Inter-model variability of projected sea level changes in the western North Pacific in CMIP3 coupled climate models     

Masakazu Sueyoshi  Tamaki Yasuda 《Journal of Oceanography》2012,68(4):533-543

We investigate sea level changes in the western North Pacific for twenty-first century climate projections by analyzing the output from 15 coupled models participating in the Coupled Model Intercomparison Project phase 3 (CMIP3). Projected changes in the wind stress due to those in sea level pressure (SLP) result in the projected sea level changes. In the western North Pacific (30?50°N, 145?170°E), the inter-model standard deviation of the sea level change relative to the global mean is comparable to that based on the multi-model ensemble (MME) mean. Whereas a positive SLP change in the eastern North Pacific (40?50°N, 170?150°W) induces a large northward shift of the Kuroshio Extension (KE), a negative SLP change in this region induces a strong intensification of the KE. Large inter-model variability of the SLP projection in the eastern North Pacific causes a large uncertainty of the sea level projection in the western North Pacific. Models with a larger northward shift (intensification) of the KE exhibit a poleward shift (an intensification) of the Aleutian Low (AL) larger than that for the MME mean. However, models that exhibit a larger intensification of the AL do not necessarily show a larger intensification of the KE. Our analysis suggests that the SLP change that induces an intensification of the KE is associated with a teleconnection from the equatorial Pacific, and that the SLP change that induces a northward shift of the KE is characterized by a zonal mean change.  相似文献   

Compound chondrule formation in the shock-wave heating model: Three-dimensional hydrodynamics simulation of the disruption of a partially-molten dust particle     

Seiji Yasuda  Hitoshi Miura 《Icarus》2009,204(1):303-315

We carried out three-dimensional hydrodynamics simulations of the disruption of a partially-molten dust particle exposed to high-speed gas flow to examine the compound chondrule formation due to mutual collisions between the fragments (fragment-collision model; [Miura, H., Yasuda, S., Nakamoto, T., 2008a. Icarus194, 811-821]).In the shock-wave heating model, which is one of the most plausible models for chondrule formation, the gas friction heats and melts the surface of the cm-sized dust particle (parent particle) and then the strong gas ram pressure causes the disruption of the molten surface layer. The hydrodynamics simulation shows details of the disruptive motion of the molten surface, production of many fragments and their trajectories parting from the parent particle, and mutual collisions among them. In our simulation, we identified 32 isolated fragments extracted from the parent particle. The size distribution of the fragments was similar to that obtained from the aerodynamic experiment in which a liquid layer was attached to a solid core and it was exposed to a gas flow. We detected 12 collisions between the fragments, which may result in the compound chondrule formation. We also analyzed the paths of all the fragments in detail and found the importance of the shadow effect in which a fragment extracted later blocks the gas flow toward a fragment extracted earlier. We examined the collision velocity and impact parameter of each collision and found that 11 collisions should result in coalescence. It means that the ratio of coalescent bodies to single bodies formed in this disruption of a parent particle is R_coa=11/(32-11)=0.52. We concluded that compound chondrule formation can occur just after the disruption of a cm-sized molten dust particle in shock-wave heating.  相似文献   

A modified method for estimating vertical profiles of turbulent dissipation rate using density inversions in the Kuril Straits     

Masahiro Yagi  Ichiro Yasuda 《Journal of Oceanography》2013,69(2):203-214

To address the lack of directly measured turbulence data in the Kuril Straits, an existing method was modified to indirectly estimate continuous vertical profiles of turbulent energy dissipation rate ε by using density inversions. A linear relationship was confirmed between directly measured ε and indirectly estimated ε from the existing method, where most of the detected density inversions were discarded as noise. The existing method thus yielded large gaps in the vertical profiles, and the gaps were much greater than the observed mean autocorrelation vertical length scale of about 10 m. To reduce these gaps and produce reasonable estimates for vertical ε profiles, the quality tests were carefully re-examined with directly measured ε data, and one of the quality tests (the water mass test) was excluded because the test rejects real density inversions even with large ε. With this modification, and interpolation and smoothing of the indirectly estimated ε with the mean correlation length scale, continuous vertical ε profiles were obtained. These profiles have an error factor of 3.3 corresponding to one standard deviation of the ratio between directly observed and estimated data, and 95 % of the data were within a factor of 10.5, with the overall correlation coefficient between smoothed directly measured ε and estimated ε equal to 0.80. This method could be useful for areas where 10^?9 < ε < 10^?6.5 W/kg, and where vertical distances between adjacent density inversions are mostly less than the mean autocorrelation scale.  相似文献   

Fragment-collision model for compound chondrule formation: Estimation of collision probability     

Hitoshi Miura  Seiji Yasuda  Taishi Nakamoto 《Icarus》2008,194(2):811-821

We propose a new scenario for compound chondrule formation named as “fragment-collision model,” in the framework of the shock-wave heating model. A molten cm-sized dust particle (parent) is disrupted in the high-velocity gas flow. The extracted fragments (ejectors) are scattered behind the parent and the mutual collisions between them will occur. We modeled the disruption event by analytic considerations in order to estimate the probability of the mutual collisions assuming that all ejectors have the same radius. In the typical case, the molten thin () layer of the parent surface will be stripped by the gas flow. The stripped layer is divided into about 200 molten ejectors (assuming that the radius of ejectors is 300 μm) and then they are blown away by the gas flow in a short period of time (). The stripped layer is leaving from the parent with the velocity of depending on the viscosity, and we assumed that the extracted ejectors have a random velocity Δv of the same order of magnitude. Using above values, we can estimate the number density of ejectors behind the parent as . These ejectors occupy ∼9% of the space behind the parent in volume. Considering that the collision rate (number of collisions per unit time experienced by an ejector) is given by Rcoll=σcollneΔv, where σcoll is the cross-section of collision [e.g., Gooding, J.K., Keil, K., 1981. Meteoritics 16, 17-43], we obtain by substituting above values. Since most collisions occur within the short duration () before the ejectors are blown away, we obtain the collision probability of Pcoll∼0.36, which is the probability of collisions experienced by an ejector in one disruption event. The estimated collision probability is about one order of magnitude larger than the observed fraction of compound chondrules. In addition, the model predictions are qualitatively consistent with other observational data (oxygen isotopic composition, textural types, and size ratios of constituents). Based on these results, we concluded that this new model can be one of the strongest candidates for the compound chondrule formation. It should be noted that all collisions do not necessarily lead to the compound chondrule formation. The formation efficiency and the future works which should be investigated in the forthcoming paper are also discussed.  相似文献   

黄土液化机理和判别标准的再研究   总被引：2，自引：0，他引：2  

袁中夏  王兰民  Susumu Yasuda  王峻 《地震工程与工程振动》2004,24(4):164-169

本文结合作者的试验研究和国外最新研究进展对黄土液化问题作了一些深入讨论。在一定的条件下,黄土可能发生液化,而且相当一部分黄土符合“修正的中国标准”。从液化机理上讲,黄土液化属于流滑。试验研究发现,黄土液化过程与应变发展有内在的联系,因而在动三轴试验中用轴向应变作为黄土初始液化的判别条件更符合实际。最后,通过对俄罗斯、美国和中国黄土的对比研究,作者认为黄土的粒度组成对黄土的液化特性有明显的影响。  相似文献   

Comparative Measurements Of Co2flux Over A Forest Using Closed-Path And Open-Path Co2analysers     

Yukio Yasuda  Tsutomu Watanabe 《Boundary-Layer Meteorology》2001,100(2):191-208

An eddy covariance system using a closed-path CO₂analyser was constructed for long-term CO₂flux measurements above a forest, and its total frequency response was valuated experimentally. The amplitude and phase responses of the system wereexamined through a preliminary test, in which a prescribed pattern of CO₂fluctuation was input to the system. The result showed that the amplitude of the output from the system was attenuated as frequency increased, with a half-power frequency of 0.3 Hz. The phase was delayed by the air sampling through a long tube, but the delay in phase decreased asfrequency increased. We then presented a new technique for the correction of flux loss due to the inadequate system response for the eddy covariance measurements of CO₂ flux. Using the present system and the correction technique, diurnal variations in CO₂ flux were measured over a temperate deciduous forest on three days in 1997. The results were compared with the CO₂fluxes measured with a fast response open-path gas analyser. The CO₂fluxes from the closed-path system agreed with those from the open-path system after the Webb, Pearman and Leuning correction was made for the latter. In the present test over a forest, the contribution of the frequency-response correction to the CO₂fluxes was small and its averaged percentage was only 3%in the daytime. However, the percentage would likely increase, if the system were applied to a shorter vegetation site where high frequency components are more important. The comparison confirmed that we can obtain correct measurements of CO₂flux using the present closed-path system and the correction technique.  相似文献   

Electron microscopy of clinoenstatite from a boninite and a chondrite     

Masayo Yasuda  Masao Kitamura  Nobuo Morimoto 《Physics and Chemistry of Minerals》1983,9(5):192-196

Clinoenstatite crystals from a boninite and the Yamato-74191 chondrite have been studied with an analytical electron microscope. (100) twins and cracks perpendicular and parallel to the c axis are characteristic of their submicroscopic textures. The frequency in appearance along the c axis and widths of the cracks have been explained by the dimensional change of the c axis in the direct transformation of protoenstatite to clinoenstatite and by the cooling rate around the transformation temperature. The cracks in the crystals from the boninite are filled with fibrous crystals of talc, while those from the chondrite are open or filled with glass in which fine crystals of plagioclase are common.  相似文献   

Advanced Micro-XRF Method to Separate Sedimentary Rhythms and Event Layers in Sediments: Its Application to Lacustrine Sediment from Lake Suigetsu,Japan     

Nagayoshi Katsuta  Masao Takano  Shin-ichi Kawakami  Shoji Togami  Hitoshi Fukusawa  Mineo Kumazawa  Yoshinori Yasuda 《Journal of Paleolimnology》2007,37(2):259-271

Event-related sedimentary layers, which are deposited occasionally due to volcanic eruptions, earthquakes or heavy rains, are often contained in the rhythmical sequences of lacustrine and marine sediments. We have developed an analytical method for separating the sedimentary rhythms and the event layers identified using the scanning X-ray analytical microscope (SXAM) and obtained sequential profiles of seven elements Al, Si, K, Ca, Ti, Mn, and Fe in the lacustrine sediment from Lake Suigetsu, Japan. Two types of event layers could be detected from the elemental composition of 33 layers of sediment: three known volcanic ash layers and 30 clay layers containing 12 turbidites. The recurrence interval of the latter, which may potentially be initiated and archived by locally important earthquakes, is estimated to be an average of 640 ± 160 years by using Sompi event analysis (SEA) based on an autoregressive (AR) model. After removing those portions that represented event layers from the elemental profiles, we obtained event-removed (ER) temporal profiles based on the tephrochronology of the three volcanic ash layers. The ER temporal profiles of manganese and iron, probably representing the siderite content, showed a millennial-scale variation in the Holocene that corresponded well with ice-rafting events in the North Atlantic.  相似文献