Origin of the giant eruption cloud of Pinatubo, June 15, 1991     

Takehiro Koyaguchi  Masami Tokuno 《Journal of Volcanology and Geothermal Research》1993,55(1-2)

The series of eruptions of June 15, 1991 at Mt. Pinatubo, Philippines were observed hourly by satellite. A giant discshaped cloud covering an area of 60,000 km² appeared in the satellite images at 14:40, Philippine time. The cloud expanded radially against wind of 20 m/s and spread to an area of more than 120,000 km² within an hour. According to eyewitness accounts there was heavy fine-ash fall after 14:00, intermittent lapilli fall started at about 14:20, and heavy and continuous lapilli fall widely started at about 15:00. The occurrence of the giant cloud roughly corresponded to the initiation of the intermittent lapilli fall.The air-fall deposits of the major eruption are widely distributed, including upwind from the vent. They are composed of 3 units; a silt-size fine-ash layer (Layer B), a lapilli layer commonly including pumice grains of > 1 cm in diameter (Layer C), a lapilli bearing volcanic sand layer (Layer D). Judging from its wide distribution and depletion of coarse, grains, most of the fine ash of Layer B is not distal deposits of a small eruption, but is originated from a large co-ignimbrite cloud. It is suggested that the major eruption started with the generation of a pyroclastic flow, which was subsequently followed by a plinian eruption resulting in the formation of the giant cloud and the lapilli fall.The results of calculations on the dynamics of eruption cloud indicate that the dimension and dynamics of the giant eruption cloud is accounted for by a plinian eruption with a magma discharge rate of the order of 10⁹ kg/s.  相似文献   

Geodetic inversion for space–time distribution of fault slip with time-varying smoothing regularization     

Jun'ichi Fukuda  Shin'ichi Miyazaki  Tomoyuki Higuchi  Teruyuki Kato 《Geophysical Journal International》2008,173(1):25-48

We have developed a new geodetic inversion method for space–time distribution of fault slip velocity with time-varying smoothing regularization in order to reconstruct accurate time histories of aseismic fault slip transients. We introduce a temporal smoothing regularization on slip and slip velocity through a Bayesian state space approach in which the strength of regularization (temporal smoothness of slip velocity) is controlled by a hyperparameter. The time-varying smoothing regularization is realized by treating the hyperparameter as a time-dependent stochastic variable and adopting a hierarchical Bayesian state space model, in which a prior distribution on the hyperparameter is introduced in addition to a conventional Bayesian state space model. We have tested this inversion method on two synthetic data sets generated by simulated aseismic slip transients. Results show that our method reproduces well both rapid changes of slip velocity and steady-state velocity without significant oversmoothing and undersmoothing, which has been hard to overcome by the conventional Bayesian approach with time-independent smoothing regularization. Application of this method to transient deformation in 2002 caused by a silent earthquake off the Boso peninsula, Japan, also shows similar advantages of this method over the conventional approach.  相似文献   

Interannual variations of the Hawaiian Lee Countercurrent induced by potential vorticity variability in the subsurface     

Hideharu Sasaki  Shang-Ping Xie  Bunmei Taguchi  Masami Nonaka  Shigeki Hosoda  Yukio Masumoto 《Journal of Oceanography》2012,68(1):93-111

Interannual variations of the Hawaiian Lee Countercurrent (HLCC) in the 2000s were investigated using satellite and Argo profiling float observations. The satellite-observed sea surface height shows that the geostrophic eastward current was anomalously strong to the west away from Hawaii in 2003 and 2005. However, the trade winds and the orographic wind curl dipole in the lee of Hawaii that drives the climatological mean HLCC were not particularly strong in these years, suggesting that the accelerations of the HLCC were not caused by the wind stress curl forcing around Hawaii and subsequent Rossby wave propagation. Using Argo observations, we found negative potential vorticity (PV) anomalies in the subsurface north of the HLCC in these 2 years. The pycnocline is lifted northward as low PV waters of different densities stack up in the vertical, and the HLCC is then accelerated via the thermal wind. The intensification and/or southward intrusion of the eastern subtropical mode water and subtropical mode water seem to have induced negative PV anomalies in 2003 and 2005, respectively. Using high-resolution ocean simulations, we confirmed the migrations of PV anomalies and their contributions to the HLCC accelerations. Although the HLCC is located away from the cores of major mode waters, our results suggest that interannual variations of the HLCC are affected by those of mode waters.  相似文献   

Decadal variability of the Kuroshio Extension: mesoscale eddies and recirculations   总被引：1，自引：0，他引：1  

Bunmei Taguchi  Bo Qiu  Masami Nonaka  Hideharu Sasaki  Shang-Ping Xie  Niklas Schneider 《Ocean Dynamics》2010,60(3):673-691

An eddy-resolving multidecadal ocean model hindcast simulation is analyzed to investigate time-varying signals of the two recirculation gyres present respectively to the north and south of the Kuroshio Extension (KE) jet. The northern recirculation gyre (NRG), which has been detected at middepth recently by profiling float and moored current meter observations, is a major focus of the present study. Low-frequency variations in the intensity of the recirculation gyres are overall highly correlated with decadal variations of the KE jet induced by the basin-wide wind change. Modulation of the simulated mesoscale eddies and its relationship with the time-varying recirculation gyres are also evaluated. The simulated eddy kinetic energy in the upstream KE region is inversely correlated with the intensity of the NRG, consistent with previous observational studies. Eddy influence on the low-frequency modulation of the NRG intensity at middepth is further examined by a composite analysis of turbulent Sverdrup balance, assuming a potential vorticity balance between the mean advection and the convergent eddy fluxes during the different states of the recirculation gyre. The change in the NRG intensity is adequately explained by that inferred by the turbulent Sverdrup balance, suggesting that the eddy feedback triggers the low-frequency modulation of the NRG intensity at middepth.  相似文献   

多传感器不同分辨率遥感数字图像的尺度转换   总被引：14，自引：0，他引：14  

布和敖斯尔  马建文  王勤学  金子正美  福山龙次 《地理学报》2004,59(1):101-110

针对日益增多的多传感器不同分辨率的遥感数字图像数据,提出其综合利用和尺度转换的有效方法。其中,作为尺度上推 (scaling-up) 技术,本研究选择IHS和小波分解变换两种数据融合方法,应用Landsat ETM+数据和IRS-1C数据进行了实例研究。发现: IHS方法操作简单,对两种待融合的图像的像元大小和像元数 (bit数) 的依赖不是很高,而对原始图像光谱信息的依赖很高,因此适用于不同传感器之间的数据融合上,其缺点就是不能够更多的保留原始多光谱数据的光谱信息。小波分解变换 (WD) 方法可以很好地保留多光谱传感器的所有光谱信息,但是在重采样中对两种待融合的图像的像元配准的要求很高,因此比较适合于对同一传感器的多光谱数据与全色光谱数据的融合上。作为尺度下退 (scaling-down) 技术,通过探讨将札幌野外实验站点数据镶嵌到高时间分辨率遥感图像的问题,提出像元级尺度扩展的具体操作方法和对NDVI图像进行扩展时出现混合像元的识别方法。应用AVHRR, MODIS, ETM+和ASTER的NDVI图像数据进行了像元尺度的扩展研究。得出: 对不同传感器的不同分辨率的数据之间进行像元级的尺度扩展后,能够较好地识别出不同地物的分布边界,较好的分辨混合像元,因此其结果可用于对不同地物分布特征的分类研究或土地覆盖变化中的时间序列变化的研究中。  相似文献   

Charcoal records from thermokarst deposits in central Yakutia, eastern Siberia: Implications for forest fire history and thermokarst development     

Fumitaka Katamura  Masami Fukuda  Nikolai Petrovich Bosikov  Roman Vasilievich Desyatkin 《Quaternary Research》2009,71(1):36-664

Macroscopic charcoal records from a thermokarst lake deposit in central Yakutia, eastern Siberia, were used to reconstruct the history of forest fires and investigate its relationship to thermokarst initiation. High accumulation rates of charcoal and pollen were coincident in the basal deposits of the thermokarst lake, which suggests that both were initially deposited on the forest floor and subsequently reworked and accumulated in the thermokarst depression. High charcoal and pollen accumulation rates in the basal deposits, dating to 11,000-9000 cal yr BP, also indicate that the thermokarst topography developed during the early Holocene. A lower charcoal accumulation rate after ca. 9000 cal yr BP suggests that thermokarst development has been inhibited since this time. It also indicates that a surface-fire regime has been predominant at least since ca. 9000 cal yr BP in central Yakutia.  相似文献   

Compensatory response of the unicellular-calcifying alga <Emphasis Type="Italic">Emiliania huxleyi</Emphasis> (Coccolithophoridales,Haptophyta) to ocean acidification     

Shin-ya Fukuda  Iwane Suzuki  Takeo Hama  Yoshihiro Shiraiwa 《Journal of Oceanography》2011,67(1):17-25

Ocean acidification damages calcareous organisms, such as calcifying algae, foraminifera, corals, and shells. In this study, we made a device equipped with a Clark-type oxygen electrode and a pH-stat to examine how the most abundant calcifying phytoplankton, the coccolithophorid Emiliania huxleyi, responded to acidification and alkalization of the seawater medium. When E. huxleyi was incubated at pH 8.2, close to oceanic pH, the medium was alkalized during photosynthesis, and the alkalization rate [determined as μmol HCl added (mg Chl)⁻¹ h⁻¹] was identical to the activity of photosynthesis [determined as μmol O₂ evolved (mg Chl)⁻¹ h⁻¹]. When pH was maintained at 7.2 by the pH-stat, alkalization activity was stimulated and exceeded photosynthetic activity, resulting in an increase in the ratio of alkalization to photosynthesis (Alk/PS). On the other hand, no alkalization and photosynthesis were observed at pH 9.2. In contrast, acidification of seawater was observed in the dark because of the release of respiratory CO₂ from cells at pH 8.2–9.2, but not at pH 7.2. When orthophosphate was rapidly depleted within a day in the batch culture, intracellular calcification gradually increased, and both photosynthesis and alkalization decreased gradually. During the period the Alk/PS ratio also decreased gradually. These results indicate that E. huxleyi possesses an ability to compensate for the acidification of seawater when photosynthesis is more actively driven than respiration. These results suggest that the E. huxleyi cells may not be severely damaged by oceanic acidification during photosynthesis because of their homeostatic function to avoid negative effects on cellular activity. Finally, we concluded that E. huxleyi cells possess a buffering ability to reduce acidification effects when photosynthesis is actively driven.  相似文献   

Source model of Noto-Hanto-Oki earthquake tsunami of 7 February 1993   总被引：1，自引：0，他引：1  

Kuniaki Abe  Masami Okada 《Pure and Applied Geophysics》1995,144(3-4):621-631

A source model was discussed for a small tsunami accompanied by the Noto-Hanto-Oki earthquake (M _s 6.6), striking Japan on 7 February, 1994. Assuming a fault model under the sea bottom, we estimated the focal parameters jointly, using synthesized tsunami source spectra as well as the tsunami numerical simulation. The fault proposed by this study consists of a plane sized 15×15 km, dipping N47°W with the dip angle of 42°, which is almost pure reverse fault (slip angle 87°) with a dislocation of 1 meter. The numerical simulation shows that the shallow sea in the source region caused a comparatively long recurring tsunami (the periods are 12–18 minutes) in spite of its small size. The model fault is corresponding to an aftershock area of this earthquake.  相似文献   

Structure of hydrous aluminosilicate glasses along the diopside-anorthite join: A comprehensive one- and two-dimensional H and Al NMR study     

Xianyu Xue  Masami Kanzaki 《Geochimica et cosmochimica acta》2008,72(9):2331-2348

We have taken a systematic approach utilizing advanced solid-state NMR techniques to gain new insights into the controversial issue concerning the dissolution mechanisms of water in aluminosilicate melts (glasses). A series of quenched anhydrous and hydrous (∼2 wt% H₂O) glass samples along the diopside (Di, CaMgSi₂O₆)—anorthite (An, CaAl₂Si₂O₈) join with varying An components (0, 20, 38, 60, 80, and 100 mol %) have been studied. A variety of NMR techniques, including one-dimensional (1D) ¹H and ²⁷Al MAS NMR, and ²⁷Al → ¹H cross-polarization (CP) MAS NMR, as well as two-dimensional (2D) ¹H double-quantum (DQ) MAS NMR, ²⁷Al triple-quantum (3Q) MAS NMR, and ²⁷Al → ¹H heteronuclear correlation NMR (HETCOR) and 3QMAS/HETCOR NMR, have been applied. These data revealed the presence of SiOH, free OH ((Ca,Mg)OH) and AlOH species in the hydrous glasses, with the last mostly interconnected with Si and residing in the more polymerized parts of the structure. Thus, there are no fundamental differences in water dissolution mechanisms for Al-free and Al-bearing silicate melts (glasses), both involving two competing processes: the formation of SiOH/AlOH that is accompanied by the depolymerization of the network structure, and the formation of free OH that has an opposite effect. The latter is more important for depolymerized compositions corresponding to mafic and ultramafic magmas.Aluminum is dominantly present in four coordination (Al^IV), but a small amount of five-coordinate Al (Al^V) is also observed in all the anhydrous and hydrous glasses. Furthermore, six-coordinate Al (Al^VI) is also present in most of the hydrous glasses. As Al of higher coordinations are favored by high pressure, Al^VIOH and Al^VOH may become major water species at higher pressures corresponding to those of the Earth’s mantle.  相似文献   

Gravity measurements with a portable absolute gravimeter A10 in Syowa Station and Langhovde,East Antarctica     

Takahito Kazama  Hideaki Hayakawa  Toshihiro Higashi  Shingo Ohsono  Shunsuke Iwanami  Tomoko Hanyu  Harumi Ohta  Koichiro Doi  Yuichi Aoyama  Yoichi Fukuda  Jun Nishijima  Kazuo Shibuya 《Polar Science》2013,7(3-4):260-277

Absolute gravity values were measured with a portable absolute gravimeter A10 in East Antarctica, for the first time by the Japanese Antarctic Research Expedition. This study aims to investigate regional spatiotemporal variations of ice mass distributions and associated crustal deformations around Syowa Station by means of repeated absolute gravity measurements, and we obtained the first absolute gravity value in Southern Langhovde on the Antarctic Continent. The average absolute gravity value at the newly installed benchmark AGS01 in Langhovde (obtained on 3 February 2012) was 982535584.2 ± 0.7 μgal (1 [μgal] = 1 × 10^?8 [m/s²]), which was in agreement with the gravity values obtained by the past relative gravity measurements within 1 mgal. In addition, the average absolute gravity value obtained at AGSaux in Syowa Station was consistent with both previous absolute gravity values and those obtained by simultaneous measurements using an FG5 gravimeter, owing to adequate data corrections associated with tidal effects and time variations in atomic clock frequencies. In order to detect the gravity changes associated with the ice mass changes and other tectonic phenomena, we plan to conduct absolute gravity measurements at AGS01 again and at other campaign sites around Syowa Station as well in the near future, with careful attention paid to the impacts of severe environmental conditions in Antarctica on gravity data collection.  相似文献