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91.
To delineate channel networks from DEMs regardless of landform type, this article proposes a new method using slope-weighted flow accumulation. To validate the method, SRTM-3, a global DEM dataset with a resolution of approximately 90 m, was used for analysis of the Loess Plateau, China. Channel networks delineated with and without slope-weighted flow accumulation were derived in both uplands and hilly lands for comparison. In the weighted flow accumulation method, the thresholds for delineating the channels were defined by detecting a turning point in the frequency distribution of the weighted flow accumulation function or by visual similarity with drainage channels extracted from topographic maps. The channel networks delineated with weighting showed closer correlation with a topographic map than the channel networks without weighting, despite the differences in thresholds. Moreover, the channel networks delineated with weighting represented the differences between landform types, while the channel networks without weighting did not. Weighting on the basis of the slope angle shows promise as a general channel delineation method which reflects the actual topography due to its hydrogeomorphological functions. 相似文献
92.
Sohiko Kameyama Urumu Tsunogai Fumiko Nakagawa Motoki Sasakawa Daisuke D. Komatsu Akira Ijiri Junko Yamaguchi Takeo Horiguchi Hiroshi Kawamura Aika Yamaguchi Atsushi Tsuda 《Marine Chemistry》2009,115(1-2):92-101
During the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study ΙΙ (SEEDS-II), we monitored variations in the concentrations of non-methane hydrocarbons (NMHCs), CH3Cl, N2O, and CH4 within a phytoplankton bloom. Stable isotopic compositions were also determined to evaluate the sources of the variations. Although there was little variation in either the concentrations or the stable isotopic compositions of alkenes, CH3Cl, N2O, and CH4 during the 23-day observation period, alkane concentrations increased substantially as the phytoplankton bloomed. The column-integrated quantities of alkanes increased to 3 times pre-bloom levels for C2H6, 5 times for C3H8, and 20 times for n-C4H10. The δ13C values of both C2H6 and C3H8 remained almost constant while concentrations increased, whereas that of n-C4H10 increased by about 12‰. To evaluate the sources of the alkanes produced during the bloom, we compared their δ13C values with those of alkanes produced in axenic phytoplankton cultures in our laboratory. We concluded that during the SEEDS-ΙΙ experiment the major portions of C2H6 and C3H8 were produced during the autolysis of diatoms cells, whereas n-C4H10 was produced during autolysis of other phytoplankton cells such as cryptophytes and dinoflagellates. 相似文献
93.
Kiyoshi Tanaka Yutaka Michida Teruhisa Komatsu Kenji Ishigami 《Journal of Oceanography》2009,65(2):165-177
We have investigated the spreading of river water in Suruga Bay by performing numerical experiments and conducting field surveys
with drifting buoys. There are clear seasonal variations in the large river discharges into the bay: increased discharge in
the rainy summer season and decreased discharge in the dry winter season. The numerical model reproduces the main feature
that has been observed in the actual sea: the river water extends gradually from the northwestern to the southeastern regions
in the bay, especially in summer. The river water spreading is greatly influenced by the bottom topography of the bay: the
Fuji River water spreads over a deep continental slope as a surface-advected plume and extends well offshore, since a large
bulge (anticyclonic eddy at the river mouth) extends well offshore and effectively transports the river water offshore. On
the other hand, the Oi River water tends to flow parallel to isobaths (along a coastline) on a shallow continental shelf as
a bottomadvected plume. Moreover, the influences of seasonal variations in the stratification and a bay-scale, wind-driven
circulation are also investigated. Trajectories of the drifting buoys, which were released around the Fuji River mouth, certainly
suggest that the bulge exists there. 相似文献
94.
The dynamics of the wind-driven circulations and surface transport processes in Suruga Bay have been examined by performing
numerical experiments. While strong winds exist outside the bay, the winds inside the bays are greatly reduced, which generates
a strong wind stress curl in winter and autumn. In particular, in winter, a strong positive curl region is located across
the bay mouth, and a strong surface circulation with counterclockwise rotation is generated beneath it. The circulation is
nearly geostrophic, but is not affected by the bottom topography in the deep bay. It is suggested that intense surface water
exchange through the bay mouth occurs in winter, whereas it is not active in the other seasons when no significant vorticity
is supplied on the bay mouth from the atmosphere. Moreover, we propose a hypothesis that the atmospheric wind stress curl
will cause the frequent appearance of the counterclockwise circulation in winter in the real ocean. 相似文献
95.
Nobumitsu Tsunematsu Hironori Iwai Shoken Ishii Motoaki Yasui Yasuhiro Murayama Kohei Mizutani 《Boundary-Layer Meteorology》2009,131(2):263-275
The relationship between local meteorological fields and the behaviour of airborne Asian dust that arrived in the Tokyo metropolitan
area on 1 April 2007 with the passage of a synoptic-scale cold front has been investigated through Doppler lidar observations,
experiments using a regional atmospheric numerical model, and analyses of surface and upper-air meteorological observations.
Results of the Doppler lidar observations showed that the Asian dust passed above the metropolitan area with strong south-westerly
winds with speeds of 15–26 m s−1. Meteorological fields reproduced by the numerical experiments showed the development of a surface-based stable layer in
the metropolitan area caused by nocturnal radiational cooling near the ground surface and south-westerly warm air advection
at upper levels. The blocking effect of the mountainous region located to the west of the metropolitan area induced an area
of stagnant air inside the metropolitan area and promoted the stable layer development. Although strong downdrafts prevailed
in the upper air, the airborne Asian dust did not spread to the ground when the stable layer was formed. These results strongly
indicate that the developed stable layer prevented strong downdrafts from spreading to the ground, acting as an obstacle to
the transport of the Asian dust particles from the upper air towards the ground. This is considered to be one of the main
causes of the low appearance frequency of Asian dust phenomena near the ground in the Tokyo metropolitan area and eastern
Japan. 相似文献
96.
Fluorite Deposits at Voznesenka in the Khanka Massif, Russia: Geology and Age of Mineralization 总被引:1,自引:0,他引:1
Kohei Sato Kazuhiro Suzuki Munetomo Nedachi Shigeru Terashima Margarita D. Ryazantseva Anatoly A. Vrublevsky + Alexander I. Khanchuk ++ 《Resource Geology》2003,53(3):193-211
Abstract. A huge fluorite deposit at Voznesenka in the Khanka massif, Far East Russia is concluded to have formed at ca. 450 Ma in Late Ordovician time based on the K‐Ar ages for Li‐micas in the fluorite ore and greisenized leucogranite within the deposit. This conclusion is inconsistent with the current view of Devonian mineralization that stemmed from widely scattered whole‐rock Rb‐Sr isotope data for the heterogeneous leucogranite stocks influenced by strong alteration. The Voznesenka and neighboring fluorite deposits may have formed in Cambrian limestone in relation to the intrusion of the Li‐F‐rich felsic magma which has a similar chemistry to representative Li‐F‐rich felsic rocks including topaz granite and ongonite or topaz rhyolite; these rocks may be classified as a specific group of highly fractionated felsic magmas. Biotite granite plutons exposed in the Voznesenka district are divided in age into two groups based on the CHIME age data for zircon, monazite and xenotime: Ordovician and Permian. The Ordovician plutons seem to be coeval to the fluorite deposits and are characterized by F‐rich chemistry, reduced nature and association of tin mineralization with the deposition of fluorite and tourmaline. The biotite granite magmas of initially enhanced F contents could have been highly fractionated to form Li‐F‐rich leucogranite cupolas that provided fluorite deposits within the host limestone. Future prospecting for similar fluorite deposits is to be focused on areas of intersection between Ordovician Li‐F‐rich granite and Cambrian carbonate sequences. The Permian granite of southeastern margin of the Grodekovo batholith is characterized by lesser F content, oxidized nature and the lack of tin and fluorite mineralization in contrast to the Ordovician granite. The result of Permian age does not support the current view of Silurian age for the batholith and requires overall chronological reinvestigation in connection with the tectonic history of the Khanka massif because the Grodekovo is a representative of Paleozoic batholiths in Primorie. 相似文献
97.
Christopher Stocker Mark Williams Tatsuo Oji Gengo Tanaka Toshifumi Komatsu Simon Wallis 《Geology Today》2019,35(1):15-19
‘We are such stuff as dreams are made on, and our little life is rounded with a sleep’. So sleep the trilobites of Yokokurayama, a sacred mountain hidden within the beautiful landscape of Japan’s Shikoku’s island. And though Prospero may have been speaking to his daughter and her fiancé (in William Shakespeare’s The Tempest), he might well have been contemplating the magnificent trilobite fossils of Yokokurayama. Japan may be better known for its sweeping volcanic landscapes, majestic castles, Shinto shrines and bullet trains, but it is also home to important collections of Silurian and Devonian trilobites. 相似文献
98.
The mechanism of the Q-burst is investigated in the time and frequency domains. Electric fields in the ELF (extremely low frequency) to VLF (very low frequency) range have been observed with a ball antenna since 2003 in Kochi City, Japan (latitude 33.3°north, longitude 133.4°east). Source-to-observer distances (SODs) of Q-bursts are estimated by analyzing the waveforms. It is found as a result that the Q-burst is produced by combination of direct and antipodal pulses from a source lightning stroke occurring all over the world. 相似文献
99.
Ares Vallis is one of the greatest outflow channels of Mars. Using high-resolution images of recent missions to Mars (MGS, 2001 Odyssey, and Mars Express), we investigated Ares Vallis and its valley arms, taking advantage of 3-dimensional analysis performed using the high-resolution stereo capability of the Mars Express High Resolution Stereo Camera (HRSC). In our view, Ares Vallis is characterized by catastrophic flood landscapes partially superimposed by ice-related morphologies. Catastrophic flood landforms include erosional terraces, grooved terrains, streamlined uplands, giant bars, pendant bars, and cataract-like features. Ice-related morphologies include probable kame features, thermokarstic depressions, and patterned grounds. Our investigations outline that throughout the Hesperian age, Ares Vallis and its valley arms had been sculpted by several, time-scattered, catastrophic floods, originating from Iani, Hydaspis and Aram Chaos. Geomorphological evidence suggests that catastrophic floods were ice-covered, and that climatic conditions of Mars at this time were similar to those of the present day. At the end of each catastrophic flood, ice masses grounded, forming a thick stagnant dead-ice body. Each catastrophic flood was followed by a relatively brief period of warmer-wetter climatic conditions, originated as a consequence of catastrophic flooding. During such periods thermokarstic depressions originated, liquid water formed meandering channels, and ice-contact deposits were emplaced by ice-walled streams. Finally, the climate turned into cold-dry conditions similar to the present-day ones, and ice masses sublimated. 相似文献
100.
Mark Williams Simon Wallis Toshifumi Komatsu Gengo Tanaka Tatsuo Oji Nicola Clark 《Geology Today》2016,32(1):21-26
Not even Hollywood could dream of a place so magical as Kyushu. The southern‐most of the four major islands of the Japanese archipelago, this is a land of volcanoes, dinosaurs, and the last stand of the Samurai. And for good measure, James Bond visited here too, in the 1967 film You Only Live Twice. The final explosive scenes of that film featured the destruction of megalomaniac Ernst Stavro Blofeld's headquarters hidden inside the crater of one of Kyushu's most emblematic volcanoes, Shinmoedake. Kyushu also straddles the largest geological structure in Japan, the Median Tectonic Line (MTL) that runs from the western approaches of the island to the central part of Honshu. The MTL has been active since the Cretaceous, and the sedimentary basins formed along its line in Kyushu contain some of Japan's most famous dinosaur finds. The MTL also defines a fundamental divide between the geological histories of the terranes north and south of its line, a history that takes us back to the origins of the Japanese archipelago half a billion years ago. 相似文献