to the presence and character of carbonate cement, with higher permeabilities common in poorly to non-cemented rocks. The relationships between lithology, oil-staining, cementation and permeability indicate that cementation preceded oil infiltration and that cementation processes exerted significant control on the evolution of the reservoir.     

Small inflation sources producing seismic and infrasonic pulses during the 2000 eruptions of Miyake-jima, Japan

During the 2000 activity of Miyake-jima volcano, Japan, we detected long period seismic signals with initial pulse widths of 1-2 s, accompanied by infrasonic pulses with almost the same pulse widths. The seismic signals were observed from 13 July 2000, a day before the second summit eruption. The occurrences of the seismic signals were intermittent with a gradual increase in their magnitudes and numbers building toward a significant explosive eruption on 18 August. After the eruption, the seismic and infrasonic events ceased. The results of a waveform inversion show that the initial motions were excited by an isotropic inflation source beneath the south edge of the caldera at a depth of 1.4 km. On the other hand, the sources of the infrasonic pulses were located in the summit caldera area. The times at which the infrasonic pulses were emitted at the surface were delayed by about 3 s from the origin times of the seismic events. It is suggested that small isotropic inflations excited seismic waves in the crust and simultaneously caused acoustic waves that traveled in the conduit and produced infrasonic pulses at the crater bottom. Considering the observed time differences and gas temperatures emitted from the vent, the conduit should have been filled with vapor mixed with SO₂ gas and volcanic ash. The change of the time differences between the seismic and infrasonic signals suggests that the seismic source became shallower within half a day before the August 18 explosive eruption. We interpret the source process as a fragmentation process of magma in which gas bubbles burst and quickly released part of the pressure that had been sustained by the tensional strength of magma.