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Volume 58
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- Reproduction of Mogi-Yamakawa's Model Using FEM -Takayuki Sakai, Tetsuya Yamamoto, Keiichi Fukui, Kenji Fujiwara, Akimi ...2007 Volume 58 Pages 1-15
Published: 2007
Released on J-STAGE: July 10, 2007
JOURNAL FREE ACCESSAnalytical solutions derived under very simplified conditions have been used to explain the crustal deformation around volcanoes. One example is Yamakawa's solution (Yamakawa, 1955), which represents surface deformation caused by small enough spherical pressure source at some depth within a semi-infinite homogeneous elastic body. However, such solutions do not exactly hold true in a real volcano, due to the volcanic edifices that project from the earth's surface, non-spherical pressure sources, inhomogeneous crustal structures, and so on. We use the finite element method (FEM) to create numerical models of a volcano for investigating crustal deformation of a real volcano. The size of the FE model or the setting of its boundary conditions will likely affect the precision of calculation for volcanic crustal deformation. Therefore, we reproduced Mogi-Yamakawa's model (or Mogi's model) using FE models of various model sizes and boundary conditions. We then quantitatively evaluated the influence of model size and boundary conditions on the precision of calculation. The results are as follows. As the FE model becomes larger, the results of FE analysis approach Yamakawa's solution, which demonstrates an improved precision of calculation. However, the smallest possible FE model is recommended so far as the necessary precision of calculation is ensured, because a large model generally produces a large number of nodes which leads to an accelerative increase in calculation time. The boundary condition of fixing bottom and side surfaces of an FE model completely is recommended because the changes in precision of calculation with distance are similar for both vertical and horizontal displacements. The vertical and horizontal sizes of the FE model remarkably affect the precision of calculation for vertical and horizontal displacements, respectively.View full abstractDownload PDF (607K) -
- Calculation by Finite Element Method -Takayuki Sakai, Tetsuya Yamamoto, Keiichi Fukui, Kenji Fujiwara, Akimi ...2007 Volume 58 Pages 17-30
Published: 2007
Released on J-STAGE: July 10, 2007
JOURNAL FREE ACCESSMogi-Yamakawa's model (or Mogi's model) has often been used to explain crustal deformation observed around volcanoes. This model is based on an analytical solution derived by Yamakawa (1955), which only holds good under the restricted condition that a small enough spherical pressure source exists at some depth within a semi-infinite homogeneous elastic body. However, there have been hardly any quantitative investigations of the application limit of this solution when a/D (a : radius of the sphere, D : depth of the sphere) increases. McTigue (1987) modified Yamakawa's solution so as to hold good even for large a/D. However, there have been no quantitative investigations of the application limit when a/D increases for this solution either. Therefore, we created large a/D numerical models using the finite element method (FEM) and found numerical solutions of surface deformation. Comparison with FE analyses clarified the limits of application of these two analytical solutions. For example, the values of a/D that agree with FE analyses within 1% are 0.22 for Yamakawa's solution and 0.45 for McTigue's solution. These two analytical solutions may hold precisely with smaller a/D values. However, the discrepancy between these two solutions and FE analysis gradually increases when a/D exceeds these values. In contrast, if D and a are determined by applying Yamakawa's solution to results of FE analyses, D is found to be determined much shallower than the true value, while a is determined with relative precision. Therefore, ΔV (volume change of the spherical pressure source) may also be estimated with relative precision.View full abstractDownload PDF (570K) -
Akio Katsumata2007 Volume 58 Pages 31-61
Published: 2007
Released on J-STAGE: July 10, 2007
JOURNAL FREE ACCESSThe magnitude determination scheme of the Japan Meteorological Agency (JMA) was revised in September 2003. This paper presents a formula for velocity magnitudes that underlies the revision. Depth dependence of the velocity magnitudes is determined so as to agree with JMA displacement magnitude for earthquakes shallower than 150km and with moment magnitudes for those deeper than 150km. The velocity magnitudes were consistent with the moment magnitude estimated with the F-net for earthquakes shallower than 550km. A comparison of velocity magnitudes and displacement magnitudes of earthquakes from 1977 to 2004 indicates that there is no noticeable temporal change except for a step of about +0.06 during the renovation of the JMA seismic network in 1994.View full abstractDownload PDF (1212K) -
Fumiaki Fujibe, Nobuo Yamazaki, Kenji Kobayashi, Hiroshi Nakamigawa2007 Volume 58 Pages 63-72
Published: 2007
Released on J-STAGE: August 01, 2007
JOURNAL FREE ACCESSLong-term changes and short-term variations of extreme temperatures in Japan were analyzed using daily maximum and minimum temperature data at 17 stations for 1931-2005, and 850hPa temperature data at 12 stations for 1961-2005. The analysis was made for (1) monthly highest, lowest and average values of departure from the climatic mean, (2) frequencies of departures exceeding 2σ , and (3) day-to-day temperature variability, which was defined the standard deviation of temperature departure. The result for maximum temperature reveals nearly parallel increase of monthly highest, lowest and average values, at a higher rate in the recent few decades (0.08°C/decade for 1931-2005 and 0.4-0.5°C/decade for 1981-2005), without a trend in day-to-day variability. A similar feature is found for 850hPa temperature. Minimum temperature shows more rapid increase than the other quantities, especially for the monthly lowest value (0.27°C/decade for 1931-2005 and 0.51°C/decade for 1981-2005), with decreasing day-to-day variability. On a short time scale of several months to a year, variations in extreme temperatures are closely related to those of monthly average temperature, and also of day-to-day variability. A lag correlation analysis and a principal component analysis indicate that the anomaly of day-to-day variability tends to last for several months to a year, and is correlated to the anomaly of north-south temperature gradient.View full abstractDownload PDF (967K) -
Tosiyuki Nakaegawa, Takayuki Tokuhiro, Akira Itoh, Masahiro Hosaka2007 Volume 58 Pages 73-83
Published: 2007
Released on J-STAGE: August 01, 2007
JOURNAL FREE ACCESSThe present study evaluates the reproducibility of the climatological seasonal cycles of three hydrological variables, soil moisture, river discharge and terrestrial water storage in the Japan Meteorological Agency Land Data Analysis (LDA) by means of a system consisting of the LDA and a global river-routing model (LDAG). LDAG satisfactorily reproduces the seasonal cycle of soil moisture at most of the observation stations; however, negative correlations are found at stations in the mid latitudes of east Eurasia. The amplitudes of river discharge are well reproduced only in a few rivers. The relative errors of the amplitudes exceed 20% in many of the rivers. The correlation coefficients of the seasonal cycle are more than 0.5 in most of the 70 rivers investigated. The phase differences occur within one month in most of the rivers. The relative errors of the amplitude of terrestrial water storage are less than 10% in five of the top 10 largest river basins, and the correlations are high at the river basins located in areas such as the tropics and the Asian Monsoon region. The LDAG phases are generally earlier, similar to those of river discharge. Close examinations demonstrate that better reproducibility requires improvements in both the numerical model and the forcing data. Despite good reproducibility only in some river basins, the hydrological variables produced by LDAG may be useful for land surface initial conditions for weather forecasts and hydrological studies.View full abstractDownload PDF (759K) -
Hiroshi Tanimoto, Yousuke Sawa, Hidekazu Matsueda, Seiichiro Yonemura, ...2007 Volume 58 Pages 85-93
Published: 2007
Released on J-STAGE: August 31, 2007
JOURNAL FREE ACCESSAn international exercise to directly assess the consistency of standards and methods for measuring carbon monoxide (CO) was conducted as part of the East Asian Regional Experiment 2005 (EAREX 2005) in the framework of the Atmospheric Brown Clouds (ABC) project. Four groups representing Japan, Korea, Hong Kong, and Taiwan made comparisons at the Gosan super-site on Jeju Island, Korea, in March 2005, by setting up individual instruments with gas standards which are commonly used in ground-based monitoring programs in Asia. Intensive comparisons between two Japanese groups showed that a non-dispersive infrared absorption (NDIR) instrument agreed fairly well with a gas chromatograph / reduction gas detector (GC/RGD) with 1-h time resolution, confirming that NDIR methods are useful for monitoring, in particular, large temporal variations of CO in ambient air. Although international comparison of ambient measurements by NDIR indicated general agreement, comparison of gas standards revealed difficulties in preparing accurate and stable standard gases for monitoring CO at ambient levels.View full abstractDownload PDF (396K) -
Shigeru Onogi, Akihiro Hori2007 Volume 58 Pages 95-101
Published: 2007
Released on J-STAGE: October 03, 2007
JOURNAL FREE ACCESSRecently, semiconductor light-emission devices, tunable-diode lasers (TDLs) and light-emission diodes (LEDs), have begun being used as light sources for infrared absorption hygrometers. In order to use these semiconductor light emission devices for a two-wavelength infrared absorption hygrometer to measure the humidity inside a cloud chamber containing ice particles and aerosols, two light beams emitted from two devices must be combined into one beam so that the hygrometer measures the same measuring volume with two wavelengths. Incandescent light has a very wide wavelength band including two wavelengths that can be used for infrared absorption hygrometers.
We decided to develop an infrared absorption hygrometer to measure the humidity inside a cloud chamber containing ice particles and aerosols using an incandescent light source and subsequently fabricated a prototype hygrometer to measure humidity at normal temperature and ordinary pressure. This prototype hygrometer has an optical beam splitter and two optical filters to measure two wavelength bands of infrared, the water vapor absorption band at 1.9μm and a nonabsorption band at 1.6μm. The prototype needs no rotating filter motor that may cause mechanical vibration, and it has variable measuring path lengths up to several meters. The calibration data demonstrate that the hygrometer has a measurement accuracy within ±5% for relative humidity when the temperature varies within two degrees. In the future, we will improve the accuracy and stability for measuring humidity and examine how to install the hygrometer in the cloud chamber.View full abstractDownload PDF (578K) -
Akiyoshi Wada2007 Volume 58 Pages 103-126
Published: 2007
Released on J-STAGE: October 12, 2007
JOURNAL FREE ACCESSWhen tropical cyclone (TC) intensity is predicted using a sophisticated numerical model under a given initial condition with a typhoon bogus, numerical problems, particularly associated with the tendency errors, arise as well as problems related to the intensity limitation due to relatively coarse horizontal resolution. In order to investigate the problems, numerical experiments are performed for nine TCs in the western North Pacific from 2000 to 2002 using the typhoon model (TYM) and typhoon-ocean coupled model (CTYM). CTYM reduces the overdevelopment that occurs in the later integration predicted by TYM due to local sea surface cooling caused by the passage of TCs. However, CTYM hardly improves the tendency errors that occur in the early integration. The errors are found in all predictions using CTYM with each of the three physical schemes and have different characteristics for typhoons Bilis (2000), Wutip (2001), and Phanfone (2002). The TC thermodynamic structures of Wutip also differ from the three predictions using CTYM with each of the three schemes even at almost the same integration time and central pressure. Under the steady-state assumption, we estimate the maximum potential intensity (MPI) for three schemes and two TCs from the two-dimensional axisymmetrical mean structure. Assuming that the MPI is estimated from the net gain energy through the isothermal process scale-analyzed from the Colioris force and adiabatic process from the centrifugal force, it is found that predominance of convective available potential energy due to the adiabatic process leads to the underdevelopment of TCs. The improvement of physical schemes in CTYM is planned for the underdevelopment: revising a surface boundary formulation or introducing a sophisticated planetary boundary formulation contributes to increasing the energy caused by the isothermal process, while revising the precipitation or cumulus parameterization contributes to reducing the energy caused by the adiabatic process.View full abstractDownload PDF (1617K) -
Hiroyuki Takayama, Hidekuni Kuroki, Kenji Maeda2007 Volume 58 Pages 127-134
Published: 2007
Released on J-STAGE: November 01, 2007
JOURNAL FREE ACCESSWe investigated the mechanism of occurrence order of two adjacent great interplate earthquakes, the Tonankai and the Nankai earthquakes, along the Nankai trough using a numerical simulation method. We set two asperities modeling the Tonankai and the Nankai earthquakes on a plate interface that is assumed to be flat or 3D curved, and adopt a rate- and state-dependent friction law to be applied to the interface. For the flat-plate interface, the occurrence order of two earthquakes is determined by chance when asperities are equal in size and have the same value of the friction parameter a-b. The smaller asperity slips first when the sizes of asperities differ, and the asperity having smaller absolute value of a-b slips first when the values differ. For the 3D-shaped interface modeled for the actual plate configuration, the eastern asperity (Tonankai) slips first and the western one (Nankai) follows when the size and the value of a-b for the two asperities are set equal. However, when the absolute value of a-b for the two asperities is 10% smaller than the former case, the western asperity slips first because the stress concentration rates at the eastern edges of the Tonankai and Nankai areas change order of magnitude depending on the value of a-b.View full abstractDownload PDF (2445K) -
Naoko Kitabatake, Shunsuke Hoshino, Kotaro Bessho, Fumiaki Fujibe2007 Volume 58 Pages 135-153
Published: 2007
Released on J-STAGE: November 30, 2007
JOURNAL FREE ACCESSTyphoon Songda (0418), which damaged much of the Japan Islands with strong winds, underwent extratropical transition (ET) and reintensified while it moved northeastward in the Sea of Japan. The features associated with Songda during ET are investigated by using data of various satellite-borne sensors. The interaction of the cyclone with the midlatitude environment is also diagnosed and discussed by using the gridded dataset of regional analysis (RANAL) produced by the Japan Meteorological Agency. The satellite observations reveals dissipation of the eyewall, formation of a convective rainband accompanied by warm frontogenesis, and some features characteristic of a wind field around a tropical cyclone undergoing ET, e.g., a "horseshoe" gale/storm-force winds shape and an axis of minimum winds extending northeastward from the cyclone center. The satellite data also suggest that a disturbance that originates in the upper tropospheric westerly interacts with the tropical cyclone at the ET stage. The representation of Songda in RANAL is generally consistent with the satellite observations. Diagnoses of upper-tropospheric flows and the quasi-geostrophic omega equation suggest baroclinic development of Songda due to its interaction with a disturbance that originates in the upper troposphere in the midlatitude westerly. Finally it is pointed out that the interaction between the tropical cyclone and the baroclinic disturbance may cause ambiguity of the cyclone center.View full abstractDownload PDF (4236K) -
Takuya Hasegawa, Tamaki Yasuda, Kimio Hanawa2007 Volume 58 Pages 155-166
Published: 2007
Released on J-STAGE: December 26, 2007
JOURNAL FREE ACCESSThe upper ocean heat content (OHC) anomaly field in the North Pacific is analyzed to explore its relationship with the Aleutian Low (AL), Kuroshio transport (KT), core-layer temperature of the North Pacific subtropical mode water (CLT), sea-surface temperature (SST), and sea-level pressure (SLP) on a multidecadal timescale. It is found that the OHC anomaly circulates clockwise around the North Pacific subtropical gyre and that the clockwise propagation is closely linked to AL, KT and CLT after 1980. It was pointed out that five years after the intensification of AL, the volume transport associated with KT started to increase, and several years later, the magnitudes of the CLT and the OHC anomalies in the region southeast of Japan also began to increase. Such a relationship is similar to that on an interdecadal scale pointed out in previous studies. It is also shown that the OHC, SST and SLP anomalies are in phase to the southeast of Japan and also in the mid-latitudes of the central Pacific to the east of the Kuroshio Extension. In these regions, the clockwise propagation of OHC is found to have been enhanced. The results of this study provide new information on the spatio-temporal variability of the OHC anomalies and their relationship to the related atmospheric and oceanic anomaly fields on a multidecadal scale.View full abstractDownload PDF (1635K)
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