Estimating the sea surface dynamic topography from Geosat altimetry data     

Kaoru Ichikawa  Shiro Imawaki 《Journal of Oceanography》1996,52(1):43-68

Optimal interpolation method is applied to Geosat altimetry data both to remove orbit error and to separate temporal mean sea surface dynamic topography (SSDT) from temporal fluctuations around the mean. Loss of long-wavelength oceanic signals at orbit error reduction procedure is smaller in this method than that in conventional collinear methods, but the areal average height over the study domain is still removed as the orbit error. The fluctuation SSDT is quantitatively evaluated by sea level data from tide gauge stations at Japanese islands. The correlation coefficient of the two sea-level variations is 0.83 when the loss of the areal average is compensated by the seasonal variation of the areal average height determined from the climatological monthly-mean SSDT. In addition, the improvement of the geoid model by combined use of Seasat altimetry data and hydrographic data is validated through the estimated temporal mean SSDT. In a local area where hydrographic data contemporary with the Seasat mission exist, the geoid model has been significantly improved so that the absolute SSDT can be determined from combination of the altimetry data and geoid model; the absolute SSDT describes the onset event of a quasi-stationary large meander of the Kuroshio south of Japan very well. Outside this local area, however, errors of several tens of centimeters still remain in the improved geoid model.  相似文献   

Clay mineral composition in shallow water sediment samples near the Antarctic Peninsula and in deep-sea core samples from the pacific and the Indian-Antarctic Basins     

Saburo Aoki  Kaoru Oinuma 《Journal of Oceanography》1980,36(1):23-29

Clay minerals in seven shallow water (100 to 600 m deep) dredged samples and in two deep-sea (3,000 to 5,000 m deep) core samples near West Antarctica were investigated by X-ray diffraction analyses. Variation of montmorillonite concentration appears to be closely related to volcanic activity. Chlorite is the most dominant constituent in most of the dredged samples, though it is not a principal component in core samples. Illite concentration is negatively correlated to that of montmorillonite. Kaolinite is found in four out of seven dredged samples near and around the Antarctic Peninsula while the content of kaolinite in two deep-sea cores from the Pacific-Antarctic Basin and the Indian-Antarctic Basin is more abundant than in the dredged samples. The clay mineral composition in the latter two basins may be closely related to volcanic activity and mechanical weathering products near and on Antarctica.  相似文献   

Quantitative risk assessment for future meteorological disasters     

Kaoru Tachiiri  Masato Shinoda 《Climatic change》2012,113(3-4):867-882

The 2007 Intergovernmental Panel on Climate Change report stated that in many regions extreme climate events are becoming increasingly frequent and that this trend will continue. However, few quantitative studies have examined the damage to society or industry that may be caused by future meteorological disasters. This study quantitatively estimates the risk of future drought and winter disasters (dzud) in Mongolia leading to massive livestock loss by applying an empirical tree-based model to data derived from the basic local trend in projections of an Earth system model (a climate model coupled with ecosystem models) based on the Special Report on Emissions Scenario A2. The results indicate that drought is the dominant factor for high livestock mortality, and the frequency of meteorological disasters leading to high livestock mortality during 2010–2099 will be lower than that during 1940–2003, mainly because of a slight increase in the leaf area index (LAI, representing forage for livestock), which is caused by increased summer rainfall. The increased precipitation in summer is likely caused mainly by increased precipitable water due to higher air temperature, rather than changes in atmospheric circulation. By the end of the 21st century, however, LAI will drop in the southern most province of Mongolia, inducing severe livestock mortality. This will be caused by extremely high temperatures, which may continue to increase in degree and extent after 2100 if climate change continues.  相似文献   

Anomalous atmospheric events leading to Kyushu’s flash floods,July 11–14, 2012     

Weili Duan  Bin He  Kaoru Takara  Pingping Luo  Daniel Nover  Yosuke Yamashiki  Wenrui Huang 《Natural Hazards》2014,73(3):1255-1267

During July 11–14, 2012, deadly floods and landslides triggered by a series of unprecedented heavy rains hit Kyushu, Japan, causing at least 32 deaths and around 400,000 evacuations. We focus on synoptic anomalies identified after inspecting rainfall patterns and documenting the conditions associated with this tragic event using data combined from the Global Rainfall Map in Near Real Time data, the NCEP/NCAR Reanalysis dataset, and the global forecast system. Rainfall maps indicated that there were many heavy rains in Kyushu in these days and this disaster was associated with the pattern of forecasts and standardized anomalies. A weather trough with positive height anomalies appeared, the center of which moved to the north of Japan over this period, which might cause wind anomalies and whereby lots of water vapor were transported to Kyushu area with up to 90 m s^?1, and high values of precipitable water formed with up to 60 mm. These results suggest that a larger-scale pattern is conducive for heavy rainfall and the anomalies put the pattern in context as to the potential for an extreme rainfall event, which can provide insights and methods for predicting extreme events’ or something similar.  相似文献   

Susceptibility assessment of the precursor stage of a landslide threatening Haivan Railway Station,Vietnam     

Lam Huu Quang  Doan Huy Loi  Kyoji Sassa  Kaoru Takara  Hirotaka Ochiai  Khang Dang  Shinro Abe  Shiho Asano  Do Ngoc Ha 《Landslides》2018,15(2):309-325

Haivan Station is an important station on the North-South railway line in central Vietnam. Field investigation has identified a precursor stage of a landslide that would threaten this railway. Therefore, a landslide susceptibility assessment for Haivan Station was urgently needed to protect passenger safety and the national railway. Conducted investigations included air-photo interpretation, drilling, ground water and inclinometer monitoring, laboratory testing, and landslide simulation. This research applied the undrained dynamic loading ring shear apparatus ICL-2 to drill-core samples from the precursor landslide. Samples for ring shear tests were taken from sandy soil layers found at depths of ~21, ~31, and ~50 m in the cores. Each of these was believed to be a possible sliding surface of a landslide, and all were tested to shear failure in the ICL-2 apparatus. The boundary between highly weathered granitic rock and weathered granitic rock was identified at about 50 m depth. The inclinometer monitoring detected slight movement at this depth. Therefore, the present day risk of a landslide forming at 50 m is higher than for one forming at either 21 or 31 m. The landslide dynamic parameters obtained from the ring shear test of the 50-m-deep sample were used in an integrated numerical simulation model LS-RAPID. The simulation result gave the critical pore-pressure ratio for landslide occurrence, and landslide’s likely maximum speed, total volume, and depth of landslide debris that could cover the railway. These estimates serve to raise awareness of the vulnerability of the Vietnam national railway sector to landslide impact.  相似文献   

Quasiperiodic small meanders of the Kuroshio off Cape Ashizuri and their inter-annual modulation caused by quasiperiodic arrivals of mesoscale eddies     

Motohiko Kashima  Shin-Ichi Ito  Kaoru Ichikawa  Shiro Imawaki  Shin-Ichiro Umatani  Hiroshi Uchida  Takashi Setou 《Journal of Oceanography》2009,65(1):73-80

A quasiperiodic variation of 100–110 days in the Kuroshio path off Cape Ashizuri, resulting from the passage of small meanders, was detected by observation with moored current meters during 1993–1995. TOPEX/POSEIDON altimeter data covering 9 years showed that the quasiperiodic variation period was not persistent and modulated twice, with a ∼110-day period from mid-1993 to late 1996, a ∼150-day period from late 1996 to mid-1999, and a ∼110-day period from mid-1999 to late 2001. The quasiperiodic variations of the Kuroshio path migration were contemporaneous with the quasiperiodic arrivals of mesoscale eddies from the east along 27–32°N over the same ∼110- and ∼150-day period quasiperiodic variations. The periodic arrivals of the eddies configure the periodic variations of the Kuroshio path and its inter-annual modulation.  相似文献   

Role of phase equilibrium in frost heave of fine-grained soil under negligible overburden pressure     

Yoshisuke Nakano  Kaoru Horiguchi 《Advances in water resources》1985,8(2):50-68

The role of the phase equilibrium of water in frost heave was studied for two kinds of soil. The rate of frost heave and the rate of water intake were measured simultaneously under various rates of heat removal. The experimental data revealed a trend common for both soils that the rate of water intake attains its maximum at a certain critical rate of heat removal. The data were analyzed by using equations accurately describing the relation between these rates. The results of the analysis indicate a serious doubt about the validity of phase equilibrium in the system. Alternatively, an assumption was introduced that supercooling occurred between a frost front and an unfrozen part of the soil. It was shown that supercooling could explain the data well under certain conditions.  相似文献   

Role of heat and water transport in frost heaving of fine-grained porous media under negligible overburden pressure     

Yoshisuke Nakano  Kaoru Horiguchi 《Advances in water resources》1984,7(2):93-102

An equation accurately describing the rate of frost heave is derived by using the mixture theory of continuum mechanics. It is shown that the rate of frost heave is determined mainly by the rate of heat removal and the rate of water intake. When the phase equilibrium holds in the system, the relation between the rate of heat removal and the rate of water intake is shown to depend mainly on the phase composition data of a given medium.By studying reported experimental data, it is found that the phase equilibrium may hold until th rate of heat removal reaches a certain critical value. When the rate of heat removal exceeds this critical value, the phase equilibrium may possibly be disrupted for some media.  相似文献   

Analysis of stream water quality and estimation of nutrient load with the aid of Quick Bird remote sensing imagery     

Bin He  Kazuo Oki  Yi Wang  Taikan Oki  Yosuke Yamashiki  Kaoru Takara 《水文科学杂志》2013,58(5):850-860

Abstract

Human activities have created high nutrient surpluses in agricultural lands due to the increasing rate of chemical fertilizer application and the increase in livestock production. To analyse the nutrient characteristics and estimate the nutrient load in streams, we conducted extensive field survey and water quality experiments from 2007 to 2008 in Koise River, a major river of the Lake Kasumigaura watershed, Japan. Water quality indicators of total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) were investigated. The nutrient loads of TN, TP and TOC, as well as dissolved total nitrogen, dissolved inorganic nitrogen, dissolved organic nitrogen, particle organic nitrogen, dissolved total phosphorus, dissolved organic carbon and particle organic carbon were also estimated for the Koise River. Seasonal variation of the nutrient concentration from 2007 to 2008 was analysed considering the river discharge variation and agricultural activities. The results showed that the irrigation water from Lake Kasumigaura has the potential ability to decrease the TN concentration and increase the TOC concentration in the Koise River. Significant correlation coefficients between nutrient load and river discharge were found. The monthly pollution loads from different sources were then evaluated based on land cover classification generated from high-resolution Quick Bird remote sensing imagery. This study presents a useful interpretation of water quality data sets with a view to obtaining better information about water quality for more effective management of water resources in river basins.

Editor Z.W. Kundzewicz

Citation He, B., Oki, K., Wang, Y., Oki, T., Yamashiki, Y., Takara, K., Miura, S., Imai, A., Komatsu, K. and Kawasaki, N., 2012. Analysis of stream water quality and estimation of nutrient load with the aid of Quick Bird remote sensing imagery. Hydrological Sciences Journal, 57 (5), 850–860.  相似文献   

Variation of the Kuroshio in the Tokara Strait Induced by Meso-Scale Eddies     

Kaoru Ichikawa 《Journal of Oceanography》2001,57(1):55-68

Temporal variations of the Kuroshio volume transport in the Tokara Strait and at the ASUKA line are decomposed by phase-propagating Complex EOF modes of high-resolution sea surface dynamic topography (SSDT) field during the first tandem period of TOPEX/POSEIDON and ERS-1 (from October 1992 to December 1993). Both variations are dominated by a mode with nearly semi-annual cycle, which indicates a series of interactions between the Kuroshio and meso-scale eddies. Namely, northern part of a westward-propagating meso-scale eddy at 23°N is captured into the southern side of the Kuroshio at the south of Okinawa, then it moves downstream along the Kuroshio path passing the Tokara Strait, and reaches to the ASUKA line where it merges with another eddy propagating from the east at 30°N. The variation at the ASUKA line is, however, less dominated by this mode; instead, it includes the SSDT variations in the south of Shikoku and the east of Kyushu which would be directly affected by eddies from the east without passing the Tokara Strait. On the other hand, the same analysis for movements of the Kuroshio axis in the Strait indicates that they are governed by short-term variations locally confined to the Kuroshio in the East China Sea without being induced by meso-scale eddies. This results, however, seem to depend strongly on a time scale of interest. It is suggested that the long-term movements of the Kuroshio axis in the Strait would demonstrate coincidence with SSDT variation in the south of Japan.  相似文献