Waveforms of Long-Period Body Waves In A Slightly Aspherical Earth Model     

Xiang-Dong Li  Toshiro Tanimoto 《Geophysical Journal International》1993,112(1):92-102

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Effect of open gap in coastal forest on tsunami run-up—investigations by experiment and numerical simulation     

Nguyen Ba Thuy  Katsutoshi Tanimoto  Norio Tanaka  Kenji Harada  Kosuke Iimura 《Ocean Engineering》2009,36(15-16):1258-1269

The objective of this study is to investigate the effects of an open gap, such as a road, in a coastal forest on tsunami run-up. A numerical model based on two-dimensional nonlinear long-wave equations was developed to account for the effects of drag and turbulence induced shear forces due to the presence of vegetation. Experiments were conducted on a forest simulated with vertical cylinders by changing the gap width. The numerical model was validated in good agreement with the experimental results. The numerical model was then applied to a wide forest of Pandanus odoratissimus, a tree species that is a dominant coastal vegetation on a sand dune in South and Southeast Asia. The effect of vertical stand characteristics of P. odoratissimus with aerial roots was considered on the drag resistance. A straight open gap perpendicular to the shoreline was used to investigate the effect of gap width. As the gap width increases, the flow velocity at the end of the open gap first increases, reaches a maximum, and then decreases, while the run-up height increases monotonously. The maximum velocity in the present condition is 1.7 times the maximum velocity without a coastal forest. The effects of different gap arrangements in the forest on tsunami run-up were also investigated in this paper. The flow velocity at the end of an open gap can be reduced by a staggered arrangement.  相似文献   

Projected future changes in the contribution of Indo-Pacific sea surface height variability to the Indonesian throughflow     

Shilimkar  Vivek  Abe  Hiroto  Roxy  Mathew Koll  Tanimoto  Youichi 《Journal of Oceanography》2022,78(5):337-352

The Indonesian throughflow (ITF) transports a significant amount of warm freshwater from the Pacific to the Indian Ocean, making it critical to the global climate system. This study examines decadal ITF variations using ocean reanalysis data as well as climate model simulations from the Coupled Model Inter-comparison Project Phase 5 (CMIP5). While the observed annual cycle of ITF transport is known to be correlated with the annual cycle of sea surface height (SSH) difference between the Pacific and Indian Oceans, ocean reanalysis data (1959–2015) show that the Pacific Ocean SSH variability controls more than 85% of ITF variation on decadal timescales. In contrast, the Indian Ocean SSH variability contributes less than 15%. While those observed contributions are mostly reproduced in the CMIP5 historical simulations, an analysis of future climate projections shows a 25–30% increase in the Indian Ocean SSH variability to decadal ITF variations and a corresponding decrease in the Pacific contribution. These projected changes in the Indian Ocean SSH variability are associated with a 23% increase in the amplitudes of negative zonal wind stress anomalies over the equatorial Indian Ocean, along with a 12º eastward shift in the center of action in these anomalies. This combined effect of the increased amplitude and eastward shift in the zonal wind stress increases the SSHA variance over the Indian Ocean, increasing its contribution to the ITF variation. The decadal ITF changes discussed in this study will be crucial in understanding the future global climate variability, strongly coupled to Indo-Pacific interactions.

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High-resolution observations of dissolved isoprene in surface seawater in the Southern Ocean during austral summer 2010–2011     

Sohiko Kameyama  Satoshi Yoshida  Hiroshi Tanimoto  Satoshi Inomata  Koji Suzuki  Hisayuki Yoshikawa-Inoue 《Journal of Oceanography》2014,70(3):225-239

We measured dissolved isoprene (2-methyl-1,3-butadiene; C₅H₈) concentrations in a broad area of the southern Indian Ocean and in the Indian sector of the Southern Ocean from 35°S to 64°S and from 37°E to 111°E during austral summer 2010–2011. Isoprene concentrations were continuously measured by use of a proton-transfer-reaction mass spectrometer combined with a bubbling-type equilibrator. Concentrations of isoprene and its emission flux throughout the study period ranged from 0.2 to 395 pmol L^?1 and from 181 to 313 nmol m^?2 day^?1, respectively, the averages being generally higher than those of previous studies. Although we found a significant linear positive relationship between isoprene and chlorophyll-a concentrations (r ² = 0.37, n = 36, P < 0.001), the correlation coefficient was lower than previously reported. In contrast, in the high-latitude area (>53°S) we identified a significant negative correlation (r ² = 0.59, n = 1263, P < 0.001) between isoprene and the temperature-normalized partial pressure of carbon dioxide (n-pCO₂), used as an indicator of net community production in this study. This suggests that residence times and factors controlling variations in isoprene and n-pCO₂ are similar within a physically stable water column.  相似文献   

Regional 3-D heterogeneities by waveform inversion – application to the Atlantic area     

Satoru Honda  Toshiro Tanimoto 《Geophysical Journal International》1987,91(3):737-753

The waveform inversion method described in Woodhouse & Dziewonski (1984) was modified to retrieve regional scale 3-D heterogeneities by using the minor arc part of seismograms. The lateral heterogeneities are expanded horizontally into blocks (10°× 10°) and radially into Legendre polynomials up to order 3 (0–670 km), and thus the results show much fine details of lateral variation than previous global scale studies. We assumed that the heterogeneities produce the perturbation of eigenfrequencies which are the minor arc average of local eigenfrequency shift. We applied the method to the upper mantle beneath the Atlantic Ocean and its environments. Care was taken about the weighting of the data set. We found that the fit of each seismogram became better when the weighting of each seismogram is proportional to the inverse of initial data residuals. Resolution is good in the triangular region surrounded by South America, Europe, and North America. Resolution is not good in the South Atlantic because of the poor path coverage. Depth resolution is not clear, because of the use of Legendre polynomials, though the results suggest a broad half-width of the order of 200 km or more. We found some similarities between previous global studies and our results. For example, low velocities beneath the East Pacific Rise, Chile Rise and Azores triple junction and a high velocity Canadian shield are obtained. However, there are also differences; the high-velocity zone beneath the Brazilian shield at shallow depth is not a prominent feature in this study. Instead, we found a somewhat unexpected feature near the Romanche and Vema fracture zones where shallow positive anomalies exist. Smoothed results calculated by the spherical harmonic expansion are also shown for the purpose of comparison with global studies.  相似文献   

Intraseasonal SST-precipitation relationship and its spatial variability over the tropical summer monsoon region   总被引：1，自引：1，他引：0  

Mathew Roxy  Youichi Tanimoto  B. Preethi  Pascal Terray  R. Krishnan 《Climate Dynamics》2013,41(1):45-61

The SST-precipitation relationship in the intraseasonal variability (ISV) over the Asian monsoon region is examined using recent high quality satellite data and simulations from a state of the art coupled model, the climate forecast system version 2 (CFSv2). CFSv2 demonstrates high skill in reproducing the spatial distribution of the observed climatological mean summer monsoon precipitation along with its interannual variability, a task which has been a conundrum for many recent climate coupled models. The model also exhibits reasonable skill in simulating coherent northward propagating monsoon intraseasonal anomalies including SST and precipitation, which are generally consistent with observed ISV characteristics. Results from the observations and the model establish the existence of spatial variability in the atmospheric convective response to SST anomalies, over the Asian monsoon domain on intraseasonal timescales. The response is fast over the Arabian Sea, where precipitation lags SST by ~5 days; whereas it is slow over the Bay of Bengal and South China Sea, with a lag of ~12 days. The intraseasonal SST anomalies result in a similar atmospheric response across the basins, which consists of a destabilization of the bottom of the atmospheric column, as observed from the equivalent potential temperature anomalies near the surface. However, the presence of a relatively strong surface convergence over the Arabian Sea, due to the presence of a strong zonal gradient in SST, which accelerates the upward motion of the moist air, results in a relatively faster response in terms of the local precipitation anomalies over the Arabian Sea than over the Bay of Bengal and South China Sea. With respect to the observations, the ocean–atmosphere coupling is well simulated in the model, though with an overestimation of the intraseasonal SST anomalies, leading to an exaggerated SST-precipitation relationship. A detailed examination points to a systematic bias in the thickness of the mixed layer of the ocean model, which needs to be rectified. A too shallow (deep) mixed layer enhances (suppress) the amplitude of the intraseasonal SST anomalies, thereby amplifying (lessening) the ISV and the active-break phases of the monsoon in the model.  相似文献   

Approximate time-dependent analysis of tunnel support structure considering progress of tunnel face     

Shunsuke Sakurai 《国际地质力学数值与分析法杂志》1978,2(2):159-175

The pressure acting on tunnel support structures generally increases with lapse in time. The pressure increase may be caused by not only the time-dependent mechanical properties of the underground medium, but also by the progression of the tunnel face. In order to clarify these two effects, three-dimensional analysis is required. In this study, however, a method which takes into account the three-dimensional effects of the tunnel face progression in two-dimensional plane strain analyses is proposedby introducing the ‘equivalent intial stress’. The proposed method can be easily applied to time-dependent analyses of the behaviour of tunnel support structures installed in a visco-elastic medium. The tunnels considered here are circular in shape, being driven in homogeneous isotropic linear visco-elastic media having hydrostatic initial stresses. In the first part of this paper, detailed discussions of the proposed equivalent initial stress are given. The second deals with the mathematical formulations for obtaining closed-form solutions for the pressure acting on tunnel support structures. In the third, numerical results and discussions are given, and special attetion is paid to the effects of both the time-dependent mechanical properties of the material and the tunnel face progression. Finally, the theoretical results obtained here are utilized for interpretation of field measurements.  相似文献   

Deep water observations of extreme waves with moored and free GPS buoys   总被引：1，自引：1，他引：0  

Takuji Waseda  Masato Sinchi  Keiji Kiyomatsu  Tomoya Nishida  Shunsuke Takahashi  Sho Asaumi  Yoshimi Kawai  Hitoshi Tamura  Yasumasa Miyazawa 《Ocean Dynamics》2014,64(9):1269-1280

Point-positioning GPS-based wave measurements were conducted by deep ocean (over 5,000 m) surface buoys moored in the North West Pacific Ocean in 2009, 2012, and 2013. The observed surface elevation bears statistical characteristics of Gaussian, spectrally narrow ocean waves. The tail of the averaged spectrum follows the frequency to the power of ?4 slope, and the significant wave height and period satisfies the Toba’s 3/2 law. The observations compare well with a numerical wave hindcast. Two large freak waves exceeding 13 m in height were observed in October 2009 and three extreme waves around 20 m in height were observed in October 2012 and in January 2013. These extreme events are associated with passages of a typhoon and a mid-latitude cyclone. Horizontal movement of the buoy revealed that the orbital motion of the waves at the peak of the wave group mostly exceed the weakly nonlinear estimate. For some cases, the orbital velocity exceeded the group velocity, which might indicate a breaking event but is not conclusive yet.  相似文献   

Reduction of future disaster damages by learning from disaster experiences     

Hiroki Onuma  Kong Joo Shin  Shunsuke Managi 《Natural Hazards》2017,87(3):1435-1452

This paper examines the effect of a country’s own past disaster experiences and nearby countries’ past experiences on subsequent disaster damage. We use global disaster data from 1990 to 2010, which include disaster-related death tolls for both natural and technological disasters that are further divided into sub-categories. Overall, we find evidence of a reduction effect of past disaster damage on future disaster damage. More detailed analyses show that an adaptation effect seems to be present for certain combinations of disaster types and levels of economic development. The results show that a country’s own experiences reduce future damage for natural disasters but that the marginal effect is larger for lower-income countries. On the other hand, for technological disasters, a robust impact of experiences was found only in higher-income countries. In terms of the disaster experiences of nearby countries, the adaptation effect was found only for natural disasters, and the marginal impact was relatively higher for higher-income countries.  相似文献   

Discussion on the Paper Entitled “On a Paradox of Elasto-Plastic Tunnel Analysis” by L. Cantieni and G. Anagnostou,Published in Rock Mechanics and Rock Engineering (2011) 44:129–147     

Shunsuke Sakurai 《Rock Mechanics and Rock Engineering》2011,44(6):767-768

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