Coastal upwelling along the north coast of Papua New Guinea and SST cooling over the pacific warm pool: A case study for the 2002/03 El Niño event     

Takuya Hasegawa  Kentaro Ando  Keisuke Mizuno  Roger Lukas 《Journal of Oceanography》2009,65(6):817-833

We investigate an overlooked mechanism—coastal upwelling—for sea surface temperature (SST) cooling in the western side of the mean location of the Pacific warm pool (WSWP: 5°S–5°N, 140°E–150°E) prior to El Niño onset. We analyze various observed data such as the TRIangle Trans-Ocean buoy Network (TRITON) moored buoy data, Conductivity-Temperature-Depth (CTD) data, satellite data and a hindcast experiment output by a high-resolution ocean general circulation model (OGCM). We focus on the precondition of the 2002/03 El Niño event, for which many datasets are available. Relatively cool water upwelled along the north coast of Papua New Guinea (PNG) during December 2001, prior to the onset of the 2002/03 El Niño event, and then spread out over a wider area to the northeast. Simultaneously, strong west-northerly surface winds occur along the north coast. Heat budget analysis of TRITON buoy data in the WSWP reveals that negative zonal heat advection due to eastward current is the main factor for cooling the mixed layer in the WSWP in contrast to the warming effect of the surface heat flux during the period. This cooling requires a source of colder water to the west. Similar analysis of OGCM outputs also suggests that the upwelled relatively cool water along the PNG north coast, and its northeastward extension to the equatorial region, contributes to cooling of the surface water over the WSWP mainly via negative zonal heat advection. Similar mechanisms are confirmed also for the 1982/83 and 1997/98 El Niño events by analyses of OGCM outputs and historical SST data. The low SST in the WSWP generated a positive zonal SST gradient together with high SST east of the WSWP. It may contribute to enhancement of the westerly surface wind in this region, leading to the onset of the 2002/03 El Niño event.  相似文献   

Upper Mantle Velocity Structure Estimated From Ps-Converted Wave Beneath the North-Eastern Japan Arc   总被引：2，自引：0，他引：2  

Toru Matsuzawa  Norihito Umino  Akira Hasegawa  Akio Takagi 《Geophysical Journal International》1986,86(3):767-787

Summary. The upper boundary of the descending oceanic plate is located by using PS -waves (converted from P to S at the boundary) in the Tohoku District, the north-eastern part of Honshu, Japan. the observed PS-P time data are well explained by a two-layered oceanic plate model composed of a thin low-velocity upper layer whose thickness is less than 10 km and a thick high-velocity lower layer; the upper and lower layers respectively have 6 per cent lower and 6 per cent higher velocity than the overriding mantle. the estimated location of the upper boundary is just above the upper seismic plane of the double-planed deep seismic zone. This result indicates that events in the upper seismic plane, at least in the depth range from 60 to 150 km, occur within the thin low-velocity layer on the surface of the oceanic plate.  相似文献   

The mass of the star formed in a cloud core     

Takenori Nakano  Tetsuo Hasegawa  Colin Norman 《Astrophysics and Space Science》1995,224(1-2):523-524

The forming star grows by mass inflow from the parent cloud core, mainly through the accretion disk. However, the core matter which has not yet contracted much is seriously disturbed by the activities of the forming star. We consider mass outflow and emission of ultraviolet radiation as such activities and determine the stellar mass as a function of the physical quantities of the parent cloud core.  相似文献   

GIS-based weights-of-evidence modelling of rainfall-induced landslides in small catchments for landslide susceptibility mapping   总被引：10，自引：0，他引：10  

Ranjan Kumar Dahal  Shuichi Hasegawa  Atsuko Nonomura  Minoru Yamanaka  Takuro Masuda  Katsuhiro Nishino 《Environmental Geology》2008,54(2):311-324

Landslide susceptibility mapping is a vital tool for disaster management and planning development activities in mountainous terrains of tropical and subtropical environments. In this paper, the weights-of-evidence modelling was applied, within a geographical information system (GIS), to derive landslide susceptibility map of two small catchments of Shikoku, Japan. The objective of this paper is to evaluate the importance of weights-of-evidence modelling in the generation of landslide susceptibility maps in relatively small catchments having an area less than 4 sq km. For the study area in Moriyuki and Monnyu catchments, northeast Shikoku Island in west Japan, a data set was generated at scale 1:5,000. Relevant thematic maps representing various factors (e.g. slope, aspect, relief, flow accumulation, soil depth, soil type, land use and distance to road) that are related to landslide activity were generated using field data and GIS techniques. Both catchments have homogeneous geology and only consist of Cretaceous granitic rock. Thus, bedrock geology was not considered in data layering during GIS analysis. Success rates were also estimated to evaluate the accuracy of landslide susceptibility maps and the weights-of-evidence modelling was found useful in landslide susceptibility mapping of small catchments.  相似文献   

The extinction coefficients in mid- and farinfrared of silicate and iron-oxide minerals of interest for astronomical observations     

Chiyoe Koike  Hiroichi Hasegawa  Noriaki Asada  Takeshi Hattori 《Astrophysics and Space Science》1981,79(1):77-85

Extinction measurements were made for some silicate and iron-oxide mineral grains in mid- and far-infrared region. For far-infrared region, high temperature magnesium silicates such as olivine and pyroxenes show the absorption spectra of steep dependence as ^–3 ( being the wavelength) with some peak structure, but the spectrum of magnetite shows ^–1 dependence.  相似文献   

Nitrogen, Oxygen and Argon Dissolved in the Northern North Pacific in Early Summer     

Noriko Nakayama  Shuichi Watanabe  Shizuo Tsunogai 《Journal of Oceanography》2002,58(6):775-785

Major gases dissolved in seawater were accurately determined with a shipboard gas chromatographic method. The standard deviations were 0.28, 0.34 and 0.36% for N₂, O₂ and Ar, respectively. The method was applied to water from the northwestern North Pacific Ocean collected in May to June 2000. We got 127 duplicate seawater samples from the surface 200 m layer at 11 stations. The O₂ concentrations obtained by this method agreed with those given by the Winkler method. All the seawater samples from the surface 200 m, especially those from the upper 30 m, were supersaturated with respect to atmospheric N₂ and Ar concentrations. In the topmost 30 m layer, the degrees of supersaturation in the inventory were 2.7–4.3% for N₂ (ΔN₂) and 1.7–2.6% for Ar (ΔAr), and their ratios, ΔN₂/ΔAr, ranged from 1.53 to 1.81. This supersaturation seems to be chiefly due to air bubbles injected into the water and dissolved due to the water pressure, because the N₂/Ar ratio of the air is around 2. The amounts of air bubbles dissolved in the upper 30 m water were relatively large, with mean value of 0.41 ml/kg or 18.4 μmol/kg. The ΔN₂, ΔAr and ΔN₂/ΔAr values were all positively well correlated with the wind velocities averaged for the last 24 hours prior to sampling, allowing the conclusion to be drawn that the weaker the wind velocity, the dissolved gas composition approaches in equilibrium with the air; while the stronger the wind velocity, it approaches in the air composition. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Gravity and S-wave modelling across the Jan Mayen Ridge,North Atlantic; implications for crustal lithology   总被引：1，自引：0，他引：1  

Rolf Mjelde  Inger Eckhoff  Ståle Solbakken  Shuichi Kodaira  Hideki Shimamura  Karl Gunnarsson  Ayako Nakanishi  Hajime Shiobara 《Marine Geophysical Researches》2007,28(1):27-41

The horizontal components from fourteen Ocean Bottom Seismometers deployed along four profiles focused along the western margin of the Jan Mayen microcontinent, North Atlantic, have been modelled with regard to S-waves, based on P-wave models obtained earlier. The seismic models have furthermore been constrained by 2D gravity modelling. High V _p/V _s-ratios (2.3–7.9) within the Cenozoic sedimentary section are attributed to significant porosities, whereas V _p/V _s-ratios in the order of 1.9–2.2 for the Mesozoic and Paleozoic sedimentary rocks indicate shale-dominated lithology throughout the area. The eastern side of the Jan Mayen Ridge is interpreted as a passive, volcanic margin, based on relatively high crustal V _p/V _s-ratios (1.9), whereas lower V _p/V _s-ratios (1.75–1.8) suggest the presence of intermediate composition crust and non-volcanic margin on the western side of the ridge. In the westernmost part of the Jan Mayen Basin, slightly increased upper mantle V _p/V _s-ratios may indicate some degree of serpentization of upper mantle peridotites.  相似文献   

Impact of quasi-decadal variability in the tropical Pacific on ENSO modulations     

Takuya Hasegawa  Kimio Hanawa 《Journal of Oceanography》2006,62(2):227-234

The impact of quasi-decadal (QD: 8 to 18 years) variability in the tropical Pacific on ENSO events is investigated. It is found that there is a significant difference in the behavior of ENSO events between the phases of positive and negative anomalies of the QD Niño-3.4 index. During the period of negative QD-scale Niño-3.4 index, ENSO events, especially La Niña events, occur more frequently, and larger amplitudes of thermal anomalies related to El Niño events appear over the central to eastern equatorial Pacific. Furthermore, propagations of upper ocean heat content anomaly and a phase relationship between upper ocean heat content and Niño-3 index in the equatorial Pacific, which have been pointed out by previous studies, are clearly detected during the period of negative QD Niño-3.4 index.  相似文献   

Simultaneous vertical measurements of in situ pH and CO2 in the sea using spectrophotometric profilers     

Yoshiyuki Nakano  Hideshi Kimoto  Shuichi Watanabe  Koh Harada  Yutaka W. Watanabe 《Journal of Oceanography》2006,62(1):71-81

We have developed new systems capable of profiling to >1000 m for measuring in situ pH and fugacity of CO₂ (fCO₂) in the ocean using spectrophotometric analysis (pH and CO₂ profilers). The in situ pH is determined by detecting the color change of the pH indicator (m-cresol purple). It can withstand ambient pressure to 1000 m depth. The CO₂ profiler analyzed in situ fCO₂ by detecting the change of pH in an inner solution, equilibrated with the seawater through a gas permeable membrane. It can be operated to 2500 m depth. We used an amorphous fluoropolymer tubing form of AF-2400 for the gas permeable membrane due to its high gas permeability coefficients. The inner solution was a mixture of 2 μM bromocresol purple (BCP) and 5 μM sodium hydroxide. This system gave us a response time of 1 minute, which is twice as fast as previous systems. The precisions of pH and CO₂ profilers were within 0.002 and 2.5% respectively. We have used these profilers to study the North Pacific, obtaining good agreement with the difference between the data from profilers and a discrete bottle of 0.002 ± 0.005 pH (SE, n = 25) and −0.4 ± 3 μatm (SE, n = 31).  相似文献   

Utility of an automatic water sampler to observe seasonal variability in nutrients and DIC in the Northwestern North Pacific     

Makio C. Honda  Shuichi Watanabe 《Journal of Oceanography》2007,63(3):349-362

Concentrations of nutrients (NO₃, NO₂, Si(OH)₄, PO₄ and dissolved inorganic carbon (DIC) were measured in a series of seawater samples collected over approximately 15 months in 2005 and 2006 by an automatic water sampler (Remote Access Sampler, RAS) in the Northwestern North Pacific. Seasonal variability and concentrations of NO₃ + NO₂ (NO_x and Si(OH)₄ were comparable to previous shipboard observations, although there were small errors associated with measurements of PO₄ and DIC. Concentrations of these nutrients began to decrease in late April. After the end of June, NO_x and Si(OH)₄ decreased rapidly, with large fluctuations. After October, these nutrients increased again until late spring 2006. The ratio of the decrease of Si(OH)₄ to that of NO_x suggests that numbers of biogenic opal-producing creatures, such as diatoms, increased after the end of June. This conclusion was supported by a rapid increase in biogenic opal flux recorded in a sediment trap at 150 m. The relationship between NO_x concentrations at the RAS depth of 35 m and NO_x integrated over the upper 100 m was determined using previous shipboard hydrocast data. This relationship was used to estimate integrated mixed layer NO_x concentration from RAS data. Estimated new production based on seasonal drawdown of integrated NO_x averaged approximately 156 mg-C m⁻²day⁻¹ annually, which agrees with previous estimates. Thus, an automatic seawater sampler that documents annual maximum and minimum nutrient concentrations and episodic events such as storms and spring blooms, which might be missed by an ordinary research vessel, will contribute to time-series observations of nutrients and, by extension, biological pump activity.  相似文献