排序方式： 共有39条查询结果，搜索用时 46 毫秒
11.
Masakazu Yoshimori Masahiro Watanabe Ayako Abe-Ouchi Hideo Shiogama Tomoo Ogura 《Climate Dynamics》2014,42(5-6):1613-1630
The finding that surface warming over the Arctic exceeds that over the rest of the world under global warming is a robust feature among general circulation models (GCMs). While various mechanisms have been proposed, quantifying their relative contributions is an important task in order to understand model behavior. Here we apply a recently proposed feedback analysis technique to an atmosphere–ocean GCM under two and four times CO2 concentrations which approximately lead to seasonally and annually sea ice-free climates. The contribution of feedbacks to Arctic temperature change is investigated. The surface warming in the Arctic is contributed by albedo, water vapour and large-scale condensation feedbacks and reduced by the evaporative cooling feedback. The surface warming contrast between the Arctic and the global averages (AA) is maintained by albedo and evaporative cooling feedbacks. The latter contributes to AA predominantly by cooling the low latitudes more than the Arctic. Latent heat transport into the Arctic increases and hence evaporative cooling plus large-scale condensation feedback contributes positively to AA. On the other hand, dry-static energy transport into the Arctic decreases and hence dynamical heating feedback contributes negatively to AA. An important contribution is thus made via changes in hydrological cycle and not via the ‘dry’ heat transport process. A larger response near the surface than aloft in the Arctic is maintained by the albedo, water vapour, and dynamical heating feedbacks, in which the albedo and water vapour feedbacks contribute through warming the surface more than aloft, and the dynamical heating feedback contributes by cooling aloft more than the surface. In our experiments, ocean and sea ice dynamics play a secondary role. It is shown that a different level of CO2 increase introduces a latitudinal and seasonal difference into the feedbacks. 相似文献
12.
Irizuki T Takimoto A Sako M Nomura R Kakuno K Wanishi A Kawano S 《Marine pollution bulletin》2011,62(10):2030-2041
This study focuses on the relationships of water and sediment quality with meiobenthos (Ostracoda) over the past 100 years, using a sediment core obtained from Suo-Nada in the Seto Inland Sea, Japan. We compared high-resolution ostracode results with geochemical and sedimentological data obtained from the study core as well as with rich environmental monitoring data that are available. R-mode cluster analysis revealed two bioassociations (BC, KA). Until the1960s, assemblages continued to show high diversity. They changed in approximately 1970, when excessive nutrients and organic matter began to be supplied, and most species decreased in number. All species of bioassociation BC were dominant again by the mid-1990s; however, those of bioassociation KA containing infaunal species did not increase and have been absent or rare since the 1970s because organic pollution of sediments has continued to date. This study provided robust baseline for ostracode-based long-term environmental monitoring in East Asia. 相似文献
13.
Hirohiko Nakamura Ayako Nishina Kotaro Tabata Masataka Higashi Akimasa Habano Toru Yamashiro 《Journal of Oceanography》2012,68(2):321-336
A time series of surface geostrophic velocity is developed using satellite altimetry data during 1992–2010 for a track across
the Kuroshio southeast of Kyushu, Japan. The temporal mean geostrophic velocity is estimated by combining the along-track
sea level anomaly and shipboard ADCP data. This approximately 6-km resolution dataset is successful in representing the Kuroshio
cross-current structure and temporal variation of the Kuroshio current-axis position during 2000–2010. The authors use this
dataset to examine the winter Kuroshio path destabilization phenomenon. Its seasonal features are characterized as follows:
the velocity shear on the inshore side of the Kuroshio becomes stronger and the Kuroshio path state becomes unstable from
the summer to winter. This evidence is consistent with the hypothetical mechanism governing the destabilization phenomenon
discussed in a previous study. Furthermore, the interannual amplitude modulation of the seasonality is examined in relation
to interannual variations in the winter northerly wind over the northern Okinawa Trough and the Pacific Decadal Oscillation
(PDO) index. The destabilization phenomenon appears 15 times in the period 2000–2010. Ten cases are related to local wind
effects, and 7 of these are also connected with the PDO index. This is probably because the winter northerly wind over the
northern Okinawa Trough is regulated by the PDO signal in interannual time-scales. Only 4 cases are related to the PDO index,
but their driving mechanism remains uncertain. 相似文献
14.
Toshiyuki Ohtsuka Mitsuru Hirota Xianzhou Zhang Ayako Shimono Yukiko Senga Minguan Du Seiichiro Yonemura Shigeto Kawashima Yanhong Tang 《Polar Science》2008,2(4):277-285
To accurately estimate soil organic carbon (SOC) storage in upper alpine to nival zones on the Tibetan Plateau, we inventoried SOC pools in 0–0.3 m profiles along an altitudinal gradient (4400–5300 m asl). We also studied vegetation properties and decomposition activity along the gradient to provide insight into the mechanisms of SOC storage. The vegetation cover and belowground root biomass showed a gradual increased with altitude, reaching a peak in the upper alpine zone at 4800–4950 m before decreasing in the nival zone at 5200–5300 m.Decomposition activity was invariant along the altitudinal gradient except in the nival zone. SOC pools at lower sites were relatively small (2.6 kg C m−2 at 4400 m), but increased sharply with altitude, reaching a peak in the upper alpine zone (4950 m; 13.7 kg C m−2) before decreasing (1.0 kg C m−2 at 5300 m) with altitude in the nival zone. SOC pool varied greatly within individual alpine meadows by a factor of five or more, as did bulk density, partly due to the effect of grazing. Inventory data for both carbon density and bulk density along altitudinal gradients in alpine ecosystems are of crucial importance in estimating global tundra SOC storage. 相似文献
15.
Ayako Fujii Sakae Toyoda Osamu Yoshida Shuichi Watanabe Ken’ichi Sasaki Naohiro Yoshida 《Journal of Oceanography》2013,69(2):147-157
N2O concentration and its isotopomer ratios were measured over a wide area from San Diego to Honolulu in the eastern subtropical North Pacific (ESNP). Waters in the study area had an N2O maximum (38.2–50.5 nmol kg?1) at 600–1000 m depth, which is similar to the profiles obtained previously in other areas in the North Pacific. We separated the seawater into five water masses (two for the surface layer, two for the middle layer, and one for the deep layer) and deduced N2O production–consumption mechanisms in each water body by use of N2O isotopomer ratios. The results showed that the mechanisms differ slightly among water masses. In the “coastal” surface layer, N2O is produced by nitrification (NH2OH oxidation). In the “open ocean” surface layer, it is produced mainly by nitrifier denitrification and to a lesser extent by nitrification under substrate-limited conditions. In both “upwelling” and “open ocean” middle layers it is produced mainly by denitrification and to a lesser extent by nitrifier denitrification. It is also partly reduced. In the deep layer, it is produced predominantly by denitrification with partial reduction. In this way, isotopomers aid elucidation of production–consumption mechanisms of N2O in the sea even though the mechanisms cannot always be ascertained. 相似文献
16.
Mjelde Rolf Aurvåg Roar Kodaira Shuichi Shimamura Hideki Gunnarsson Karl Nakanishi Ayako Shiobara Hajime 《Marine Geophysical Researches》2002,23(2):123-145
The horizontal components from twenty Ocean Bottom Seismometers deployed along three profiles near the Kolbeinsey Ridge, North Atlantic, have been modelled with regard to S-waves, based on P-wave models obtained earlier. Two profiles were acquired parallel to the ridge, and the third profile extended eastwards across the continental Jan Mayen Basin. The modelling requires a thin (few 100 m) layer with very high V
p/V
s-ratio (3.5–9.5) at the sea-floor in the area lacking sedimentary cover. The obtained V
p/V
s-ratios for the remaining part of layer 2A, 2B, 3 and upper mantle, correspond to the following lithologies: pillow lavas, sheeted dykes, gabbro and peridotite, respectively. All crustal layers exhibit a decreasing trend in V
p/V
s-ratio away-from-the-axis, interpreted as decreasing porosity and/or crack density in that direction. A significant S-wave azimuthal anisotropy is observed within the thin uppermost layer of basalt near the ridge. The anisotropy is interpreted as being caused by fluid-filled microcracks aligned along the direction of present-day maximum compressive stress, and indicates crustal extension at the ridge itself and perpendicular-to-the-ridge compression 12 km off axis. Spreading along the Kolbeinsey Ridge has most likely been continuous since its initiation ca. 25 Ma: The data do not suggest the presence of an extinct spreading axis between the Kolbeinsey Ridge and the Aegir Ridge as has been proposed earlier. The V
p/V
s-ratios found in the Jan Mayen Basin are compatible with continental crust, overlain by a sedimentary section dominated by shale. 相似文献
17.
Hiroshi Ichikawa Hirohiko Nakamura Ayako Nishina Masataka Higashi 《Journal of Oceanography》2004,60(2):351-363
To better understand the mechanism underlying the variation of the Kuroshio south of central Japan, we have examined the variability
of current structure in its upstream region, southeast of Amami-Ohshima Island in the northern Ryukyu Islands. By combined
use of ship-mounted Acoustic Doppler Current Profiler (ADCP) and the TOPEX/POSEIDON satellite altimeter data on Path 214,
the sea surface absolute geostrophic currents were estimated every ten days from January 1998 to July 2002. The 4.5-year mean
surface current was found to flow northeastward north of 26.8°N with a maximum speed of 14 cm s−1 over the shelf slope at 3000 m depth. The moored current-meter observations at three or four mooring stations from Dec. 1998
to Oct. 2002 suggested the existence of a northeastward undercurrent with a maximum core velocity of 23 cm s−1 at 600 m depth over the shelf slope at 1600 m depth. The mean volume transport in the top 1500 m between 27.9°N and 26.7°N
is estimated to be 16 × 106 m3s−1 northeastward, including the subsurface core current related component of 4 × 106 m3s−1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Atsushi Inagaki Manabu Kanda Nurul Huda Ahmad Ayako Yagi Naoyuki Onodera Takayuki Aoki 《Boundary-Layer Meteorology》2017,163(2):161-177
Sonic anemometer measurements are analyzed from two primary field programs and 12 supplementary sites to examine the behaviour of the turbulent heat flux near the surface with high wind speeds in the nocturnal boundary layer. On average, large downward heat flux is found for high wind speeds for most of the sites where some stratification is maintained in spite of relatively intense vertical mixing. The stratification for high wind speeds is found to be dependent on wind direction, suggesting the importance of warm-air advection, even for locally homogenous sites. Warm-air advection is also inferred from a large imbalance of the heat budget of the air for strong winds. Shortcomings of our study are noted. 相似文献
19.
Ayako Shinozaki Hiroyuki Kagi Hisako Hirai Hiroaki Ohfuji Taku Okada Satoshi Nakano Takehiko Yagi 《Physics and Chemistry of Minerals》2016,43(4):277-285
Stability and phase relations of coexisting enstatite and H2 fluid were investigated in the pressure and temperature regions of 3.1–13.9 GPa and 1500–2000 K using laser-heated diamond-anvil cells. XRD measurements showed decomposition of enstatite upon heating to form forsterite, periclase, and coesite/stishovite. In the recovered samples, SiO2 grains were found at the margin of the heating hot spot, suggesting that the SiO2 component dissolved in the H2 fluid during heating, then precipitated when its solubility decreased with decreasing temperature. Raman and infrared spectra of the coexisting fluid phase revealed that SiH4 and H2O molecules formed through the reaction between dissolved SiO2 and H2. In contrast, forsterite and periclase crystals were found within the hot spot, which were assumed to have replaced the initial orthoenstatite crystals without dissolution. Preferential dissolution of SiO2 components of enstatite in H2 fluid, as well as that observed in the forsterite H2 system and the quartz H2 system, implies that H2-rich fluid enhances Mg/Si fractionation between the fluid and solid phases of mantle minerals. 相似文献
20.
Ayako?ShinozakiEmail author Hisako?Hirai Hiroyuki?Kagi Tadashi?Kondo Taku?Okada Daisuke?Nishio-Hamane Shin-ichi?Machida Tetsuo?Irifune Takumi?Kikegawa Takehiko?Yagi 《Physics and Chemistry of Minerals》2012,39(2):123-129
High pressure and temperature reactions of a mixture of forsterite and hydrogen molecules have been carried out using a laser
heated diamond anvil cell at 9.8–13.2 GPa and ~1,000 K. In situ X-ray diffraction measurements showed no sign of decomposition
or phase transitions of the forsterite under these experimental conditions, indicating that the olivine structure was maintained
throughout all runs. However, a substantial expansion of the unit cell volume of the forsterite was observed for samples down
to ~3 GPa upon quenching to ambient pressure at room temperature. The Raman spectroscopy measurements under pressure showed
significant shifts of the Raman peaks of the Si–O vibration modes for forsterite and of the intramolecular vibration mode
for H2 molecules toward a lower frequency after heating. Additionally, no OH vibration modes were observed by Raman and FT-IR spectroscopic
measurements. These lines of evidence show that the observed volume expansion in forsterite is not explained by the incorporation
of hydrogen atoms as hydroxyl, but suggest the presence of hydrogen as molecules in the forsterite structure under these high
pressure and temperature conditions. 相似文献