Heat transport variation due to change of North Pacific subtropical gyre interior flow during 1993–2012     

Akira Nagano  Shoichi Kizu  Kimio Hanawa  Dean Roemmich 《Ocean Dynamics》2016,66(12):1637-1649

Applying segment-wise altimetry-based gravest empirical mode method to expendable bathythermograph temperature, Argo salinity, and altimetric sea surface height data in March, June, and November from San Francisco to near Japan (30^° N, 145^° E) via Honolulu, we estimated the component of the heat transport variation caused by change in the southward interior geostrophic flow of the North Pacific subtropical gyre in the top 700 m layer during 1993–2012. The volume transport-weighted temperature (T_I) is strongly dependent on the season. The anomaly of T_I from the mean seasonal variation, whose standard deviation is 0.14^°C, was revealed to be caused mainly by change in the volume transport in a potential density layer of 25.0?25.5σ_??. The anomaly of T_I was observed to vary on a decadal or shorter, i.e., quasi-decadal (QD), timescale. The QD-scale variation of T_I had peaks in 1998 and 2007, equivalent to the reduction in the net heat transport by 6 and 10 TW, respectively, approximately 1 year before those of sea surface temperature (SST) in the warm pool region, east of the Philippines. This suggests that variation in T_I affects the warm pool SST through modification of the heat balance owing to the entrainment of southward transported water into the mixed layer.  相似文献   

Regionality of deep low-frequency earthquakes associated with subduction of the Philippine Sea plate along the Nankai Trough, southwest Japan     

Shoichi Yoshioka  Mamiko Toda  Junichi Nakajima 《Earth and Planetary Science Letters》2008,272(1-2):189-198

The Fukuoka District Meteorological Observatory recently logged three possible deep low-frequency earthquakes (LFEs) beneath eastern Kyushu, Japan, a region in which LFEs and low-frequency tremors have never before been identified. To assess these data, we analyzed band-pass filtered velocity seismograms and relocated LFEs and regular earthquakes using the double-difference method. The results strongly suggest that the three events were authentic LFEs, each at a depth of about 50 km. We also performed relocation analysis on LFEs recorded beneath the Kii Peninsula and found that these LFEs occurred near the northwest-dipping plate interface at depths of approximately 29–38 km. These results indicate that LFEs in southwest Japan occur near the upper surface of the subducting Philippine Sea (PHS) plate. To investigate the origin of regional differences in the occurrence frequency of LFEs in western Shikoku, the Kii Peninsula, and eastern Kyushu, we calculated temperature distributions associated with PHS plate subduction. Then, using the calculated thermal structures and a phase diagram of water dehydration for oceanic basalt, the water dehydration rate (wt.%/km), which was newly defined in this study, was determined to be 0.19, 0.12, and 0.08 in western Shikoku, the Kii Peninsula, and eastern Kyushu, respectively; that is, the region beneath eastern Kyushu has the lowest water dehydration rate value. Considering that the Kyushu–Palau Ridge that is subducting beneath eastern Kyushu is composed of tonalite, which is low in hydrous minerals, this finding suggests that the regionality may be related to the amount of water dehydration associated with subduction of the PHS plate and/or differences in LFE depths. Notable dehydration reactions take place beneath western Shikoku and the Kii Peninsula, where the depth ranges for dehydration estimated by thermal modeling agree well with those for the relocated LFEs. The temperature range in which LFEs occur in these regions is estimated to be 400–500 °C.  相似文献   

Erratum to “Regionality of deep low-frequency earthquakes associated with subduction of the Philippine Sea plate along the Nankai Trough,Southwest Japan” [Earth Planet. Sci. Lett. 272 (2008) 189–198]     

Shoichi Yoshioka  Mamiko Toda  Junichi Nakajima 《Earth and Planetary Science Letters》2009,277(1-2):292

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A new set of MCSST equations for NOAA-9/AVHRR     

Shoichi Kizu  Futoki Sakaida 《Journal of Oceanography》1996,52(2):235-249

A new set of multi-channel sea surface temperature (MCSST) equations for the Advanced Very High Resolution Radiometer (AVHRR) on NOAA-9 is derived from regression analyses between two-channel brightness temperatures andin situ SST obtained from moored buoys around Japan. Two equations are derived: one for daytime and the other for nighttime. They are linear split window type and both the equations contain a term dependent on satellite zenith angle, which has not been accounted for in the previous daytime split window equations for NOAA-9. It is shown that the new set of equation can give SSTs in much better precision than those without the zenith-angle-dependent terms. It is also found that the split window equation for NOAA-9 provided by the National Oceanographic and Atmospheric Administration/National Environmental Satellite, Data and Information Service (NOAA/NESDIS) considerably underestimates the daytime SSTs; sometimes nighttime SSTs are evenhigher than daytime SSTs. This is because the zenith angle effect to the radiation deficiet is neglected in the daytime equation by NOAA/NESDIS. By using the new MCSST equations, it is expected that the quality of satellite MCSST would be much improved, at least in regional applications around Japan, for the period of NOAA-9's operation.  相似文献   

Large kinetic power in FRII radio jets     

Hirotaka Ito  Motoki Kino  Nozomu Kawakatu  Naoki Isobe  Shoichi Yamada 《Astrophysics and Space Science》2007,311(1-3):335-339

We investigate the total kinetic powers (L _j) and ages (t _age) of powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C 219) by the detail comparison of the dynamical model of expanding cocoons with observed ones. It is found that these sources have quite large kinetic powers with the ratio of L _j to the Eddington luminosity (L _Edd) resides in 0.02<L _j/L _Edd<10. Reflecting the large kinetic powers, we also find that the total energy stored in the cocoon (E _c) exceed the energy derived from the minimum energy condition (E _min): 2<E _c/E _min<160. This implies that a large amount of kinetic power is carried by invisible components such as thermal leptons (electron and positron) and/or protons.  相似文献   

Short-term variability of Jupiter’s extended sodium nebula     

Mizuki Yoneda  Masato Kagitani  Shoichi Okano 《Icarus》2009,204(2):589-596

Ground-based optical observations of D₁ and D₂ line emissions from Jupiter’s sodium nebula, which extend over several hundreds of jovian radii, were carried out at Mt. Haleakala, Maui, Hawaii using a wide field filter imager from May 19 to June 21, 2007. During this observation, the east-west asymmetry of the nebula with respect to the Io’s orbital motion was clearly identified. Particularly, the D₁+D₂ brightness on the western side of Jupiter is strongly controlled by the Io phase angle. The following scenario was developed to explain this phenomenon as follows: First, more ionospheric ions like NaX⁺, which are thought to produce fast neutral sodium atoms due to a dissociative recombination process, are expected to exist in Io’s dayside hemisphere rather than in the nightside one. Second, it is expected that more NaX⁺ ionospheric ions are picked up by the jovian co-rotating magnetic field when Io’s leading hemisphere is illuminated by the Sun. Third, the sodium atom ejection rate varies with respect to Io’s orbital position as a result of the first two points. Model simulations were performed using this scenario. The model results were consistent with the observation results, suggesting that Io’s ionosphere is expected to be controlled by solar radiation just like Earth.  相似文献   

Physical conditions producing slab stagnation: Constraints of the Clapeyron slope, mantle viscosity, trench retreat, and dip angles   总被引：1，自引：0，他引：1  

Yoku Torii  Shoichi Yoshioka 《Tectonophysics》2007,445(3-4):200-209

Recent seismic tomography has revealed various morphologies in the subducted lithosphere. In particular, significant flattening and stagnation of slabs around the 660-km boundary are seen in some areas beneath the northwestern Pacific subduction zones. We examined the cause of slab stagnation in terms of the Clapeyron slope of the phase transformation from ringwoodite to perovskite + magnesiowüstite, trench retreat velocity, dip angles, and high viscosity of the lower mantle based on two-dimensional (2-D) numerical simulations of thermal convection. In particular, we examined the conditions necessary for slab stagnation assuming a very small absolute value of the Clapeyron slope, which were proposed based on recent high-pressure, high-temperature (high P–T) experiments. Our calculations show that slabs tend to stagnate above the 660-km boundary with an increasing absolute value of the Clapeyron slope, viscosity jump at the boundary, and trench retreat velocity and a decreasing initial dip angle. Stagnant slabs could be obtained numerically for a realistic range of parameters obtained from high P–T experiments and other geophysical observations combining buoyancy, high lower-mantle viscosity, and trench retreat. We found that a low dip angle of a descending slab at the bottom of the upper mantle plays an important role in slab stagnation. Two main regimes underlie slab stagnation: buoyancy-dominated and viscosity-dominated regimes. In the viscosity-dominated regime, it is possible for slabs to stagnate above the 660-km boundary, even when the value of the Clapeyron slope is 0 MPa/K.  相似文献   

Differential timing of vertical-axis block rotations in the northern Ryukyu Arc: Paleomagnetic evidence from the Koshikijima Islands,Japan     

Satoshi Tonai  Yusuke Suganuma  Juichiro Ashi  Tetsumaru Itaya  Hisashi Oiwane  Shoichi Kiyokawa 《Tectonophysics》2011,497(1-4):71-84

Over 300 samples for paleomagnetic analysis and K–Ar dating were collected from 27 sites at NW–SE and NE–SW trending dike swarms (herein, NW dikes and NE dikes, respectively) in the Koshikijima Islands, northern Ryukyu Arc. The NW dikes are Middle Miocene in age and have directions (D = ? 37.7^°, I = 51.8^°, α₉₅ = 9.6^°, and κ = 40.8) that are deflected westward relative to the stable eastern Asian continent. Conversely, the NE dikes, of Late Miocene age, have directions (D = 16.1^°, I = 57.7^°, α₉₅ = 7.1^°, and κ = 41.9) that show no such deflection. These differences are interpreted as indicating that the Koshikijima Islands underwent approximately 40^° of counter-clockwise rotation during the Middle to Late Miocene. A synthesis of the paleomagnetic and structural data suggests a three-stage history of extensional deformation: (1) displacement upon normal faults (F₁ faults) without vertical-axis block rotation, (2) strike-slip reactivation of F₁ faults and oblique-normal displacement on NE–SW-trending faults (F₂ faults) with vertical-axis block rotation, and (3) oblique-normal displacement on F₂ faults without vertical-axis block rotation. Regional differences in the timing and amount of counter-clockwise vertical-axis block rotations indicate that the northern Ryukyu Arc rotated as several distinct rigid blocks.  相似文献   

P‐O‐rich sulfide phase in CM chondrites: Constraints on its origin on the CM parent body          下载免费PDF全文

Ai‐Cheng Zhang  Shoichi Itoh  Hisayoshi Yurimoto  Wei‐Biao Hsu  Ru‐Cheng Wang  Lawrence A. Taylor 《Meteoritics & planetary science》2016,51(1):56-69

CM chondrites are a group of primitive meteorites that have recorded the alteration history of the early solar system. We report the occurrence, chemistry, and oxygen isotopic compositions of P‐O‐rich sulfide phase in two CM chondrites (Grove Mountains [GRV] 021536 and Murchison). This P‐O‐rich sulfide is a polycrystalline aggregate of nanometer‐size grains. It occurs as isolated particles or aggregates in both CM chondrites. These grains, in the matrix and in type‐I chondrules from Murchison, were partially altered into tochilinite; however, grains enclosed by Ca‐carbonate are much less altered. This P‐O‐rich sulfide in Murchison is closely associated with magnetite, FeNi phosphide, brezinaite (Cr₃S₄), and eskolaite (Cr₂O₃). In addition to sulfur as the major component, this sulfide contains ~6.3 wt% O, ~5.4 wt% P, and minor amounts of hydrogen. Analyses of oxygen isotopes by SIMS resulted in an average δ¹⁸O value of ?22.5 ‰ and an average Δ¹⁷O value of 0.2 ± 9.2 ‰ (2σ). Limited variations in both chemical compositions and electron‐diffraction patterns imply that the P‐O‐rich sulfide may be a single phase rather than a polyphase mixture. Several features indicate that this P‐O‐rich sulfide phase formed at low temperature on the parent body, most likely through the alteration of FeNi metal (a) close association with other low‐temperature alteration products, (b) the presence of hydrogen, (c) high Δ¹⁷O values and the presence in altered mesostasis of type‐I chondrules and absence in type‐II chondrules. The textural relations of the P‐O‐rich sulfide and other low‐temperature minerals reveal at least three episodic‐alteration events on the parent body of CM chondrites (1) formation of P‐O‐rich sulfide during sulfur‐rich aqueous alteration of P‐rich FeNi metal, (2) formation of Ca‐carbonate during local carbonation, and (3) alteration of P‐O‐rich sulfide and formation of tochilinite during a period of late‐stage intensive aqueous alteration.  相似文献   

Stress field change around the Mount Fuji volcano magma system caused by the Tohoku megathrust earthquake, Japan     

Eisuke Fujita  Tomofumi Kozono  Hideki Ueda  Yuhki Kohno  Shoichi Yoshioka  Norio Toda  Aiko Kikuchi  Yoshiaki Ida 《Bulletin of Volcanology》2013,75(1):1-14

Crustal deformation by the M _w 9.0 megathrust Tohoku earthquake causes the extension over a wide region of the Japanese mainland. In addition, a triggered M _w 5.9 East Shizuoka earthquake on March 15 occurred beneath the south flank, just above the magma system of Mount Fuji. To access whether these earthquakes might trigger the eruption, we calculated the stress and pressure changes below Mount Fuji. Among the three plausible mechanisms of earthquake–volcano interactions, we calculate the static stress change around volcano using finite element method, based on the seismic fault models of Tohoku and East Shizuoka earthquakes. Both Japanese mainland and Mount Fuji region are modeled by seismic tomography result, and the topographic effect is also included. The differential stress given to Mount Fuji magma reservoir, which is assumed to be located to be in the hypocentral area of deep long period earthquakes at the depth of 15 km, is estimated to be the order of about 0.001–0.01 and 0.1–1 MPa at the boundary region between magma reservoir and surrounding medium. This pressure change is about 0.2 % of the lithostatic pressure (367.5 MPa at 15 km depth), but is enough to trigger an eruptions in case the magma is ready to erupt. For Mount Fuji, there is no evidence so far that these earthquakes and crustal deformations did reactivate the volcano, considering the seismicity of deep long period earthquakes.  相似文献