CO<Subscript>2</Subscript> Flux Measurements over the Sea Surface by Eddy Correlation and Aerodynamic Techniques     

Toru?Iwata  Keiko?Yoshikawa  Katsutoshi?Nishimura  Yoshihisa?Higuchi  Takao?Yamashita  Shigeru?Kato  Eiji?OhtakiEmail author 《Journal of Oceanography》2004,60(6):995-1000

The measurements of the vertical transport of CO₂ were carried out over the Sea of Japan using the specially designed pier of Kyoto University on September 20 to 22, 2000. CO₂ fluxes were measured by the eddy correlation and aerodynamic techniques. Both techniques showed comparable CO₂ fluxes during sea breeze conditions: −0.001 to −0.08 mg m⁻²s⁻¹ with the mean of −0.05 mg m⁻²s⁻¹. This means that the measuring site satisfies the fetch requirement for meteorological observations under sea breeze conditions. Moreover, the eddy diffusivity coefficient used in the aerodynamic technique is found to be consistent with the coefficient used in the eddy correlation technique. The present result leads us to conclude that the aerodynamic technique may be applicable to underway CO₂ flux measurements over the ocean and may be used in place of the bulk technique. The important point is the need to maintain a measuring accuracy of CO₂ concentration difference of the order of 0.1 ppmv on the research vessels or the buoys.  相似文献   

Depth dependence of target strength of live kokanee salmon in accordance with Boyle's law   总被引：3，自引：5，他引：3  

Mukai  Tohru; Iida  Kohji 《ICES Journal of Marine Science》1996,53(2):245-248

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Decomposition characteristics of particulate organic matter in hiroshima bay     

Tohru Seiki  Etsuji Date  Hirofumi Izawa 《Journal of Oceanography》1991,47(5):207-220

The decomposition characteristics of particulate organic matter (POM) sampled with plankton nets in Hiroshima Bay were investigated under aerobic conditions in a laboratory experiment.The POM derived from plankton consisted of both a labile fraction (70–80 % of the whole) and a refractory fraction (20–30%). The labile fraction was completely decomposed within 40 days at 20°C. Although the concentrations of particulate organic carbon (POC) decreased gradually with time, an apparent lag phase was recognized in the decomposition of particulate phosphorus (PP) at an early stage, which might result from a specific uptake of dissolved inorganic phosphorus (DIP) by bacteria. A comparison of the metabolic activity between dissolved organic matter (DOM) and POM by measuring ATP contents showed that the former was one order of magnitude larger than the latter.On the other hand, there was no significant difference among the decomposition rates of POM collected at various depths. The change of the first-order rate constant (k) for the POM decomposition by temperature was expressed ask=0.0329 exp(0.0644T), and the Q₁₀ value was 1.94. There were fairly large variances ink values obtained from the various plankton species. Thek values averaged 0.144 day^–1 and ranged from 0.078 to 0.20 day^–1 at 20°C.  相似文献   

Jellyfish patch formation investigated by aerial photography and drifter experiment     

Shinya Magome  Tomohiro Yamashita  Takeshi Kohama  Atsushi Kaneda  Yuichi Hayami  Satoru Takahashi  Hidetaka Takeoka 《Journal of Oceanography》2007,63(5):761-773

Jellyfish patch formation is investigated by conducting a drifter experiment combined with aerial photography of a sustained patch of the moon jellyfish in Hokezu Bay, Japan. Jellyfish patches are aggregations of individuals that are caused by a combination of swimming (active influence) and advection by currents (passive influence). The drifter experiment involved the injection of 49 drifters around a distinct surface patch of jellyfish within an area of approximately 300 m × 300 m. The drifters’ motion, caused only by the passive influence, was recorded in a series of 38 aerial photographs taken over approximately 1 h. The ambient uniform current field larger than the patch scale was estimated from the movement of the centroid position of drifters, while the distribution of horizontal divergence and relative vorticity around the patch was estimated from the time-derivative in areas of triangles formed by the drifters. The centroid positions of both drifters and patches moved stably toward the bay head at different speeds. The difference vector between the patch and drifter centroids was directed to the sun, and was opposite to the ambient current. The distributions of vorticity and divergence around patches exhibited inhomogeneity within the patch scale, and the drifters in this nonuniform current field aggregated near the convergence area within 1 h. The results suggest that horizontal patch formation is predominantly influenced by passive factors at the surface of Hokezu Bay. Furthermore, the upward swimming against downwelling may make sustained patch in surface layer.  相似文献   

Relationship between acoustic backscattering strength and density of zooplankton in the sound-scattering layer   总被引：1，自引：0，他引：1  

Iida  Kohji; Mukai  Tohru; Hwang  DooJin 《ICES Journal of Marine Science》1996,53(2):507-512

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Earthquake rupture complexity due to dynamic nucleation and interaction of subsidiary faults     

Teruo Yamashita  Yasuhiro Umeda 《Pure and Applied Geophysics》1994,143(1-3):89-116

We numerically study the dynamic interaction of propagating cracks. It is assumed that propagating cracks can nucleate and drive subsidiary cracks because of shear strain enhancement near the propagating crack tips. The critical strain fracture criterion is assumed in the analysis. Intense interaction is expected to occur among the cracks. All the cracks are assumed to be parallel and antiplane strain deformation is assumed in the computation.In the interaction of two non-coplanar cracks, a strain shadow is formed in the neighborhood of each crack because of the strain release by the introduction of the crack. The growth of each crack is accelerated when the propagating tips of each crack are outside of the strain shadow of the other crack. In general, the crack tips enter the strain shadow, and the crack tips decelerate. The calculation shows that only one of the two cracks can continue to grow, and the other's growth is decelerated and arrested. If we can assume that the suite of cracks interact in a pairwise manner only, then this may suggest that only a limited number of cracks can continue to grow during the final stage of the rupture process. Hence the crack interaction causes complexity in dynamic earthquake faulting. The concepts of barrier and asperity have been employed by many researchers for the interpretation of complex seismic wave data. However, the physical realities of such concepts are obscure. Our calculations show that dynamic crack interactions can produce barriers and asperities in some cases; the crack tip deceleration or arrest due to the interactions among non-coplanar cracks can be interpreted as being due to a barrier. The dynamic coalescence among the coplanar cracks can be regarded as an asperity.Umeda found a localized area that strongly radiates high-frequency seismic waves in the epicentral areas of some large shallow earthquakes. He defined this as an earthquake bright spot. Our analysis implies that only a limited number of cracks continue to grow when many interactive cracks nucleate, and that all other cracks stop extending soon after nucleation. Hence, if the nucleation and termination of several cracks occur in a localized area, it will be observed seismologically as an earthquake bright spot. This is because it is theoretically known that the sudden termination of crack growth and dynamic crack coalescence efficiently emits high-frequency elastic waves.  相似文献   

Scattering of elastic waves by a fracture zone containing randomly distributed cracks     

Jun Kawahara  Teruo Yamashita 《Pure and Applied Geophysics》1992,139(1):121-144

We theoretically study the scattering ofP, SV andSH waves by a zonal distribution of cracks, which simulates a fault fracture zone. An investigation is conducted how the geometrical properties of the crack distribution and the frictional characteristics of the crack surface are reflected in the attenuation and dispersion of incident waves, as well as in the amplitudes of the transmitted and reflected waves from the zone. If the crack distribution within the fault zone changes temporally during the preparation process of the expected earthquake, it will be important for earthquake prediction to monitor it, utilizing the scattering-induced wave phenomena.We consider the two-dimensional problem. Aligned cracks with the same length are assumed to be randomly distributed in a zone with a finite width, on which elastic waves are assumed to be incident. The distribution of cracks is assumed to be homogeneous and sparse. The crack surface is assumed to be stress-free, or to undergo viscous friction; the latter case simulates fluid-filled cracks. The opening displacement of the crack is assumed to be negligibly small. The idea of the mean wave formalism is employed in the analysis, and Foldy's approximation is assumed.When the crack surface is stress-free, it is commonly observed for every wave mode (P, SV andSH) that the attenuation coefficientQ ^–1 peaks aroundka1, the phase velocity is almost independent ofk in the rangeka<1 and it increases monotonically withk in the rangeka>1, wherek is the intrinsicS wavenumber anda is the half length of the crack. The effect of the friction is to shift the peak ofQ ^–1 and the corner of the phase velocity curve to the low wavenumber range. The high wavenumber asymptote ofQ ^–1 is proportional tok ^–1 independently of model parameters and the wave modes. If the seismological observation thatQ ^–1 ofS waves has a peak at around 0.5 Hz in the earth's crust is combined with our results, the upper limit of crack size within the crust is estimated about 4 km. The information regarding the transmitted and reflected waves, such as the high wavenumber limit of the amplitude of the transmitted wave etc., allows estimation of the strength of the friction.  相似文献   

Energy transfer among Pb, Ce and Mn in fluorescent calcite from Kuerle, Xinjiang, China     

Aierken Sidike  X.-M. Wang  Alifu Sawuti  H.-J. Zhu  I. Kusachi  N. Yamashita 《Physics and Chemistry of Minerals》2006,33(8-9):559-566

Natural calcite from Kuerle, Xinjiang, China, shows orange-red fluorescence when exposed to short-wave ultraviolet (UV) light (Hg 253.7 nm). Photoluminescence (PL) emission and excitation spectra of the calcite are observed at room temperature in detail. The PL emission spectrum under 208 nm excitation consists of three bands: two UV bands at 325 and 355 nm and an orange-red band at 620 nm. The three bands are ascribed to Pb²⁺, Ce³⁺ and Mn²⁺, respectively, as activators. The Pb²⁺ excitation band is observed at 243 nm, and the Ce³⁺ excitation band at 295 nm. The Pb²⁺ excitation band is also observed by monitoring the Ce³⁺ fluorescence, and the Pb²⁺ and Ce³⁺ excitation bands, in addition to six Mn²⁺ excitation bands, are also observed by monitoring the Mn²⁺ fluorescence. These indicate that four types of the energy transfer can occur in calcite through the following processes: (1) Pb²⁺ → Ce³⁺, (2) Pb²⁺ → Mn²⁺, (3) Ce³⁺ → Mn²⁺ and (4) Pb²⁺ → Ce³⁺ → Mn²⁺.  相似文献   

Dynamic branching, arresting of rupture and the seismic wave radiation in self-chosen crack path modelling     

Nobuki Kame  Teruo Yamashita 《Geophysical Journal International》2003,155(3):1042-1050

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Dynamic nucleation process of shallow earthquake faulting in a fault zone     

Nobuki Kame  Teruo Yamashita 《Geophysical Journal International》1997,128(1):204-216

Two distinct phases are commonly observed at the initial part of seismograms of large shallow earthquakes: low-frequency and low-amplitude waves following the onset of a P wave ( P ₁) are interrupted by the arrival of the second impulsive phase P₂ enriched with high-frequency components. This observation suggests that a large shallow earthquake involves two qualitatively different stages of rupture at its nucleation.
We propose a theoretical model that can naturally explain the above nucleation behaviour. The model is 2-D and the deformation is assumed to be anti-plane. A key clement in our model is the assumption of a zone in which numbers of pre-existing cracks are densely distributed; this cracked zone is a model for the fault zone. Dynamic crack growth nucleated in such a zone is intensely affected by the crack interactions, which exert two conflicting effects: one tends to accelerate the crack growth, and the other tends to decelerate it. The accelerating and decelerating effects are generally ascribable to coplanar and non-coplanar crack interactions, respectively. We rigorously treat the multiple interactions among the cracks, using the boundary integral equation method (BIEM), and assume the critical stress fracture criterion for the analysis of spontaneous crack propagation.
Our analysis shows that a dynamic rupture nucleated in the cracked zone begins to grow slowly due to the relative predominance of non-coplanar interactions. This process radiates the P₁ phase. If the crack continues to grow, coalescence with adjacent coplanar cracks occurs after a short time. Then, coplanar interactions suddenly begin to prevail and crack growth is accelerated; the P₂ phase is emitted in this process. It is interpreted that the two distinct phases appear in the process of the transition from non-coplanar to coplanar interaction predominance.  相似文献