The interanual rainfall variability in Indonesia corresponding to El Niño Southern Oscillation and Indian Ocean Dipole     

Hendrawan I Gede  Asai Koji  Triwahyuni Andhit  Lestari Diah Valentina 《海洋学报(英文版)》2019,38(7):57-66

The Impact of the Indian Ocean Dipole(IOD) and the El Ni?o Southern Oscillation(ENSO) event for Indonesian rainfall has been investigated for the period from 1950 to 2011. Inter-annual change of IOD and ENSO indices are used to investigate their relationship with Indonesian rainfall. By using the wavelet transform method, we found a positive significant correlation between IOD and Indonesian rainfall on the time scale of nearly 2.5–4 years.Furthermore, the positive significant correlation between ENSO(sea surface temperature anomaly at Ni?o3.4 area indices) and Indonesian rainfall exists for shorter than 2 years and between 5.5 to 6.5-year time scales.  相似文献   

Study on the selection of unsaturated flow model for the different types of soil and soft rock   总被引：1，自引：1，他引：0  

Sajeewani Rajika Amarasinghe  Kunio Watanabe  Koji Ishiyama 《Environmental Earth Sciences》2011,64(7):1795-1805

Precise estimation of unsaturated hydraulic properties of porous media is indispensable in various study areas, such as analyzing the moisture flow, the drying process occurring from the surface, and the pollutant migration beneath the ground surface. Although many empirical/theoretical models describing the unsaturated hydraulic properties have been proposed by several previous researchers, the best model for the different types of soil/rock may not be identical. Thus, the model selection process and the estimation technique of the parameters included in the models should be developed. In the present study, the inverse technique based on the transient evaporation change was investigated to select the model and estimate the model parameters. The experimental work was based on a relatively low permeable soft rock and a relatively high permeable sandy soil (Toyoura standard sand). Experimental equipment was developed to precisely measure the evaporation rate for the high permeable sandy soil. The Genetic Algorithm (GA) was adopted in the inverse technique as an optimization tool. In order to simplify the problem, only the drying process from the saturated condition was considered. It was established that the information concerning the transient evaporation change could be used for the model selection and parameter estimation. Further, the saturation distribution could be used for the selection of the models. The present study provides important information for the development of the model selection process.  相似文献   

Upwelling in the Alaskan Beaufort Sea: Atmospheric forcing and local versus non-local response     

Robert S. Pickart  Michael A. Spall  G.W.K. Moore  Thomas J. Weingartner  Rebecca A. Woodgate  Knut Aagaard  Koji Shimada 《Progress in Oceanography》2011,88(1-4):78-100

The spin up and relaxation of an autumn upwelling event on the Beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models. The event occurred in November 2002 and was driven by an Aleutian low storm. The wind field was strongly influenced by the pack-ice distribution, resulting in enhanced winds over the open water of the Chukchi Sea. Flow distortion due to the Brooks mountain range was also evident. Mooring observations east of Barrow Canyon show that the Beaufort shelfbreak jet reversed to the west under strong easterly winds, followed by upwelling of Atlantic Water onto the shelf. After the winds subsided a deep eastward jet of Atlantic Water developed, centered at 250 m depth. An idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm. The disparity in wave speeds between the sea surface height signal—traveling at the fast barotropic shelf wave speed—versus the interior density signal—traveling at the slow baroclinic wave speed—leads to the deep eastward jet. The broad-scale response to the storm over the Chukchi Sea is investigated using a regional numerical model. The strong gradient in windspeed at the ice edge results in convergence of the offshore Ekman transport, leading to the establishment of an anti-cyclonic gyre in the northern Chukchi Sea. Accordingly, the Chukchi shelfbreak jet accelerates to the east into the wind during the storm, and no upwelling occurs west of Barrow Canyon. Hence the storm response is fundamentally different on the Beaufort slope (upwelling) versus the Chukchi slope (no upwelling). The regional numerical model results are supported by additional mooring data in the Chukchi Sea.  相似文献   

Importance of intracellular Fe pools on growth of marine diatoms by using unialgal cultures and on the Oyashio region phytoplankton community during spring     

Koji Sugie  Kenshi Kuma  Satoshi Fujita  Satomi Ushizaka  Koji Suzuki  Tsutomu Ikeda 《Journal of Oceanography》2011,67(2):183-196

We report on the ability for luxury Fe uptake and the potential for growth utilizing intracellular Fe pools for 4 coastal centric diatom isolates and in situ phytoplankton assemblages, mainly composed of diatoms. Iron uptake of the diatom isolates and natural phytoplankton assemblages in the Oyashio region during spring blooms were prevented by adding hydroxamate siderophore desferrioxamine B (DFB). After the addition of DFB, intracellular Fe in the diatom isolates supported 2.4–4.2 cell divisions with 1.2–2.6 Chl a doublings. The intracellular Fe was primarily used for cell generation rather than Chl a production, leading to a reduction in the Chl a cell quota in the Fe-starved cells with time. The metabolic properties of the Fe-starved cells with their cell morphologies were different among species or genera. An on-deck incubation experiment also exhibited 1.9 cell divisions and 0.81 Chl a doublings of phytoplankton after the addition of DFB, also indicating the preference of cell generation over Chl a production. A decrease in the level of cellular Chl a, a main light-harvesting pigment in Fe-starved diatoms, may become a superior survival strategy to protect the cells from high irradiance that can cause photo-oxidative damages through photosynthesis. Such relatively low-Fe with high-light conditions could often occur in surface waters of the Oyashio region from spring to summer.  相似文献   

Heterogeneity in supraglacial debris thickness and its role in glacier mass changes of the Mount Gongga   总被引：3，自引：0，他引：3  

Yong Zhang  Yukiko Hirabayashi  Koji Fujita  ShiYin Liu  Qiao Liu 《中国科学:地球科学(英文版)》2016,59(1):170-184

In the Tibetan Plateau, many glaciers have extensive covers of supraglacial debris in their ablation zones, which affects glacier response to climate change by altering ice melting and spatial patterns of mass loss. Insufficient debris thickness data make it difficult to analyze regional debris-cover effects. Maritime glaciers of the Mount Gongga have been characterized by a substantial reduction in glacier area and ice mass in recent decades. The thermal property of the debris layer estimated from remotely sensed data reveals that debris-covered glaciers are dominant in this region, on which the proportion of debris cover to total glacier area varies from 1.74% to 53.0%. Using a physically-based debris-cover effect assessment model, we found that although the presence of supraglacial debris has a significant insulating effect on heavily debris-covered glaciers, it accelerates ice melting on ~10.2% of total ablation zone and produces rapid wastage of ~25% of the debris-covered glaciers, leading to the similar mass losses between the debris-covered and debris-free glaciers. Widespread debris cover also facilitates the development of active terminus regions. Regional differences in debris-cover effects are apparent, highlighting the importance of debris cover for understanding glacier mass changes in the Tibetan Plateau and other mountain ranges around the world.  相似文献   

Spatial distribution and cell size of aerobic anoxygenic phototrophic bacteria in the Uwa Sea,Japan     

Yuki Sato-Takabe  Shotaro Suzuki  Ryuki Shishikura  Koji Hamasaki  Yuya Tada  Takafumi Kataoka  Taichi Yokokawa  Naoki Yoshie  Satoru Suzuki 《Journal of Oceanography》2015,71(1):151-159

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Scoria cone formation through a violent Strombolian eruption: Irao Volcano, SW Japan     

Koji Kiyosugi  Yoshiyuki Horikawa  Takashi Nagao  Tetsumaru Itaya  Charles B. Connor  Kazuhiro Tanaka 《Bulletin of Volcanology》2014,76(1):1-14

Scoria cones are common volcanic features and are thought to most commonly develop through the deposition of ballistics produced by gentle Strombolian eruptions and the outward sliding of talus. However, some historic scoria cones have been observed to form with phases of more energetic violent Strombolian eruptions (e.g., the 1943–1952 eruption of Parícutin, central Mexico; the 1975 eruption of Tolbachik, Kamchatka), maintaining volcanic plumes several kilometers in height, sometimes simultaneous with active effusive lava flows. Geologic evidence shows that violent Strombolian eruptions during cone formation may be more common than is generally perceived, and therefore it is important to obtain additional insights about such eruptions to better assess volcanic hazards. We studied Irao Volcano, the largest basaltic monogenetic volcano in the Abu Monogenetic Volcano Group, SW Japan. The geologic features of this volcano are consistent with a violent Strombolian eruption, including voluminous ash and fine lapilli beds (on order of 10^?1 km³ DRE) with simultaneous scoria cone formation and lava effusion from the base of the cone. The characteristics of the volcanic products suggest that the rate of magma ascent decreased gradually throughout the eruption and that less explosive Strombolian eruptions increased in frequency during the later stages of activity. During the eruption sequence, the chemical composition of the magma became more differentiated. A new K–Ar age determination for phlogopite crystallized within basalt dates the formation of Irao Volcano at 0.4?±?0.05 Ma.  相似文献   

Relationships between volcano distribution, crustal structure, and P-wave tomography: an example from the Abu Monogenetic Volcano Group, SW Japan     

Koji Kiyosugi  C. B. Connor  D. Zhao  L. J. Connor  K. Tanaka 《Bulletin of Volcanology》2010,72(3):331-340

Achieving an understanding of the nature of monogenetic volcanic fields depends on identification of the spatial and temporal patterns of volcanism in these fields, and their relationships to structures mapped in the shallow crust and inferred in the deep crust and mantle through interpretation of geophysical data. We investigate the spatial and temporal distributions of volcanism in the Abu Monogenetic Volcano Group, Southwest Japan, and compare these distributions to fault and seismic data in the brittle crust, and P-wave tomography of the crust and upper mantle. Essential characteristics of the volcano distribution are extracted by a nonparametric kernel method using an algorithm to estimate anisotropic bandwidth. Overall, E-W elongate smooth modes in spatial density are identified that are consistent with the spatial extent of P-wave velocity anomalies in the lower crust and upper mantle, supporting the idea that the spatial density map of volcanic vents reflects the geometry of a mantle diapir. While the number of basalt eruptions decreased after 0.2 Ma, andesite eruptions increased and overall volume eruption rate is approximately steady-state. Estimated basalt supply to the lower crust is also constant. This observation and the spatial distribution of volcanic vents suggest stability of magma productivity and essentially constant two-dimensional size of the source mantle diapir since 0.46 Ma.  相似文献   

Holocene paleolimnological changes in Lake Skallen Oike in the Syowa Station area of Antarctica inferred from organic components in a sediment core (Sk4C-02)     

Genki I. Matsumoto  Yukinori Tani  Koji Seto  Tomoko Tazawa  Masumi Yamamuro  Takahiro Watanabe  Toshio Nakamura  Tetsuo Takemura  Satoshi Imura  Hiroshi Kanda 《Journal of Paleolimnology》2010,44(2):677-693

Antarctic climate changes influence environmental changes at both regional and local scales. Here we report Holocene paleolimnological changes in lake sediment core Sk4C-02 (length 378.0 cm) from Lake Skallen Oike in the Soya Kaigan region of East Antarctica inferred from analyses of sedimentary facies, a range of organic components, isotope ratios of organic carbon and nitrogen, and carbon-14 dating by Tandetron accelerator mass spectrometry. The sediment core was composed of clayish mud (378.0–152.5 cm) overlain by organic sediments (152.5 cm-surface). The age of the surface and the core bottom were 150 (AD1950-1640) and ca. 7,030 ± 73 calibrated years before present (cal BP), respectively, and the mean sedimentation rate was estimated to be 0.55 mm/year. Multi-proxy analyses revealed that the principal environmental change in the core is a transition from marine to lacustrine environments which occurred at a depth of 152.5 cm (ca. 3,590 cal BP). This was caused by relative sea level change brought about by ongoing retreat of glaciers during the mid-Holocene warming of Antarctica, and ongoing isostatic uplift which outpaced changes in global (eustatic) sea level. The mean isostatic uplift rate was calculated to be 2.8 mm/year. The coastal marine period (378.0–152.5 cm, ca. 7,030–3,590 cal BP) was characterized by low biological production with the predominance of diatoms. During the transition period from marine to freshwater conditions (152.5-approximately 135 cm, ca. 3,590–3,290 cal BP) the lake was stratified with marine water overlain by freshwater, with a chemocline and an anoxic (sulfidic) layer in the bottom of the photic zone. Green sulfur bacteria and Cryptophyta were the major photosynthetic organisms. The Cryptophyta appeared to be tolerant of the moderate salinity and stratified water conditions. The lacustrine period (approximately 135 cm-surface, ca. 3,290 cal BP-present) was characterized by high biological production by green algae (e.g. Comarium clepsydra and Oedegonium spp.) with some contributions from cyanobacteria and diatoms. Biological production during this period was 8.7 times higher than during the coastal marine period.  相似文献   

Post‐depositional alteration of shallow‐marine tsunami‐induced sand layers: A comparison of recent and ancient tsunami deposits,Onagawa Bay,northeastern Japan          下载免费PDF全文

Koji Seike  Genki Kobayashi  Kazuhiro Kogure 《Island Arc》2017,26(2)

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